Strange false positive

[GarethHorne]

Any thoughts on this one, I'm getting this sort of warning on a semi-regular basis, it usually occurs when maneuvering, if I turn the aircraft transponder to standby it disappears, reappears when I switch it back to ACS. I've got the Hex code entered correctly and Mode CS Filter set in PilotAware as far as I can see..

thanks

Gareth

[Admin]

Hi Gareth

can you expand on 'maneuvering'
is this including climb/descend ?
also, (as always) can you let me have your track file ?

This is almost certainly your own transponder mode C response not being filtered.
We can investigate the from the track file, we are also adding more logging information in the next release to help further improve the filtering of ownship mode C transmissions.

Thx
Lee

[GarethHorne]

here's the track file Lee

https://www.dropbox.com/s/2uelmdumi7zasxe/2018-08-28_11-14.trk?dl=0

Its usually when I reach a turn point, or obit for some reason. Soon as I bank into a turn, that's when it happens, not really noticed it when climbing or descending.

thanks

Gareth

[Admin]

Its usually when I reach a turn point, or obit for some reason. Soon as I bank into a turn, that's when it happens, not really noticed it when climbing or descending.

Maybe the electrons are rolling to one side and not traveling through the wires correctly

No, but seriously, this is totally weird, let me take a look at the track see if I can determine anything

Thx
Lee

[PaulSS]

Even though my PAW is still in its box and I don't know what I'm talking about, if it were me I'd be checking for a dodgy connection with the 1090 MHz antenna and cables, especially if it is a PAW Classic with the MCX adapter. I base this purely on the fact that it only happens when you're manoeuvring and it is associated with the transponder returns (and the MCX adapters have proved troublesome in the past.....according to these hallowed web pages).

[GarethHorne]

I'd be surprised if it is a dodgy connector Paul, everything appears tight. I'd suspect the reason for it showing up when maneuvering is the distance and hight I'm flying from a radar ground station. As I lift the wing in a turn I'm guessing it provides just enough change in the position of the transponder aerial for it to be picked up by a ground station and the transponder to start replying to it.

Why my own transponder signal is not been screened out by the PilotAware filter and why it's showing a spurious ID on the screen, that I can't explain..

[davidbu99]

I posted recently the same issue with ghost targets. In my case it would happen just with straight & level flight and has been a fairly common occurrence for me for some time. The PFLAA sentence in Gareth's track file being consistent with the ones I have, i.e. same Relative North distance, no Relative East, no track, turn rate or groundspeed, and an ID starting "FF". I've just upgraded to Rosetta so will try again soon.

$PFLAA,3,1500,,-46,1,FF01F2!C-01F2,,,,-10.2,8*18
AlarmLevel = 3
Rel North = 1500
Rel East =
Rel Vertical = -46
ID Type = 1
ID = FF01F2!C-01F2
Track =
Turn Rate =
GroundSpeed =
ClimbRate = -10.2
Aircraft Type = 8*18

below an extract of a similar PFLAA sentence from one of my recent logs:

https://www.dropbox.com/s/pptipmxkgt7i4ii/2018-08-17_11-56.trk?dl=0

$PFLAA,3,1500,,-33,1,FF0A60!C-0A60,,,,0.0,8*04
AlarmLevel = 3
Rel North = 1500
Rel East =
Rel Vertical = -33
ID Type = 1
ID = FF0A60!C-0A60
Track =
Turn Rate =
GroundSpeed =
ClimbRate = 0.0
Aircraft Type = 8*04

[GarethHorne]

Thanks David - glad to hear I'm not the only one seeing the issue. I guess I'll have to try turning off mode C detection next time and see what the result is.

[Paul_Sengupta]

Why my own transponder signal is not been screened out by the PilotAware filter and why it's showing a spurious ID on the screen, that I can't explain..

The algorithms for detecting your own transponder and filtering it out for Mode C are being constantly refined in order to try and come up with the best way of doing it, i.e. so that your own transponder gets filtered out but you don't miss any conflicting traffic. Sending the log files to Lee should mean that he can see what's going on and further refine the algorithms for future software deployments.

[GarethHorne]

Must admit I'd forgotten there's no registration data contained in a mode C transponder signal, thanks for the explanation Paul, I see why it's not a simple matter to screen out my own transponder now. Look forward to trying out the next software build to see if it's improved.