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Author Topic: Troubleshooting the spurious position bug  (Read 10324 times)

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DaveReid

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Troubleshooting the spurious position bug
« on: February 27, 2010, 11:10:16 AM »
In the course of developing ADS-B decoding software for a client, I've been looking at the RadarBox position decoding bug that affects some ATPs and assorted other aircraft.

I'm close to formulating a theory re the nature of the bug, which will hopefully lead to a fix that AirNav can implement, but in the meantime it would be helpful to know if anyone has seen spurious position data for any of the following other aircraft:

43E7DD M-SPEC B350
A0055E N100GV GLF5
A00986 N101MH GLF5
AE0876 01-0025 GLF5

MTIA
Dave
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eggplant

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Re: Troubleshooting the spurious position bug
« Reply #1 on: February 27, 2010, 12:37:16 PM »
Hi Dave,

I have whacky positional data for the first three. No record of the last one. Let me know if you'd like details.

Cheers

Victor
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DaveReid

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Re: Troubleshooting the spurious position bug
« Reply #2 on: February 27, 2010, 01:33:22 PM »
I have whacky positional data for the first three. No record of the last one. Let me know if you'd like details.

Thanks.  Simply the fact that you're able to confirm my suspicions is a great help.

AirNav: I would strongly question the wisdom of displaying decoded coordinates where the NUC_P is 3 and the CPR encoded longitude is all zeroes - that's what the invalid packets from the above aircraft appear to have in common.
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eggplant

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Re: Troubleshooting the spurious position bug
« Reply #3 on: February 27, 2010, 03:53:01 PM »
The tech details actually mean little to me (well nothing actually!), but it sounds like you have had an Eureka moment ! Well done.

Airnav - Would your techs like to comment ? I know the spikes on the polar diagram aren't a big concern to most, but I must admit I find them rather irksome. It would be good if they could be despatched ?
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eggplant

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Re: Troubleshooting the spurious position bug
« Reply #4 on: March 03, 2010, 09:05:32 PM »
Airnav - Is there any comment from your side on this subject ?
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AirNav Support

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Re: Troubleshooting the spurious position bug
« Reply #5 on: March 03, 2010, 09:54:48 PM »
It is being investigated and details have been passed to our development team.
Contact Customer/Technical support via:
http://www.airnavsystems.com/contact.html
[email protected]

DaveReid

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Re: Troubleshooting the spurious position bug
« Reply #6 on: March 03, 2010, 10:02:12 PM »
I'm expecting them to hire me any day now :-)
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eggplant

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Re: Troubleshooting the spurious position bug
« Reply #7 on: March 03, 2010, 10:48:48 PM »
Thanks for your response Airnav.
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radarspotter10

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Re: Troubleshooting the spurious position bug
« Reply #8 on: March 04, 2010, 12:33:04 AM »
I'm expecting them to hire me any day now :-)


From pat

dumpty

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Re: Troubleshooting the spurious position bug
« Reply #9 on: March 04, 2010, 07:42:19 AM »

bratters

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Re: Troubleshooting the spurious position bug
« Reply #10 on: March 04, 2010, 04:19:53 PM »
Add N93M to the list Dave another GLF5 showing 1493nm from centre of  england at 16.15 today.

DaveReid

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Re: Troubleshooting the spurious position bug
« Reply #11 on: March 04, 2010, 05:17:56 PM »
Add N93M to the list Dave another GLF5 showing 1493nm from centre of  england at 16.15 today.

Thanks for the heads-up, just in time to get the packet analyser on this one !

Same thing seems to apply as before: spurious DF17 AP squitters with NUC_P = 3 and the CPR encoded longitude all zeroes.

Not that I had any acknowledgement from AirNav following my original post - I think I'll stop trying to be helpful :-)
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bratters

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Re: Troubleshooting the spurious position bug
« Reply #12 on: March 04, 2010, 07:28:36 PM »
Dave - going back a long way - maybe a year - I recall that my first long distance bizarre positions were all USA reg. Gulfstreams. At the time I ascribed those to deliberate obfuscation of their positions for reasons one can only surmise.

That may well be rubbish but it certainly seems to be a predominantly Gulfstream phenomenon.

Hawkeye

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Re: Troubleshooting the spurious position bug
« Reply #13 on: March 04, 2010, 09:50:34 PM »
Ref reply#10

He must have been really shifting, -  just west of me at 1635 :-)

Syd

DaveReid

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Re: Troubleshooting the spurious position bug
« Reply #14 on: March 05, 2010, 07:27:57 AM »
Dave - going back a long way - maybe a year - I recall that my first long distance bizarre positions were all USA reg. Gulfstreams. At the time I ascribed those to deliberate obfuscation of their positions for reasons one can only surmise.

That may well be rubbish but it certainly seems to be a predominantly Gulfstream phenomenon.

I don't think it's deliberate, if only because it's dead easy to filter out the erroneous position transmissions, leaving the good ones.  But I would certainly agree that GLF5s seem to be the main culprits.

This is eerily similar to a bug in BaseStation a few years ago where spurious positions were being shown, mostly for Canadair Challenger aircraft.

The bug was subsequently fixed by Kinetic - I didn't have a packet monitor in those days, so I don't know the exact details, only the symptoms.
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