Hallo gentleman.
The "telemetry channel" is the 1st and 3rd charachter we use in the "telemetry spot".
As you know, the lelemetry spot is similar to a normal spot (callsign, locator, dBm) but all of these info are "fake".
So, a "fake" callsign may be any callsign the coding firmware would create but, since we have the need to find it in the "spot sea" between all other billions of spots, we need to search only some callsign.
So, firmware chooses 1st and 3rd characher you set up as "channel". If you choose Q and 0, all your telemetry spots will be like Qx0yzk, where only x, y, z and k may change, but Q and 0 are fixed.
So, you can be sure that is your spot.
Of course, we hope no more than one ham radio amateur launcher uses that channel, otherwise may be an interference in decoding telemetry spots.
Now we can choose only callsign beginning with 0 (zero) and Q, because there are no ham radio callsign assigned by authorities around the world that begins with these two charachters.
Hope this helps.
73 de IZ7VHF, Roberto, southern Italy.
Roberto Pietrafesa