Online SSTV Encoder & Decoder Tool
This free SSTV converter lets you convert SSTV audio to image or image to SSTV audio directly in your browser—no software install, no SSTV decoder app download. SSTV (Slow Scan Television) transmits still images as audio signals; each image takes tens of seconds to over two minutes. Use this sstv online app for ham radio, ISS SSTV events, or as an sstv generator to create your own transmissions.
About SSTV
SSTV (Slow-scan Television) is a retro yet powerful technique that encodes still images into audio frequencies for long-distance transmission. Widely used by Ham radio hobbyists and the ISS, it enables the exchange of visual data over standard radio channels through a distinct "chirping" sound.
Signal Structure
A typical SSTV signal consists of:
- Leader tone: ~300 ms at 1900 Hz for gain adjustment and sync.
- Sync pulse: 1200 Hz to mark the start of each line or field.
- VIS code: 7-bit encoding that identifies the transmission mode (e.g., Scottie 1, Martin 1); the receiver uses this to select decode parameters.
- Image data: Each line contains pixels; each pixel’s brightness is represented by a frequency between 1500–2300 Hz (black = 1500 Hz, white = 2300 Hz). Color modes transmit separate G-B-R channels in sequence.
Encode & Decode Principles
Encoding: Map each pixel’s brightness or R/G/B values to frequencies in the 1500–2300 Hz range, generate corresponding sine waves, and insert sync pulses and separators per the mode specification.
Decoding: Use Goertzel or similar frequency analysis on the audio to recover the dominant frequency in each time window as a brightness value, then reassemble lines and channels into an image. This tool uses 96 kHz sampling for adequate time resolution.
Common Modes
| Mode | Resolution | Type | Duration |
|---|---|---|---|
| Scottie 1 | 320×256 | Color | ~110s |
| Scottie 2 | 160×256 | Color | ~71s |
| Martin 1 | 320×256 | Color | ~114s |
| Robot 36 | 320×240 | Grayscale | ~36s |
| Robot 8 | 120×120 | B&W | ~8s |
Scottie and Martin use G-B-R channel order; Robot 36 transmits luminance only and suits weak signals; Robot 8 is the low resolution option (120×120 B&W) with the fastest transmission, good for quick tests.
Use Cases
- Amateur radio: Exchange images on HF, VHF/UHF simplex or repeaters; send QSL cards, etc.
- ISS SSTV events: The ISS transmits SSTV on 145.800 MHz; receive with a handheld and antenna, then use this sstv to image converter—microphone mode works great for live decoding.
- Education: Learn about analog signal modulation and the relationship between audio spectra and image encoding.
- Offline sharing: Encode images to WAV and share via voice channels, radios, or recordings.
How to Use This SSTV Decoder Online
SSTV Audio to Image (Decode)
- Upload file: Drop or click to select a WAV file—from local SSTV recordings or radio captures.
- SSTV decoder online microphone: Select “Microphone” → click “Start Listening” → play SSTV audio; the image updates in real time. Stops automatically after ~2 minutes (or stop manually). Ideal for receiving ISS or live radio.
- If auto-detect fails, manually select the same mode used when encoding.
- Click “Download PNG” to save the decoded image as a PNG file.
Image to SSTV Audio (Encode — SSTV Generator)
- Select an encode mode (Scottie 1/2, Martin 1, Robot 36/8).
- Drop or click to upload an image.
- Click “Generate SSTV Audio” → download the WAV file. Use this SSTV encoder as an sstv generator for your own transmissions.
Free SSTV converter—runs entirely in the browser. All audio and image processing is local; no data leaves your device. No sstv decoder app or sstv encoder software required.
