Aircraft Orientation Issues When Using Funke Transponders for ADSB Out

[bnmont]

I have a Funke TRT800, latest 6.3 software and hardware having taken Funke up on their substantial discount offer  to upgrade from a 5.2 software transponder. At the moment I dont believe it is functioning correctly with the uncertified GPS data being sent to it. This despite assurances from Funke that all has been tested and certified.

Below is part of an email sent to Funke from which I'm awaiting a reply

Dear Michael,
Please can you ask you tech guys to explain the attached tracks as displayed on the ADSB exchange site. The first is  G-CIJO my plane equipped with the latest Funke TRT and 6.3 software. NMEA data in at 9600 bd.   Consistently my plane is shown as tracking North when obviously not going in that direction. Only just prior to landing does the plane show the correct orientation.

https://globe.adsbexchange.com/?icao=406cb1&lat=52.132&lon=-0.314&zoom=11.0&showTrace=2021-05-02      The Track replay of G CIJO  Funke equipped  Sunday 2nd May 2021

My Friend who was flying in loose formation with me whose Trig equipped is perfectly tracked on the adsb exchange site and also performs correctly when .trk files are replayed via the Aircrew website.

We have looked at the $GPRMC messages grom PilotAware to the transponder and all appears correct.

I'm awaiting a response from Funke, they were also sent the $GPRMC messages relating to the attached track.

Obviously I'm concerned how my plane is displayed via EC. How does my plane get depicted on Skydemon when its "reversing" down the track being flown?

Regards Brian

[bnmont]

Further attachments

[exfirepro]

Hi Brian,

That certainly doesn’t look like a ‘fix’ to me. Sounds like Funke still have some work to do. Please keep us posted.

Regards

Peter

[bnmont]

 Hi Peter,

Yes I'm afraid it doesnt look great.

I'm aware of one other aeroplane fitted with a Funke TRT800 and the 6.3 software. This also doesnt track correctly when on ADSB exchange.
What would be helpfull is if other such aeroplanes  with GPS from uncertified source could look at how their aeroplane is reported as tracking via one of the tracking sites.

Also if anyone has a screen shot of Skydemon (others available) showing your plane clearly not following the track being flown. Obviously these will not be easily come by, needing someone PAW equipped in loose formation with both flying the same track.

 What really concerns me is what is depicted when an aeroplane is "reversing " down the track being flown. Does it have a direction vector still pointing north when actually travelling South? Maybe there is no vector shown at all?



In response to a previous email I received this reply.

Dear Brian,

yesterday I had a long discussion with our tech guys. Actually they say
... well they have no explanation. We tested and certified our software
and we can say that the TRT reports only the data it gets.

The only way to find out what happens is to monitor the GPS-input and
compare it with the ADS-B-output. We have done this in extensive tests,
all works well. We can never be absolutely sure that there are no errors
in software so what we have to do is the monitoring described above.
This would require any kind of device recording the RS232-data.

Since I am not aware of the ADS-B-receivers used for your recording I
would like to note that we found some problems with ADS-B-recording
here. E.g. some receivers calculate heading and speed based on position
data rather than the data in the RMC. Especially for slow planes this
can result in erratic result.

Please do not hesitate to contact me for any further question.

Kind regards


So now Funke have the $GPRMC messages for a track bing flown and the resulting display on adsb exchange. The flight was also monitored by a friend PAW equipped,  at many points my vector and the aeroplanes actual direction of travel didnt coincide with the track being flown.

I will post Funke's next response when I get it.

Regards Brian

[CliveJ]

Image of the start up message from the new Funke. Worked fine and showed it's track fine yesterday. That was looking on FR24, haven't yet had a chance to check it with another aircraft and PAW or SE.

My old Funke transponder worked fine with a Garmin or a PAW GPS 232'd into it but I couldn't get the numbers up to get it approved as it wasn't doing what it needed to. My new one does and I may now go for the approval.

Reading the post above with interest. Regards, Clive

[CliveJ]

I've not used the GPS Global exchange before but just had a play with it interrogating my flight last eve and I do indeed appear to be going backwards and sideways.

I then looked at my flight on FR24 and I was always going forwards, as I was when I checked the flight at the time.

I then looked at G-CIJO's flight on Flight radar from 2/5 and it was always going forwards. It looks like something to do with the functionality of the GPS Global exchange's presentation of the flight data. That doesn't show what's being presented during live flight of course but as I understand it any system will join up individual position reports and string them together so it's where you are each time your transponder transmits.

Is the heading data sent out with the position data? I don't know how it works, maybe someone that does can tell me?

Regards, Clive
P.S. how do you insert a picture in this Forum? Can't seem to figure that out...

[exfirepro]

Hi Clive,

Thanks for the feedback. I am also not familiar with the ADSB Exchange tracking site, so unable to comment, but will take a look. What we are of course most interested in is what is showing up on our own and other ‘in aircraft’ traffic awareness systems. This is best reported from another aircraft flying with or in close proximity to you, though re-running your flight track from PilotAware through the Aircrew playback tool may also help show what is going on, see https://Aircrew.co.uk/playback .

To add photos, use the ‘Attachments and other options’ tool - below the window you are typing in, but be aware that you need to ensure that each photo (or the group of photos in an individual post) total no more than 512Kb in size. There are several photo processing apps which allow you to reduce the electronic size of photos, for example by resizing and re-saving as .jpg files where necessary. Which are available depends on the device you are using.

Hope this helps

Regards
Peter

[GeoffreyC]

I've not used the GPS Global exchange before but just had a play with it interrogating my flight last eve and I do indeed appear to be going backwards and sideways.

I then looked at my flight on FR24 and I was always going forwards, as I was when I checked the flight at the time.

I then looked at G-CIJO's flight on Flight radar from 2/5 and it was always going forwards. It looks like something to do with the functionality of the GPS Global exchange's presentation of the flight data. That doesn't show what's being presented during live flight of course but as I understand it any system will join up individual position reports and string them together so it's where you are each time your transponder transmits.
...

I've been flying with G-CIJO and have seen first hand on my pilot aware the incorrect funke transponder direction information showing his plane always pointing North rather than correctly showing the plane orientation.   It's not constant though, sometimes his plane points in the right flight direction, sometimes it points North.   I've taken screen shots of the issue for Brian to send to Funke.    We've put this 'flipping' of direction to sometimes my PAW is picking up his transponder signal and sometimes it picks up his pilotaware signal,  PAW correctly sends the direction track and so when receiving PAW signal the plane tracks in the right direction,  when receiving the transponder it points North.

And we think this is the cause of the discrepancy between adsb exchange (which as it says is displaying ADSB information) and flight radar 24.  FR24 says that it gets its track information from ADSB receivers AND glidernet (which is linked to the Atom grid network to receive PAW signals)  We think its is prioritising the glidernet traffic displays over the ADSB, hence why FR24 shows the right orientation but ADSB exchange doesn't.

You make a good point that the flight replay websites could be interpreting the flight information and determining their own orientation information, not displaying what is actually received.  We can't know for sure whether that is the case or not, but I can say with absolute confidence that Brian's PAW/Funke transponder combo will sometimes show the plane on the right track and sometimes it pointing North.  The North orientation usually appears when we are further apart in flight and when we're not in the locality of a PAW ground station - further strengthening our view that its the transponder at fault.

Geoffrey

[bnmont]

I have heard back from Funke today. It appears that I didn’t attach the $GPRMC file on the email to them. So job to do.
What is interesting to me though is that any Trig equipped aeroplane always seems to track correctly on Adsb exchange and also via the PilotAware ground stations, whereas my plane often is displayed tracking incorrectly on the same sites. I’m pretty certain that the GPRMC messages going to the transponder are correct.

 
Regards Brian

[CliveJ]

Further to the reports above of Funke TRT800 I did some testing today and was monitored by two EC units, my Brand new TXP is a ZTRT800 with V6.3.

I was maneuvering whilst talking to a friend monitoring my flight from his aircraft on the ground. He has SkyEcho displaying on SkyDemon and also Garmin GDL393D with it's own display.  On both displays my aircraft's heading was shown pointing North and when interrogated showed 359 or zero. The positioning and movement was as would be expected.
So there is definitely something amiss in the Transponders output compared to other manufacturers.
At the time FR24 was showing it's usual jumpy but generally correct track direction.

I've just had a look at my flight on the ADSB exchange and the heading was 0.0 or very close zero throughout with the icon pointing North.

On FR24 the heading looks normal with the icon changing to match the track and the track readout changing accordingly.

What I don't know as I mentioned before is how the track is derived on any of these systems, and what is actually transmitted by the TXP within it's extended information. The GPS signal is currently from a Pilot Aware unit, I can fairly easily move this to a Garmin GPS as I have that available too.

I had a chat with Norwich Radar but their system paints in responses and they figure the track out from the movement of the contact so they couldn't help. All aspects of the TXP's transmission were OK as far as They were concerned.

I'm ready to contact with Funke but thought I'd see if there was any feedback to Brian yet?

Regards, Clive

[bnmont]

Hi Clive
Not much to report back yet. I had an earlier reply which basically said that the GPRMC messages being sent to the transponder had no position or speed included. And that therefore the transponder wouldn’t work correctly. Said it was a PilotAware error. When I pointed out that the aircraft was stationary at the airfield they were quick to admit they had got it wrong. I have since sent the correct GPRMC files to match the flight linked above. As far as I can see at all times when airborne PilotAware was sending all the correct info to the transponder. Funke have said it’s may be due to having a slow ground speed.
  If I hear more I will post

Regards Brian

[CliveJ]

Hi thanks for getting back with the reply.

I've been learning some more and seems the data transmitted should indeed include the heading.
I found and example of a transmitted NMEA string
$GPRMC,161229.487,A,3723.2475,N,12158.3416,W,0.13,309.62,120598, ,*10
RMC—Recommended Minimum Specific GPS Data
The 309.62 was the course so it certainly looks like the GPS data that the TXP is transmitting likely should include the heading.
So the question is why isn't the Funke sending out the heading information......

Seems strange that other folk's TXP manage to transmit the heading but the Funke won't. We do have examples of the PAW GPS output being used elsewhere successfully?

As I said I was flying and my friend got a screenshot of the info my TXP was transmitting and it was North all the while.

How are you reading the GPRMC messages?

Do you think it's worth me swinging mine across to the Garmin? Just to prove it's not the Pilot Aware?

Regards, Clive
 

[grahambaker]

Call me Mr Pedant, but a GNSS receiver has no idea of your heading, in the aeronautical sense. All it can derive is your actual track, which is surely what you mean.

[CliveJ]

Yes, but you knew what I meant so you are indeed a pedant!

[exfirepro]

Hi Clive
Not much to report back yet. I had an earlier reply which basically said that the GPRMC messages being sent to the transponder had no position or speed included. And that therefore the transponder wouldn’t work correctly. Said it was a PilotAware error. When I pointed out that the aircraft was stationary at the airfield they were quick to admit they had got it wrong. I have since sent the correct GPRMC files to match the flight linked above. As far as I can see at all times when airborne PilotAware was sending all the correct info to the transponder. Funke have said it’s may be due to having a slow ground speed.
  If I hear more I will post

Regards Brian

Hi Brian,

Had another read back through this entire thread and info on previous issues with Funke Transponders published elsewhere. Interestingly Funke’s comment (my bold above) seems to be reflected in my viewing of your earlier ADSBExchange track - where the only point at which your aircraft turned to face in the correct direction was when you (presumably) slowed prior to landing, though strangely not reported from the FR24 playbacks. I would also concur with your and Geoffrey’s earlier conclusions re his display reporting (correctly) from your PAW when at close range and your transponder when further apart (i.e. when your PAW signal dropped out), though I’d be surprised if this was due to FR24 prioritising PAW reports over ADSB. If they receive P3i reports at all, they will only be from those ‘non-PAW’ OGN Stations that have upgraded to run on 0.2.8ARM. This would however, certainly suggest that to discount this effect when gathering evidence, you need to be accompanied by another aircraft flying far enough apart to preferably NOT be within optimal PAW reception range.

@Clive,

Yes, two comparative test flights - ideally accompanied by the same aircraft, perhaps using a ‘non-paw’ ADSB detector, or if using PAW, keeping fairly well distanced - with the first run ‘as is’ (i.e. using the PAW GPS data to feed your Txpdr) and a second using the GPS input from your Garmin would be good, if you could manage to do that.

Best Regards

Peter