SSTV.org.uk

PD mode

PD50

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, 52 s.

PD50 SSTV BBC-style colour test card
PD50 test card, 320 x 256

Mode spec

Short namePD50
Support statusSupported in app
Spec statusSupported in app; public VIS and timing summary are separated from the app raw timing fields.
Duration49.688 s
Frame320 x 256
Data lines128
Public VISVIS 93 (0x5D)
Standard VIS code0x5D (93)
Extended/N-VISNo
Color modelYCrCb
Component sequenceY-RY-BY-Y
Line rate309.131 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 duration49.688 s
App frame320 x 256
App raw VIS0xDD (221)
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

  • PD50 is a medium-length standard colour PD mode: 49.688 s, 320 x 256, YCrCb.
  • PD50 uses Y-RY-BY-Y pair-line colour-difference scanning, giving two luma passes around shared chroma samples in the PD family.
  • PD50 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.
  • PD50 has a checked public timing summary plus app timing fields, so the public spec and implementation timing can be compared line by line.

Tradeoffs

  • PD50's 49.688 s airtime is practical for casual contacts, while the 320 x 256 frame still gives less margin than the longer high-detail modes.
  • PD50 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 0xDD and app timing fields are generated from sstv/sstv/sstv/sstvparam.swift during the website build.