SSTVAE

A hybrid-digital SSTV mode for HF radio: images are sent as the continuous-valued latents of a convolutional autoencoder, modulated onto OFDM carrier amplitudes. The decoder is trained with a simulated HF channel in the loop, so quality degrades gradually with SNR instead of falling off a digital cliff. Inspired by FreeDV RADE.

⚠️ Working beta. Decoded successfully over the air, but the on-air format is not frozen — expect incompatible changes. Both stations must run the same code and the same checkpoint; there's no handshake, so a mismatch decodes to noise rather than erroring.

Contents

• v1.pt — the published checkpoint (10.3 M params, 640×480)
• sstvae/, scripts/train.py, pyproject.toml — model and training code, matching this checkpoint

The command-line tools (encode / decode / live receive) and full documentation live in the project repository, github.com/arodland/SSTVAE, not here. The tools fetch v1.pt from this repo automatically, so there's nothing to download by hand.

Performance

Measured end-to-end through the real modem and a simulated channel, on validation images, PSNR in dB:

mode	time	clean	10 dB	6 dB	0 dB
A	32 s	24.7	24.4	24.0	22.3
B	64 s	25.7	25.4	25.0	23.5
C	95 s	26.0	25.8	25.5	24.1

~1200 Hz occupied bandwidth, ~4.5 dB envelope PAPR, >±50 Hz frequency offset tolerance. Below about −2 dB SNR the limit is acquisition — you get no image rather than a poor one.

Output is a reconstruction, not a photograph: fine detail, small text especially, can come back subtly wrong rather than merely blurry. Don't use it where exactness matters.