Request: Dump1090-fa - Add RSSI (signal strength) to mode-a/c output

FA Staff,

This is a low-priority request to consider adding RSSI (signal strength) to the binary output for mode-a/c messages.

Dump1090-fa is outstanding, and my preferred version of dump1090. It does a great job of decoding mode-a/c, which I use with other software like PlanePlotter for things like mode-a/c mlat and Beamfinder Plus mode-a/c, which determines position based on the known locations of radar sites. My only very minor thing I miss in dump1090-fa is the output of RSSI signal strength.

Examples below show samples from view1090, pulling beast TCP 30005 from dump1090-fa with --modeac enabled in both.


This is a mode-a/c reply that is certainly a squawk = 1200.

*1200;
Time: 68636143610.17us
DF:32 Mode A/C Reply
  Other Address: 001200 (Mode A)
  Squawk:        1200

This is a mode-a/c reply that could either be a squawk or an altitude.

*4710;
Time: 68636129206.08us
DF:32 Mode A/C Reply
  Other Address: 004710 (Mode A)
  Baro altitude: 4200 ft
  Squawk:        4710

This is a sample DF17 extended squitter.

*8dae620650738438adf63f0bc798;
CRC: 000000
RSSI: -3.1 dBFS
Score: 25 (DF17_UNKNOWN)
Time: 68636351394.33us
DF:17 AA:AE6206 CA:5 ME:50738438ADF63F
Extended Squitter Airborne position (barometric altitude) (10) (reliable)
ICAO Address: AE6206 (Mode S / ADS-B)
Air/Ground: airborne
Baro altitude: 22000 ft
CPR type: Airborne
CPR odd flag: odd
CPR latitude: 30.84616 (7254)
CPR longitude: -86.53716 (128575)
CPR decoding: local
NIC: 10
Rc: 0.025 km / 0.0 NM
NIC-B: 0
NACp: 10
SIL: 2 (p <= 0.001%, unknown type)


Dump1090-fa also outputs RSSI for both TIS-B and ADS-R received from a ground station. It even has RSSI for air-to-air and TCAS traffic. The only thing missing RSSI is the mode-a/c. I believe this is possible, because testing the original 2014 Malcolm Robb versions of dump1090 shows that it does output mode-a/c signal strength usable by programs like view1090 and PlanePlotter.

I realize that mode-a/c is not used on the FA network and would definitely not add any value to your business model. I suspect that by adding mode-a/c RSSI, that would make the excellent dump1090-fa even more valuable to those that use it for other networks and programs. That would likely attract some new users that also support FA. Whenever I recommend a version of dump1090, I always suggest dump1090-fa! The very slight increase in CPU and data flow would only be for those choosing to enable mode-a/c using the --modeac option. There would be no impact at all for the majority of users that do not use mode-a/c. Obviously, mode-a/c is not ever uploaded to the FA network, so there would be no impact there.

Thank you for considering this.

Regards,
-Dan

Note: I am a fairly long-time FA user. My only other new topic post ever was back in December 2019 below when your software engineers worked with me to support PlanePlotter users switching from PP “secondary sharing” to direct FA sharing. That change was greatly appreciated by many users of that software.

Unique Identifier: xxxx Assigned to PlanePlotter sites for transition?

The current A/C demodulator doesn’t compute a signal strength at all, which is why you’re not seeing it in output, but it’s certainly something that could be added.

(Mode A/C and Mode S have different modulation schemes, so there’s separate code for those two paths)

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