Noise on GNS 430W

Hi
I have now 60h on my -10 and suffer of bad noise of my COMM 1 GNS430W.
It is constantly receiving loud noise when the engine is running. Often it is ok on my home frequency 122.15 but permanently noise is present on 124.xxx frequencies.
The COMM 1 is connected to a belly mounted Comant C-122 antenna which is attached by screws and nut plates. The antenna came with a cork gasket which I used.
Here are my set of questions. The radio receives fine when engine is not running, so I guess that grounding of antenna or cabling should not be the cause of the issue. What could be the potential source of the noise? How can I identify it?

I took all electric circuits one by one off-line without success.

Any ideas are appreciated

Thanks
Mike

Greetings Mike,

What ignition system(s) do you have? I've had corrosion on spark plug terminals create enough radio interference to break the squelch. Mine are automotive style plugs.

Do you have an EFIS or steam gauges? Some EFIS systems generate RF noise. This, added to engine noise, can break radio squelch. If this is the issue then the radio is OK and fixing the EFIS is normally easy to do.

I had ignition noise from the lightspeed EI. Added a big filter capacitor to the avionics bus, gone, no more noise.

Thanks you all for your feedback I'll see if I can get to the root cause next weekend and will post the result.

Mike

Mike,

You are aware that you can change the squelch set point (strength of signal required to trigger radio). This doesn't solve why there is noise but allows you to mask the problem. Instructions are in the maintenance manual. You have to set it at 3 frequencies. Be sure to move the cursor to "Save Calibration" and then hit enter. I changed mine from 39 to 30 (makes it take a larger signal to trigger) and it made a huge difference.

Jim Butcher