A couple years ago I purchased a Numark PT-01 portable record player after reading and watching some reviews online. Fully aware that portable record players don’t come close to delivering the high fidelity of a good home turntable set up, I wanted something I could use to play records while sitting out on the porch in the evening.
There aren’t many options in portable record players, and the vast majority of what is available are all based on the same cheap plastic architecture featuring a Chuo Denshi ceramic cartridge. The Crosley Cruiser in all its varieties is ubiquitous as are the Victrola clones. Neither are renowned for their high fidelity and are panned by most ‘serious’ audiophiles.
While the Numark PT-01 features the same cheap plastic mechanism belt driven by a DC motor as the Crosleys and Victrolas, but had some attractive features not found in those players. The Numark has an adjustable tone control and a pitch control, two were nice pluses, but even better, the PT-01 can be powered by six D-cells, unlike the Crosley and Victrola portables that must be powered from a wall wart transformer.
The PT-01 only has a monaural full range 3″ speaker, but to my ear, that’s a better choice than the smaller stereo speakers mounted too close together in the Crosley and Victrola. LIke the Crosley and Victrola, the Numark does have RCA jacks for full stereo out, and two headphone jacks – both 1/8″ and 1/4″ – which surprisingly produces very decent sound when a good set of stereo headphones are use.
Playing records on the PT-01 on the front porch has been absolutely delightful over the past two years, and I was so impressed with this $100 portable player that I had gifted one to my 8 year old godson and 12 year old granddaughter. Both children have enjoyed the record player and both continue to grow their record collections.
Modifying the Numark PT-01
The PT-01 has something of a cult following and is also available in a ‘scratch’ version. Several aftermarket firms have marketed modifications for the PT-01 and as someone who enjoys mucking around with electronic devices, I found myself unable to resist the allure of making a few mods to my record player.
This weekend I installed a better speaker, the Jesse Dean Designs Puck-It platter support and PCB tone arm & pre-amplifier kit to allow me to use a magnetic cartridge.
The speaker was an easy upgrade, as the speaker has the same dimensions as the stock speaker. The Puck–it platter support, which adds rigidity to the plastic platter was also a simple upgrade, as it just firmly presses into the center of the bottom of the platter.
The Jesse Dean Designs Puck-It Platter support (L), and the Celestion replacement speaker (R)
The installation of the new tone arm was a bit more involved, but again, wasn’t difficult, and my installation took about a half hour’s time on the workbench guided by the excellent Jesse Dean YouTube step-by-step directions found here.
The tone arm kit comes with everything needed for the mod including, in addition to the tonearm itself, a compact pre-amp, two breakout boards, connection wires with connectors and hardware.
The tonearm is a bit unconventional and a thing of beauty. It’s actually a printed circuit board, which allows it to be thin and connections from the cartridge to the back of the arm are built-in as traces on the board. It also features a nifty built in white LCD under the head shell area.
The bottom of the flat tone-arm
The Ortofon OM 5e cartridge mounted to the PCB tone arm.
L: Bottom view of cartridge mounted to the tonearm. R: The Jesse Dean kit comes with a nifty magnet insert that goes into the original tone-arm holder. A very cool design, indeed!
The accessory boards needed for the pre-amp are very well engineered to fit into the existing PT-01 architecture without the need to drill additional holes. Each of the three boards mounts neatly using existing screws.
I did, however encounter a very minor fitment issue when installing the pre-amp break out board. I could not mount it square to the existing PCB as two electrolytic capacitors interfered with the end of the break out board. It was no matter to mount the board slightly counterclockwise on the mounting screw axis. This was the only glitch I ran into when installing the tonearm kit. It was an easy and relaxing project to work on on an Easter Sunday afternoon.
L: The power break-out board installed in the bottom half of the PT-01 cabinet. C: The Pre-amp board and pre-amp break-out board installed. (Note there was insufficient room to mount the break-out square to the main PCB due to the placement of two electrolytic caps). R: The power and tone arm connections on the pre-amp board.
Powering up the PT-01 for a test run before closing up the cabinet, I found that everything worked properly. I queued an album and made sure to listen on a set of headphones to make sure I was getting stereo L/R audio, something that wouldn’t be obvious listening through the monaural speaker if one of the channels wasn’t properly connected.
Overall, I’m very pleased with the results. As expected there is a much improved higher fidelity sound due to the replacement of the ceramic cartridge with the higher end Ortfoon moving magnet cartridge. It’s definitely not audiophile quality, which is to be expected, but for the cost of these few accessory parts, my beloved portable record player has been appreciably improved. And, here comes summer!
This past week I had the opportunity to glom onto a business trip my wife was taking to San Francisco on the cheap. As her travel and lodging was being covered, I was able to enjoy a mini-vacation for the cost of an airplane seat – not too shabby!
As we have visited San Francisco a couple of times in past years, and despite the fact we never tire of the “City by the Bay,” we thought it would be fun to do a side trip to Yosemite National Park, which I had not previously experienced. It is a four hour drive from San Francisco – but a scenic one.
I realized this was a pretty good opportunity to practice my POTA activation skills and to test some of my new gear including the End Fed Half Wave antennas I recently constructed. I’ve never flown with more ham gear than an HT or two in the past, so going through TSA with a complete HF go-bag was going to be a new experience as well, one from which I learned a few things.
Packing for the trip
I decided that my Xiegu G90 DSP transceiver would be a good choice to fly with as it is compact and although it only puts out 20 watts, it should perform well at the higher altitudes found around the edge of Yosemite, even on SSB.
I packed the G90 in its original box, which not only provided protection for the rig with the Styrofoam inserts, but it also provided enough space to tuck in a mini un-un, some power cables, a copy of the manual, my mini log book, and a pencil.
I printed an official copy of my FCC license and included that as well in the G90 box and, using a Brother label maker, I labeled the outside of the box, “Property of Amateur Radio Station AB1DQ, Cheshire CT.” While based on the accounts of flying with ham gear that I read that others shared online, I didn’t anticipate much difficulty going through TSA with my shack-in-a-bag, but I felt a professional looking packing job might be useful if any TSA agent asked hard questions.
Originally I planned to power the rig from the rental car battery, I made two sets of power cables that terminated in PowerPole connectors that interfaced with the G90 power cord. One set had battery post clamps to attach directly to the car battery, and the other had a 12 volt cigar lighter plug. Based on the 8 amp rated current draw of the G90 at maximum 20 watt output, I felt I didn’t run much risk of blowing the 15 amp cigar lighter fuse, but I did pack extra fuses just in case.
Then I decided for not much more space (but a bit more weight) in my go bag, I should bring a LiFEPO4 battery and charger which would allow me more flexibility to operate, should I want to, after we returned the rental car for the San Francisco portion of our trip.
I found a deep cycle 12Ah 12.8 battery on Amazon that met my specs for less than $60. I made a short jumper cable terminating in PowerPole connectors which I pre-attached to the battery. Like the rig, I kept the battery in its original packaging in my go-bag, again labeling the box with my callsign and contact information. The battery did catch the attention of the TSA agent, but after a careful visual inspection, she returned it to its box and handed it back to me.
My antenna plan was to use an End Fed Half Wave. A couple of months back I built a pair of 49:1 un-uns from HFKits.com, and had yet to try them out on the air. This seemed like a great opportunity, so I packed both along with 60′ length of basic hookup wire to use as the radiating element.
I have been one who has always struggled with launching lines into trees for my wire antennas, so after some YouTube research, I thought I’d try something new. – an arborist throw-line attached to a 12 oz weight. Given the altitude of the park’s rim from where I planned to operate, I didn’t need too much height for the antenna, The 20-30′ or so I could get the high end up in a sloping configuration should suffice, so the throw-line seemed like a promising option.
I found just the thing again on Amazon, and I also decided to add a collapsible throw line storage cube, which would allow me to keep the line untangled during transport and deployment. The cube was great because it folds flat but its 16″ square sides meant that it would not fit in my duffel bag go-kit, so the throw line and storage cube would have to be packed into my checked suitcase. The flatness of the collapsed cube made it easy to pack at the bottom of my checked full size suitcase along with my clothes for the trip.
I used a couple of gallon size Ziplock bags to pack the miscellaneous items I would need, including my Morse key, 60′ of antenna wire, additional pencils and a pencil sharpener, a couple of power cable extension cords, etc. All items, aside from the throw line and cube, fit nicely in a small duffel bag along with my laptop, a couple of books and a few other carry on items for the trip that would stow nicely in the overhead bin.
Aside from the visual inspection of my carry-on bag by TSA, with the careful attention given to the battery, I had no problems taking the go-kit through airport security and onto the plane. I wasn’t asked any specific or probing questions about the contents of my bag.
We were staying at the Yosemite Valley Lodge while in the park, which we found to be great accommodations for our visit. However, being deep in the park valley, with rising mountains on all sides, it made sense to find a spot from which to operate that was higher up off the canyon floor. And, while I’m aware that a big part of the POTA program is to present ham radio in a positive light to the uninitiated, and as much as I love being that goodwill ambassador for our hobby, I tend to get nervous when I’m being watched, particularly when I’m not completely familiar with gear or a configuration I haven’t tried before. So I was also looking for an operating site that was a bit more remote with less foot traffic.
After studying a map of the park, I decided a good bet would be to drive west up Big Oak Flat Road towards Porcupine Flat which was north of us and had a picnic area. However, the Tioga Road is closed in the wintertime, so we ended up stopping near Toulumine Grove at the road closure.
There was a convenient parking area there at 37-706250 N, -119804167 W which provided both altitude and minimal foot traffic. The spot looked ideal for my planned activity so I parked the rented Ford Edge and began my set up.
This was the first time I tried a throw-rope and I found the deployment to be about as easy as it seemed in the YouTube videos I had watched. However, due to some chronic shoulder pain I’ve been experiencing in my right arm, I have been lacking my usual range of motion and wasn’t able to get the bean bag weight over my chosen branch, but needed to settle for the next one below, which I estimated to be about 20′ up.
I detached the throw weight and connected the the end of my 60′ antenna wire to the rope and hoisted it up to the branch and tied the throw rope to the trunk of the tree. I asked my wife to stretch out the sloping antenna wire to the point where it met the ground and I repositioned the car.
I attached the end of the antenna wire to the un-un and connected the un-un to the G90 via a 25′ length of RG58. The antenna was sturdy and up high enough that any passersby should not run into it, but I realized after the fact that I failed to make appropriate use of the strain relief on the un-un. (See right most photo below for how to do it right!)
While I should have taken the time before flying off on my trip to test and trim my wire element to obtain a minimal SWR, I didn’t have the opportunity to do so, but I was pleased that the G90’s auto tuner was able to obtain a 1.8:1 SWR.
Initially I powered the G90 via the cigar lighter plug I fashioned, but found the voltage reading on the G90 panel to be right around 11.0 V. Upon switching to the LiFePO4 battery, the G90 was reading around 13.0 V. so I continued to use the battery.
The immediate advantage to operating (very) remotely and on a battery, is how quiet, nay, silent, the HF bands are. A far cry from the noise floor that is typical at my home QTH fixed station.
I began calling CQ POTA on SSB on 14.324 and over the hour I had available to operate that day, I made 11 contacts. Fewer than I had hoped for, but enough to make my activation successful.
With my 20 watts and a wire, I worked as far north as NL7V in Fairbanks AK who rated my signal 53, as far east as K9ICP in Greenwood IN who reported my signal 59, and as far south as W5NM in Las Cruces NM who provided a 55 report. Included in my 11 contacts was a single Park-to-Park contact with K7CAN who was activating Minidoka Internment National Historic Site, Park K-0849 in Idaho. We swapped 59 reports.
Lessons Learned & Conclusions
I mentioned due to our compressed travel schedule, I only had about an hour of operating time, but it didn’t matter as I had a great deal of fun. This was only my sixth activation in over two years, so I’m still very much green and learning.
The positive takeaways from this trip was I learned how to effectively and efficiently pack an HF go-bag for air travel, and while I will need more practice, I did successfully and quickly deploy my EFHW antenna with the arborist throw line.
Areas for personal improvement include the proper testing of new gear at home before traveling to a park. I shared that despite not testing my un-un and antenna prior to traveling, I had an adequate SWR once on site. (I did bring extra wire and a pair of nippers in the event my SWR was so far off I needed to do major mods on site.)
Finally despite the entire station fitting comfortably in my go-kit duffel bag as carry -on luggage, the bag was pretty heavy and given my shoulder pain I mentioned above, it was a bit uncomfortable to lug through the airport and stow in the overhead bin. Thus, I splurged and stopped at a UPS store to have the radio and battery shipped home to me so I didn’t have to fuss with the weight or the TSA on the trip home. That ran me about $60 for packing and shipping, but the gear did arrive home safely.
Finally, I’m planning on issuing QSLs to all stations I worked during my POTA activation. I still love collecting cards and am one of those old-school hams who hangs wallpaper. I had sent out cards for some of my previous activations, primarily to ops who indicated they were welcoming of receiving cards and would reciprocate.
I’ve designed a commemorative card for my Yosemite activation and will be printing the cards at home on card stock.
My ham resolution for 2023 is to get on the air much more than I have in recent years and I’m planning on making POTA activations a major part of that goal. The Yosemite trip was a great, albeit limited experience, that helped me build confidence and comfort.
What suggestions, thoughts or ideas do you have to share that I and others may use as we take to the parks with our rigs? Do you have a memorable POTA experience to share? Feel free to add a comment or contact me directly by email at email@example.com.
73 & thanks for reading! James
AB1DQ, James & XYL Ellen, at the Tunnel View Scenic Overlook in Yosemite National Park, February 2023. This photograph was taken by a charming young Ukrainian woman we met at the overlook. She shared some of her story of the affect the Russian invasion has had on her and her family and we had the opportunity to express our heartbreak and our support for her people.
The Somerville, Massachusetts institutionfades away.
According to the company website, Nissenbaum Auto Parts was founded in 1910, by Jacob Nissenbaum, a Jewish immigrant who fled the repressions of czarist Russia, drove a horse and buggy as he collected rags and paper in Somerville and Cambridge.
Over the decades, future generations of Nissenbaums joined the business, in 1929, Joseph, Jacob’s son replaced the horse and carts with trucks and grew the business by purchasing scrap cars.
In 1937, Jacob retired, and Joseph passed away, leaving his son Max to take over as owner and manager who expanded the property and by the mid 50s, Nissenbaum’s started selling auto and truck parts, allowing customers to remove their own parts from the scrapped cars. The first state approved auto body incinerator was erected in 1964 and used until 1967, when vehicles were brought to the shredder.
The fourth generation recyclers, Joseph and Allen, joined the business in the mid 1960s and since that time, Nissembaum’s has dealt primarily in older automobile salvage. Today Neil Nissenbaum marks the fifth generation of family ownership, working alongside his father Joseph, who was 83-years-old in 2022 and his 78-year-old uncle, Allen
The property is now scheduled to be part of the Boynton Yards project, which opened a nine-story building nearby in May 2022, the first of four buildings planned for the life sciences.
According to the Boston Globe, the family listed the property for sale in December 2020, after discussions and years of watching how the neighborhood might change. The time felt right, the Nissenbaums reported.
Another factor, they said, is that demand for car parts has fallen off, particularly in a longtime blue-collar city that has seen more and more gentrification.
Not many years ago, Allen said, “everyone in Somerville had a used car. Who lives here now? People who ride a bicycle and drink latte. None of that group needs us.”
The Nissenbaums know their family history well, and they relate it with pride. They’re also realists, and they figure that the business will fade from most people’s memories after the new Somerville rises there.
“The name has been out front for 112 years. But when people drive down the street in five years, they won’t know we were here,” Allen said.
I shot these photographs on a Sunday morning in February 2023 with fellow photographers, Dave Brigham and Mike Zeis. Dave, Mike and I are holding tight to the remnants of the 20th century world we grew up in. We share an enthusiasm for fading architecture of the 20th century and a love for hand-painted signage and urban blight and our visit to Nissenbaum’s did not disappoint.
The above photographs were made with my Olympus PEN EP-2 digital camera. Please feel free to leave your comments or share your memories of a fading Somerville as gentrification continues to re-invent the city.
I was thrilled to see that the good folks at the Four State QRP Group released the 4th revision of their popular Bayou Jumper 40M CW Transceiver designed by Jim Giammanco N51B and David Cripe NM0S last year.
The Bayou Jumper, first released in 2017, is a 40M QRP transceiver that is an homage to the classic Paraset, the legendary transmitter/receiver supplied to the resistance groups in France, Belgium and the Netherlands during World War II.
The Bayou Jumper, an updated solid state CW only radio kit is intended to be fitted into a hinged wooden suitcase style box available from Hobby Lobby or any other similarly sized box.
Given my recent obsession with building QRP radios and accessories into empty cigar boxes, I felt the Bayou Jumper would make an excellent candidate for cigar box treatment. I found a gorgeous Perdomo 20th Anniversary cigar box in my stash that was approximately the right size, featured gorgeous red and gold artwork on a black background and was constructed of heavier wood than many of the other cigar boxes in my collection.
The Bayou Jumper front panel was a perfect flush fit left to right in the Perdomo box, and only fell 1/2″ short front to back. I modified the box by gluing a 1/2″ square dowel along the top hinged edge to fill the empty space.
Other mods I made to the cigar box included:
Adding weights to the bottom of the box to prevent the radio from tipping over backward when the lid was up and to provide a little more heft,
Adding a pair of latches to be able to secure the lid closed, and,
Reinforcing the original pressed in hinges with three supplemental screw-in hinges.
Building the Kit
I chose the Bayou Jumper to be my 2022 Christmas project. Professionally I have worked in an administrative role in higher ed for the past two decades and one of the biggest perks of working at most leading universities is they completely shut down for an extended winter recess. Building an electronic kit during my winter recess takes me back to my teenage years when I’d spend my holiday break from school constructing the electronic kits I received as Christmas gifts.
I encountered only two minor issues in building the Bayou Jumper Revision D that were hardly a problem, barely an inconvenience.
The first was a missing resistor, R15, a 1/4 watt 100K ohm resistor. I have never experienced a missing part when building a 4SQRP kit and it’s probably just as likely I dropped or lost the resistor than it was wasn’t shipped in the kit. Regardless, I had the correct value resistor on hand in my home stock supply.
The second matter involved the jumper wires provided to supply current to the multi-color LED on the front panel from the main PCB. The instructions stated the kit included a 12″ jumper wire with header pins included in the kit that needed to be cut in half to make two jumpers. However, the jumper wire included in my kit was only 5.5″ long and once cut it in half as the instructions directed, one of the resulting leads was too short to mate to the header pin on the PCB.
As with the missing resistor, I had plenty of jumper wires that I use for breadboard prototyping on hand and was able to create the necessary jumper wires with sufficient slack to reach the contact points.
All in all, the kit went together in just 3 days’ time as I prefer to work slowly and methodically whenever I build a kit. (Whenever I rush through a project I typically find that any time I saved working quickly would be lost in extensive time consuming trouble-shooting that would be needed!)
Winding the Transformer
The Bayou Jumper features three inductors etched into the PCB but still requires the winding of a single transformer on a T 6-7 toroid core. I have never found winding coils to be difficult or stressful, and in fact, I generally enjoy it especially when the kitter provides excellent directions and illustrations, which 4SQRP did.
The transformer required 3 windings, one of 19 turns, one of 4, and the last of 2. The completed transformer can be soldered to either the top or bottom side of the PCB, based on the builder’s preference and tje screen printing on the circuit board makes installing the completed transformer essentially foolproof. I chose to mount the transformer to the bottom side of the board to make it easily accessible for adjusting the spacing of the winding to adjust the receiver’s tuning range.
The Bayou Jumper’s crystal socket accepts the classic FT-243 crystal form, a popular Cold War era crystal size that today is no longer manufactured and increasingly rare.
The Bayou Jumper comes supplied with a pair of HC-49 crystals for 7.030 and 7.122 MHz, and two crystal adapter boards to fit the HC-49 crystals into the FT-243 sockets.
Vintage FT-243 cases are large enough to accommodate modern small HC-49 crystals and with its 3 screws, the FT-243 can be easily opened and re-sealed, making it possible to re-stuff FT-243 cases for modern QRP use.
Using several of the FT-243 crystals for non-amateur frequencies that I picked up at ham-fests, I have modified 9 crystals for use on the 40 meter CW sub band, all ready to go in my Bayou Jumper.
Receiver Alignment and Final Assembly
Again, the excellent directions made aligning the receiver a snap. Instructions are provided for a variety of alignment methods using an oscilloscope, a frequency generator or a calibrated receiver capable of CW reception. Having all three available to me, I tried all three methods and was pleased when all three were in sync.
I started taking a frequency reading with the tuning dial set to the low end of the scale with my O-scope and read 6.897 MHz.
Next I tried sweeping the dial of my frequency counter to spot the point where oscillation could be heard in the earphones. My frequency counter has an analogue scale and was able to read the resonant frequency at about 6.9 MHz.
Finally I set my portable C. Crane Skywave SSB travel radio for LSB and tuned to the 6.900 and tuning up and down was able to hear the receiver’s oscillator at about 6.895 MHz.
Following the directions to adjust the tuning range by spacing the L1 windings on the transformer closer together or further apart and then adjusting the C30 trimmer, I was able to achieve a final tuning range of 7.000 – 7.167 MHz which should be more than adequate for the CW sub-band I would use.
Finally, I followed the directions to verify regeneration and was happy to find that my receiver needed no further adjustment. Satisfied with my work, I mounted the radio in the cigar box and am looking forward to putting my Bayou Jumper on the air.
Stay tuned for Part II where I will report on my experience operating the Bayou Jumper on the air and any future adjustments or modifications.
My second HecKits build was a great experience – just like my first!
I have become a big fan of the HecKits QRP kit line. A few months back, while looking for a modern dip meter kit, I discovered HecKits and ordered their FET Dip Meter. My experience was with that first kit was great in every way. I was impressed by the high quality of the materials and components, the easy to follow directions, the excellent documentation, and the outstanding customer support courtesy of Darrel Heckendorf, the man behind HecKits.
My wife gifted me the HecKits QRP mW meter as a birthday gift this year and I had the time this past weekend to tackle the project.
Once again, HecKits gets the highest marks for its documentation. The construction manual, sent by PDF by Darrel, was comprehensive, easy to follow and full of detailed illustrations. And again, I was very impressed with the high quality of the parts and materials included in the kit. Everything needed to complete the project is included and the fit and finish is unparalleled.
I was very impressed with the screen printed plated through PCB and included in the kit is a handsome precision drilled metal enclosure giving the finished project a professional appearance. While building the meter, I frequently paused to appreciate the high attention to detail that was put into the kit. For example, the manner in which the BNC connectors mate with the PCB and back panel of the enclosure shows precision engineering that went into developing the kit.
I was able to assemble the kit from start to finish in about three hours’ time – and I do work slowly and try to be meticulous in my work. The meter requires the builder to wind two toroids – a task that I never mind – and again the detailed directions would make it nearly impossible for even a novice builder to fail.
I did run into a small glitch, however. When I finished assembling the kit and began the calibration process, I was disappointed to find that the meter was not responding when I first applied power.
I removed the PCB from the chassis to begin troubleshooting. I had assumed perhaps I messed up the polarity on a diode or tantalum capacitor, but quickly discovered the problem was the ham-fisted way I inserted one of the ICs into the DIP socket, smooshing one side of the pins against the socket. I carefully straightened the pins, reinserted the chip and VOILA! All was well.
HecKits gets big props for the calibration process too. All that is required is a precision voltmeter and an RF tuning tool or eyeglass screwdriver. The kit has a multi-turn pot on the PCB that is used to adjust input voltage for calibration purposes. Once the builder sets the input voltage to the specification, the meter is adjusted for full deflection at 10 watts, 1 watt and 100 milliwatts by adjusting the corresponding trimmer pot on the PCB. What a snap!
I’m eager to add my new wattmeter to my QRP station and I look forward to my next HecKits build. You can get your own HecKits QRP meter or one of their other fine kits on their website – https://heckits.com/shop-heckits. I highly recommend their products for anyone who enjoys building their own QRP gear.
Have you built a HecKits kit? What was your experience? Please leave a comment or drop me a line at firstname.lastname@example.org.
Thanks for taking the time to visit my blog! 72 de AB1DQ / James
This August I picked up a pair of Heathkit HD-16 Code Practice Oscillators for $10 at the flea market at the ARRL New England HamXposition in Marlboro, Massachusetts. The CPOs were tech-specials, non-functional, but ‘mostly there’ with only a few missing parts.
BEFORE: What $10 will buy you at a ham radio flea market.
The HD-16 was Heathkit’s second code practice oscillator, introduced in 1974 and following the first Heath CPO, the CO-1 which was first sold in 1959. The HD-16 was sold until 1974, replaced by the HD-1416 in 1975 which sold with a few cosmetic variations until 1990.
Up until the turn of the century, prospective hams needed to demonstrate the ability to copy and send Morse Code at 5 words per minute (WPM) along with passing the written practical exam to earn the entry level Novice Class license. Advancing to higher class license classes required the upgrading ham to demonstrate the ability to send and receive code at faster speeds – 13 WPM for the General license and 20 WPM for the Amateur Extra Class.
In 1999 the FCC eliminated the 13 and 20 WPM upgrade exam requirements requiring hams to only demonstrate an ability to send and receive code at 5 WPM for high frequency privileges. Then, in 2006, the FCC eliminated all Morse Code testing altogether in accordance with the worldwide policy change the International Telecommunication Union made in 2003,authorizing each member country to determine whether or not to require individuals to demonstrate Morse code proficiency for licensing.
Despite the fact that hams no longer have to demonstrate the ability to copy and send Morse Code, operating CW or Continuous Wave with code remains as popular as ever in amateur radio. Many hams today choose to learn the code and many of us (yours truly included – a ham who only needed to pass a 5 WPM exam back in 2002), very much enjoy ‘pounding brass.’
Thus, the code practice oscillator, or CPO for short, was and remains a very useful piece of equipment for any ham aspiring ham to operate using Morse Code.
My Restoration Project
I began by disassembling both units completely and saving the screws, nuts and other hardware in (what else?) a cigar box in order not to lose any original parts.
The guts of both CPOs liberated from their cabinets.
I washed the cabinet parts in warm water and dish soap and gently scrubbed away at the stains with a soft brush. The back halves of both cabinets were scuffed and scratched badly so I chose to re-paint them in flat black.
Purists would only use the signature Heathkit dark green paint, but I didn’t have any on hand and, while I appreciate complete restorations of antiques, my philosophy for repairing old radio gear has always been to take advantage of what is available to make the vintage equipment usable to me today.
After sanding the enclosure backs with a fine grit sandpaper I applied 3 thin coats of flat black paint and then coated all pieces with 2 coats of clear coat. To compliment the blacked out cabinet sides, I also painted the speaker grilles with flat black paint and replaced the enclosure screws with new black screws.
On to the electronics
I found the original HD-16 manual online and printed a copy for reference. Like all Heathkit manuals, the HD-16’s was well written and included the schematic, complete specs, and some nice content on circuit theory and Morse Code.
Heahtkit HD-16 schematic from the original manual.
From the original Heath manual…
The unijunction transistor, Q1, is a special type of semi-conductor device, with two bases and one emitter, which acts as a relaxation oscillator in the following manner: When the key is closed, capacitor C2 is charged by the battery voltage through resistor R1 and the Tone control until the Emitter (E) voltage reaches the point at which the Emitter is forward biased with respect to B2.
Emitter current then flows because the dynamic resistance between the the Emitter and base one (B1) then drops to a low value. R2 drops the battery voltage to a low level, permitting C1 to charge to a higher voltage than B2.
Capacitor C1 discharges through the Emitter and Volume control until the voltage at the Emitter drops to the point where the Emitter is no longer biased. The cycle then repeats itself at a rate governed by the setting of the Tone control.
The pulsating base current, or oscillator signal, is developed across the Volume control. From the arm of the Volume control, the signal is coupled through the normally closed contacts of the phones jack to the speaker.
The lamp circuit uses the key as a switch that makes and breaks the C cell battery voltage to the lamp.
On Unijunction Transistors
When I first glanced at the HD-16 schematic, I didn’t notice that the transistor was neither a familiar BJT or a FET. Upon closer study I noticed that Q1 is a “unijunction” transistor and was labeled with two bases, B1 & B2 and an Emitter, E.
Schematic symbols for the UJT: N-type on left, P-type on right
My immediate concerns were how rare the 4JX5E670 is, and whether they or a solid equivalent can be found at a fair price today should I need to replace them. My concerns were tempered however by the excitement that this project is going to afford me the opportunity to learn something new.
Up to this point in my life, I have had a cursory knowledge of transistors. I knew the difference between NPN and PNP Bipolar Junction Transistors – their construction and function – and I had a very basic understanding of how a Field Effect Transistor differed from a BJT.
Doing a little Googling, I learned that UJTs could only function as a switch and not as an amplifier. This made sense as the ability to generate pulses would be key to function as an oscillator at the heart of the HD-16.
Structure of a P-type UJT (source: Wikipedia)
Back to the project… assessing the damage.
At first glance, one HD-16 was missing its lamp and the C cell battery holder. The C cell battery holder in the other HD-16 was extremely corroded. Also missing were three of the four 9 volt snaps. One of the 10K tone potentiometers was gunked up and the shaft would not turn. Otherwise, everything else appeared to be present…. not bad.
I grabbed a 10K pot from my on hand parts stock and replaced the seized control and I soaked the other pots as well as the switches with de-oxit and worked the contacts.
I decided to replace the 0.22 uF capacitors with a pair of new Mylar caps from my stock. I did not test the fixed resistors and I didn’t even bother to check to see whether I had any 4JX5E670 UJTs in my parts supply. I would dive deeper and replace any of these parts if the oscillators failed after the other work I did.
I debated whether to replace the lamps with LEDs, a popular and logical mod. Doing so meant I could eliminate the 1.5 volt batteries altogether and complete the mod by adding a dropping resistor from the 9V batteries and rewiring the SPDT switch.
I liked the way the original incandescent dial lamp looked so I didn’t do a mod for LEDs. Since I needed to replace one of the missing C cell holders and the remaining one was badly corroded, I replaced both with modern plastic holders. I attached the new holders to the inside of the cabinets using 3M 2 sided tape.
I was unable to determine whether the HD-16 was a DIY kit or was sold only as a completed unit as I couldn’t find a construction manual online. So I took the time to sketch out the schematic and trace the parts layout creating a pictorial diagram I could use to confirm the circuit was complete.
Putting it all together
I worked on both oscillators side by side, working through each step of the restorations on one unit, then the other. It made sense to work this way as I could stay focused on each step as I worked.
After completing the parts replacement I grabbed some batteries and tested each HD-16 before attempting reassembling. Fingers crossed, both worked fine and I was relieved I didn’t have to address replacing the unobtainium transistors.
One of the completed electronic restorations – ready for testing and reassembly.
Reassembly went smoothly. I started by replacing the lamp grommet and inserting the lamps into their holes on the top of the enclosures and then installing the speakers and grilles.
Next I reattached the springs on the backs of the cabinets – this was Heathkit’s clever idea to secure the 9 volt batteries securely in place – and I stuck the new C cell holders onto the back of the enclosure using 3M double sided tape.
Next I installed the switches, confirming that they were properly oriented to light the lamp when set to “LIGHT,” and then I re-inserted the two potentiometers and the key and phones jacks to the front panel.
The last thing I did before closing up the cabinet was to secure the terminal strip to one of the speaker screws. The space available was tight, but not impossible. I took special care to make sure that the transistor and other component leads weren’t shorting out against each other. I did another test of both units before closing up the cabinets.
Both HD-16 cabinets ‘re-stuffed’ and ready for buttoning up.
Both HD-16s had the original metal foil serial number sticker stuck inside the cabinets, but they were in bad shape and not salvageable. So I created a “new-retro” style serial number sticker for each unit in order to preserve each CPO’s history.
AFTER: Two restored Heathkit HD-16 Code Oscillators ready for use!
Do you or did you have a Heathkit Code Practice Oscillator? If so, which model and how did you like it? Comments and questions encouraged. Drop me a line at email@example.com to join the conversation!
A fun, easy-to-build, weekend radio kit project that is the latest to get the AB1DQ Cigar-Box treatment.
It’s no secret that as a modern day electronics kit builder, I have a fondness for the fine kits currently being offered by the Four State QRP Group and it’s also no secret that one of the biggest gateways to my ham radio ticket was the years I spent as a SWL in my teen years.
Is it any surprise then, that I would at some point build the 4SQRP Group’s excellent long-running Ozark Patrol Shortwave Receiver? Quoting, their website,
…this kit was designed in homage to simple beginners regenerative receivers of a generation ago. Many current hams and radio enthusiasts were introduced to the hobby by building and listening to such classics as the Radio Shack Globe Patrol, or the Knight Ocean Hopper. … the Ozark Patrol is offered so that the builder of today can relive the excitement of tuning in the world on a simple receiver circuit.
Once again, you’re singing my song 4SQRP – count me in!
About the Kit
While still an undergrad at Columbia University, legendary radio pioneer Edwin Armstrong patented the regenerative receiver in 1914 and it was leaps and bounds ahead of the then state-of-the-art receiver circuit.
By applying some of the output signal from a vacuum tube back into the input signal in phase, a feedback loop is created that greatly amplifies the signal by as much as 1,700 times. A regeneration control is used to gradually adjust the amount of feedback to the point of oscillation where the signal will distort. The regenerative receiver features improved sensitivity and selectivity over other receiver designs of its day.
The Ozark Patrol circuit, designed by David Cripe, NM0S, replaces the vacuum tube of Armstrong’s era with a common NPN bipolar transistor. The kit has only 38 through-hole components for the kit builder to attach making for a build time for me of under two hours.
The Ozark Patrol also features the modified surface mount technique known as the “Pittsburgh Method” of construction, pioneered by Joe Porter, WØMQY. Leaded components are directly soldered to pads on the back copper layer of the circuit board (which also makes the front panel of the radio), forming a ground plane to shield the radio from hand capacitance effects while tuning.
I previously built the 4SQRP Murania one transistor “Boy’s Radio” kit that used the Pittsburgh Method and it was a positive experience. You can read about that build here.
Building the Ozark Patrol
I built the kit in under three hour’s time over a couple of days. As I’ve come to expect from 4SQRP, the kit was well packaged, complete and not missing any parts, and the step by step instructions were for the most part very clear and easy to follow. A couple of times I did find myself referring to photos of others’ builds for clarity – particularly when working with the tuning capacitor and the ‘gimmick capacitor.’
The kit requires the builder to wind a single toroid inductor, 20 turns on a T-50-2 core and its the first step of assembly. Because I started my build in the evening after a long work day, I chose to wind the toroid later when I was feeling 100% fresh, and instead started my build by attaching the resistors, diodes and fixed capacitors.
A novelty feature of this kit is that it requires the builder to wind a ‘gimmick capacitor’ to couple the antenna to the tuning capacitor. This low value capacitor is easily made by twisting about an inch of magnet wire with insulated hook up wire. I had no difficulty doing this, and I apparently did it correctly as my receiver worked the first time.
The instructions suggest that the radio can be made or less selective by tightening or loosening the twist so I may choose to experiment with this. Fellow kit builder and blogger, Mike Simpson, has a really great post about his build of the Ozark Patrol here in which he describes his mod adding a varicap in lieu of the gimmick cap for coupling and tuning the antenna. Check it out!
The Cigar Box Treatment
The Ozark Patrol comes with a slab of soft pine wood which is intended to be used as a base. The circuit board/front panel is screwed to the board at 90 degrees leaving the guts exposed for viewing and the easy attachment of the antenna and ground wires.
I initially envisioned mounting the radio on the top or the bottom of a cigar box and attaching a handle to fashion a finished radio resembling a portable transistor radio of my childhood years.
Looking through my stash of cigar boxes I found an Oliva box with a hinged lid that had almost the exact dimensions of the Ozark Patrol circuit board. What good fortune!
Using a box cutter, I carefully pried off the bottom of the box and then smoothed the edges, removing excess dried glue with a fine grit sandpaper.
The location of the screw holes on the circuit board unfortunately were spaced to fall just inside the edges of the cigar box sides. I addressed this by adding square dowel reinforcements to the four inside corners of the box using wood glue. Once dried and set, the dowels provided both a space to drill pilot holes for the PCB screws and reinforcement for the box itself.
Finishing touches included using brass thumb screw hardware mounted to the side of the box for retro- looking antenna and ground terminals and attaching a decorative drawer pull to the top to provide a carrying handle.
Inside, I attached the 6 AA battery holder to the box lid, making sure that I left sufficient slack in the leads for the lid to open completely. I also cemented a copy of the schematic inside the lid. In the end I have a very retro- looking suitcase shortwave radio that has a bit of resemblance to portable radios like the Zenith Trans-Oceanics of an era gone by.
How did it work?
Last night I set the radio up in a second floor bedroom, attaching a ground wire running to the ground lead of a power outlet and a random length of wire for an antenna suspended to the light fixture. I also shut off the LED room lights which made a difference in lowering noise.
Tuning the radio was definitely a fiddly process, but it was also a ton of fun. I easily picked up 3 or 4 AM shortwave broadcasters on one band and hams operating CW (Morse Code) on the other. Success!
I would highly recommend the Ozark Patrol kit for any kit builder, or aspiring kit builder. The kit shouldn’t present too much of a challenge for even a new kit builder and the finished radio works and is fun to operate.
Have you built the Ozark Patrol or a similar kit? Perhaps you built the Radio Shack Globe Patrol back in the day? Please leave a comment or drop me a line at firstname.lastname@example.org to share your experience!
“Creativity is inventing, experimenting, growing, taking risks, breaking rules, making mistakes and having fun.” ~Mary Lou Clark
Ham radio is unlike and superior to all other hobby radio services as it not only allows licensed operators to build, test and experiment with our radios and other equipment, we are encouraged to do so.
Long before I earned my ham radio license, I’d spend hours on end as a child creating various projects fueled by my imagination, using the never ending supply of empty cardboard Dexter cigar boxes my grandfather had stashed in our basement.
Several of my creations in my early adolescence involved radio & electronics projects. Besides providing me with a stash of cigar boxes to play with, my grandfather also had a fairly complete electronics workbench in our basement, complete with tools, tubes, parts, dozens of radio & TV carcasses in various states of disrepair and a treasure trove of 1960s era magazines including such titles as Pop Electronics. My grandfather had also taken the DeVry Home Radio & Television course before I was born and to my delight, all of his workbooks and home projects were under the workbench.
As a licensed ham radio operator for the last 20 years, one of my favorite aspects of our hobby is kit and scratch building and operating with QRP gear I’ve built myself. Over the years I’ve built projects into aluminum chassis, atop breadboards, in tuna tins and even tiny mint cans. Following in my grandfather’s footsteps in yet another way, I’ve become something of a cigar aficionado in recent years and found myself amassing my own stash of cigar boxes. It wasn’t too long before inspiration struck and I put one and one together.
Why the Cigar Box Chassis?
My cigar box fascination blends two of my leisure loves – radio & cigars. It also gives me the opportunity to challenge my creativity and express myself through unique projects. Building with cigar boxes also connects me to my childhood roots, per above, as well as the very roots of amateur radio, taking me back to the early era of breadboarding. Finally point-to-point construction using terminal strips and increasingly rare leaded components is not only ‘going retro,’ it’s also a lot easier on us older folks. While the parts got smaller, our vision got weaker and our hands a bit shakier!
There are several advantages a cigar box chassis brings to your project, such as:
adding flair & artistic touch to the project,
being available in different sizes and shapes,
being much easier to drill and cut than metal chassis,
being easily oriented in various ways to accommodate specific project needs.
having multiple construction planes – the top & bottom of lid, and the bottom of box.
providing space to store cables, accessories, and documentation inside the box.
Conversely, there are a few disadvantages to be aware of when building a project into a cigar box, such as:
varying quality of construction,
cheaper flimsy boxes may be difficult to drill and cut cleanly,
boxes with thicker lids and sides, make the mounting of some parts difficult,
lacking the inherent shielding and common ground plane of a metal chassis,
hinged lids may make for challenging parts placement and wire routing.
“The creative adult is the child who survived.” ~Ursula Le Guin
There are several contemporary kits that I became aware of that helped spark my imagination for my cigar box builds. These included the very fine line of Peebles Originals kits which featured point-to-point construction on a wooden base. I had build a few of the Peebles kits including a one tube regen receiver I built with my 12 year old niece a few years ago.
My good friend, and radio cuckoo soulmate, W1YSM, Dr. Ed Snyder, gave me a wonderful gift a few years ago, the Thames & Kosmo Radio Ace, a mid-2000s one tube regen BCB & SW receiver ‘kit’ built into a nicely finished wooden base. This wonderful kit didn’t require assembly but came with a wonderful step-by-step book explaining how radio and this specific circuit works.
Inspiration also came from the Four State QRP Group’s venerable Bayou Jumper QRP transceiver kit, which is a scaled down solid state replica of a WW2 era ‘paraset‘ rig. The kit is intended to be built into a wooden suitcase box.
Sources of inspiration from L-R: a Peebles Original 1 tube regenerative receiver, the 4SQRP Bayou Jumper transceiver, the Thames & Kosmo Radio Ace.
Where to find cigar boxes
The best place to find cigar boxes is your local cigar shop. Search for them in Google and call around. Better yet, pay your local shop a visit. I have gotten all the boxes I’ve ever needed from the Owl Shop in New Haven (where I’m a regular customer). The Owl Shop puts out dozens of cigar boxes on the curb each week and they are free for the taking. Some shops will charge you for empty boxes and in my experience, you can find great boxes for under $10.
Online sources for cigar boxes include eBay and Etsy as well as craft suppliers such as Michael’s, Hobby Lobby and cigar box guitar kitter CBGitty.
Tools for the job.
In addition to your usual electronic kit tools (solder iron, nippers, pliers, screwdriver) you will need some basic woodworking tools for preparing the cigar box.
A small drill press with a set of hole saw bits will go a long way in terms of being able to drill neat and precise holes for mounting speakers, meters, tube sockets and holes for switches, potentiometers, varicaps and power, antenna and key sockets.
You will also want to have a small hacksaw and coping saw, files and sandpaper. A square with level is essential for precisely locating the places you want to drill.
I also recommend having a good set of drawing tools that include rulers, compasses and protractors. I am a huge proponent of taking the time to sketch out your box layout and design before drilling any holes. I keep a lab notebook in which I document all of my projects. This is taking the adage, measure twice, cut once to the next level. It’s time well spent and in the end you will have a nice record of your projects, not unlike your logbook of on air contacts.
Keys for success
Proper planning is the biggest key to success, but other keys include:
Keep & use a workbench notebook. Document all aspects of your project and sketch the circuit, parts and chassis layout. When laying out placement of parts, measure and remeasure. Then measure again.
Challenge yourself to k three-dimensionally. You have several planes on a cigar box in which to place parts – the top and bottom of the hinged lid, the bottom of the box, and the inside and outsides of the four sides.
Prototype whenever possible!
Keep leads short, but allow enough space for troubleshooting and future mods.
Keep damaged boxes for properly sizing holes for future projects.
Cigar box anatomy and project layout
Start by considering the cigar box from all angles. Turn it over and rotate it and imagine how you want the finished project to look. Consider various placements of parts, controls and circuit boards or terminal strips. Keep the end user in mind and consider ease of use and ergonomics.
You need to pay special attention to the location of the hinge for boxes with hinged lids. The hinged edge is the only place you can route wires from the lid to the bottom or other sides of the box. The back side of the box will logically become the front side of your project where you may want to place switches and controls.
You will also need to be mindful about the depth of parts, measure for adequate room and alignment of all parts when the lid is closed. Consider too that cigar boxes are sometimes made of thin wood and weren’t intended to contain or support heavier components like transformers. Support and balance are both important. You may wish to reinforce the lid or sides by gluing in square dowels. You can also add corner reinforcements found at your local hardware store for additional reinforcement.
Relocating controls off of the PCB
Many modern kits have switches, pots and other controls mounted along the edge of the printed circuit board and are intended to meet the front panel of an enclosure. Sometimes this makes for an easy way to mount a project inside a cigar box. Another option is to move or replace these parts with chassis mounted parts that you can reposition on the front or top of the cigar box. This gives you more flexibility in terms of control placement.
Being non-conductive, your wooden cigar box won’t provide shielding like a metal chassis. This may lead to problems in terms of hand capacitance or interference from other nearby appliances that generate RF. Lining the inside of the cigar box with a layer of heavy duty foil can help. Foil is easily cut & sized and adheres quite well with white glue or a glue stick. Heavy duty aluminum foil is good and cheap, and copper foil is even better but costs more.
I recommend measuring the inside dimensions of your cigar box and then sketching out a pattern on graph paper. Then, using a cutting mat and ruler, transfer the pattern to the foil and carefully cut the foil. Then, starting from the bottom of the box, use glue stick to apply the foil.
Potentiometer and varicap shafts, switches, and other chassis mounted connectors may be too short or shallow for thicker cigar box lids or sides. One solution is to countersink a larger diameter hole on the outside of the box to provide space to flush mount a lock washer and nut. However, many cigar boxes feature soft wood which may easily splinter. When enlarging a drilled hole in soft or thin wood, use a larger drill bit and turn it gently by hand.
“You can’t use up creativity. The more you use, the more you have.” ~Maya Angelou
Some selected AB`1DQ creations
To perhaps help spark your imagination and as a means to illustrate some of the construction points I outlined above, the remainder of this article showcases a few of my cigar box projects.
Basic Code Practice Oscillator
I recently built a basic 2 BPT code practice oscillator using the Boy Scout WN0BSA schematic found all over the internet and sketched out my parts layout using Windows Paint.
This project was a bit of pure nostalgia for me as my first childhood cigar box build was a simple transistor CPO similarly mounted in the same fashion with the key attached to the lid in an old Dexter cigar box.
For a simple old school project, I decided to use a pair of terminal strips mounted on the bottom of my cigar box. My CPO layout pushes the abilities of the cigar box a bit further. Choosing a cigar box with a flat lid that folds out flat to the rest of the box when opened and placed upside down, I mounted a J38 key to the lid and pasted a copy of the International Code next to it. With the speaker also mounted to the bottom of the box, the end result is a nifty flip open all in one CPO.
This project was a bit of pure nostalgia for me as my first childhood cigar box build was a simple transistor CPO similarly mounted in the same fashion with the key attached to the lid in an old Dexter cigar box.
QRP Guys 40 Meter Easy Receiver
I loved the basic kit offerings from the folks at Pacific Antenna. A few years back, along with my fellow advisors to the Amateur Radio Club at Yale, we led a Wednesday Night Workshop at the Yale Center for Engineering Innovation and Design.
The workshop was intended to introduce the uninitiated Yale students, faculty and staff to the basic principles of RF and after a brief presentation, the group paired up and each team built the Easy Receiver Kit. Despite the fact most had never soldered, in the end we had successfully built 10 out of 10 kits. The students in particular were overjoyed when they were able to hear their radios oscillate on an HF rig we brought in.
I decided to give my Easy Receiver the cigar box treatment and mounted it in a small CAO Perfecto cigar box. This is an example of where I measured and drilled out properly spaced holes in the cigar box lid so I could mount the lightweight PCB using just the shafts of the potentiometers.
I added an 8 ohm speaker to the lid, a switchable 3.5mm audio out jack for the use of phones, along with a chassis mounted coaxial barrel power connector, an on-off switch and a power on LED indicator.
Utilitarian LM386 Audio Amplifier
The LM386 audio amp IC makes it simple to add an audio stage to any receiver project. The chip requires no more than a handful of passive components to build a robust amplifier and the internet is flush with schematics and plans. Here is a schematic for the most basic LM386 audio amplifier, taken from the www.circuitbasics.com website.
If you don’t have the necessary components on hand in your parts bin, there are many kits available online with the PCB and all necessary components, aside from the speaker. Prices range from about $10 from US retailers and can be found literally for pennies offered by Chinese retailers like AliExpress.com
While I have incorporated this amplifier into some of my receiver projects, I have also come to appreciate the value of having a standalone amplifier on the operating bench.
Here’s a cigar box build from a kit that also includes a tone control. Again, I mounted the PCB directly to the lid of the cigar box measuring and drilling holes to accommodate the board mounted potentiometers. The SPST toggle power switch is chassis mounted and placed in line with the volume and tone control.
The “transistor tester” kit is fairly ubiquitous online these days and as a frequent kit builder, I have found it to be an indispensable tool when working with small leaded components given their shrinking size and my diminishing vision as I get older. The tester has three terminals to which you can attach resistors, capacitors, inductors, diodes and transistors. The 2 line display returns the type of component and its value and will even indicate the terminals for diodes and transistors.
I built my transistor tester into a cigar box, mounting the display, controls and the terminals to the top of the box. I used three 6-32 screws for the terminals and they are spaced so I can hold most 2 leaded components directly to them for testing. I store three alligator clip jumper cables inside the box when not in use so they are at the ready for short components or when testing three leaded components like BJTs.
I made a couple of mods, replacing the on board trimmer pot that controls display contrast with a same value chassis mounted pot and I moved the power on LED from the PCB to the cigar lid as well.
Ramsey QRP-20 CW Transmitter
Ramsey was a prolific retailer of simple electronic kits and offered a wide variety of ham radio kits as well as other non-radio projects. Their products featured a nifty two piece black plastic project box with pre-drilled end pieces to accommodate the controls for the specific project.
I had built several of their kits over the years, but sadly it’s been a while as the company abandoned the hobby kit business several years ago.
This past winter I spotted an unbuilt Ramsey 20M transmitter kit available online at a not-so-unreasonable price. I purchased it and really enjoyed putting it together. The kit came with the black plastic enclosure, but I realized the dimensions of the PCB were nearly a perfect fit for the inside of the small Oliva Nub cigar box.
I have already blogged about my build, which you can read in detail here.
Since my build, I I made a mod in order to give me not two, but three selectable frequencies. I added an octal tube socket to the left side of the cigar box and installed another DPDT toggle switch. The octal socket will accommodate two FT243 crystals so by wiring per my diagram below, I now have a versatile QRP rig.
The Heil Pine Board Project Reimagined
Many folks reading this may already be aware of the Pine Board Project, an old school DIY AM transmitter project with four distinct sub-projects – field strength meter, power supply, audio pre-amp w/ equalization and the transmitter itself.
About five years ago (my how time flies!) Bob Heil presented the projects with step by step instructions and updates each week on the HamNation podcast. And the project was also featured in QST, and on Heil Sound website.
I initially built the project as originally presented on slabs of pine wood but then converted my build into cigar boxes. As with the Ramsey QRP-20 above, I have already blogged about my transformation of the power supply here.
I plan to revisit my build and expand my blog post on the rest of the project in the future, but in the meantime, here are some photos of my cigar box mods.
Ham radio is unique among all radio-service hobbies as we are not just allowed, but encouraged, to build our own gear and to experiment.
Working with cigar boxes scratches my creative itch as I build gear that is uniquely me.
Where will you find your niche? My charge to you: GO MAKE STUFF!
Thanks for taking the time to read my article. If you enjoyed it or have further questions or want to share ideas or want to leave any other feedback, please leave a comment below or feel free to drop me a line at email@example.com.
I would love to hear what is on your workbench these days!!!
As I venture deeper into scratch building I’ve recently become aware of how useful it would be to have an old school dip meter on the workbench to verify the resonance of LC circuits in the receiver circuits I’ve been experimenting with.
In the back of my mind I’ve always been aware of the existence of the dip meter and the tube era term “Grid Dip Meter” seems to have been rooted in my mind going back to childhood. I’m fairly certain the term appeared on amateur licensing exams I’ve sat for, and I know it was ubiquitous in many of the old 60s era Pop Electronics I used to read in my grandfather’s radio shop.
I started a search online to learn more about the history, design, use and availability of dip meters, sometimes called ‘dippers’ today. In the solid state era, field emission transistors (FETs) and sometimes bipolar junction transistors (BJTs) have largely replaced .
FUN FACT: FET based dippers are sometimes called Gate Dip Oscillators while BJT based dippers are sometimes called Emitter Dip Oscillators.
The dip oscillator isn’t a precision instrument by today’s digital standards and several factors could lead to inaccuracies. Despite that, it has numerous practical uses in the amateur radio station. In addition to being used to measure the properties of resonant circuits, filters, and antennas, a grid dip oscillator can also be used as a signal generator, to measure individual component capacitance or inductance and they may also be used for transmission line testing.
I discovered that back in the day, the amateur radio builder had several options to assemble their own GDO from kits. As expected, Heathkit offered several dippers in kit form throughout their history including the Model GD-1 and later, the HD-1250.
I found several of these old Heathkit GDOs available online and at pretty reasonable asking prices. But as always, when buying used vintage electronic gear, it’s a crap shoot in terms of whether the item bought sight unseen will come complete and be operable. So I decided to explore whether any of the niche kitters offered a modern day equivalent that I could build myself.
This is where I discovered HecKits (www.heckits.com) operated by kit designer and ham radio operator WA7OIB, Darrel Heckendorf. Darrel offers several kits priced under $100 that may be of interest to the QRP builder including an SWR Bridge/Frequency Counter, a Step Attenuator, a CW Keyer, and of interest to me, an FET Dip Meter.
I ordered the FET Dip Meter kit online and quickly received an email from Darrel, thanking me for my purchase, asking me to confirm my shipping address and to inquire whether or not I wanted him to include the optional 6M coil. I had initially missed this email and by the time I replied a day later, I had discovered Darrel had already shipped the kit with the 6M coil at no extra charge and the kit arrived a couple of days later… wow!
I sat down to build the kit this weekend and it was the perfect project for a relaxing Saturday afternoon at the workbench. My initial HecKit experience was everything I look for in kit building.
The kit was well packaged and parts were in clearly labeled zip lock bags. The quality and the fit and finish of the PCB and project case were exceptional. The plastic case fit together precisely and has a nice quality feel about it. The PCB was not thin and flimsy and it featured double sided holes. While it did not have silk screening for parts placement, that was not a problem because the instructions included a large easy to follow diagram of parts placement on the PCB.
Overall, the instructions and documents which Darrel sent by email as a PDF along with my order confirmation was exceptional. Darrel provides a nice introduction to the product and includes several links to learn more about the theory and operation of the dip oscillator and the step by step directions are very easy to follow. Documentation included not only the PCB parts placement diagram, but also full schematics and very clear easy to understand directions for winding the interchangeable coils.
I give Darrel and HecKits high marks for putting together what I would consider a perfect DIY kit. It’s worth mentioning too that the kit came complete with no parts missing.
From start to finish I spent less than 3 hours on the build with the exception of winding the coils, which I still need to do. Generally I don’t mind winding toroids and coils, but the coils for this kit are just a bit small and a tad fiddly for my aging eyes and increasingly shaky hands to easily manipulate, so I thought I’d complete the other coils later on this weekend when I’m feeling fresh. The kit did come with the first coil covering the 1.3 – 2.8 MHz range pre-assembled and it allowed me to verify that my meter worked properly upon completion of the build.
If you’re a QRPer and a builder like me check out Darrel’s offerings at www. heckits.com. As I mentioned, there are several other projects on his site that have caught my eye, particularly the Step Attenuator and the QRP mW meter. I look forward to putting my dipper into use on the workbench as well as my next HecKits build.
Thanks for taking the time to read my blog today. Please leave a comment and let me know if you’ve built this kit or any other of the HecKit lines or share your experience with using a dipper in your station.
Every Spring Yale University organizes a fitness program for the community called The Yale Trail in which staff are encouraged to start a daily walking program. Last Spring, I posted a single photo taken during each of my morning walks to my Instagram account under the title “Good Morning New Haven.“’
The 2022 program is now underway and runs through May 10, 2022. This year I intend to post a photo a day taken while walking along Dixwell Avenue.
Besides being perhaps the best named road in all of New Haven County, Dixwell Ave. is a commercial and residential wonderland that stretches for several miles through New Haven, Hamden, and North Haven and is positively stupid with urban delights such as hand painted murals, colorful signage, fascinating architecture, and intriguing statements of ethnicity and individuality. See below for a description of my photographs above and links to learn more about my subjects.
WHAT’S A HIPSTAMATIC?
Hipstamatic is an iPhone camera app that allows the photographer to emulate a variety of toy and lo-fi film cameras.
Toy camera photography became a cult thing in the photography community in the 90s and into the 21st century. Using cheap plastic medium format cameras such as the Diana and the Holga, renowned for aberrations such as light leaks and ill-formed plastic lenses, photographers are able to produce very distinctive ‘sloppy’ and artsy photos.
The Hipstamatic app allows the user to change virtual lenses, films, flashes to produce digital images that have the qualities of toy camera photographs. For this years gallery I have chosen a combination of settings that produces over-saturated high contrast images with a distinctive black rounded border that emulates the Through-The Viewfinder style of photography.
Please consider bookmarking this page and coming back each day to see what has caught my eye. This year I am challenging myself to take all photographs with the Hipstamatic toy camera app on my iPhone SE using the same settings for a cohesive gallery. I hope you enjoy my efforts.
TWENTY YEARS AGO, TODAY the FCC sent greetings and I was issued my first amateur radio license, Technician Class ticket, call sign KB1IAR.
Two weeks prior on a chilly Thursday evening, I had nervously sat for, and passed, the Element 2 license exam held at the Red Cross on Gano Street in Providence, RI.
A lifelong ambition, and something I rightfully should have done during my teen years as all the seeds and passion for all things radio were already planted and had taken root, was finally achieved at the age of 35.
Sometime that January I was in my local Radio Shack purchasing materials to erect a long wire antenna for my shortwave radios at the new house I had purchased in Manville, RI when I spotted the Now You’re Talking! Technician Class amateur license guide on the shelf.
I flipped through the pages and thought to myself, why not? The material looked straightforward, most of the technical electronic material was already familiar and I thought that if nothing else it would kind of neat to hold an amateur radio call sign, even if I never actually purchased a radio and got on the air.
This was also in the months immediately following the 9/11 attacks and it seemed like being able to communicate with others should more horrific acts occur, might be a good idea. So, I made an impulse purchase of the study guide and after two or three weeks I felt I was ready to take the test.
I of course DID get on the air pretty quickly. The first radios I purchased was a pair of Icom IC-1000H FM 2-meter transceivers, one I installed in my Ford Focus, and the second went into my first ‘radio shack’ an unused bedroom that served as my ‘man cave’ in our new home. This bedroom conveniently had the access door to the attic which allowed me to easily snake coax from the radio into the attic where I had installed a Ringo Ranger vertical antenna.
I also purchased my first hand-held radio, an Icon IC-V8 which was an entry level bare bones 5-watt transceiver for the 2-meter band. The IC-V8 was a distinctive looking radio with it’s green plastic casing and non-rectangular body. I still have the IC-V8 and use it on Tuesday evenings in the warmer weather months to check into the Meriden Amateur Radio Club Tuesday night 2-meter net from the front porch here in Cheshire.
It wouldn’t be long before I upgraded to my General Class license a few months later earning me HF privileges that would allow me to work other hams around the world on the shortwave bands, but today I fondly recall and feel nostalgia for my initial experiences as a Tech.
The past two decades have been nothing short of TOTALLY AWESOME and I expect the next twenty to be just as good! If you are considering getting your ham radio license, I wholeheartedly encourage you to go for it. It’s never been easier to earn that first license and there are many resources out there to help you prepare for your exam. I’d be happy to help point you in the right direction if you’d like – drop me an email at firstname.lastname@example.org.
This morning I completed the Front Panel Board, the second board of the Elecraft K2 HF Transceiver Kit build that I began at the start of the year. After completing the Control Board on January 17, I took a complete month off working on other weekend projects before starting the Front Panel on February 21. I did state from the get go that I was going to take my time with this, my most ambitious kit build, and I’m staying true to my word.
The Front Panel Board is where all of the user controls are mounted. These include the large rotary encoder/tuning knob, the numeric keypad and pushbuttons, and five variable resistors. This section also includes the graphical LED status bar display and the LCD main display.
Assembly of the front panel starts by soldering the sixteen tactile push button switches to the printed circuit board. For a proper and neat professional appearance, it’s essential that all of the switches be mounted at a precise uniform distance from the surface of the board.
Elecraft provides a nifty switch spacing tool in the kit which is essentially a thin narrow bit of PCB material that is placed under each switch which is then pushed flush to the spacing tool. This clever method worked exceptionally well for me.
After the switches are mounted, the board is populated with the usual components – resistors, capacitors, diodes and transistors. The front panel board has four ICs including the large 40 pin U1 which is mounted on the bottom side of the board and behind the display.
The front panel board also has a good bit of hardware to be attached including the eight-pin microphone jack and several spacers. Up to this point the instruction manual has been absolutely excellent in providing detailed easy to follow accurate directions.
However, I did encounter some difficulty when it came to mounting the main display components which consists of two backlight LEDs, their spacers, a white cardboard reflector, a frosted plastic diffuser, and the 40 pin LCD.
As I discussed in my previous post, the Elecraft K2 is a fabulous kit, but it’s a rather old kit, first prototyped a quarter century ago – in 1997! Understandably in the time since its introduction, some components become ‘unobtainium’ as the years go by. Vendors come and go and with advancing technology, manufacturers discontinue production of now archaic through-hole components with today’s increasing popularity of SMD architecture.
Thus, when one buys a K2 kit today, it will come with several pages of errata that must be carefully consulted and reviewed. Builders in 2022 will find themselves crossing out sections, sometimes whole pages, of the original manual, and adding notes about the replacement modern components packaged with their kit.
This was the case with the display assembly. I was instructed to cross out most of the directions pertaining to the installation of the display on pages 27 and 28 of the manual and to follow the alternative directions provided as errata.
The revised directions call for the builder to first insert the leads of a pair of rectangular LEDs through plastic spacers and solder the LEDs flush to the board to the left and the right side of where the LCD will be mounted.
Between the two LEDs, the builder places a white cardboard backlight reflector and then mounts a frosted plastic diffuser by placing it over the the two LEDs on the left and the right side. The diffuser has an indent on each side to accomondate the LEDs.
I found this all went precisely as described until I came to the step that instructed me to place the LCD flush on top of the diffuser and then solder the 20 pins of the LCD to the associated pads on the PCB.
None of the LCD pins were long enough to go through the holes in the pads on the board. If pressed flush to the diffuser the LCD pins just barely touched the pads.
I carefully checked the instructions and my work. I was certain I mounted the LEDs correctly and flush to the board with their spacers, and the cut outs on the bottom side of the plastic diffuser neatly accommodated the LEDs perfectly.
Realizing that proper positioning of the LCD would be critical for the PCB to properly fit in the front panel and knowing that not getting the spacing correct would also give the finished radio a sloppy appearance, I reached out to Elecraft for help via their website.
I dreaded the prospect of having to de-solder 20 pins and run the risk of damaging the LCD if I needed to remove it after it was soldered in place. I wanted to get as much information as I could before proceeding.
I received an email reply from Dave at Elecraft who is their K2 support guy within a couple of days. Dave stated that it was ‘perfectly normal’ for the LCD pins to just touch the top pads on the PCB and that they do not need to protrude through the holes. He said that his last K2 build was like this and suggested that I carefully solder the 20 pins from the topside, but to make sure the LCD is level and parallel to the board.
I did as Dave recommended, carefully aligning the LCD so it was level and evenly spaced above the board. I started by soldering each of the corner pins and confirming the LCDs position after each solder joint. Once done, I applied solder to the pads on the bottom of the board to let it flow through the hole to help ensure solid contact.
However, after I soldered just under half of the LCD pins, I realized I had left out the cardboard reflector. D’oh! There was no way I could slide the stiff cardboard under the pins at this point and I didn’t want to have to de-solder so many pins, so I came up with a workaround.
I took a piece of white copier paper and cut a rectangle to the same size as the cardboard reflector. Cutting the paper in half, I was able to slip both halves between the gap in the pins on the bottom of the LCD and position them in proper place. I held them in place with a bit of cellophane tape.
From here on out the rest of the front panel assembly went smoothly. Again I encountered the need to reference the errata for the main encoder knob as Elecraft includes a different unit than the one referenced in the original instruction manual. The encoder in my kit required me to solder a few parts into an auxiliary board to which the encoder was attached. The auxiliary board is then attached to the back of the front panel board.
The last step was to mount the completed front panel board inside of the front panel. Before doing so, the manual lists about 30 resistance checks for the board. Each test point checked out as specified to ground – excellent!
I was very pleased that after I carefully mounted the board the front panel looked perfect. All of the push buttons were a proper and uniform height through the holes on the panel. All knobs, including the main encoder dial, were also correctly mounted and turned with ease. Best of all the main display LCD that caused me so much grief, looked perfect under the front bezel.
“Unique ham radio kits for the budget minded.” That’s what the masthead proclaims on the QRPGuys website and that is exactly what you’ll find there – a collection of project kits for the builder/QRPer that aren’t found on other kit sites and all offered at a more than fair price.
Current transceiver kits include their AFP-FSK Digital Transceiver, now in its third edition and they also offer a wide variety of other QRP essentials including several antennas and tuners, test gear including power meters, attenuators and filters and other accessories,
The QRP Guys are an affiliation of a “who’s who” of QRP building and will give you an idea of the innovative and high-quality products they develop. Ken LoCasale (WA4MNT) provides kit mechanical design, board layout and documentation, and NorCal cofounder Doug Hendricks (KI6DS) is credited with logistic support and beta testing.
Circuit design is by Steve Weber (KD1JV) of Pacific Antenna, Dan Tayloe, creator of the N7VE SWR Bridge, and Cliff Donley (K8TND). Both Steve and “Kazu” Terasaki (AG5NS) author firmware, technical assistance is given by beta builder Yin Shih (N9YS) and John Stevens (K5JS) is credited with assisting Ken with website maintenance.
Building the QRPGuys 40-30-20 M End Fed Antenna
The QRPGuys multiband end fed antenna meets my definition of an easy build with only 16 solder-in components on the main tuner circuit board and the two traps. I started as I do with all of my kit builds by inventorying and arranging all of the parts. I have been using cigar boxes with clasps on their lids to prevent me from losing small parts before they are needed. Cigar boxes are also ideal for storing works in progress kits when a project will extend beyond a single building session.
The prospective builder should be forewarned that of those sixteen components, four of them are inductors that must be hand-wound on toroid coil forms. Many builders seem to abhor the winding of coils, and while I find it sometimes fiddly work, I’ve come to not mid the process.
I give props to the writers of the QRPGuys manual, as they provided some of the clearest instruction on how to wind the inductors, including the number of loops and where to place the taps. The manual also includes a nicely done illustration of each inductor and hints on how to assure the builder wound them correctly.
The inclusion of Thermaleze® brand magnet wire for the inductors was also a nice feature – the enamel coating was quickly dispatched after a few seconds of exposure to my Zippo cigar torch.
The entire build, including the winding of the four toroids, building the traps and measuring the three driven element lengths of wire took me less than 2 hours working at a leisurely pace on a winter’s Sunday morning.
About the Antenna
Field testing this antenna will have to wait a few more weeks for more reasonable weather here in Connecticut, but my plan is to use this antenna for QRP POTA activations this year with various homebuilt radios such as the Ramsey QRP20 transmitter I assembled last week. The end-fed design should make for easy deployment as a sloper while operating from the field with easy access to the tuning controls from my operating position.
The tuner circuit design is as straightforward as it gets – your basic tunable L-C circuit with a varicon capacitor. But the kit also employs the N7VE LED absorption bridge that keeps SWR to a minimum of 2:1 when set to the tune position. According to the kit documentation, the LED indicates only reflected power. Full LED brilliance will indicate an SWR at 4:1 or greater. At half brilliance SWR is approximately 2:1, and the LED will completely extinguish at 1:1.
I was impressed with the apparent high quality of the PCBs and components, and I found the instructions and supporting documentation to be exceptionally well written – easy to follow and understand.
If you would like to build the QRPGuys Multi-band End Fed Antenna, you can purchase the kit on their website here. The current price of the kit is $40 USD.
If you have built this kit, or have any questions or comments, please feel free to leave a comment or drop me a line at email@example.com.
One of the now defunct electronics kitters, whose products I personally appreciated ‘back in the day,’ was Ramsey Electronics.
Ramsey, which still exists as a firm today, but no longer sells electronic kits, produced a fairly expansive line of straight forward do it yourself solder kits that were not too complicated for the new to intermediate builder, and that came with exceptional documentation which not only provided the builder with detailed step-by-step instructions, but also included information on circuit theory explaining why and how it worked, and what the sub-circuits and individual components did. Often included were suggestions for kit mods, sometimes as provided by previous builders of the kit. Their motto was “Build It, Learn It, Achieve It, and Enjoy It!“
After providing great kits to the electronics hobbyist community for more than four decades, Ramsey shut down its kit division in 2016 and has been sorely missed by hams and other electronics hobbyists ever since. Today the occasional unbuilt Ramsey kit will appear at local hamfests and on eBay, so if you’ve never had the experience of building a Ramsey kit, there’s still a bit of hope for you. For an appreciation of the breadth of their kit offerings, you can browse of one of their catalogs here.
Building a 90’s era Ramsey Kit – the QRP20 CW Transmitter
Recently, after coming across the Ramsey Active SW antenna kit I built back in the 90s, before I earned my ham ticket, but was an active shortwave listener, I found myself feeling nostalgic for the Ramsey kit experience and found an unbuilt 20 meter transmitter kit on eBay. When the auction ended four days later my bank account was $32 lighter and I found myself eagerly waiting for my new kit to arrive.
The kit promptly arrived a few days later, well packaged, and just as described. I was happy to see that it was unopened and complete. My winning lot included not only the QRP20 transmitter kit, but also the matching plastic case complete with pre-drilled and labeled front and back panels.
Given my recent obsession for building ham gear into cigar boxes, I planned to skip the signature Ramsey case but I realized the pre-drilled front and back panels would make an excellent template for drilling out my cigar box cabinet.
The QRP20 enjoyed favorable reviews on eHam Product Reviews with a solid four out of five stars average rating. Common among the reviews were observations that the transmitter was easy to assemble and had no drift or chirp. Several builders commented they had upgraded the cheap driver and amp Q2 and Q3 that shipped with the kit for more robust transistors for increased RF output.
The QRP20 is specified to put out 1.0 watts of RF power drawing 1/4-amp current from a 12-15 VDC source and it has two unique features to set it apart from competitors’ offerings.
The first is a space on the PCB to install a second crystal or to wire in a crystal socket. The second frequency, or socket, is selected by a pushbutton on the front panel. Ramsey included a single 14.060 crystal with the kit and leaves it to the builder to use the second crystal slot to accessorize as he desires. (I plan to add a crystal socket myself.)
The other welcome feature is the QRP20’s built in T/R switch – a nice bonus feature that will make for easy mating to the matching Ramsey HR20 DC receiver or any other QRP receiver.
Ramsey offered the QRP20 for many years and over that time, the circuit was tweaked, the instruction manual was updated, and eventually some parts were substituted for others.
The manual in my kit was copyright 1990 and in addition to the manual, the kit included a large separate fold out parts finder diagram of the circuit board. This was most useful as this generation of the QRP20 PCB did not include screening on the component side showing individual part layout. With the Parts Finder diagram laid out on my workbench I had no difficulties identifying where every component belonged.
Assembly took about 2 hours over 3 sessions. I tend to work slowly and deliberately when kit building, and I’m a big proponent of the adage, measure 2x, cut once. In kit building, I tend to identify/measure component values thrice, solder once.
I mentioned above that over time, Ramsey modified the circuit and also some components were changed, most likely due to changing availability from suppliers. I encountered a couple of these changes in my build – all of which involved the inductors – which required a bit of extra caution on my part.
First, the Parts Finder showed a square footprint for L1, an inductor with a tuning slug. The diagram labeled it as L1 40M, with two arrows pointing to where the solder points were for the inductor. The 20-meter version of the kit that I was building, included an axial inductor with no tuning slug, the type that looks like a resistor complete with color-code bands.
The parts list stated that L1 for the QRP20 may have been either a 2.2 uH or a 3.9 uH inductor. I was able to confirm that my kit included a 2.2 uH inductor by the red-gold-red color code, and I verified the value with my L/C meter.
Inductors L2, L4, and L5 presented a bit of a challenge too. Every printed reference to these 3 inductors in the manual stated they were 220 uH and the parts list on page 20 described them as molded brown with red stripes. There was no mention in the printed instructions that the kit may have included an alternative set of inductors with different values for L2, L4 and L5. However, on the page 20 parts inventory was a parenthetical hand-written statement under the printed entry for these inductors which read “or 100uH -green 100.” There were three beehive shaped green components with a ‘100’ stamped on the top, so I felt confident these were L2, L4 and L5.
Lastly, L3 and L6 were 1.0 uH inductors but neither the instruction manual nor the parts inventory described their appearance or markings. I found two wire-wound inductors in the parts bag but they had no color code or printed markings and they were too long to easily fit in the matching holes on the PCB. But by process of elimination, I concluded these were L3 and L6 and again I confirmed their value with my L/C meter. I needed to use extra caution to carefully bend the leads 180 degress, back under the inductor body, and then 90 degrees again through the PCB holes.
The only other construction issue worthy of mentioning is the special care I took take to properly identify the leads for the four bipolar transistors. While the Parts Identifier diagram had a circular outline for each transistor with a flattened side, it did not label any of the holes as B, C and E. I connected each transistor to my transistor tester to identify the base, collector and emitter, drew a diagram in my notebook to keep the terminals straight and then cross referenced my sketch with the the schematic and Parts Layout to make sure I got these right. Having to resolder transistors after I snipped the excess leads would be a pain.
Cigar Box Considerations and Mods
I chose a nice small Nub cigar box for my QRP20 cabinet. The cigar box dimensions were 6 1/4″ x 4 7/8″ x 2 1/2″ which meant it should nicely accommodate the Ramsey 4″ x 4 3/4″ PCB. My plan was to mount the circuit board to the bottom of the cigar box and drill out holes on the front of the box to accommodate the tuning potentiometer and the crystal selector push button switch. The meant with careful drilling, I could mount both the pot and the switch direct to the PCB as Ramsey intended and have them poke through properly aligned holes in the front of the cigar box.
However, the depth of the box was a bit too long, which meant the rear connections soldered to the circuit board (antenna, receiver null, power connection and key) would not reach the back panel of the box and I would have to use chassis mounted parts for these connectors with jumpers to their connections on the PCB. I had a pair of chassis mount BNC RF connectors on hand as well as DC power barrel connector. I had a nice NOS Radio Shack momentary push-on push-off SPST button switch that I wanted to add to the back panel, so I relocated the 1/8″ jack for the key to the side panel.
Admittedly, the power switch isn’t really necessary as the transmitter is powered by an external connection to 13.8 VDC but since I added the switch, I thought it would be a nice touch to put place a miniature LED power on indicator on the front panel.
As the typical 5mm LED has a current draw of 20 mA and can handle forward voltage of 2 VDC max, I’d need to include a dropping resistor so the LED wouldn’tfry when connected to the 13.8 VDC power source.
The formula to calculate resistance is R = (Vs – Vf) / If where: Vs is Supply Voltage Vf is Forward Voltage Drop for the LED If is Forward Current Drop for the LED
Doing the math for the 13.8 VDC source: R = (13.8 – 2.0v) / 0.02 R = 590 ohms
(I padded the results a bit and grabbed a 660 1/4-watt resistor out of my stock supply.)
As mentioned, the cigar box would require precise measurement. Locating the placement of the four holes on the bottom of the cigar box for mounting the PCB was easy and a good starting point.
My plan was to use 5/8″ spacers to elevate the PCB so the tuning knob would be exactly halfway between the top and the bottom of the front panel. This is where the Ramsey provided front panel came in handy as a template to get the spacing for the hole for the crystal selection push button spot on.
Since the pushbutton switch is closer to the PCB than the tunining potentiometer, I decided to place the power on LED directly above the button to give the front of the transmitter a nice symmetrical appearance.
Using the Ramsey rear panel piece again as a template, I was able to drill out nice venly spaced holes to mount the BNCs, power connector and power switch.
The Nub cigar box I chose for this project was a good choice not only because of its size, but also because it doesn’t have a hinged lid. The top of the smal Nub box slides on and off, which means it’s not suited for mounting radio controls to. The QRP20 transmitter with its limited operator controls made the Nub box a fine choice.
Testing and performance
Once completed, I tested my QRP20 in the shack, connecting it to a wattmeter and my dummy load. I connected my Lionel J38 straight key and powered it up with 13.8 volts DC from my Ameritron shack power supply.
Tuning my Xiegu G90 transceiver in the shack to 14.060 I was hearing my signal spot-on with the tuning knob set just past mid-point (6 on the scale of 10). I was very pleased to see I was getting just under 1.0 watts RF out…. Success!
I’d like to take this nifty 20M transmitter out into the field this summer for some QRP POTA/SOTA ops. So I will next need to consider what I will use for a matching receiver. I’ve got a few DC receiver kits I’ve previously built on hand including the most excellent TenTec 1056, a Pacific Antenna Easy Receiver, and appropriately enough, a Ramsey HR series receiver. However, all of these were built for 40 meters. I could modify one of them for 20 meters or I could build something new. Stay tuned.
Before I take this li’l rig out, I plan to complete a couple of mods. I mentioned I want to add an external crystal socket to make full use of the crystal selector button and I believe I will also try swapping out Q2 and Q3 for a bit more oomph. While I love QRP, going from 1.0 watt to 2.5 watts out could make an appreciable difference.
So, I had fun with this build, it brought back memories of Ramsey kit builds from years ago, and in the end I have a nice servicable 20 M QRP rig for future field ops.
What’s your story? Have you ever built a Ramsey kit? What was your experience? Do you miss Ramsey? What other kit providers today are filling the gap Ramsey left behind?
Drop me a line at firstname.lastname@example.org or leave a comment and let me know what you think!
The second build in Bob Heil’s Pine Board Project is the power supply. Both the transmitter as well as the pre-amplifier feature vacuum tubes which means they require a high DC voltage for the tube plates (B voltage) as well as a lower 6.3 VAC filament voltage.
I had previously built the AES K101 battery eliminator kit for my vintage Arborphone coffin radio, which I no longer needed it for. The K101 is currently collecting dust on a workshop shelf and would have worked well with the Pine Board project. But building is fun, and Bob provided schematics and instructions for a nice simple classic tube power supply designed around the 6X5 rectifier tube.
Thanks to Bob’s excellent online documentation and HamNation videos, I had no difficulty building the power supply. The only modification I made to my build, besides choosing to mount it in a cigar box rather than on a slab of pine, was that I added a neat-O vintage NOS voltage meter.
The power supply worked great, put out about 180VDC B+, and it looked great (to me anyway!)
However, a couple of months ago, when I finally completed my build of the transmitter (watch for my future blog post), I was disappointed to record less than one watt into my dummy load on both 40 and 80 meters. I assumed I had botched something in my transmitter build and began to retrace and double check my work only to discover that all looked right.
I went back to Bob Heil’s Pine Board Project website and discovered that since he published the original plans for the power supply, which I had used, he had since uploaded modified plans replacing the 6X5 rectifier tube with a solid-state bridge rectifier. In a more recent video upload, Bob explained that changing the rectifier would result in a significant increase in B+ voltage and that it would in turn increase the transmitter RF out to the neighborhood of 5 watts.
Following the updated schematic and layout plan, I modified my power supply but soldering a bridge rectifier to an octal tube base and disconnecting the center tap on the power transformer as instructed. This worked as described – my B+ voltage was now approaching 400 volts and the transmitter was putting out over 4 watts into my dummy load.
However, all was not right in the world. Upon closer inspection of the revised schematic, I saw that where there was a single B+ output originally, the capacitor/resistor network was reconfigured with two taps so a B+ of lesser than 200 VDC would be available for the 12AX7 tube in the pre-amp. According to the datasheet, the plate voltage on the 12AX7 should not exceed 300 volts.
I attempted to modify my power-supply for the second tap but ran into difficulty doing so. The version I build had included a third filter cap but the Heil redesign returned to two filter caps. I became vexed and now realized I had misunderstood the bleed resistor in my initial 3 cap build to be part of the resistor voltage drop circuit in the newly published solid-state design. Regardless of where I tried to tap the circuit for the second B+ voltage, it always equaled the near 400+ volts I was now getting on my first tap.
I decided since I had a bag full of bridge rectifiers, a drawer full of 20 MFD 450V caps in my workshop, I would salvage the transformer and begin a completely new build of the power supply this weekend working directly from the new Heil schematic.
I wanted to expand on my meter mod – since the power supply would be providing two different B+ voltages, I planned to add a second meter so I could easily confirm that B+1 for the transmitter and B+2 for the pre-amp were not the same and appropriate for their respective circuits. I purchased a pair of modern 500 volt meters since my vintage NOS meter I originally used maxed out at 300 volts.
I also decided since all of the components excepting the power transformer and meters would be mounted on the bottom side of the lid, I would abandon the terminal-strips and point-to-point wiring and instead use a perforated PCB board to make a subassembly for the filter caps and voltage drop resistors. Working rom the schematic, I designed the layout on my PC first and the built to my design.
Next, I chose an appropriate cigar box from my stash for the build. Since I planned to mount the two meters to the top of the lid this time, I chose my Leather Rose cigar box as it was the widest. It was an excellent choice, I think, with one problem.
The shallow wide box was designed to hold a couple dozen cigars and the lid only needed to seal the box to protect the contents from drying out. The strain put upon the flimsy staple hinges by the heavy transformer was a bit much and I plan to replace the hinges with sturdier ‘real hinges.’
Once the chassis was drilled out, the rest of the assembly went smoothly and quickly. Having all of the capacitors and resistors on the PCB subassembly made for short work of all connections once the board and other chassis mounted parts were attached. Before mounting the transformer, I made all of the output connections and built a ground bus. Once the transformer was attached, it did not take long to wire up the power cord, fuse, switch and 6.3 VAC pilot light.
I completed all of the work over my Saturday and Sunday morning this weekend, working slowly and carefully. My patient deliberate methods paid off as there were no snap, crackles or booms or smoke or open flames when first fired up.
Finally, I want to acknowledge that this project produces lethal voltages, something we don’t deal with much anymore in this era of silicon devices. I grew up mucking around in high-voltage hollow state radio & TV chassis, and I am well aware of the proper precautions necessary for safety’s sake.
Despite the fact my regular practice is to discharge electrolytic caps and I try to be super mindful about knowing what I am touching with my hands when exploring a circuit, still I managed to shock myself a couple weeks ago while trying to diagnose why my two B+ voltages were the same after I did the first solid state mod. I was holding the power supply in my hand with the box opened, visually examining the circuitry when I accidentally touched the power out terminal strip on the top side of the box lid with my right hand.
Fortunately, despite my negligence, I did have my left hand in my pocket, a good safety practice I learned early on to prevent lethal currents from passing through the heart. That said, I encourage anyone who may be inspired by my blog and Bob Heil’s excellent plans to give this project a try – do be knowledgeable about the dangers of working with lethal voltages and how to be safe. In the end, you are solely responsible for any risks you take building or working on such circuits.
Have a comment, question, or a personal experience to share? Post a reply or please drop me a line at email@example.com.
Legendary sound engineer Bob Heil, architect behind many signature rock artist signature sounds (The Who, The Grateful Dead, Peter Frampton, Joe Walsh to name a few), is also renowned in the amateur radio community.
Bob has engineered and his firm Heil Sound retails high performance microphones and other premium gear for the ham community, he has authored books and numerous articles for the ham community and is one of the most sought-after speakers for amateur radio conferences. Bob hosted the popular TWiT video podcast HamNation from 2011 through 2020; archived copies of the podcast remain a valuable resource to hams today.
In the Spring of 2017, Bob Heil introduced to the amateur radio community, The Pine Board Project, afour-part do-it-yourself AM transmitter project. In earlier times, building your own gear was a larger part of the ham radio experience. RF theory and design made up a larger portion the exam material and while studying, many prospective Novices would construct their own basic receivers and transmitters while studying for their licenses.
Plans for these projects were widely published – from the American Radio Relay League’s handbook and monthly magazine, QST, to other popular radio and electronics magazines such as CQ, 73, Popular Electronics, Radio TV Experimenter, and Elementary Electronics.
The Heil Pine Board project was a throw-back to these times. Bob broke the project into four separate sub-projects for the builder to construct: an RF field strength meter, a high voltage power supply, an audio pre-amplifier and equalizer, and a 40/80-meter transmitter capable of approximately 5 watts AM output.
Several episodes of HamNation included featured segments in which Bob would take the prospective builder through circuit design, parts layout, and circuit theory. Bob published the schematics and board layout diagrams on the Heil website and even provided parts lists with sourcing information, giving the names of firms that carried some of the obscure parts from an earlier era, along with stock numbers and prices.
Bob’s enthusiasm for the projects as expressed in the videos was infectious. His presentation style was straight forward, detailed and inviting for the new builder. Along the way he featured photos and reports of viewers’ work.
I was hooked from the get-go. I grew up spending hours on ends in my grandfather’s TV/radio workshop in our basement and had read dozens and dozens of articles for building projects that appeared in the yellowing pages of his electronics magazines from the 60s. I had built many an electronic kit in my time, but beyond the occasional simple crystal radios or basic transistor circuits, I never did much scratch building.
I started building the projects a couple of years ago, closely following the directions and completed the field strength meter, the power supply and the pre-amplifier. Then, true to form, I either got distracted by other things (other projects, family, work, life itself).
Last summer (2021) I made a resolution to focus and complete the unfinished projects on the shelves of my workshop and decided it was time to complete the Heil project.
Friends who know me well, know that in recent years I had enjoyed the occasional cigar. Many a workweek transitioned into the weekend by enjoying a fine Leaf by Oscar and an Old-Fashioned with my dear friends Carl & Steve at the Owl. Every week or so, the Owl staff would leave empty wooden cigar boxes out at the curb for folks to take and I started nabbing a few thinking they might make good chassis for ham radio projects.
Since then I had built a few recent projects into my cigar boxes and thought that it might be fun to put my cigar box spin on Bob Heil’s transmitter project and built the transmitter into a cigar box and then rebuilt the other projects into their own cigar boxes.
At this point I’m going to blog on my Heil Pine Box/Cigar Box Project experience in a series of articles, starting with the power supply. As I mentioned I initially built this on a pine board and my initial build used the 5XT rectifier tube using Bob’s original design. I have replaced the 5XT with the solid-state rectifier, building the modified power supply as designed by and published by Bob.
Thanks again to Bob Heil for designing and sharing and promoting the Pine Board Project – it has provided me with hours and hours of enjoyment so far, and there’s much more fun ahead.
Have you built the Pine Board Project? Leave me a comment or drop me a line at firstname.lastname@example.org. Jump to my post about my power supply build here.
As the proverb goes, a journey of a thousand miles begins with a single step. So, after procrastinating for two plus years after my XYL and soulmate Ellen gifted me the Elecraft K2 HF Transceiver Kit for our tenth anniversary, I finally got my nerve up to start what will easily be my most ambitious kit build ever.
It is my intent to blog about my experience as I proceed, circuit board by circuit board, sharing my experience and inviting others who have built the K2 to share as well.
The Control Board
Having set up and outfitted a new protected work bench using a folding banquet table in the shack where I will work only on the K2, I started work on the first circuit board, the Control Board on January 9, 2022.
As with many kits I’ve built, the Elecraft instructions call for the builder to start by inserting and soldering all of the fixed resistors first. As others have reported, I found the instructions to be, for the most part, very well written. The instructions for the fixed resistors provided each resistor’s value in ohms as well as the color code and the builder is encouraged to install the resistors with the first color band towards the top or the right of the circuit board to facilitate verifying the correct resistor is in the correct space when reviewing or troubleshooting your work.
As electronic components have gotten increasingly smaller, my vision has gotten progressively worse as I’ve gotten older. Whenever kit building, I always verify values with my VOM before inserting any resistors into a circuit board. After installing the 13 resistors, the instructions called for the installation of seven resistor arrays and one trimmer pot, all easily identified.
Next the builder needs to install an 82 mH inductor, which I confirmed I had the correct part with my L/C meter, followed by a pair of silicon diodes. I then encountered the first variation in my kit. Where the original PCB had a screened space for D3, the instructions called for an 82K ohm resistor to be installed here.
The instructions next call for the builder to install and solder in place 36 fixed capacitors. Identifying and verifying the value of each capacitor was a notable challenge. Not only were the stamped or printed values on the caps miniscule, the capacitors also varied in type, shape, and manufacturer and it was clear that some of Elecraft’s suppliers changed over the twenty-five years they have been offering the K2 kit, as some of the caps did not match in appearance to the identifier pictures in the otherwise excellent parts list in the appendix.
To guarantee I placed the correct capacitor in the correct space, I took the time to identify every capacitor and laid them out neatly on my workbench in the same order the instructions called for their installation.
To identify the values, I used the camera on my iPhone and zoom in on the part. Sometimes when the value is etched on the capacitor, I needed to shift it so my bench light catches the labeling just right to read. I took the time and used my L/C meter to verify the value of every capacitor.
Once all of the capacitors were laid out in the order of installation, I carefully installed each capacitor into its space, having taken the time again to double-check values with the L/C meter. It was a slow process, but in the end, I felt very confident all of the capacitors were soldered in the correct space giving me peace of mind. Trouble shooting for mis-placed capacitors would be a very tedious process if necessary.
The next several steps went along easily as I installed the electrolytic capacitors, a trimmer cap, a dozen bipolar junction transistors, a pair of crystals, two voltage regulators, one IC socket and various connectors. All of these parts were easily identified, and when working with the transistors, I proceeded in the same manner as I did with the fixed caps, identifying and verifying value, arranging them in the order of installation and double-checking values as I installed each.
Now it was time to install the ICs on the control board, and this is where I first ran into trouble.
The very first chip was an NE602, the AGC mixer. I mentioned that the K2 has been on the market for twenty-four years and over the course of a quarter century, technology moves on and the availability of parts change. By the time Elecraft had kitted my specific K2, the NE602 was no longer widely available in through-the-hole DIP casing. The industry had since begun moving on away from through-the-hole components in favor of tiny, less expensive surface-mount versions.
Instead of the DIP version of the NE602, my kit came with an equivalent SMD NE612 which was pre-soldered to a small square ‘carrier board.’ The carrier board is a PC board cut to the same footprint of an 8 pin DIP case and the builder is instructed to cut eight 1-inch pieces of wire, insert them into the eight holes on the carrier board, solder them in place, then insert the bottom ends of these wires through the DIP-spaced holes and solder to the control board.
I damaged the carrier board while attaching the wires by working sloppily with a too-hot iron. The carrier board was not of the same high quality as the control board which featured double plated holes. The carrier board had plating only on the top of the holes, and I managed to lift the plating off of the number 2 and number 3 hole, breaking connectivity. I tried to bridge the contacts to the chip contacts with a solder blob, but that only made a bigger mess of things.
Elecraft has a form on their website to order replacement parts and I reached out on January 1qth to inquire about purchasing a replacement NE612 and carrier board. I did receive an acknowledgement that they received my inquiry from a mail bot, but as of this writing, four days later I have not received an actual reply.
In the meantime, I began wondering whether I could still find DIP cased versions of the NE602 elsewhere online. I searched Mouser, Digi-key, eBay and Amazon and found that an Amazon vendor had some available, which I ordered. The vendor did not disclose the name of the manufacturer nor the source country, but I’m assuming the chips were manufactured in China. I did order five (there are three others elsewhere in the K2) and they arrived within a day or two.
I discussed my dilemma with one of my Elmers, Steve, KZ1S, who has built many a kit in his day and is a physics professor who works with electronic circuits and RF in his work.
Steve offered a couple of suggestions. The first was to use a proper SMD to DIP converter board with proper pins spaced correctly. I liked this idea very much, but the drawback is that it would require me soldering the SMD chip to the converter board and again, with my failing vision and dexterity, this would be a bit of an unpleasant challenge.
Steve also suggested looking for genuine NOS chips online, either on eBay, or from Radwell International. Steve mentioned you can source just about any obsolete part with Radwell, but they can be expensive. I did locate the NE602s on there with a retail price of about $5 – not a deal-breaker, but given I need four for the K2, that’s an additional $20 + shipping.
For the time being, I decided to place a DIP socket on the control board and once in place, I inserted the NE602 of dubious origin I purchased from Amazon in the socket. For the time being this would let me continue with the build and be able to test resistances. I could then swap out the AGC chip for a genuine NOS or SMD + converter at a later date.
I finished the build of the control board this morning, directly soldering in the remaining ICs and adding the two CW key-shaping capacitors on the solder side of the board.
After carefully double-checking all of my work, I used my VOM to perform the resistance checks. All of my test resistances were within range, excepting U6 pin 29 (DASH) and U6 pin 30 (DOT/PTT) which were marginally over spec. The acceptable range for both is 70K – 90K ohms and I measured 96.6K on pin 29 and 96.8K on pin 30. I will revisit these values later.
So that concludes the build of the first circuit board, the Control Board. I counted a total of 110 components soldered to the board and I completed the work in eight days working at my deliberately leisurely pace.
I welcome comments and suggestions from any and all, particularly from anyone who has built the K2 and had to deal with the SMD carrier board themselves. Drop me a line at email@example.com to share your thoughts and opinions.
I built my first electronic DIY kit when I was about 10 years old. Dad brought home the Radio Shack One-Tube AM receiver P-Box kit and we spent the better half of the following Saturday at the workbench in the basement building it together.
It was an amazing formative experience – spending the day working on the project with dad, learning about the various electronic components and how they worked in the circuit, and getting my first try at soldering.
I treasured the completed radio and can vividly recall that magic moment when I first clipped the ground wire to an exposed gas pipe behind the parlor stove, sticking the hard plastic crystal earpiece in my ear and tuning the loopstick and hearing WBZ in Boston coming in loud and clear on the radio dad and I built out of a handful of parts.
This was the first of many Scie`nce Fair™ P-Box kits I would build throughout my early teen years. No Christmas or birthday was complete without one (or two!) new kits. I remember building the organ, the two-transistor AM radio, the “GoofyLight,” the indoor/outdoor electronic thermometer, the moisture detector, the AM Wireless microphone and the frequency standard.
I was hooked on kit-building and at some point, in my teen years I saw my first Heathkit catalog and was blown away at the more complex scale and wide variety of Heathkits… radios, hi-fi gear, test equipment, computers, even television sets. I began setting my sights on taking my kit-building to the next level.
However, in the mid- to late- eighties my focus and all of my earnings went into getting through college. By the time I had the time and disposable income to return to the kit-building workbench, the Heathkit era was sadly over.
At the turn of the century, I was in the position to have the time and money to return to my radio and electronics hobby. In 2002 I earned my amateur radio license and from the get-go started building ham-radio related kits. These included receivers and QRP transmitters and a variety of accessories like tuners, station clocks, sold by kitters such as Oak Hills Research, Four State QRP Group, MFJ, Small Wonders Lab, TenTec, and Rex Harper (QRPMe), among others. These were fun builds and there is nothing like using gear you built to make contacts on the air.
However, even the best ham gear I built still fell short of having built and having a showpiece full feature 100-watt multi-mode transceiver like the venerable HW101 in my shack.
In 1998, Elecraft, a new retailer of amateur radio gear was founded in California by Wayne Burdick and Eric Swartz with the introduction of their first product, the K2, an HF transceiver that could be purchased as a kit or fully assembled.
The K2 features dual VFOs with multiple memories, split TX/RX operation, RIT/XIT, full break-in CW, memory keyer, narrow IF crystal filtering, and IF derived AGC and the base radio can be built as a 5-watt QRP CW rig with optional accessory boards available to add SSB and amplify the RF output to a full 100 watts.
Initial reviews by the ARRL and other professional publications as well as those written by amateurs who have built and operated the K2 were excellent. The consensus was that the K2 has become a worthy choice for builders lamenting the disappearance of Heathkit. Reviews cited that the Elecraft kits were well packaged, completed, and the instruction manuals and documentation provided was detailed and easy to follow – not unlike the Heathkit manuals of a prior generation. Elecraft also got high points in published reviews for excellent customer support.
A bit over two years ago, my wife Ellen gave me the K2 kit, along with the 100 watt amplifier board and the SSB board as a gift for our tenth wedding anniversary. (I frequently point out that no man ever married better than I!)
Although I wanted to build the K2, and indeed put it on my gift ‘wish list’ – I let it sit in the workshop for over two years! I knew the project would take months on end to complete, and in order to succeed I would need to maintain a clean workspace, take my time and work slowly and diligently.
I think I have many fine qualities, but I’d be the first to tell you attention to detail and neatness are not among them. I was further intimidated by the fact that electronic components have gotten smaller while I have gotten older. My vision, which was always poor from birth, wasn’t getting better and my hands are starting to get a little shaky.
I finally resolved as we headed towards 2022 to tackle the K2. I created a new ‘protected’ workspace in my shack/mancave, moving in a folding banquet table, topping it with a pair of self-healing cutting mats and setting up my magnifier lens, solder station, some essential hand tools and my VOM, capacitance/inductance meter and my laptop.
The bigger resolution was to keep this space protected and clean. I resolved to not let this space become cluttered. I would not place anything not Elecraft related on this dedicated workspace, and I also resolved to clean up the space every time I stopped work, making sure I didn’t leave any loose parts out.
And with all that in mind, I finally started my build this month and my intent is to blog about the experience here and intend to blog as I complete each board. I invite you to join me for the journey. I hope those who have already built the K2 reach out with comments, tips and tricks – any input will be most appreciated. I also hope that this blog may be a resource or an inspiration for other builders.
Build this low power dirty AM transmitter and learn about RF modulation.
In the 21st century we have all become accustomed to our connected high-tech lifestyle and we more or less take our internet based social and commercial connectivity for granted until the ‘network goes down.’ Much of the technology that drives our digital being are computer based, but another essential element is radio technology, without which we would find ourselves much less connected.
How does ‘radio’ work?
Long before manipulated radio waves were used to provide the backbone of today’s digital cellular and cloud based information network, those of us who grew up in the twentieth century knew radio primarily as a means to enjoy music, news and talk, via the AM and FM radios in our homes and cars. But what is radio?
Simply put, radio is the transmission and reception of electromagnetic waves that are encoded with data. The data could be spoken word, music, or digital data like text and email messages or larger digital files like software or other data files.
The data that can be transmitted via radio waves exists as low-energy signals and they must be attached to a high-energy signal called a carrier wave in order to be transmitted. A carrier wave is at a significantly higher frequency than the input signal and is typically sinusoidal.
The mixing of the signal with the carrier wave is a process called modulation. There are several ways a carrier can be modulated, the two most common modes of modulation for an audio signal is amplitude modulaion (AM) and frequency modulation (FM). (Another common method of modulation a carrier signal that is beyond the scope of this article is phase modulation (PM)).
Amplitude modulation involves varying the signal strength, or amplitude, of the carrier wave in direct proportion to the message signal. Frequency modulation involves varying the frequency of the carrier wave in dirrect proportion of the message signal.
A simple low power AM radio transmitter
It is possible to construct a very simple low power transmitter built around the ubiquitous 555 Time Integrated Circuit which is capable of demonstrating the principle of amplitude modulation by mixing an audio signal with a carrier signal that can be transmitted to and received by a AM radio receiver.
The 555 timer chip was designed in 1971 by Hans Camenzind and has remained one of the most popular and versatile integrated circuit chips ever produced. Simple when compared to today’s chips which may contain tens of billions of transistors, the 555 has 25 bipoloar transistors, 15 resistors and 2 diodes.
The 555 chip has three distinct modes of operation – monostable, bistable, and astable.
The monostable mode is also known as the one-shot mode and will output a single pulse of current for a specified length of time. The bistable mode is also known as the flip-flop mode and alternates between two stable states, on and off, controlled by the trigger and reset pin.
The astable mode is also known as the oscillator mode and can be used to generate a carrier wave that could be modulated in a model RF transmitter circuit. We will employ this feature of the 555 chip for our transmitter circuit described below.
Traditionally the carrier wave in a radio transmitter is a continuous sinusoidal wave. However, the 555’s output is digital, either on or off, so the resulting wave is a square wave. An alterenating current sine wave is smooth and continuous and is optimal for carrying an information signal, but the square wave will work for our purposes.
I will now present and describe a simple AM radio transmitter circuit that you may wish to construct to observe and demonstrate radio modulation. This circuit design can be found on hundreds of websites oftentimes with small variations component value changes or minor modificaitons to the basic circuit. The circuit I present here is based on the core circuit, nominally modified to reflect what I have found to work well on my bench. I encourage readers who take the time to build my circuit to experiment and share modifications letting us know how you may have enhanced performance.
We will start by looking at the transmitter circuit by its three sub-circuits. The first is the oscillator circuit that produces the carrier wave, the second is the audio input sub-circuit, and thirdly we add the output amplifier and antenna.
1.) The Oscillator
The schematic diagram below is built upon the basic 555 astable circuit and this is the heart of the transmitter. The frequency of the carrier wave output on pin 3 is controlled by how rapidly capacitor C1 charges and discharges. The values of resistors R1, R3 and R4 will determine how quickly C1 charges.
When the charge of C1 reaches 2/3 of the control voltage Vcc, the output at pin 3 goes high. When the charge of C1 discharges to 1/3 of Vcc, the output at pin 3 goes low. Changing the resistance of the RC circuit by adjusting R4 will inversely change the output signal frequency. Increasing R4 will decrease the frequency and decreasing R4 will increase the frequency.
2. Audio Input
When a low energy audio signal is injected at the control pin, pin 5, the 555 will mix the input signal with the signal of the carrier wave and produce an amplitude modulated output signal at pin 3, output.
It is important to note that because the carrier wave generated by the 555 oscillator circuit is a digital pulse wave, where the output goes from completely on to completely off, the modulation of the carrier isn’t pure amplitude modulation, but pulse amplitude modulaton.
The pulse modulated RF signal will not be able to capture all of the fine detail of the input signal and you will notice that as a result, that the sound coming from the receiver speaker will sound a bit choppy and not as pure as you are accustomed to.
3. RF Amplification and Signal Output
The modulated RF signal is output at pin 3 of the 555. Attaching a simple piece of wire to pin 3 will serve as a crude antenna causing the modulated signal to be transmitted, or radiated into space where it can be picked up by properly tuned radio receivers.
Because this is an exteremely low power transmitter, I have added a single NPN bipolar junction transmitter (2N3904) at pin 3 to perform as an amplifier to boost the output signal strength. The base of the transistor is connected to output pin no. 3 of the 555 and the antenna wire will be connected to the transistor emitter. Power is supplied to the transistor via the collector.
An ideal length for the transmitting element for a radio antenna is 1/4 of the signal wavelength. This length gives us an efficient antenna length where the signal will resonate with minimal loss of signal. What would that length be for this transmitter?
Radio wavelength is calculated as the speed of light, (the speed at which RF waves also travel,) expressed in meters per second divided by frequency expressed in Hertz. The speed of light is 299,792,458 meters / second and the frequency range of the standard AM broadcast band in North America is 550 – 1700 KHz. Doing the math we learn that the broadcast band wavelength ranges from 176.3 meters to 545.1 meters.
Dividing these figures by four, we calculate the optimal antenna length for our transmitter would need to be between 44 and 136 meters or 144.36 to 446.19 feet! Constructing such an antenna for a simple circuit would be impractical and costly.
In this build we are using a piece of wire that is approximately one meter or a bit over 39 inches long. Because such a short antenna length is non-resonant and because the transmitter signal output is very week, you will find draping your antenna wire over the radio receiver establishing a loose coupling to the receiver will give you best results.
If you decide to build this circuit you may wish to experiment with different antenna designs to see how the may affect the range of your output signal. You may try a longer wire and another website suggests using a(n empty) beer can as an antenna.
Ham radio operators often make use of coils when antenna space is limited. Adding a tightly wound wire coil will add inductance allowing a physically shortened loaded antenna become more resonant at a longer wavelength. The concept of designing inductance loaded antennas is a concept goes beyond the scope of this article, but there is no shortage of excellent websites available that cover this topic if you are curious and know how to use the Google.
Using the transmitter
Once you have built the transmitter circuit, using it is straightforward and should be fairly intuitive. In addition to connecting the antenna wire to the transistor emitter and draping it over the receiver, you will of course need to supply a control voltage and an audio signal.
I have found that a 9 volt battery works well with this simple circuit as it is compact and will provide plenty of current to drive the circuit. The 555 will work with a Vcc ranging from 5 to about 15 volts giving you plenty of options.
For my audio source, I initially used the audio output from my laptop but have found that using my Activo CT10 MP3 player works much better as the MP3 player puts out a stronger high res audio signal.
Once you have made the above connections, start the audio source music playing and tune the radio receiver to about 600 kHz. Slowly fine tune the receiver up and down until you can hear the audio signal. It should be heard somewhere near 600 kHz, either slightly above or below.
Once you find the signal, try tweaking it by adjusting R4 on the transmitter using either an RF tuning tool or a mini-screwdriver.
Experiment by moving the antenna wire back form the receiver and raising it and lowering it. How does position change the receiver’s ability to pick up the signal?
What are some other ways you can improve the transmitters performance?
I mentioned above that this is a dirty transmitter. This term means that the output signal is not well-filtered. Transmitted radio waves by nature produce harmonic signals on even multiples of their frequency. In fact, when you are listening to the radio output around 600 kHz, you are actually tuned to the first harmonic as the circuit’s output frequency is somewhere between 200 and 300 kHz (see oscilloscope photo above).
Try tuning the radio receiver slowly up the dial. You ought to be able to also hear the transmitted signal just below 900 kHz and again around 1200 kHz and perhaps just under 1500 kHz. These are all harmonic signals and this type of unfiltered signal would not be acceptable for any FCC licensed radio transmitting station – wheter commercial or amateur. Harmonics can be mitigated through the use of electronic filters.
It should also be noted that it is of course illegal for anyone not holding a valid FCC license to transmit radio signals. A commercial license is required to broadcast radio signals on the US AM band and it is also illegal for anyone to interfere with commercially licensed stations.
If you successfully build this circuit, you will see that it is not capable of transmitting a signal to receivers located more than a foot or two away at best. You should not modify the circuit presented here to further amplify the signal to gain further range.
If you would like to build this circuit, I have prepared a complete kit that includes a solderless breadboard, all of the necessary electronic components including the audio input jack, the battery snap, pre-cut jumper and antenna wires. I have also written highly detailed and illustrated step-by-step instructions that should guarantee a successful build every time.
The kit requires no soldering with a limited number of step-by-step instructions to make the project easy and fun withe guaranteed success.
For a limited time, the cost of the kit including postage-paid shipping via USPS to domestic addresses is currently $22.00. The complete kit will be shipped in a padded envelope and instructions and documentation will be sent in PDF format via email.
Solderless 555 AM Transmitter Kit
Domestic US Customers Only
Thanks for reading and please share your thought and experiences. You may drop me a line at firstname.lastname@example.org.
I passed through my hometown of Lawrence, Massachusetts this past Sunday afternoon, returning home to Connecticut after a weekend visit with family and friends at Hampton Beach.
I strolled through the O’Connell South Common which, located two blocks down the street from the Market Street three-decker I grew up in, held many childhood memories such as feeding the squirrels with my grandfather, smoking Lark cigarettes filched from my grandmother’s pack with my friend Georgie under the slide, and sledding down the hill on chilly winter days with my sister and dad. So many memories.
I remember on a long ago Saturday afternoon, using the bathroom under the bandstand where I encountered a custodian watching wrestling (or perhaps it was candlepin bowling?) on a B&W TV in his small office in the Men’s Room. He seemed quite content passing the time in his subterranean porcelain fiefdom.
Can you ever go home again? I think if we’ve held on tight to the small and seemingly insignificant memories, perhaps we never left?