Mode S Transponder checking?

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Christopher Rose
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Mode S Transponder checking?

Post by Christopher Rose » Sun Sep 18, 2016 11:30 pm

I have a Funkwerk TRT800 mode S transponder, every time I talk to Aberdeen Radar they tell me they cannot see me.
I have subsequently called both Edinburgh Approach and Leuchars LARS and they can see me.
I have checked my antenna connections and found them to be in good condition.
Transponder display shows it both sending and receiving.
I am now wondering if the transponder is working intermittently. I looked at yesterday's flight on Flightradar24 and I can see sections of my flight.

Has anyone else experienced a problem like this?

What did you do about it?

Chris

tnowak
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Re: Mode S Transponder checking?

Post by tnowak » Mon Sep 19, 2016 8:02 am

Maybe that you happened to be in an area of poor Aberdeen radar coverage?
Try flying higher to see if that helps.
Unlikely there is anything wrong with your transponder if Edinburgh, Leuchars and FR24 is seeing you.
Is your transponder antenna mounted on a metal ground plane of the required area?

Tony Nowak
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Christopher Rose
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Location: Scotland

Re: Mode S Transponder checking?

Post by Christopher Rose » Mon Sep 19, 2016 11:26 pm

Thanks for reply.

It's a metal aircraft, but thanks for the idea.

While transiting Aberdeen zone (Stonehaven-Peterhead lane) on Saturday, ATC restricted me to 'not above 2000' Northbound. Southbound they had me down to not above 1000' so I couldn't climb. It happened a year ago too, this time I was running along the western edge of their zone at 'not above 3000' and they couldn't 'see' me.

The trace on Flightradar24 from Saturday has big gaps in it even when I was outside the zone at 3000'. Previously I have had a continuous trace in that area. So that was why I asked if there was a way to check an intermittent transponder.

Ian Melville
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Re: Mode S Transponder checking?

Post by Ian Melville » Tue Sep 20, 2016 6:41 am

Do you know anyone with a Pilot Aware unit? Providing range is not excessive and there is no obstructions(line of sight) they should be able to track you monitoring the transponder.

I assume you are not using ADSB?
Ian Melville
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tnowak
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Re: Mode S Transponder checking?

Post by tnowak » Tue Sep 20, 2016 7:59 am

I assume your transponder antenna is in good condition (not covered in oil or the porcelain insulator cracked)? Good ground connection at the antenna to your airframe?
If all is good, based on what you have reported, I think you may have a transponder fault.
3000ft is a good height and, I am sure, you would have good line of sight to Aberdeen's radar head.

Tony
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Frank Parker
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Re: Mode S Transponder checking?

Post by Frank Parker » Tue Sep 20, 2016 11:59 pm

I had a similar problem which turned out to be due to corrosion beneath the antenna and the aircraft skin. Cleaned it up and it has worked perfectly since then.
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John Clarke
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Re: Mode S Transponder checking?

Post by John Clarke » Thu Sep 22, 2016 12:58 am

I can't really offer too much in the way of useful advice but I wouldn't be too concerned about FR 24 coverage as this depends on ground stations feeding data into the system and without ADSB you will find large gaps in coverage. I've noticed this on my own flights. I have the same transponder and haven't had a problem with being seen by anyone. As others have pointed out, it seems strange that it's only Aberdeen that has problems seeing you.
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Rob Swain
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Re: Mode S Transponder checking?

Post by Rob Swain » Thu Oct 13, 2016 2:29 pm

Mode C not mode S but...

I get good contact with every facility I work except Newquay - they can never see my mode C returns. Been like that for the past 3 or 4 years.

Life's too short to worry about it as I only go down that way two or three times a year.
I'll probably Mode S'ify soon anyway. Be interesting if they can see that!
Rob Swain
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Christopher Rose
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Location: Scotland

Re: Mode S Transponder checking?

Post by Christopher Rose » Wed Feb 15, 2017 9:23 am

Thanks everyone for your advice.

I sent the TXPDR off to funke and they put a new receiver in it and updated the software.
I put a new aerial in the aircraft.
I tried it with a Pilotaware and it worked fine.

Thanks again

Chris

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