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 In this book, Jones goes on to predict that super-regens will be superseded (!)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.
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