Building the 4SQRP Ozark Patrol Shortwave Regenerative Receiver

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.

http://www.4sqrp.com/ozarkpatrol.php

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!

In Conclusion

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 james@ab1dq.com to share your experience!

©2022 James M. Surprenant / AB1DQ