SSTV.org.uk

PD mode

PD240

Higher-resolution color work where longer transmission time is acceptable.

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, 250.329 s.

PD240 SSTV BBC-style colour test card
PD240 test card, 640 x 496

Mode spec

Short namePD240
Support statusSupported in app
Spec statusSupported in app; public VIS and timing summary are separated from the app raw timing fields.
Duration248.017 s
Frame640 x 496
Data lines248
Public VISVIS 97 (0x61)
Standard VIS code0x61 (97)
Extended/N-VISNo
Color modelYCrCb
Component sequenceY-RY-BY-Y
Line rate119.992 lpm
Public timing profilePublic PD timing: 20.000 ms sync, 2.080 ms porch, odd-line Y, averaged R-Y, averaged B-Y, even-line Y; repeat pairs until the mode-specific line count is complete.
App duration248.017 s
App frame640 x 496
App raw VIS0xE1 (225)
App timing profileApp RX line fields: sync 20 ms; front porch 2 ms; back porch 2 ms; separator/blank 0 ms; video tones 1500-2300 Hz around 1900 Hz.
App RX sync20 ms
App RX front porch2 ms
App RX back porch2 ms
App RX separator/blank0 ms
App subcarrier1900 Hz
App deviation400 Hz
App tone range1500-2300 Hz

Strengths

  • PD240 is a extended high-detail PD mode: 248.017 s, 640 x 496, YCrCb.
  • PD240 uses Y-RY-BY-Y pair-line colour-difference scanning, giving two luma passes around shared chroma samples in the PD family.
  • PD240 has explicit app timing fields: 20 ms sync, 2 ms front porch, 2 ms back porch, 0 ms separator/blank, and 1500-2300 Hz around 1900 Hz video tones.
  • PD240 has a checked public timing summary plus app timing fields, so the public spec and implementation timing can be compared line by line.

Tradeoffs

  • PD240's 248.017 s transfer can carry more picture detail, but it occupies the channel longer and is less forgiving of fades across the 640 x 496 frame.
  • PD240 colour-difference coding can preserve useful luminance detail, but chroma edges may look softer than full-rate RGB modes after weak-path reception.

Source notes

Public VIS/timing labels are normalized from checked SSTV references where available. App raw VIS 0xE1 and app timing fields are generated from sstv/sstv/sstv/sstvparam.swift during the website build.