[amsat-bb] why AX.25 packet standard in Amateur satellite

Joe Fitzgerald jfitzgerald at alum.wpi.edu
Wed May 4 23:28:56 UTC 2016

On 5/3/2016 12:59 AM, shakeel -ur-rehman via AMSAT-BB wrote:
> I am confused what is the requirement  for ax.25 encoding /decod in telemtry or in telecommand or in both
> what is the significance of using ax.25 in satellites .why we require this .

Thanks for the question.   Many spacecraft designers chose AX.25 because
many hams around the world already had TNC's with the capability of
decoding it.   This was more important 20 years ago before there was
enough spare compute power available in hamshacks.    These days, it is
practical to do all the processing with commodity PCs, making different
modulation and coding schemes feasible such as the DPSK used on FunCube
and the FSK "Data Under Voice" used on AO-85.   Of course for unique
communication methods, the satellite operator must make ground station
software available, and recruit a motivated team of operators to go
through the trouble of installing and operating it.    Thus, some
builders still choose to use AX.25 so they did not have to invent anythign.

The command scheme is similarly varied.   The designer must devise a
scheme that is both reliable and secure against mischief.

As ever, engineering is the art of compromise!

73 de KM1P Joe

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