[A-DX] DK5LA / SSDV / Slow Scan Digital Video

So Jan 13 11:35:21 CET 2019


"....To arrange taking the picture, Reinhard Keuhn (DK5LA) used his 
array of yagi antennas to command Longjiang-2 to take an image and 
transmit it back to Earth. The commands Reinhard sent were generated by 
MingChuan Wei from the Harbin team that built the Longjiang satellites. 
The Dwingeloo telescope, as well Robert Mattaliano in North America, 
Mike Rupprecht in Germany and Imants Tukleris in Latvia were able to 
receive and decode the packets with image data and upload it to the 
Harbin telemetry portal.

"....The image data was transmitted using SSDV encoding, originally 
designed by radio amateur Philip Heron for balloon transmissions. 
Because of the low data rate, downloading a 640-by-480 pixel image is 
slow and takes around 20 minutes...."





"...A robust packetised version of the JPEG image format.
Only JPEG files are supported, with the following limitations:
  - Greyscale or YUV/YCbCr colour formats
  - Width and height must be a multiple of 16 (up to a resolution of 
4080 x 4080)
  - Baseline DCT only
  - The total number of MCU blocks must not exceed 65535....."



"....SSDV (Slow Scan Digital Video) is a packetised digital form of SSTV 
(Slow Scan TeleVision). It can be used to transmit small images along 
with the regular telemetry transmitted by a payload during flight. Any 
digital mode that can carry text or data can be used, although the 
current implementation is limited to 8-bit RTTY (Radio TeleTYpe)...."