Number of drones in the same perimeter might be too low

[valentinb]

The number of drone in the same perimeter might be to low.

Why isn't frequency an option ? Reducing the size of messages is another option.

[pjalocha]

One could switch to modulation without the Manchester encoding and gain twice the data capacity. This will likely increase the SDR reciever complexity, as Manchester encoded packets have a very distinct spectral signatuture which is exploited with the OGN network receivers.

We loose as well compatibility to the nRF905 chip which can only do Manchester encoding at the single data rate.

We could switch to 433MHz band which is wider in bandwidth and have the SDR receiver receive and process 2MHz of RF bandwidth. This however means new antennas, current OGN network can not be used, more CPU load, new RF noise environemnt, etc. This would need more time for research and development.

[optimaltracking]

FLARM compatibility is a constraint so difficult to avoid Manchester and 868Mhz

[pjalocha]

nRF905 compatibility inflicts the following:

• GFSK modulation: +/-50kHz deviation and BT=0.5
• 100kbps data rate, Manchester encoded thus from the user point of view 50kbps
• Channel spacing 200kHz thus only 868.2 and 868.4MHz is possible if 868.0-868.6MHz band is chosen.
• Fixed sized packets, up to 32bytes of user data
• Preamble: the nRF905 sends 10bits where the last 8bits are 0xF5 (normally the RF chips have some degree of flexibility here, as they can't rely on perfect preamble reception).