Garmin GTX 327 Audio Noise?

[9GT]

I have a Garmin stack in my plane that has worked flawlessly for almost two years. About a month ago, I started to hear an audio noise through the headset that was a steady clicking sound about once every one second. Not overly loud and not enough to interfere with communications, but it is annoying. It goes away for about 5 seconds when you talk or there is radio traffic, then returns. I have traced it to the Garmin GTX 327 transponder. When I turn that off, the clicking stops. It almost sounds like the I am hearing the transponder transmit its ping? I have the GMS 340 audio panel also. Any ideas of a possible solution before I pull theses out and send them in to the avionics shop? I also unfortunately am using a BMA power panel and am worried that somehow that has something to do with it, though I don't quite know how? Bad ground????

 

[apatti]

Since it worked fine for an extended period of time it would have to be something has changed. One thing that comes to mind is the transponder antenna connections. Make sure the antennal is still well grounded and not corroded. A high SWR is one possible cause.

Also, if the antenna connections are not tied down well and subject to a lot of vibration, you could be having trouble there. Did you use the "good stuff" (RG400 or RG 142)? RG58 is probably more prone to have trouble over time.

While you are on the ground, perhaps you could lightly "jiggle" (a technical term) some of the wires to see if the problem lessens or increases.

Also check the audio wiring. Are the shields still well grounded? Do you hear the problem in both the co-pilot and pilot positions? The five second phenomenon sounds like it is associated with the squelch. I am thinking that when the squelch is broken, the audio lines are being actively driven. When the radio output is squelched, the audio lines are an open circuit and more apt to be interfered with by a small signal coupling in from the outside.

Perhaps you could isolate it by selecting an unused input on the 340. Do you have any wires connected to COM3? Most don't. If you still hear the noise, it is not getting in via the audio lines. Then, I'd look at power and ground.

Well, not an exact answer. But hopefully it gives you some ideas of some things to try. Good luck and please report back. The resolution to things like this add a lot to the knowledge base here.

 

[9GT]

Thanks for your input Tony. It gives me a place to start looking and eliminating the simple solutions. I'll report back what we find when I get a chance to look at it.

 

[9GT]

Noise Issue Update

We finally got around to looking into the noise issue today. It is definitely the transponder causing the noise because when you turn off its power,,,it stops. We checked the antenna connections and ground plane along with the power and grounds with no luck. I have a BM power board that has been problems since day one. Thinking that the power board may be the cause, we disconnected the GTX 327 power and ground leads, tried different ports with no luck, and also connected the 327 to an isolated 12V battery,,,,still no joy. Wiggled wires and coax,,,ect. I think that the next step will be to fly out to PTK Oakland Avionics and see if they have an answer. I am sure it is the transponder ping I am hearing about once every second. Its really frustrating because everything worked good for a8 months!

 

[IowaRV9Dreamer]

check the headset

Hi 9MT - here is an odd thought. I have Lighspeed classic ANR headset, which of course has an on/off switch. I've randomly noticed a faint "chirp" sound every few seconds.. but it always came and went. I never thought much of it.

Until yesterday. I had just taken off and tower cleared a jet behind me. I turned left earlier than I've ever turned before and was rewarded with a much louder "chirp". I looked out my window and noticed that the terminal radar had just swung past me. It was pretty close because of my early turn and my low altitude.

That got my attention - so I noticed that every time that radar antenna spun past me, I got a chirp in my headset. Sometimes louder than others, depending on how close I was to the antenna.

I turned off the ANR headset switch and the chirps went away. I guess my ANR headset is getting interfered with by the radar.

If you have electronics in your headset, maybe they are being interfered with by your own transponder. It would be easy to try a different headset.

Just a thought - and it doesn't explain why it is a "new" problem.

Good luck!

 

[AirHound]

We finally got around to looking into the noise issue today. It is definitely the transponder causing the noise because when you turn off its power,,,it stops. We checked the antenna connections and ground plane along with the power and grounds with no luck. I have a BM power board that has been problems since day one. Thinking that the power board may be the cause, we disconnected the GTX 327 power and ground leads, tried different ports with no luck, and also connected the 327 to an isolated 12V battery,,,,still no joy. Wiggled wires and coax,,,ect. I think that the next step will be to fly out to PTK Oakland Avionics and see if they have an answer. I am sure it is the transponder ping I am hearing about once every second. Its really frustrating because everything worked good for a8 months!

Did you ever figure it out? I have the same issue in an RV12 with different brand equipment but same symptoms?