PilotAware
British Forum => Technical Support => Topic started by: tnowak on September 26, 2018, 09:37:55 am
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A general question:
Does PAW send continuously updated position data to the connected transponder for ADS-B ES out?
A friend with this setup is seeing some strange data on FR24, especially airspeed (in FR24) which is all over the place.
If a Mode S ES transponder isn't interrogated by ground radar how often should it send ES data all by itself?
Every 16 seconds or thereabouts?
Tony
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Hi Tony
A general question:
Does PAW send continuously updated position data to the connected transponder for ADS-B ES out?
GPS messages are sent every second.
A friend with this setup is seeing some strange data on FR24, especially airspeed (in FR24) which is all over the place.
Very strange.
If a Mode S ES transponder isn't interrogated by ground radar how often should it send ES data all by itself?
Every 16 seconds or thereabouts?
Tony
This will be dependant upon the transponder itself, but I think it is supposed to send an ES message twice a second.
Now, bear in mind an ES transmission is actually a group of possibilities, and not a case of
/Squawk/IDENT/Lat/Long/Alt/Speed in each transmission, each of the bits of imformation are spread over a number of data packets.
Thx
Lee
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Hi Lee,
Thanks. I think the issue is with his Funke TRT800 transponder needing a firmware upgrade.
Will report back when his issue is resolved.
Tony
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Hi Tony,
It's probably worth doing a search of this Forum for the TRT800. I'm sure I remember various problems being experienced with that transponder but I can't remember the outcome or whether there was a solution.
I would do the search myself but have to go and do battle with typhoon number 23 and hope it doesn't get too close to Okinawa tonight :)
Cheers,
PaulSS
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Hi Paul,
Tony has had dealings with the infamous Funke ‘requirement to update before you can add ‘ES’’ before, so knows the ins and outs, though this looks like it might be partly an FR24 rather than simply a Funke issue. Yes, please keep us updated Tony.
Hope you have a safe flight tonight Paul!
Best Regards Both
Peter
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Might have known I was trying to teach egg-sucking :-\
It was an interesting evening/morning but I think tomorrow will be a bit more of a challenge, with the typhoon moving north over Japan. This was this morning's TAF for our jaunt through Okinawa (Rwy 36). It was bad enough landing but then had to take off again and go to Hong Kong. Glad to say its very pleasant here :)
Just thought I'd edit this and add a shot of the ACARS report of the weather we grabbed as we went past Okinawa on the way back from Hong Kong today. Probably not ideal as an alternate :o
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^^^^^^^
Not really sure a ‘like’ was what I meant - ‘impressed’ would be more appropriate, though perhaps not in my flexwing. I like a challenge and have flown in some pretty ‘interesting’ winds, but it gets a bit hard to ground handle at 40kts - never mind 70 :-\
Respect
Peter
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@Exfirepro
Ahem. What was that comment the other day about "3 axis bottle merchants" when I mentioned the go-arounds and diversions I'd seen at EGPH on 360Radar
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That was just a wind-up (or possibly a 'Wind' up) :-\ You well know my 'limits' - or then again, maybe we haven't reached them yet 8)
Regards
Peter
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Well, my friend has had his Funke back and it had a firmware upgrade.
Unfortunately it has made no difference to what is seen on FR24. His cruise speed varies signifcantly from 40 Kt or less to 250 Kt or more.
He doesn't fly like that!
I can only think of two reasons why this may happen:
1. The ADS-B Out position data is in error somehow although the FR24 track looks reasonable.
2. The position data is somehow being stored/delayed occasionally by the transponder before transmissions. So the calculated speed between data transmisisons (position) varies.
Any ideas where to look to fix this issue?
Oh, it is a PAW Classic.
Tony
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Hi Tony
Are we sure that the trace that is being shown on FR24 is from ADS-B and not MLAT ?
Do you know which NMEA messages the FUNKE is using to determine the ground speed ?
it is easy to take a look at the .trk file and see if there is anything strange in there
Thx
Lee
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Hi Lee,
The trace is ADS-B as he was flying at 2000 ft in an area of good FR24 coverage (southern England).
Is there a way to check for ADS-B data when viewing playback tracks on FR24?
Are you saying that the Mode S ADS-B data transmitted via a transponder includes ground speed messages?
I thought FR24 calculated that based on the time taken to travel between Lat/Lon corordinate pairs.
Thanks
Tony
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Hi Tony,
Hi Lee,
The trace is ADS-B as he was flying at 2000 ft in an area of good FR24 coverage (southern England).
Is there a way to check for ADS-B data when viewing playback tracks on FR24?
I am not sure TBH, but FR24 will capture MLAT(Mode-S) and ADS-B, so the first thing to determine.
is whether the data on FR24 based upon the Mode-S transmissions (via MLAT) or ADS-B transmissions
Are you saying that the Mode S ADS-B data transmitted via a transponder includes ground speed messages?
I thought FR24 calculated that based on the time taken to travel between Lat/Lon corordinate pairs.
No Ground speed is transmitted as part of the Extended Squitter.
The question is, what NMEA message is the transponder using to create that groundspeed component, then we can cross reference that in the .trk file
IIRC, it is one of the following
- GPVTG
- GPRMC
Thx
Lee
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Hi Lee,
Let me get back to you about this issue.
It has it has just been discovered that Funke never upgraded the hardware, just the firmware, although they were asked to do both.....
Hardware is still at the "non ADS-B" level.
Thanks
Tony
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It has it has just been discovered that Funke never upgraded the hardware, just the firmware, although they were asked to do both.....
Hardware is still at the "non ADS-B" level.
Hi Tony,
In which case, I am guessing the FR24 trace you were looking at was most likely MLAT and not ADS-B
Thx
Lee
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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
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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
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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
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You can use the "Playback" function in FR24, select your aircraft and see if it says "T-MLAT1" or "T-EGxxx" under "radar"
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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
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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
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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
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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?
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Hi Tony,
Please post the NMEA messages so we can take a look
Thx
Lee
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I can post the received ADS-B data as received on the ground (thanks to Phil Lee). Will that be good enough?
Tony
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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
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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
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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
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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
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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