I am a seasoned aero-RC junkie taking my first steps in autonomous flight. My goal is, along with a group of fellow geeks, to explore and develop the possibilities of a semi-autonomous UAS for wilderness search in nordic/ subarctic conditions.
I recently received my first APM/IMU unit from DIYdrones and had planned on using XBee 868MHz modules for flight data telemetry to the GCS I bought along with the APM/IMU. Reading on, I found that not everything is as bright and beautiful as I thought at first.
I had planned to use the XBee link at 868MHz for flight data but found that here in Europe we have a problem with that frequency space due to duty cycle limitations. In the US the 900 MHz band is free and one can use for example the 2.4GHz forFPV video link and 72MHz for RC control and 900 MHz for data telemetry. Here in Europe, 900 MHz is strictly reserved for GSM-mobile telephony and the only real alternative for us, the 868 band is hardware throttled to a 10% duty cycle.
Deeply exploring the possibilities I find that for hobby FPV/UAS use we only have two really "free" frequencies to play with, 35MHz for RC control and 2.4GHz for RC or data/FPV link. There is no other good frequency free for data telemetry. 5.8GHz might be an alternative but there we are getting into range issues. Other "free" bands such as the 27MHz, the 40MHz and the 433MHz ("PMR")band are unsafe due to their free-for-all use ( 40MHz for RC cars, 7MHz banned, 433MHz is widely used for small com-radios (Personal Mobile Radio or PMR).
So... we are in a tight spot here east of the big pond.
My question to the UAV community is this:
Is it possible to use the audio part of a 2.4GHz downlink to carry the telemetry data?
If so, where to start?
Seeing as I am not interested in recording or downlinking audio, why not use the audio channel for low bandwidth flght data telemetry.I woudl have thought that someone already had cooked up a solution but I have not been able to find one.
As I am interested in long-range, I have already ordered a 1W 2.4 GHz transmitter to test.
Now I want to see if I can use it for both FPV / OSD video and for flight data telemetry using the audio channel or another mix.