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 .
Shakeel,
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