SSTV Encoder
Turn a picture into a slow scan television transmission. Eleven modes, rendered in your browser and downloadable as a WAV.
What SSTV is
Slow scan television sends a still picture over a voice radio channel as audio. Brightness becomes frequency: roughly 1500 Hz is black and 2300 Hz is white, with a 1200 Hz pulse marking the start of each line. A receiver listens to the tones and rebuilds the image line by line, which is why a single frame takes minutes rather than a fraction of a second.
It is still in regular use on the amateur bands, and the International Space Station transmits SSTV images during special events, which anyone with a handheld radio can receive.
Choosing a mode
Modes trade resolution against time on the air. A longer transmission carries more detail but is more likely to be spoiled by fading or interference.
| Mode | Frame | Time | Best for |
|---|---|---|---|
| PD50 | 320×256 | 50 s | Quick contacts, poor conditions |
| Martin M2 | 320×256 | 58 s | A fast colour frame |
| PD90 | 320×256 | 90 s | A good general default |
| Scottie 1 | 320×256 | 110 s | Very widely received |
| Martin M1 | 320×256 | 115 s | The most common colour mode |
| PD120 | 640×496 | 126 s | Higher resolution |
| PD160 | 512×400 | 161 s | Detail on a smaller frame |
| Wrasse SC2-180 | 320×256 | 182 s | Strong colour rendition |
| PD180 | 640×496 | 187 s | Detail, good conditions |
| PD240 | 640×496 | 248 s | High detail, patient operators |
| PD290 | 800×616 | 290 s | The most detail available here |
Every transmission begins with a calibration header and a VIS code, a short burst of tones that tells the receiver which mode is coming so it can configure itself automatically.
Sending it
- Play it into a radio. Feed the audio into a transmitter's microphone input, or simply hold a speaker near the microphone for a local test.
- Licensing applies to transmitting, not to this page. Generating the file is unregulated. Putting it on the air needs the appropriate amateur licence for the band and power you use.
- Test without a radio. Play the WAV into a decoder app on a second phone. That verifies the file before you go anywhere near an antenna.
- Keep the level sensible. Overdriving the input distorts the tones and the received picture tears.
Questions
Can this decode SSTV as well?
Not yet. This tool encodes only. Decoding needs sync detection and timing recovery, which is a substantial piece of work rather than the reverse of encoding.
Why is my picture cropped?
SSTV frames have fixed dimensions. By default the image is scaled to fill the frame and the overflow is trimmed. Switch off the framing option to fit the whole picture inside instead, with bars at the edges.
Why is the file so large?
A WAV holds uncompressed audio, and these transmissions are minutes long. PD290 produces about 25 MB. Convert to a compressed format afterwards if you need to move it around, but transmit from the WAV where you can.