SSTV.org.uk

History

The practical history of pictures by sound.

SSTV became useful because a still image can survive inside a narrow audio channel. Its history is less about video spectacle and more about timing, synchronization, tone mapping, and compatibility between operators.

Milestones

  1. 1957-1958, Copthorne Macdonald's amateur SSTV experiments: Macdonald's work established the idea that a still image could be scanned slowly enough to fit inside audio-rate radio channels instead of broadcast-television bandwidth.
  2. 1960s, voice-bandwidth image practice: amateur SSTV grew around the practical constraint that an SSB voice channel can carry audio tones, not full-motion television bandwidth. The central engineering problem became stable sync, tone mapping, and clock timing.
  3. Robot hardware era: Robot Research hardware popularized color-difference and monochrome Robot modes. The VIS calibration header gave receivers a machine-readable mode identity instead of relying only on operator notes.
  4. Martin, Scottie, and Wraase families: ROMs, dedicated hardware, and early computer systems added RGB mode families with recognizable line timing, component order, and operating cultures. Martin M1/M2 and Scottie S1/S2 became durable compatibility targets.
  5. Pasokon and PD higher-resolution modes: longer modes such as P3/P5/P7 and PD120/180/240/290 traded airtime for larger frames and better image detail, useful when a planned transmission has enough pass or channel time.
  6. Sound-card SSTV: programs such as MMSSTV moved decode/encode work onto commodity computer audio, added MP/MR/ML experimental modes, and introduced 16-bit VIS or N-VIS style identifiers for software-era modes.
  7. Public satellite SSTV: ARISS and satellite operators made scheduled image reception a public activity. Recent ISS events continue to publish exact UTC windows, downlink frequency, and mode, commonly Robot 36 for short public transmissions.
  8. Mobile receive and transmit tools: iPhone and iPad apps now combine live spectrum, microphone receive, file decode, transmit audio generation, satellite pass context, and mode lookup in a portable signal desk.

Why modes multiplied

Airtime

Robot 36 finishes in about 36 seconds; PD240 takes about 248 seconds. Longer modes can carry larger frames or more color detail, but they demand a cleaner channel and more time.

Color coding

Martin, Scottie, Wraase, and many AVT rows use RGB-style component scans, while Robot, PD, and many MMSSTV rows use luma plus color-difference components.

Identification

Classic modes use VIS-style identification. MMSSTV MP/MR/ML rows use extended 16-bit VIS, and narrowband MP-N/MC-N rows use N-VIS style identifiers.

Reading old mode tables

Historical SSTV mode lists are not all equally precise. The Dayton N7CXI paper explicitly limits itself to modes with hard timing data and excludes AVT timing tables. The OK2MNM mode-list PDF is broader and includes many uncommon rows with duration, VIS, raster, and line rate, but it is still not a line-by-line implementation spec for every family. This site keeps those distinctions visible on each mode detail page.

Sources