SSTV.org.uk

PD mode

PD90

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, 92.307 s.

PD90 SSTV BBC-style colour test card
PD90 test card, 320 x 256

Mode spec

Short namePD90
Support statusSupported in app
Spec statusSupported in app; public VIS and timing summary are separated from the app raw timing fields.
Duration89.995 s
Frame320 x 256
Data lines128
Public VISVIS 99 (0x63)
Standard VIS code0x63 (99)
Extended/N-VISNo
Color modelYCrCb
Component sequenceY-RY-BY-Y
Line rate170.676 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 duration89.995 s
App frame320 x 256
App raw VIS0x63 (99)
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

  • PD90 is a medium-length standard colour PD mode: 89.995 s, 320 x 256, YCrCb.
  • PD90 uses Y-RY-BY-Y pair-line colour-difference scanning, giving two luma passes around shared chroma samples in the PD family.
  • PD90 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.
  • PD90 has a checked public timing summary plus app timing fields, so the public spec and implementation timing can be compared line by line.

Tradeoffs

  • PD90's 89.995 s frame is a balanced choice, but it still needs a stable path for the full 320 x 256 scan.
  • PD90 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 0x63 and app timing fields are generated from sstv/sstv/sstv/sstvparam.swift during the website build.