SSTV on Linux

The permission that catches everyone

Receive works, the waterfall looks right, and PTT does nothing. This is the single most common Linux problem in digital modes and it has nothing to do with your radio.

Serial devices — including USB-serial adaptors and the CAT ports built into modern rigs — belong to the dialout group on Debian and Ubuntu. Your user account is not a member of it by default, so the software cannot open the port to assert PTT.

sudo usermod -a -G dialout $USER

Then log out and log back in. This part is important and routinely skipped: group membership is established when your session starts, so opening a new terminal changes nothing. A reboot certainly works if you would rather not think about it.

You can confirm it took effect with groups, which should now list dialout.

Audio, in the PipeWire era

The historical advice about ALSA versus PulseAudio versus JACK is mostly obsolete. Modern desktops run PipeWire, which presents itself through the ALSA and PulseAudio interfaces, so applications written for either simply work.

What still matters is what happens to the audio in transit:

• Turn off noise suppression and echo cancellation. Both are designed for voice calls and both treat a steady SSTV tone as noise to be removed. This is the same problem Windows has, under different names.
• Pick the device explicitly. Do not rely on the default input; if the desktop reassigns it when a headset appears, your decoder goes deaf.
• Leave automatic gain control off. Riding the level through a transmission is exactly the distortion you are trying to avoid.

wpctl status lists what PipeWire currently sees, which is usually the fastest way to work out whether the rig’s USB codec has been detected at all.

You do not need JACK

JACK is superb at what it was built for: routing audio between applications with minimal latency, for music production. SSTV needs neither. A picture takes two minutes; a few tens of milliseconds of latency is irrelevant, and there is no second application to route audio to.

If a guide has you installing JACK, qjackctl and a patchbay for SSTV, it is almost certainly written for a workflow where a separate decoder and a separate transmitter program had to be connected. With a single self-contained program that requirement disappears.

Rig control

Most Linux ham software drives radios through hamlib, which is a fine library and one more thing to install, version-match and debug.

Open Signal has CAT control for Kenwood, Elecraft, Yaesu and Icom compiled in, so there is no hamlib package to align with. The trade is the usual one: less to configure, and only the rigs that are supported are supported.

What good looks like

1. User is in dialout, verified with groups.
2. Rig’s USB codec appears in wpctl status.
3. All enhancement, suppression and AGC disabled on that input.
4. Input and output devices selected explicitly in the software.
5. Levels set so ALC barely moves — see audio levels and ALC.

Get those five right and Linux is as reliable a platform for pictures as anything else. Get the first one wrong and you will spend an evening convinced your radio is broken.