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Wednesday, October 20, 2021

Super-Regeneration is Super-Strange

Farhan VU2ESE is largely responsible for this.  He has recently been talking about VHF.  (More about this in due course.).  This started me thinking about my failed effort in London to get on 2 meter AM.   My plan was to use the transmit portion of this HW-30 (above) with a 2-to-10 downconverter and my trusty Drake 2-B for receive.  

Tony G4WIF also bears some responsibility:  When I expressed interest in Farhan's VHF work, Tony sent me two articles from SPRAT.  Both of them were about super-regenerative receivers.  

Farhan's comments caused me to pull the HW-30 out of storage.  I started poking around the transmitter.  But then I noticed something:  On receive, the AF amplifier was obviously working.  Then, when I tuned through the 2 meter band, the rest of the receiver seemed to be working too.  I fired up the HP-8640B sig gen on 2 meters and turned on the AM modulation.  Indeed, the old receiver was inhaling!  

This launched me into an effort to understand how super-regenerative receivers work.  There are a lot of really weak explanations out there. You get the distinct impression that the person explaining the circuit does not understand it himself.  This makes explaining it very difficult.  I am not the only one to notice this phenomenon:  Mike WU2D commented on this in one of his excellent super-regen videos.  This one:  

Mike very kindly said the operation of this circuit seems like "magic."  I was thinking more in terms of Voodoo.  

Howard Armstrong discovered super-regeneration years after he invented plain old regeneration.  The new discovery came around 1921.

It looks like VHF guru Frank Jones had very early misgivings about super-regeneration.  In his 1934 classic 5 Meter Radio Telephony, Jones seems unenthusiastic about the circuit and about our ability to understand it:  "To explain, simply, exactly how this form of detection takes place is not a simple matter, but some of its characteristics are easy to visualize."  In this book, Jones goes on to predict that super-regens will be superseded (!) by superhets.  Indeed, in his 1961 book VHF for the Radio Amateur there are no super-regen circuits; all the receive systems are down-converters to HF receivers. 

Still, with that HW-30 hissing away right next to me, I feel I need to understand how the super-regen works.  I'm not there yet, but I'm trying.  Here are some good resources: 

A good article from Wireless World 1946:  

A student's write up of his effort to understand: 

But the best so far (for me) is from Frederick Terman (one of the founders of Silicon Valley) in  his 1943 classic Radio Engineer's Handbook.  Click on the images for a clearer view. 

I will definitely try to get the HW-30's 5 watt AM transmitter going.  I am not so sure I'll do anything with the receiver.  I think this is a matter of picking your battles and "finding joy."   I didn't find joy in FT-8, so I stopped working with it.  Same with my HA-600A, DX-40 Novice rig.  Same with CW in general.  And the same with SDR.  I suspect that super-regen receivers may also fall into this category.  I mean, let's face it, if you are not fond of ordinary regens, is there any real chance that you will like SUPER-regens?  Even Frank Jones seems to have disliked them.  And there is a reason Howard Armstrong moved on to superhets -- they are better! But still, that receiver is hissing away at me...  Stay tuned. 


  1. As a Novice almost 60 years ago, 2 meter AM was still king. I built and operated the Twoer for many years until FM edged AM out. I admit, I knew nothing of how the circuits worked. But thanks to Heathkits excellent instructions I had many many great hours of chatting with fellow hams around my small valley. I hope you can get it on the air. And learn about it in the way.

  2. Good work Bill. I think of a superregen as a gated oscillator switched on or off (quenched)at a constant rate.

    Perhaps now best suited to OOK for UHF remote garage door & gate openers? Still, though, as you’ve shown, superreggen analysis reveals amazing physics and surprising complexity.

    I've found that mostly clever people that design superregenerative circuitry.

    Their greatest virtue seems to be amazingly low current consumption. I built a cat toy receiver using a SAW oscillator up at ~ 480 MHz that consumed 1.1 mA and worked perfectly from a tiny battery.

    As you know, superregens prove susceptible to overload from strong in-or-out of band carriers, may offer poor RF selectivity, their RF radiation may aggravate local radio enthusiasts, they suffer from temperature drift, and if another such enthusiast operates their superregen nearby – you might both suffer woes.

    Love VHF AM and Heathkit topics.

    73. T

  3. I think the receiver in the twoer radiated better than its transmitter! W i d e as a barn door too…

  4. I played briefly with a Twoer as a Novice in Murfreesboro in 1970, when FM repeaters in nearby Nashville were coming on the air. It was possible to slope-tune the FM signal with the Twoer, so I got my first taste of listening to FM repeater traffic on 146.76 MHz. Later, after upgrading to Advanced in the spring of 1971, I built an HW-101 and put up a homebrew quad for 20-15-10 on a house-bracketed 40 foot tower and inverted vee made of electric fence wire for 40 and 80 on a 50 foot push-up mast. I was in ham heaven!

    I ended up with a Gladding 25 as my first real introduction to two meter FM repeaters when I went to college in 1972. As a college student 1972-1977 with no permanent address (dorm/apartment in Cookeville and co-op in Huntsville) I ended up operating almost exclusively mobile FM, and added a GLB Channelizer so that I could synthesize frequencies for the Gladding. Those two took the place of my glove box in my 68 Cougar, along with a touch-tone pad in a box on my console, so I could make autopatches.

    The only HF operation during 1972-1974 was at the club station at TTU in Cookeville. In 1975 I made the colossal mistake of ordering a Heath SB-104. I finally got rid of it in the Dayton flea market a couple of frustrating years later. That was the last Heathkit I ever owned.

    I finally ended up with an Icom IC-735 when they first came out (1982, I think) and held on to it until about 2009, when I finally upgraded to an Elecraft K3. Wow, what a difference!

    I now have a K3s/P3 combo, and just recently 'went QRO' for the first time in 50 years as a ham, by adding a used KPA500/KAT500 combo. I'm still learning how to use those (and when!).

    I'm still using a quad on a 40 foot tower, but this one was based on a commercial spider-boom, and I restrung it for 20/17/15/12/10/6, and I'm running a ZS6BKW dipole at 35 ft, using the KAT3 or KAT500 antenna tuners to run that on 80/60/40/30.

    If I get the itch, I have a 160 sloper I can hoist up on the telescoping mast.

    Back in ham heaven!

  5. Hi Bill, I built a Fredbox HT a few years ago. It's a low power AM 2 meter HT transceiver. I thought it would be fun to do a demonstration at my club using a Heathkit Twoer and the Fredbox to communicate between them. I setup the correct crystal for the Twoer and it seemed to be working at home. When I got to the club meeting I noticed that the Twoer receiver seemed to be having trouble. When it was time for the demonstration the Twoer was completely deaf. Fortunately I had set my FT-60 with a channel for AM reception at the proper frequency and I turned that on, went out to the parking lot and was getting thumbs up from the club members that they could hear the Fredbox loud and clear 100 yds from the FT-60. After the partial failure I tried again at home and the Heathkit work ok with the Fredbox. After delving into this further I discovered that when people were using those Twoers from Heathkit they became unusable in areas that had lots of two FM activity nearby. That super regen, with it's lack of selectivity, is very easily swamped with strong FM and that's what probably happened at my club meeting. I have since moved up to the HW-17A which is better but not a great receiver either.

  6. Bill, Don't give up on 2 meter AM! You don't need a crowd to have fun with it- just one or two guys nearby. If you want to take a stab at a Fredbox I have a PCB and most of the parts you need to build one. The tricky part is taking IF coils apart and rewinding them. It does also have a regen receiver (full disclosure) but if you get no AM contacts you can retune to listen to the local airport. One more point- the Twoer receiver is rubbish but the HW-17 isn't too bad and the transmit side works great. We have an AM 2 meter net in the Chicago area and I got great signal reports with that (HW-17)transmitter.
    John KC9OJV


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