transponder noise on com radio

[funflying]

As I continue to set-up the Skyview panel and test my avionics I noticed while listening on the SL40 when the transponder was turned on noise started. It was a noise similar to someone sending morris-code. I had a friend on the passenger headset and he heard it too. Of couse when the transponder was turned off the noise quit.

I checked the transponder antenna to be sure the connection was not going to ground and the coax was good, both in the cable and the short adapter.

Looking for any ideas or similar experence. Thanks

[yankee-flyer]

So THAT's what that Morse (pretty much always the same combination) is coming from. I don't get it all the time but do get it on occasion in flight. VERY interested in answers.

Wayne 143WM

[Dave62]

Morse is probably your cell phone. Been there done that.
Dave (Swift Driver)

[funflying]

It is not any distinguishing code but it was the best way to describe the sound. I have just listened while in the garage. No engine run yet to see if this make a difference or drowns out the "morse code" noise.

[funflying]

One reports some intermittent noise, and one believes it might be cell phone noise.

Any other guesses to the black magic that is radio electronics?

I also checked the antenna wires as they traveled through the panel base and to their respective antennas. They start through different plastic snap bushings, then over the rudder pedals, still not right side by side but in the same neighborhood. They the transponder antenna wire goes off by itself to the antenna and the com. wire heads to the mid-fuslage area.

[MacPara]

I still don't fully understand the nature of this noise. Do you hear that constantly when the transponder is enabled? Or is it only audible when the transponder is actually transmitting? Depending on the answer I might come up with an idea or two ...
BTW, is the panel cover screwed on or are the avionics accessible when you hear that noise? Did you prime/paint the interior or is everything just bare alclad?

[funflying]

MacPara,

Any ideas welcome. Let me try and answer your questions. The noise is constant when the xponder is on, either on or alt. The cover is not screwed on yet so all wiring is acceptable when that noise occurs.

The interior is painted but behind the panel bare on the base and back of the firewall. The cover is primed but not on yet.

Thanks

[BigJohn]

Patrick,

Can you give us an idea of how loud the transponder noise is? Loud or faint? There are faint noises in most aircraft intercom circuits , since it is nearly impossible to prevent any transfer at all of RF energy between nearby circuits. This noise is detectable in a quiet environment, but once the engine is running you may not even hear the faint noise level.

Not saying you don't have some kind of issue there, but it may not be a real problem once you get operational.

John

[funflying]

Thanks John,

The noise is more on the faint side listening in the garage at home, but definitely audible once the transponder is on or alt.

I have noticed other noise filters, AP servos and strobes, and wanted to make sure I didn't miss a filter for the transponder.