SSTV.org.uk

FAX mode

FAX480

FAX family analog SSTV operation and compatibility reference.

Supported in app

Mode sample

BBC-style colour test card and app-generated audio

The image is generated locally for this mode's raster. For supported modes, the audio sample is encoded from that image with the SSTV Signal Desk transmitter code, then published as lossless FLAC for static playback.

FLAC, 48 kHz, 16-bit mono, 139.229 s.

FAX480 SSTV BBC-style colour test card
FAX480 source card, 512 x 480
FAX480 SSTV round-trip decoded test card
Receiver decoded FAX480 from the FLAC-restored WAV, 480 lines.

Round-trip decode evidence

Encoded, compressed losslessly, restored, then decoded.

The published FLAC is restored to WAV and passed through the SSTV Signal Desk receiver sample harness. The receiver decoded FAX480 from the FLAC-restored WAV and wrote 480 image lines for this FAX480 test card.

Open the generated decode report

Mode spec

Short nameFAX480
Support statusSupported in app
Spec statusSupported in app; public VIS and timing summary are separated from the app raw timing fields.
Duration138.62912 s original frame; 133.632 s line payload
Frame512 x 480 image (+20 phasing lines)
Data lines480 image lines + 20 phasing lines
Public VISOriginal Dayton framing has no VIS; the later catalog profile uses VIS 85 (0x55)
Standard VIS codeNot applicable or not published in checked sources
Extended/N-VISNo
Color modelBW
Component sequenceY
Line rate215.517 lpm
Public timing profileOriginal FAX480 timing: monochrome 512 x 480 image, exact 4.99712-second alternating-tone header, 20 white phasing lines, then 480 image lines; every transmitted line has a 5.12 ms sync plus a 262.144 ms scan. The later profile replaces the header and phasing interval with VIS 85.
App duration133.632 s
App frame512 x 480
App raw VIS0x55 (85)
App timing profileApp RX line fields: sync 5.12 ms; front porch 0 ms; back porch 0 ms; separator/blank 0 ms; video tones 1500-2300 Hz around 1900 Hz.
App RX sync5.12 ms
App RX front porch0 ms
App RX back porch0 ms
App RX separator/blank0 ms
App subcarrier1900 Hz
App deviation400 Hz
App tone range1500-2300 Hz

Strengths

  • FAX480 is a standard-length large-frame FAX mode: 138.62912 s original frame; 133.632 s line payload, 512 x 480 image (+20 phasing lines), BW.
  • FAX480 uses monochrome Y FAX-style scanning; the catalogue caveat is recorded as: Original Dayton framing has no VIS; the later catalog profile uses VIS 85 (0x55). Timing and VIS identity stay separate.
  • FAX480 has explicit app timing fields: 5.12 ms sync, 0 ms front porch, 0 ms back porch, 0 ms separator/blank, and 1500-2300 Hz around 1900 Hz video tones.
  • FAX480 has a checked public timing summary plus app timing fields, so the public spec and implementation timing can be compared line by line.

Tradeoffs

  • FAX480's duration caveat matters: 138.62912 s original frame; 133.632 s line payload. Keep that distinction visible when checking the full 512 x 480 image (+20 phasing lines) scan.
  • FAX480 has this VIS caveat: Original Dayton framing has no VIS; the later catalog profile uses VIS 85 (0x55); receivers that require a normal Robot VIS announcement may need manual FAX-style setup.

Source notes

Public VIS/timing labels are normalized from checked SSTV references where available. App raw VIS 0x55 and app timing fields are generated from sstv/sstv/sstv/sstvparam.swift during the website build.