SSTV.org.ukSSDV link reference
SSDV defines image packets. It does not prescribe one modulation. Recover the correct link frame before applying the SSDV packet layout and JPEG reconstruction algorithm.
| Profile | Rate | Input | Signal/framing |
|---|---|---|---|
| 1200 AFSK / AX.25 | 1200 bit/s | Demodulated audio | 1200 Hz mark and 2200 Hz space; NRZI, HDLC flags, bit stuffing and AX.25 frame check. |
| 9600 FSK / AX.25 | 9600 bit/s | Discriminator/baseband audio or I/Q | G3RUH scrambling, NRZI and HDLC deframing after 9600-symbol/s baseband recovery. |
| 9600 GFSK / AX.25 | 9600 bit/s | Baseband audio or I/Q | The receive profile uses the shared 9600 FSK/G3RUH recovery path for Gaussian-shaped FSK signals. |
| 1200 BPSK / AO-40 | 1200 symbols/s | Audio; 1500 Hz reference carrier | Differential BPSK recovery followed by AO-40 synchronization, deinterleaving and concatenated error correction. |
| IL2P | 1200 AFSK or supported FSK baseband | Audio or I/Q | IL2P sync, protected headers and Reed-Solomon-protected payloads; reconstructed AX.25 metadata where applicable. |
| Slow FSK / SSDV | 800 bit/s default | 1600/2400 Hz audio tones | The 2.0 runtime uses an SFSK sync word, a little-endian payload length and CRC16-CCITT over length plus payload. |
| SatNOGS IQ | Recording-dependent | Complex I/Q | An I/Q input and profile-search route, not a distinct modulation or packet format. |
| Doppler search | Underlying profile-dependent | Complex I/Q | Frequency-offset search around supported link profiles, followed by normal frame validation. |
Automatic selection searches supported candidates. Selecting the known profile limits that search and makes a station log easier to interpret. SatNOGS IQ and Doppler search are acquisition routes, not universal satellite decoders.
1200 Hz mark and 2200 Hz space; NRZI, HDLC flags, bit stuffing and AX.25 frame check.
SSDV packets in AX.25 UI information fields; source and destination callsigns belong to the outer frame.
The AX.25 frame CRC and the SSDV CRC/FEC protect different layers. A valid radio frame need not contain SSDV.
The complete digital test card carried in AX.25/SSDV packets.
48,000 samples/s · 1 channel · 126.67 s
Lossless FLACPCM16 WAVSSDV packetsReconstructed JPEG
All AX.25/SSDV packets recovered from generated WAV; JPEG reconstructed.
The complete digital test card carried in AX.25/SSDV packets.
48,000 samples/s · 1 channel · 108.80 s
Lossless FLACPCM16 WAVSSDV packetsReconstructed JPEG
All AX.25/SSDV packets recovered from generated WAV; JPEG reconstructed.
G3RUH scrambling, NRZI and HDLC deframing after 9600-symbol/s baseband recovery.
AX.25 information fields, classified as SSDV or telemetry after the frame is recovered.
A voice-filtered speaker output can remove the baseband content. Use a discriminator output or an SDR path.
AX.25 test frame carrying NATIVE9K6FIXTURE; no image payload.
48,000 samples/s · 1 channel · 0.04 s
Generated by the pinned library's native transport fixture generator.
Interleaved signed PCM16 little-endian I,Q pairs; AX.25 test payload, no complete image.
96,000 samples/s · 2 channels
Complex I/Q data. Import as I/Q with the listed sample rate and I,Q channel order; speaker playback is not a decode preview.
Generated by the pinned native transport fixture generator.
The receive profile uses the shared 9600 FSK/G3RUH recovery path for Gaussian-shaped FSK signals.
AX.25 frames; Gaussian pulse shaping is a transmitter property rather than an SSDV packet option.
The library's shared 9600 fixture demonstrates framing, not every Gaussian filter bandwidth or transmitter deviation.
AX.25 test frame carrying NATIVE9K6FIXTURE; no image payload.
48,000 samples/s · 1 channel · 0.04 s
Generated by the pinned library's native transport fixture generator.
Differential BPSK recovery followed by AO-40 synchronization, deinterleaving and concatenated error correction.
256-byte AO-40 telemetry frames. The spacecraft payload layout must be known before extracting an image.
A recovered AO-40 telemetry frame is not automatically an SSDV image. The supplied waveform carries test telemetry.
A coded 256-byte test telemetry frame; no image payload.
48,000 samples/s · 1 channel · 4.33 s
Generated by the pinned library's native transport fixture generator.
IL2P sync, protected headers and Reed-Solomon-protected payloads; reconstructed AX.25 metadata where applicable.
AX.25-compatible information payloads, then SSDV/telemetry classification.
IL2P is a link format, not a JPEG codec. Both sender and receiver must agree on modulation and framing.
An IL2P frame carrying TEMP=21.4,V=8.1 telemetry; no image payload.
48,000 samples/s · 1 channel · 0.23 s
Generated by the pinned library's native transport fixture generator.
The 2.0 runtime uses an SFSK sync word, a little-endian payload length and CRC16-CCITT over length plus payload.
Telemetry or SSDV packets in a length-delimited frame; least-significant-bit-first byte recovery.
This is the library's specific SFSK framing. It does not mean arbitrary balloon RTTY or every slow-FSK satellite is supported.
Telemetry plus the first SSDV packet only; an incomplete image example.
48,000 samples/s · 1 channel · 3.03 s
Generated by the pinned library's native transport fixture generator.
An I/Q input and profile-search route, not a distinct modulation or packet format.
A supported demodulator must recover the spacecraft's link frames before SSDV reconstruction can begin.
SatNOGS branding or a stereo WAV extension does not identify the modulation, sample rate, I/Q order or frequency offset.
Interleaved signed PCM16 little-endian I,Q pairs; AX.25 test payload, no complete image.
96,000 samples/s · 2 channels
Complex I/Q data. Import as I/Q with the listed sample rate and I,Q channel order; speaker playback is not a decode preview.
Generated by the pinned native transport fixture generator.
Frequency-offset search around supported link profiles, followed by normal frame validation.
The search does not change the SSDV packet layout or the spacecraft's telemetry schema.
This is an acquisition aid. It cannot make an unknown link format decodable or recover missing samples.
Interleaved signed PCM16 little-endian I,Q pairs; AX.25 test payload, no complete image.
96,000 samples/s · 2 channels
Complex I/Q data. Import as I/Q with the listed sample rate and I,Q channel order; speaker playback is not a decode preview.
Generated by the pinned native transport fixture generator.
The shared library includes KISS/AX.25 framing and a TCP helper. The 2.0 app's source picker exposes audio/file input and SDR sample servers, not a KISS TCP source. A Dire Wolf KISS stream is already demodulated frame data; it is not PCM audio and cannot be supplied to the rtl_tcp input.
The normal SSDV packet has type 0x66 and 32 parity bytes. The no-FEC packet has type 0x67 and a larger JPEG-fragment payload. AO-40 or IL2P error correction, when present, belongs to the outer radio link. Never remove SSDV parity merely because a transport has its own FEC unless the transmitter actually uses the no-FEC packet layout.
Profile names and app entry points were checked against the 2.0 release source on 28 September 2026. The downloads use its pinned RadioSignalKit revision. A telemetry fixture demonstrates a link's framing; only the complete SSDV samples are presented as image-reconstruction examples.