SSTV.org.uk

PD mode

PD120

High-compatibility satellite and event SSTV mode with more detail than Robot 36.

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, 128.424 s.

PD120 SSTV BBC-style colour test card
PD120 test card, 640 x 496

Mode spec

Short namePD120
Support statusSupported in app
Spec statusSupported in app; public VIS and timing summary are separated from the app raw timing fields.
Duration126.112 s
Frame640 x 496
Data lines248
Public VISVIS 95 (0x5F)
Standard VIS code0x5F (95)
Extended/N-VISNo
Color modelYCrCb
Component sequenceY-RY-BY-Y
Line rate235.982 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 duration126.112 s
App frame640 x 496
App raw VIS0x5F (95)
App timing profileApp RX line fields: sync 20 ms; front porch 0 ms; back porch 2.08 ms; separator/blank 0 ms; video tones 1500-2300 Hz around 1900 Hz.
App RX sync20 ms
App RX front porch0 ms
App RX back porch2.0799999999999996 ms
App RX separator/blank0 ms
App subcarrier1900 Hz
App deviation400 Hz
App tone range1500-2300 Hz

Strengths

  • PD120 is a standard-length high-detail PD mode: 126.112 s, 640 x 496, YCrCb.
  • PD120 uses Y-RY-BY-Y pair-line colour-difference scanning, giving two luma passes around shared chroma samples in the PD family.
  • PD120 has explicit app timing fields: 20 ms sync, 0 ms front porch, 2.08 ms back porch, 0 ms separator/blank, and 1500-2300 Hz around 1900 Hz video tones.
  • PD120 has a checked public timing summary plus app timing fields, so the public spec and implementation timing can be compared line by line.

Tradeoffs

  • PD120's 126.112 s frame is a balanced choice, but it still needs a stable path for the full 640 x 496 scan.
  • PD120 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 0x5F and app timing fields are generated from sstv/sstv/sstv/sstvparam.swift during the website build.