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  • Stuart Longland (VK4MSL)stuartl@longlandclan.id.au
    May 18, 2026, 5:02 AM

    Silly SDR question for people.

    At the moment @vk4msl_sstv is down because I had to grab the radio I use for it to run a number of WICEN events… e.g. it was the base packet station radio at Kilkivan.

    Using a full-blooded 100W rig like a FT-897D is a bit overkill too.

    I have a headless Raspberry Pi 4 that I use for that SSTV bot. Headless meaning not only does it not have a monitor, it also doesn't run X or Wayland. That rules out anything GUI-based like GQRX, and no, I'm not going to run VNC/RDP/NX/Spice/<insert GUI remote desktop protocol here>.

    Is there a SDR receiver that can drive a RTL-SDR dongle and decode SSB audio for piping to another application (either via Pipewire or TCP sockets) and be controlled via a CLI? I have an upverter to shift HF into VHF, I just need something to decode the I/Q data and control the VCO in the RTL-SDR.

    #AmateurRadio #SDR

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Replies

  • Stuart Longland (VK4MSL)stuartl@longlandclan.id.au
    May 18, 2026, 5:05 AM

    I'm guessing something could be cooked up using the GNURadio framework, but was hoping there might be an off-the-shelf "daemon" service that someone's done.

    (I could do it myself I guess like I hacked up `slowrx` to make `slowrxd`. But why DIY if someone's done it for you?)

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  • ChuckChuckMcManis@chaos.social
    May 18, 2026, 5:40 PM

    @stuartl Sorry. As I understood your question it was this,

    "I've got an RTL-SDR type dongle and upverter, I need [missing thing] that control the SDR and can decode SSB audio and pipe it into an app."

    I have found small integrated RasPi compute module boxes do that [missing thing] part well. (Clockwork Pi, ReTerminal). 1/2

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  • ChuckChuckMcManis@chaos.social
    May 18, 2026, 5:44 PM

    @stuartl When I re-read your question I realized that you were saying you wanted to use the headless RasPI SSTV box. But no remote GUI protocol. Perhaps just run a TCP-IQ server on the RasPi? Send the IQ data to an app on your laptop/desktop? Something like Spyserver? That would avoid the remote gui protocol and its an off the shelf solution. 2/2

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  • Stuart Longland (VK4MSL)stuartl@longlandclan.id.au
    May 18, 2026, 7:52 PM

    @ChuckMcManis No, because `slowrxd` is running on the RPi4, if I did what you're suggesting there, I'd be sending the I/Q data off elsewhere to be decoded, then sending the decoded audio *back* to the RPi4 to demodulate the SSTV transmission.

    Utterly pointless.

    This is a headless station. There's no phone. There's no laptop. There's no desktop. There's no monitor. Just a radio, a RPi4, and an Internet connection. It hears a SSTV signal, it decodes it, it slaps it up on the Internet via the @vk4msl_sstv bot and throws the image up on a website.

    Putting a second machine in only moves the problem, because the second machine will be headless like the first.

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  • ChuckChuckMcManis@chaos.social
    May 18, 2026, 8:51 PM

    @stuartl @vk4msl_sstv

    Ah got it. I went back and read your 'hacking sstv' web page. One answer is to just write a program that tunes your SDR to the band where the SSTV images are being transmitted, capture the transmission and decode them and then post them to the Fediverse. That all works fine on a headless RasPi with an SDR dongle and an internet connection.

    It's interesting that few do it this way.

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  • Stuart Longland (VK4MSL)stuartl@longlandclan.id.au
    May 18, 2026, 8:53 PM

    @ChuckMcManis Yes, that is one way… my question was whether someone had written such a program, because the idea that I'm the first person in the world to want to do this seemed odd. Why re-invent the wheel?

    Turns out, `rtl_fm` exists (as per @ai6yr 's post elsewhere in this thread). Not a 100% solution, but 90% of the way there.

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  • ChuckChuckMcManis@chaos.social
    May 18, 2026, 8:56 PM

    @stuartl @ai6yr

    Yeah, I thought about rtl_fm as a good example of how it would be coded. I would be surprised if you were the first to want to do this, but not surprised in the least that someone did it and didn't bother to make it hugely visible.

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  • ChuckChuckMcManis@chaos.social
    May 18, 2026, 8:57 PM

    @stuartl
    @ai6yr

    And in the way of these things, after writing it and publishing it, two or three people will come out of the woodwork and say "Oh I did that same thing years ago!" without having ever told anyone else apparently.

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  • ChuckChuckMcManis@chaos.social
    May 18, 2026, 9:02 PM

    @stuartl @ai6yr
    LOL. Yeah, but I would bet you a donut that in the initial commit of the code all it did was demodulate WBFM and then someone said, "Well it could also do ..." and that got added on. You could hack it to also demodulate SSTV and add a switch to tell it to produce .png files or something and the cycle would continue. 😆

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