Saturday, June 29, 2024

Built the Sputnik regenerative receiver

When I was a teenager and just starting to tinker with electronics I built a regenerative receiver kit from the local Tandy (RadioShack) store. It was a great success and I was able to listen to the big shortwave broadcasters on it.

I know that Bill often mentions that regenerative receivers may be haunted on his Soldersmoke blog. The DX Explorer site describes a rather neat regenerative receiver named Sputnik. The author also links to a way to order a very nice board from PCBWay. I ordered and quickly received five copies of a very nicely done board.

Most of the components I had but the ten turn pot had to be ordered in. I used a T50-2 toroid core rather than the air-core inductors. At first it didn't oscillate. My initial thought was that the tickler coil was not the right polarity but it turned out that my 2N2222s have collector and emitter reversed. Ralph, VK3ZZC, suggested that they might be fakes but the gain seemed fine.

The coil has a single turn that can be connected to a frequency counter. I have it going to my CRO and it's helpful for reading frequency and seeing when regeneration is starting. While you can, kind of, listen to single sideband, AM is best. Here's a bit from 7125 this morning.

I didn't have any 1N4001s in stock and tried another power rectifier that didn't seem to work as a varicap diode. I did have a genuine varicap in the junk box but it was too sensitive. Richard, VK3LRJ, gave me some 1N4004s and they work fine although tuning is very sensitive.

The radio is pretty hard to operate and one must juggle, RF gain, tuning and regeneration.

My memory might be rosy but the Tandy pegboard kit was easier to use than this design. It might be this one. There's a lot more electrical noise around these days and many of the big shortwave broadcasters have gone so perhaps the golden age of listening to BBC on a three transistor radio are over.

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