Running the 262 transponder with 250+ trouble free hours over 1 1/2 years in an RV9. About 2 weeks ago was informed it wasn't working, then whoops see you now. Since then has become more off then on. Screen is all lit up appropriately, even with the blinking "R" as normal. Other then checking for wires and coax, which I will do once I get the energy to rip my baggage compartment off and crawl in the back, has anyone seen this? Why would I see the interrogation but they don't see me? Don't mind doing the work but would like a clue as to where to look for first.
Intermittent Transponder
- Thread starter rtairey
- Start date
jakej
Well-Known Member
If you had not changed anything & the system was working well it could be the coax or antenna, it's same as what can happen with any transmitting system - you can receive on a simple piece of wire but to transmit properly you must have a 'tuned' antenna.
What type & model of transponder antenna do you have ? If it's the rod type (with ball on the end) then they can easily be damaged (broken internally) when bumped - commonly happens when washing the plane etc.
Can you post a photo of the BNC fitting ( looking down on it from above) on the antenna ? I have seen a situation where 2 of the BNC socket segments were missing causing an intermittent connection with the avionics guys spending a bit of time time testing transponder & replacing coax without finding the fault - guess I got lucky
. This may not be the solution in your case but it's worth looking at when you crawl into the back.
HTH
Jake J
What type & model of transponder antenna do you have ? If it's the rod type (with ball on the end) then they can easily be damaged (broken internally) when bumped - commonly happens when washing the plane etc.
Can you post a photo of the BNC fitting ( looking down on it from above) on the antenna ? I have seen a situation where 2 of the BNC socket segments were missing causing an intermittent connection with the avionics guys spending a bit of time time testing transponder & replacing coax without finding the fault - guess I got lucky
. This may not be the solution in your case but it's worth looking at when you crawl into the back.HTH
Jake J
- Joined
- Mar 23, 2005
- Messages
- 13,226
The first thing we would suggest is having the bi-annual transponder check run. This should tell you what is up.
Both of these were on my short list of issues/solutions. The antenna is indeed the short rod with ball type located underneath midship. I have seen instances of these being knocked off, mine seems intact at least externally (on my checklist). I will have a look from the inside. The biannual avionics / transponder check is coming up in a couple months anyway, will pull it up.
Look for corrosion at the antenna end. Very common over time. especially if the antenna gets wet it wicks in through on some antenna designs, consider the dissimilar metals mixed water and electricity. The corrosion will build up and start conducting thereby degrading the signal. And that includes all the other antennas especially the com antenna.
jakej
Well-Known Member
Just a point - it may 'look' ok but the rod could be broken further in, you should check also with a multimeter especially if the rod is even slightly bent
Jake J
Re: Intermittent Transponder - update
Took the recommendation and removed the antenna. It looked in perfect shape but someone on the field had a spare so I figured I would swap them up out. When I removed the antenna and the backing plate, there was a thin film of oil from the belly between the backing plate and the fuse skin. Could this have caused ground plane issues? When Wx clears, will try the new antenna.
Took the recommendation and removed the antenna. It looked in perfect shape but someone on the field had a spare so I figured I would swap them up out. When I removed the antenna and the backing plate, there was a thin film of oil from the belly between the backing plate and the fuse skin. Could this have caused ground plane issues? When Wx clears, will try the new antenna.
jakej
Well-Known Member
That oil won't be an issue - as you have a '9 I don't understand the comment about a backing plate, didn't you use a doubler rivetted to the skin ? & had made sure that the star washer was making a good contact (bonding) with the skin ?
If you have a loose plate between the washer /nut & aircraft skin then you'll need to make sure that the bonding is good there too.
Despite the above comments, & you knowing that the system was working, it's most likely still to be the antenna itself IMO if nothing was changed before it went 'bad'
Jake J
jakej
Well-Known Member
I've just sent you a PM
To close this out, I replaced the antenna. As well, obviously cleaned up the oil between the fuse and backing plate (backing plate is not riveted in, held in with the nut holding the antenna). Took it up and ATC says it is a string signal. Thanks all for the comments. Xponder will get checked at next annual.
jakej
Well-Known Member
Glad you got it sorted - it would be nice for all to know which 'fix' did it - one way to find out is to use a multimeter to check continuity between the tip of antenna & centre socket where BNC pin goes in, please
Jake J