Faulty Transponder

[T18]

I wonder if anyone can point me in the right direction on how to resolve my problem. I fly an LAA aircraft and during the past two flights have been advised by radar units of primary contact only. When pressing the test button on the squack box it shows green. Where should I start trouble shooting.


Thanks in anticipation.

T18

[mono]

You're going to need a radio engineer. The test on those transponder boxes is very basic. It could be an antenna problem or the box itself could be U/S (despite the green test indication).

[Hasherucf]

If its of the older type it will have a cavity and when you turn it on you will hear it 'singing' to you , a high pitched sort of noise.

Other things that may be wrong is the framing is out or its low on transmission power. Check your antenna for damage and corrosion

Some of the older units and encoders need a warm up time . Don't just turn it on from cold when ATC requests it. Warm up time can be up to 8 minutes.

Really you need someone to go over the system with a transponder test box. Mostly the systems are simple and easy to fault

[T18]

Thanks Hasher, the unit had been on for at least fifteen minutes, I will check the antena and wiring next visit.

Regards,
T18

[pulse1]

We had a similar problem. Cleaned the antenna and it worked perfectly. I understand that a very thin film of oil can corrupt the signal.

[T18]

Thank for the response people, Pulse 1, you got it in one. Check the cable which antenna is the TX?... OOPS, only one antenna, it looks like the tx one has been removed perhaps during a washing cycle.

Now on the look-out for a replacement antenna.

Obvious really now that I know what has gone wrong, don't use a long handled brush to wash the underside of the toy!

Regards T18.

[mono]

I'm not aware of any transponders that use a separate antenna for TX and RX. There are newer models that have upper and lower antennae but from your posts I don't think you have this type. In all probability the antenna missing is the only one for the transponder.