Using PAW as a source for ADS-B ES out

[Sky-runner]

I'm not sure if this helps the conversation, but I too have been struggling to understand why FR24 shows a very spikey speed curve for my ADSB-out transmissions.

I have a Funke transponder that the manufacturer has confirmed has the correct H/W (800ATC-H-(210)-(210)) and S/W (5.3) to enable ADSB-out. The GPS information is provided to the transponder from a Kanardia Horis. When I first configured the ADSB-out a friend's PAW confirmed "CSA" for my aircraft. So from my limited understanding FR24 should be able to derive the speed information accurately from the ADSB-out transmissions and not need to do MLAT calculations. I'm not an expert in this area as you can tell!

Regards,

Chris

[tnowak]

Chris,

Your symptoms are identical to what my friend gets, except his Funke isn't currently at the latest h/w version.
He is about to spend more money with Funke!
I contacted FR24 asking how they calculate speed but the answer wasn't informative.
They also said you cannot tell from the downloaded FR24 CSV file if the data is MLAT derived or true ADS-B Out.

Is there any way for the PAW "system", including OGN link-up etc. to examine what is actually being transmitted ADS-B -wise?

Tony

[Admin]

Is there any way for the PAW "system", including OGN link-up etc. to examine what is actually being transmitted ADS-B

OGN-R only captures P3I and Flarm - so that will not help
PilotAware received P3I and ADS-B (and Flarm indirectly from OGN-R)
so the direct reception of ADS-B will contain the Extended Squitter data

This extended squitter data contains the GroundSpeed, but this is academic, as it all depends what FR24 is looking at.

Thx
Lee

[xtophe]

You can use the "Playback" function in FR24, select your aircraft and see if it says "T-MLAT1" or "T-EGxxx" under "radar"

[tnowak]

I did some analysis over the weekend using Google Earth and importing the kml files from SD and FR24.
I haven't played much with Google Earth but it has some really good capabilities.
I think the issue is an FR24 issue as FR24 gets the calculated groundspeed wrong if the transponder "pings" are irregularly spaced.
In the example I was looking at there was one instance of a gap in "pings" of nearly 60 seconds. FR24 "speed" varied considerably for a few seconds at this point.
My friend was flying over the weekend so I could observe his flight in realtime.
FR24 showed fluctuating groundspeed whereas PlaneFinder showed the correct groundspeed which didn't vary by more that 1-2 Kt.
I have some support questions logged with both FR24 and PlaneFinder. Will let you know what they say.

Tony

[tnowak]

Well, groundspeed is indeed transmitted in the ADS-B Out data stream, so it isn't calculated by the flight tracking websites.
So, I wonder why Planefinder shows smooth and correct ground speeds whereas FR24 shows silly groundspeeds quite often...
Anyone else on here with a Funke TRT800 transponder and ADS-B Out?
Tony

[tnowak]

The investigation continues!
I have now obtained the raw ADS-B Out data from a recent flight and see that the "groundspeed" data within the ADS-B Out datastream seems quite wrong.
For example, it should be around 75 kts for this flight but the data output in the ADS-B stream is in the range 24.0 to 32.0

Is any data processing/conversion carried out by PAW before passing the data to the transponder?

Tony

[Ian Melville]

75kts is 38m/s. Coincidence? I seem to recall messages from a device were in m/s for speed and metres for alt. Was that FLARM?

[Admin]

Hi Tony,
Please post the NMEA messages so we can take a look

Thx
Lee

[tnowak]

I can post the received ADS-B data as received on the ground (thanks to Phil Lee). Will that be good enough?

Tony

[exfirepro]

Tony,

As soon as I saw your post yesterday, I was thinking along the same line as Ian, that this could be a ‘units’ issue, but couldn’t get my head round the math at the time.

If you say the transmitted groundspeed was 24 to 42, and if this is metres per second, that equates to (roughly) 50 to 65 Knots - which is certainly in the right ballpark.

It wouldn’t be the first time we have come across a problem caused by cross-unit conversions !

Lee should be able to check once he gets the data.

Regards

Peter

[Admin]

Is any data processing/conversion carried out by PAW before passing the data to the transponder?

Not really, these are basically the messages output from the GPS.
these are also sent to SD, EasyVFR etc.

Were the navigation tools showing the correct speed ?

thx
Lee

[tnowak]

Hi Peter,

Lee now has the raw data file from the ADS-B transmissions and we are getting the PAW track file.
I am fairly sure that SD displayed the groundspeed correctly so I wonder if something is happening to the data inside the Funke transponder?

Thanks
Tony

[exfirepro]

Hi Peter,

Lee now has the raw data file from the ADS-B transmissions and we are getting the PAW track file.
I am fairly sure that SD displayed the groundspeed correctly so I wonder if something is happening to the data inside the Funke transponder?

Thanks
Tony

IIRC the results of the Project EVA trials into the reliability of ModeS-ES using GPS position data from an uncertified GPS source proved that the position data was highly accurate - except for one specific transponder which apparently always transmitted position East of Greenwich (West of course being a ‘negative’ number) even when the aircraft position was West! Pretty sure I also read something recently re the current trials to establish whether there are any issues running a portable ADSB Out device (SkyEcho) concurrently with an active Mode S Transponder. Yet again, the only issue noted was reportedly with one transponder. Guess which make?

Glad I bought Trig.

I look forward to Lee’s findings with interest.

Regards

Peter

[tnowak]

Hi Peter,

My friend confirmed that the groundspeed as displayed in SkyDemon was correct.

As the same GPS source is used for both SD and ADS-B Out purposes that means only two possible causes for wrong groundspeed?
1. PAW possibly is doing 'something" to the data stream being sent to the transponder.
2. The transponder is not formatting the received data correctly before transmission.

Regards

Tony