Super-regenerative UHF Transceivers.

[Argus25]

Recently on the forum there was some talk of super-regenerative receivers.

A while ago I constructed a pair of super-regenerative UHF transceivers, photos attached.

The circuit architecture is really a classic American design using one 6CW4 Nuvistor and two germanium transistors, but in this case an OC71 and an AC188. The 6CW4 acts as a super-regnerative detector, or modulated oscillator, the transistors are either the modulator in TX mode or audio amp in receive mode.

The cases are alloy pre-coated types from RS which were protected with a heavy coat of tape while drilling etc.

I wasn't happy with the pseudo self tapping screws for the backs and I noted their thread pitch and diameters were almost the same as the tap required for 1/8" BSW Heli coils, so I tapped those and fitted the coils to the holes, so the rear case screws are now stainless steel 1/8 BSW and screw in and out smoothly without any significant wear.

Also the remaining screws are 3mm metric titanium, the nyloc nuts you see on the transformer mounts are also titanium.

I lined the battery bay with rubber and manufactured a clamp on a brass hinge with a wingnut lock. The brass work , including the antennas I had nickel plated.

The labels are engraved formica, attached to the case with 1.4mm hex head brass screws with threads cut into the alloy case.

Since the space available for the 6V battery was perfect for a lantern battery with spring connections, I also made a custom battery connector for that from an acrylic plate with nickel plated brass inserts. When doing a project it is worth the delay to have brass parts electroplated. I made a pcb for it that was not specified in the original design so as to help keep it orderly.

I wanted to make the units look like they had escaped from the TV series Lost in Space, since its a mid '60's design and I put a small loop in the top of each antenna for artistic appeal, though the original design had a version of this too so as to prevent being poked by a sharp wire end.

This 420MHz circuit, originating from the 1966 ARRL handbook, has been reported to have managed 30 mile line of sight communication.

The handsets used are simply standard telephone ones with a carbon mic (not shown in attached photos). I have some vintage black handsets to go with them.

I could attach the circuit if there was any interest.

[G6Tanuki]

Fascinating! I'd love to see the circuit. And I love the style of the case etc too - it fits in with my 'post-WWII military/industrial' aesthetic.

Have you tried them in anger? If so what sort of range do you get? The RF side would I guess have the same sort of performance as the WWII-era Joan-Eleanor "S-phones" [one version of which operated around 450MHz and were good for half a mile or so in not-too-overgrown country].

[Al (astral highway)]

Beautiful and delightful work, Argus25.

Thanks for sharing these. I love the details and the labelling, and the overall aesthetic.

And to think some people are satisfied with a twenty quid Chinese dual bander, the fools!

[Al (astral highway)]

It's completely fascinating work. I love the engraved formica labels, they are stunning.

How did you fashion those?

[Andrew2]

I can only echo what other contributors have said. The work is wonderful, and those labels look absolutely authentic. I'm full of envy.

[ionburn]

Very professional!

[Argus25]

I will post the circuit tonight.

The formica labels were done at the time by a local engraving shop.

Thanks all for the kind remarks.

I forgot to mention the HT battery is a 45V type that sits under the clamp on the top of the lantern battery. I got them as reproductions from AES, but I don't have any 45V batteries currently.

I tested the units and got good communication easily one km away. I have not attempted the 30 mile line of sight test though.

[Al (astral highway)]

Great, I’m looking forward to that. I love Nuvistors and used one in a UHF converter to listen to space satellites!!

[Argus25]

Circuit attached.

It is clever the way they change the operating conditions of the Nuvistor to either act as a plain oscillator for TX or an interrupted one for super-regenerative receive just by adding the RC time constant in the grid circuit. The simplicity of it versus its functionality has always appealed to me.

[Al (astral highway)]

Thank you, the circuit is fascinating. Really brilliantly conceived, with not a component wasted.

I see what you mean about the RC function, wonderful!

[Argus25]

While we are on this topic of super-regenerative transceivers, I have attached what amounts to a "hand held" version of these, this one from 16 years earlier, Oct 1950 and running on 144MHz, it uses a 958 Acorn tube with a split stator tuning cap in the tank circuit and for the audio part uses a 3V4. They put the mic & earphone into the case to make a "gigantic walki-talkie". I think the image is pretty cool.

(Of note on the magazine cover, notice the Australian made AWV valves, every bit as good as RCA's originals)