Hacking the R-390A military shortwave radio receiver to transmit as well


After getting his hands on this relic [Gregory Charvat] manage to hack it, converting the receiver into a transceiver.

It may be old, but the R-390A is nothing to scoff at. It’s abilities include AM, code, and FSK operation from 500 kHz to 32 MHz. But it is a receiver with no way of transmitting on the same bands. This is where [Gregory’s] hack comes into play. He rerouted the variable-frequency oscillator feed inside of the R-390A in order to use his 20M single-sideband unit. Basically what this does is allow him to control everything from the 390, using the microphone from the SSB — along with some switching hardware — to transmit his own messages.

His demo video starts with him making a few contacts using the hacked equipment. He then spends some time at the whiteboard explaning the changes. This portion went over our heads, but it becomes more clear when he cracks open the case and shows the actual modifications.

12 thoughts on “Hacking the R-390A military shortwave radio receiver to transmit as well

  1. RF engineer here. His description is right on. The reason he can do this is because those old R-390s are so overbuilt, there’s signal left over for him to use as a reference for his transmitter. A few other components, and voila, the tuning of the receiver also tunes the transmitter.

  2. Duh, just find the matching, 650-pound, T-368 transmitter that “goes” with the R-390A. ;)


    I’d love to have an R-390A, but you’d be very lucky to find a complete, let alone working one for less than $700 nowadays, and that certainly won’t be a Collins-built example. That’s a hard pill to swallow just for the cool factor, being as a Hammarlund SP-600 JX can be had for around $150, and is just about as good of a receiver.

  3. While I like the Hammarlunds, they aren’t as cool as a R-390, nor do they have “digital” tuning. Just kidding. The R-390 is still my favorite receiver. I grew up with one in the Navy. Solid as anything and extremely stable.

  4. His mastery of radio is impressive but that’s nothing compared to his mastery of other sciences. Check out his accomplishemnt in quantum physics. Apparently he built a device to affect the outcome of events at the quantum level after they happen. At the press of a button he made Schrodinger’s cat disappear!

    And is that time travel too? I have never heard anyone who appears so young refer to Megacycles. Or has he mastered the medicine of aging too?

    1. I noted the use of a person first gotten intersected in electronics. My formal electronics started when the *Hertz convention was first being adopted, but or text books still used cycles. I’m apt to say either, I doubt Mr, Hertz minds at all.

  5. The Hammerlunds were indeed very good receivers, and National put out a couple of very nice winners as well. If they didn’t have enough drive to split as he did with the 390, it would be easy to add an RF amp inline after the split.

  6. in the late 60’s at clark airbase we picked up several r390;s signal converters, signal test equipment still in their original shipping crates at the base dump,, navy could not get any
    an the air force was discarding new units can’t name all the things we found there,, what we
    did not get was trashed by doziers this was1968….I was an E-3 at the time..h

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