SSTV.org.uk

Scottie mode

Scottie DX

Scottie 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, 271.205 s.

SDX SSTV BBC-style colour test card
SDX test card, 320 x 256

Mode spec

Short nameSDX
Support statusSupported in app
Spec statusSupported in app; public VIS and timing summary are separated from the app raw timing fields.
Duration268.894 s
Frame320 x 256
Data lines256
Public VISVIS 76 (0x4C)
Standard VIS code0x4C (76)
Extended/N-VISNo
Color modelRGB
Component sequenceG-B-R
Line rate57.123 lpm
Public timing profilePublic Scottie DX timing: VIS 76; Scottie line structure with 9.0 ms starting sync, sync between Blue and Red, 1.5 ms separator/porch pulses, and 345.600 ms color scans.
App duration268.894 s
App frame320 x 256
App raw VIS0xCC (204)
App timing profileApp RX line fields: sync 9 ms; front porch 0 ms; back porch 0 ms; separator/blank 1 ms; video tones 1500-2300 Hz around 1900 Hz.
App RX sync9 ms
App RX front porch0 ms
App RX back porch0 ms
App RX separator/blank1 ms
App subcarrier1900 Hz
App deviation400 Hz
App tone range1500-2300 Hz

Strengths

  • SDX is a extended standard colour Scottie mode: 268.894 s, 320 x 256, RGB.
  • SDX keeps the classic Scottie G-B-R RGB order, which makes colour order predictable for receivers expecting VIS 76 (0x4C).
  • SDX has explicit app timing fields: 9 ms sync, 0 ms front porch, 0 ms back porch, 1 ms separator/blank, and 1500-2300 Hz around 1900 Hz video tones.
  • SDX has a checked public timing summary plus app timing fields, so the public spec and implementation timing can be compared line by line.

Tradeoffs

  • SDX's 268.894 s transfer can carry more picture detail, but it occupies the channel longer and is less forgiving of fades across the 320 x 256 frame.
  • SDX sends colour sequentially in RGB; sync drift can appear as colour fringing before the whole frame becomes unreadable.

Source notes

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