PilotAware
British Forum => Technical Support => Topic started by: G-JBVP on August 06, 2017, 06:14:30 pm
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Have been getting spurious contacts showing aircraft Reg as G-OO2D or various last two letters G-OO?? With contact at same height and position as my aircraft with red warning circle.
Any ideas what's causing this?
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Can you post screenshots of your PAW home and config pages? Also, could you post a link to your log file? or send it to Lee.
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I think you may mean C-xxxx
Where xxxx is an incrementing hex counter.
These are indicating Mode-C responses, what do you mean by spurious?
What qre your Mode C/S config settings ?
Thx
Lee
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Lee
Bŷ spurious I mean giving a warning of very close proximity red warning circle showing 0 feet height difference, looked like reg started with G but could be a C.
I will send you a screenshot of PAW & Config screen when I next fly.
Brian
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Brian, do you have a transponder? If so is it mode C or S ?
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Yes mode S I have setup our transponder code to be filtered out, perhaps should have mentioned using Skydemon
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Hi Brian
Your Mode-S transponder will also reply to Mode-C interrogation
So you need to select the ModeCS+Filter option
Sounds like what you are reporting
Thx
Lee
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Why would that show G(or C)-00?? I was expecting Brian to say Mode C.
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Lee
ModeCS+filter option is selected.
Brian
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I would have expected you to have the error all the time, but just in case.. Can you confirm the hex code in the transponder is the same as set in PilotAware, which of course should match GINFO.
DId you send. Copy of the log to Lee?
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Hi Brian,
If I can get the track, that would be useful
In the latest release, Mode-C contacts are reported (as they are received) as an incrementing count
so first Mode-C is assigned
C-0001
next
C-0002
etc...
This is because for Mode-C there is no ICAO code, but we need some identifier.
This identifier is then reused IF I think I receive a new Mode-C ping from the same transponder, this is done by a pretty complicated DSP algorithm that is looking at
time of arrival, altitude variation, signal power variation.
so if you see an ID of C-xxxx, this indicates a Mode-C response.
This is the probelm with Mode-C
PilotAware cannot know if the Mode-C response to an interrogation came from your transponder.
using the '+Filter' option, it tries to learn that a Mode-C response of high strength and similar height is probably the local transponder, so it reads the strength and assigns a hi power blocking filter, the filter recedes over time.
Where this does not work is when your transponder is NOT interrogated, and then suddenly receives an interrogation, at this point Pilotaware has not gone through the 'learning' phase, so reports the Mode C signal, it is subsequently filtered.
if over time you receive no more interrogations, the filter drops, you receive an interrogation, and again it is reported
Thx
Lee
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using the '+Filter' option, it tries to learn that a Mode-C response of high strength and similar height is probably the local transponder, so it reads the strength and assigns a hi power blocking filter, the filter recedes over time.
Where this does not work is when your transponder is NOT interrogated, and then suddenly receives an interrogation, at this point Pilotaware has not gone through the 'learning' phase, so reports the Mode C signal, it is subsequently filtered.
if over time you receive no more interrogations, the filter drops, you receive an interrogation, and again it is reported
Just for my education, can I just confirm that PAW does not permanently remember what it has learnt about your own Mode C? Why is this? How long does it take before it forgets what it has learnt(which, of course, assumes your Mode C has not been interrogated in the meantime)? How long does it take to re-learn, or does it just start all over again each time it is started?
Just interested, is all (as they might say in the US of A) :)
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Just for my education, can I just confirm that PAW does not permanently remember what it has learnt about your own Mode C? Why is this? How long does it take before it forgets what it has learnt(which, of course, assumes your Mode C has not been interrogated in the meantime)? How long does it take to re-learn, or does it just start all over again each time it is started?
Just interested, is all (as they might say in the US of A) :)
The 'learning' as I term it, consists of telling PilotAware it is situated close to a Mode-C transponder.
From this it deduces that the highest power Mode-C transmission, at the same height - must be coming from the local transponder.
when it receives a Mode-C Ping it sensitizes the filter based upon the received signal strength, the filter itself decays over time, I dont recall the exact number I think it is a minute, bear in mind your transponder will be interrogated every 2 seconds, so if your transponder is not interrogated for one minute the filter has effectively stopped working, which means the first time you get interrogated again, it will report your own transponder - then ignore it
So where this approach falls down is when you move in/out of areas where your transponder is interrogated, but in this case it should only report once.
There is no way around this, there is no way of ignoring your own Mode-C transponder, as there is no way of identifying it, with Mode-S its easy.
thx
Lee
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Thanks, Lee, all very clever stuff :)
I've got a Mode S transponder (still in the box, as is my PAW) so I'm obviously not going to be affected but it is interesting to see how you try to deal with the Mode C boxes. I can't wait to start playing with my gizmos but it's going to be some time yet :'(
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Lee
PDF's of various screenshots attached.
1 of 2 posts
Brian
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Lee
PDF's of various screenshots attached.
2 of 2 posts
Brian
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Hi Brian
Config settings all look good.
Are you able to supply the track file for your flight ?
Under the Track option
thx
Lee
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Hi Lee
Didn't fly today just ran these off while I was at the airfield, will send track log next time I fly
Brian
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You can download old track logs for flights when you experienced the issue.
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Hi Lee
Have downloaded a couple of tracks but files to big to send over the forum, can you send me your email address for me to send them over.
FYI flew for 4+ hrs yesterday and only had one of these spurious contacts about an hour into the first leg of my flights so leave it with you as the whether it's worth spending any more time investigating.
Brian
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Brian,
Since we first released the original Mode C 'Beta', Lee has done a considerable amount of work to reduce spurious alerts, as a result of which these are now much less prevalent than with the original Mode C software. Work on this issue is however still ongoing to try to improve things even further, so track files indicating spurious alerts will all be useful.
The best method of transfer for large files is to put them in 'Dropbox' (you can set up a limited size Dropbox account for free). Put the files you want to allow access to in a folder and PM a link to that specific folder to 'Admin' (or anyone else) via the 'Messages' Board. (Right click on the folder and you will see an option to 'Copy Dropbox Link'). If your Dropbox gets too full, you can just delete files or move them over to store elsewhere on your PC or wherever.
Regards
Peter
(PilotAware Engineering)
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Peter
Not that familiar with Dropbox but I think I have done it, should be 3 track files
Brian
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Have you sent the three links to Lee?
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Or just one link to the folder containing the 3 track logs ;)
Hopefully Lee will acknowledge receipt.
Peter
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Hi Chaps
Please excuse Lee if he doesn't respond in his usual brilliant way but he is on holiday this week. 8)