SSTV.org.uk

MMSSTV mode

MMSSTV MR175

Software-era analog SSTV operation and MMSSTV compatibility.

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, 177.742 s.

MR175 SSTV BBC-style colour test card
MR175 test card, 320 x 256

Mode spec

Short nameMR175
Support statusSupported in app
Spec statusSupported in app; public VIS and timing summary are separated from the app raw timing fields.
Duration175.192 s
Frame320 x 256
Data lines256
Public VISExtended VIS 0x4C23 (19491; MMSSTV 16-bit code)
Standard VIS codeNot applicable or not published in checked sources
Extended/N-VISExtended VIS
Color modelYCrCb
Component sequenceY-RY-BY
Line rate87.675 lpm
Public timing profileMMSSTV MR/ML timing: 9.000 ms sync, 1.000 ms separator, Y scan, 0.100 ms last-pixel pulse, half-width R-Y, 0.100 ms last-pixel pulse, half-width B-Y, 0.100 ms last-pixel pulse.
App duration175.192 s
App frame320 x 256
App raw VIS0x4A23 (18979)
App timing profileApp RX line fields: sync 9 ms; front porch 0 ms; back porch 1 ms; separator/blank 0 ms; video tones 1500-2300 Hz around 1900 Hz.
App RX sync9 ms
App RX front porch0 ms
App RX back porch1 ms
App RX separator/blank0 ms
App subcarrier1900 Hz
App deviation400 Hz
App tone range1500-2300 Hz

Strengths

  • MR175 is a long-form standard colour MMSSTV mode: 175.192 s, 320 x 256, YCrCb.
  • MR175 identifies through Extended VIS 0x4C23 (19491; MMSSTV 16-bit code), separating MMSSTV-era modes from the 7-bit VIS space used by older analog families.
  • MR175 has explicit app timing fields: 9 ms sync, 0 ms front porch, 1 ms back porch, 0 ms separator/blank, and 1500-2300 Hz around 1900 Hz video tones.
  • MR175 has a checked public timing summary plus app timing fields, so the public spec and implementation timing can be compared line by line.

Tradeoffs

  • MR175's 175.192 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.
  • MR175 uses Extended VIS 0x4C23 (19491; MMSSTV 16-bit code); standard 7-bit VIS-only decoders may not auto-label it without MMSSTV extended-VIS support.

Source notes

Public VIS/timing labels are normalized from checked SSTV references where available. App raw VIS 0x4A23 and app timing fields are generated from sstv/sstv/sstv/sstvparam.swift during the website build. Public MMSSTV VIS 0x4C23 differs from app raw 0x4A23; both values are shown.