SoftRF + Mode C transponder

[Moshe Braner]

A friend flew with SoftRF and he also has a Mode-C transponder in his glider.  Looking at the traffic data saved in his SoftRF flight log, his transponder's approximate position was occasionally reported by ATC via the TIS-B service.  (This is in the USA.)  And that caused some collision alarms, as if it was another aircraft.  Note that Mode S transponders (and ADS-B) and SoftRF in the same aircraft can, and should, be configured to transmit the same aircraft ICAO ID.  In that case SoftRF ignores any transmissions by or about the same aircraft.  But Mode C transponders only transmit a squawk code, and TIS-B generates a random hex ID (starting with "2").  In the next version of SoftRF I'll change the code to not generate collision alarms for TIS-B traffic.  The radar-based position is not accurate enough for collision warnings anyway.   Such traffic will still be reported (in PFLAA sentences) so it will be visible on the attached glide computer.

[Moshe Braner]

I should have mentioned that the SoftRF device in this case has the ADS-B receiver module added, that is how the TIS-B transmissions were received.

[FrankT]

Thank you for the information and upcomming changes.

Frank

Op dinsdag 26 augustus 2025 om 18:54:13 UTC+2 schreef Moshe Braner: