We like regenerative receivers. They perform well and they are dead simple to create. Example? [Radio abUse] modified a few existing designs and built a one-transistor receiver. Well, one transistor if you don’t count the dozens that are probably on the audio amplifier IC, but we won’t quibble. You can watch a video about the simple receiver — which looks good on a neatly done universal board — below.
The coil of #22 wire dominates the visual layout, and we imagine winding it might have been the most time-consuming part of the project. The layout would work with a single-sided PCB and would be a great board to produce by hand if you were inclined to develop that skill.
Regenerative receivers work by holding an amplifier just shy of oscillating at a certain frequency. This provides extremely high gain at a particular frequency which allows just a single stage to really pull in signals.
We were a little sad to find out there was a plan to tear the radio down to build something else. But, we suppose, that’s progress. We’d be tempted to make a module out of the audio amplifier and then keep the RF section intact. But, then again, we have a lot of partial projects like that gathering dust on the shelf, so maybe that’s not such a great idea.
While regenerative receivers aren’t the most common architecture today, they still have their place. The inventor, Edwin Armstrong, developed quite a bit of radio tech that we still use today.
Actually, when regens were king, kicking them into oscillation was often important. You needed that if receiving morse code, the oscillation beating the incoming signal down to audio. When oscillating, it’s really the same concept as a direct conversion receiver.
In the 1920s, parts were big, and expensive, hence simplicity reigned. But solid state made things small, and cheap. So you can do things like add a stage between the antenna and set ctor, for isolation. Helps keep the regen from becoming unstable as the antenna waves in tye wind. Add some voltage regulation, you would if it’s an oscillator. Add that multi-stage audio amplifier.
Over twenty years ago, Charles Kitchin went back and reviewed early literature on the regen, and then moved forward with various regen projects. (He did the same, to a lesser extent, for superregenerative receivers, which are just an extension of the regen.). I’d point to his work before some random project on the web, especially when many such circuits these days derive from his work. Can’t tell with this one, I won’t watch videos to see a schematic.
Turning the regen up into oscillation is good for receiving SSB too.
+1 for the video ref. I hate it when I get to see the essence of the message the author is trying so hard to put across, only for the video to pan back to a fidgety talking head.
I too dislike videos with schematics. The one for this circuit can be found here: http://www.electroniq.net/radio-frequency/am-regenerative-receiver.html
Agreed, and thanks for the link.
Nice, but it requires power. I’d like to see more crystal receivers.
In a disaster situation where you can’t get batteries or power, a crystal
receiver will at least pick up something.
I tested one back in my college days using more modern parts from an actual AM radio – turning cap, coil on ferrite rod and germanium diode and fed it through an amplifier. Unfortunately the selectivity wasn’t very good and there was a lot of interferences from the crowded AM spectrum in downtown. It was a 5 minutes hack and I didn’t keep it.
As for power, use a small solar panel + rechargeable batteries for emergency.
^tuning cap
A battery could be made by anyone with a penny, a galvanized nail and a potato. All were easy to find even when the trench radio came about. And it doesn’t have to be a potato. People use Lemons, limes, watermelons, tomatoes and more. A soldier could listen to the news and then eat his lunch each day.
I wouldn’t be surprised if the penny and galvanized nail stuck into a dead horse or other corpse worked as a battery too.
Let’s be thankful nobody tried that in the trenches or those trench radios might have ended up being called “corpse radios”.
The regen receiver in this one has only one transistor. And the transmitter has only one transistor. And it made 20 two-way contacts. https://hackaday.com/2019/11/09/just-how-simple-can-a-transceiver-be/
Decades ago, I bought several boxes through an auction at the tech school I was attending.
Among those boxes were coils such as those shown in the Title Photo, along with an oscillograph.
Not knowing what they represented or how to use them, I tossed them out.
B^(
Maybe that is why I’m a border line hoarder today…
B^)
> we imagine winding it might have been the most time-consuming part of the project.
You make it sound harder than it is. It is a good meditation from crazy life.
I watched TV while winding my a couple of Tesla coils – similar dimensions and 2X as tall with much finer wires. You just need a small piece of tape when you are interrupted by bathroom break or munchies.
Well it isn’t hard but it is time consuming to do well. I had a friend who decided waiting at the airport was a good time for coil winding. After being surrounded by TSA and police he has not done that again.
The tuning coil used as an antenna will create a null when mounted vertically. If you move it around carefully, the station will dissappear completely. Definitely needs to be horizontal.
Fall is almost here, and that means long winter nights are coming, and radio experiments are one way to use them productively. Regenerative receivers are like electronic haiku; you can do so much with so few parts.
I recommend trying to get your hands on some open-air tuning capacitors; they’re getting harder to find. And try to get a few tubes (triodes, mainly) to play with. It’s very gratifying to make a simple working receiver using one or tubes. I’ve had good luck with Soviet ex-military tubes.
Look for designs based on the KOSMOS Radiomann; this is a design that uses a tube (dual triode) but runs on ~12 to 20 volts DC, so no scary high-voltage supplies needed.
While regen readios are nice, I’ve always had a soft spot for “reflex” radios.
RF is amplified, then meets a high pass / low pass filter.
Then it gets rectified and turned into an audio signal – and fed back into the SAME transistor.
At the output, the audio goes via the low pass path to an optional final buffer amplifier.
Can someone tell me what the oscillator topology is? It looks like a Vackar with the feedback between collector to base, but lacked the capacitor divider.
can it be modified to receive FM (slope detection)?
The ‘386 audio amp stage is almost a commodity; it shows up often in so many designs. I’ve started buying ‘386 amp modules from the far east. Easy to hook up, usually no layout or feedback issues to solve, and easy to move the module to different projects as desired.
Current mirror cascode regenerativer receiver:
https://archive.org/details/trf-radio-circuit
How many of us started by building simple radio receivers? I remember getting a Heathkit crystal radio kit for Christmas when I was about 12. It fascinated me. I also had one of those rocket crystal sets. Then I built sets from salvaged components. I purchased a surplus military field strength meter which was essentially a crystal set with a sensitive meter and front end L/C circuits covering the HF bands. When connected to my 40 meter ground plane antenna I could hear tons of SWBC stations using high impedance military headphones. Something about simple receivers that still fascinates me. I’ve been gathering components to build crystal and regen rigs and can’t wait for those long winter nights.
Jim WB4ILP
Hello, we recently published a modern version of the shortwave Audion receiver in HBradio 3/2023.
The project in entirely in public domain (including Gerbers), and also described on GitHub:
https://github.com/USKA-FOS/HB9TRU-Transistor-Audion
A single LC parallel circuit serves as the frequency-determining element; the coil is “plug-in” and
user-made; if a frame-coil is used, it serves as well as the antenna. The circuit uses classical
and SMD-component; the SMD mounting on a copper-backplane PCB is crucial for eliminating
any hand-sensitivity and internal feed-back of the circuit.
The circuit runs on a single AAA-cell and can be mounted in less than 2 hours, using commonly available soldering equipment, and fine soldering wire, and provides a true WHW experience!
73 de Edgar, HB9TRU