QRPGuys End-Fed Multiband Antenna

“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.

This easy to build kit has a minimal number of parts.

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 diagram from the instruction manual clearly depicts how to wind the four inductors.

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 james@ab1dq.com.

72 de AB1DQ/James

The Murania “One Transistor” Boy’s Radio Kit

INTRODUCTION & CONSTRUCTION

The Four State QRP Group (Oklahoma – Kansas – Arkansas – Missouri, in case you were wondering), founded in 2003, is one of the best developers and retailers of high quality and reasonably priced QRP (low power) ham radio and other do it yourself electronics kits.

I have a few of their kits over the past few years, most recently including the Bayou Jumper Paraset transceiver last year. I presently have the NM0S 4S-Tuner/Antenna Coupler kit on order.

Tonight I tackled one of their popular new non-ham radio kits, the Murania, a one transistor Tuned Radio Frequency (TRF) AM broadcast band receiver kit. The kit was designed by NM0S, David Cripe, who has engineered several of the 4SQRP kits.

The documentation for the Murania tells of the advent of transistor radios in the 1950s and how radios with 1 or 2 transistors were considered toys and therefore not taxed like radios containing more transistors. These 2 or less transistor “toy” radios became known as “Boy’s Radios” and are highly collectible today.

The designers of Boy’s Radios employed some creative design techniques to maximize the performance of these minimalist circuits, with sometimes amazing results. The Murania kit was inspired the design of those simple high performing transistor radios.

Unpacking the Murania kit.

My Murania kit arrived quickly within 2 days of placing my order online….WOW!

The Murania features a unique construction technique called “Pittsburgh Construction” developed by W0MQY , Joe Porter, in which components are soldered to the surface of pads on a silk screened double sided PCB.

Like other 4SQRP kits, the assembly manual needs to be downloaded from their website. Documentation is very good with clearly expressed step by step directions, but lacks pictures which might be helpful in illustrating potentially confusing steps for the newbie builder, such as the correct orientation of a polarized component such as an LED, diode or electrolytic cap.

The 4SQRP website suggest the kit can be built in about 2 hours time, and that was my experience. The radio is built in five stages… (1) wind the coil, (2) build the voltage regulator, (3) build the audio amp, (4) build the RF circuit, (5) final assembly.

1. Winding the Coil

The first task is to wind the coil which consists of 37 turns of No. 22 AWG enamel wire around a ferrite core. The instructions call for covering the core with a layer of masking tape first and using masking tape to hold the first and last winding in place.

My first attempt at
winding the coil.

I chose to use black electrical tape, and that was definitely a mistake – the electrical tape made it difficult to compress each winding snug against the previous winding and it didn’t do a very good job of holding the first and last winding in place.

I believe this may have also affected performance of my radio (see below). I am planning on modding the set and rewinding the coil with 61 turns (also, see below) and will use the recommended masking tape at that time.

2. Voltage Regulator

The first circuit constructed is the power supply/voltage regulator which consists of installing the volume control pot and attached power switch, one electrolytic capacitor, the battery connector, another capacitor and a resistor and the LED which serves three functions – power on lamp, signal strength indicator, and voltage regulator delivering 1.6 – 1.8 +VDC to power the radio.

I appreciated that the instructions called for testing the voltage regulator circuit before proceeding on to the audio amp stage. My Murania was putting out 1.792 VDC+ within the acceptable range of 1.6 – 1.8 volts.

3. Audio Amplifier

The Murania has a single stage of audio amplification based on the 2N3904 NPN transistor that drives the speaker through a matching transformer.

Other components in the stage included a pair of capacitors, a single resistor and of course, the transformer and speaker.

4. RF Stage

The bulk of the RF work is handled by a single IC, the TA7642, which has its origins in the late 1960s. Equivalent to the ZN914 and MK484, the TA7642 contains ten transistors and performs the task of RF amplification, audio detection, and automatic gain control. The documentation points out that with the TA7642, it is possible to construct a Tuned Radio Frequency receiver with useful sensitivity and selectivity, using only a handful of components and that this device served as the basis of many radio receivers that were the successors to the Boy’s Radios.

The 10 transistor equivalent circuit of the TA7642 per the datasheet.


Like the voltage regulator and audio amplification stages the RF stage went together without a hitch. All parts in the kit were properly identified and clearly referenced in the assembly manual. The etching on the circuit board made mis-installation pretty much an impossibility if you’re paying attention to what you’re doing.

The assembled Murania TRF radio ready for testing.

5. Final Assembly

After testing the radio to make sure it works (it did), the last step was to assemble the rest of the cabinet which is comprised of five additional pieces of yellow PCB material with pads strategically placed to match up for soldering to connect.

The pieces fit together perfectly, although I should have taken time as recommended in the directions to file off burs and rough spots so the pieces fit together more perfectly. Overall this is a pretty ingenious way to build a radio cabinet.

PERFORMANCE AND MODS

I was very pleased that the radio worked right away. I was able to pick up several AM stations with ease. Stations received were clear and the audio, while not as loud as I would have liked, was not distorted.

One problem I did encounter that is worth mentioning is that after I tested the radio on my bench I attached the back to the radio and brought it to my wife to show off my handiwork.

She was impressed, however when she turned the radio on, the LED lit up but there was no sound coming from the speaker – absolute silence – UGH!

I took the back off and quickly diagnosed the problem – the top of the 9V battery was shorting the speaker terminals – a problem easily fixed with a piece of electrical tape across the speaker terminals.

I did expect the radio to be a little more sensitive than it was initially and I realized that the radio’s performance might have been inhibited by my sloppy coil winding.

The unmodified Murania Schematic ©NM0S, 4SQRP Group

Online I found a list of three simple mods for the radio published by Jim Marco, WB2LHP in MI, the third of which that involves additional windings on the coil so I thought I’d give them a try.

Here are Jim’s mods…

1. Detector Gain Control…

FLOAT the wiper lug of R3 and place a jumper between the PADS for the R3 wiper and the high side of R3.

Lift the leg of R1 that intersects with R2 and R3 and connect a jumper between the floated leg of R1 and the wiper of R3.

According to Jim, this allows R3 to control the gain of the detector stage in the TA7642 acting similar to a regen control where there is both volume and gain reaction. The audio amp runs wide open and R3 should be adjusted for the best sounding audio.

2. Reduced audio distortion…

Changing R2 from 1K to 2.7K biases the output stage of the TA7642 for linear operation.

3.Frequency coverage and dial mapping…

Increasing L1 from 37 turns to 61 turns and removing C8 centers the frequency coverage and makes the dial tracking spot on…

The revised schematic based on WB2LHB’s mods

I am pleased to say that the mods were easy to accomplish and I had no difficulty with any of them. I did not have a 2.7K ohm resistor on hand so I tied a 2.2k and a 470 ohm resistor in series for R2. Using the recommended masking tape instead of rubbery electrical tape on the ferrite rod made a world of difference too – winding the 61 turns was a snap.

My modified Murania – notice the new ferrite coil, the replacement of R2, the removal of C8 on the right, and the jumper going from R1 over the speaker to the VR R3.

And how did it work? Even better than before – the radio seems to be more sensitive and is picking up more stations and the audio is definitely more crisp as promised. If you’re looking for a fun one-evening project that will take you back to your earlier days of melting solder – the Murania TRF receiver is worth building.

©2019 JMSurprenant