Anybody have experience with In -line noise filters ? One for coax and 1 for dc power?

Depends. Audio range? RF? etc. They are easy to find and not very expensive, but you need to specify it correctly.

Thanks for the reply.

I have a Flightline 760 installed in a Champ 7AC with and o-235. After a lot of hours chasing down multiple suggestions jacks,headsets,grounding wires, battery terminals etc etc. I'm thinking that it's a $700 radio that needs some help.

Example last night I replace the PTT and was checking that it keyed. So I had the radio on inside my hangar no engine running.....quite as a church mouse. My nipp-co heater kicked on and even the blower motor came in noisy so it's almost like it's coming through the antenna, which is brand new and so is the coax cable grounded etc etc.......
Back to the maybe it's just and inexpensive radio that needs help with a in-line power filter and and antenna filter

Just thoughts

How about with the antenna disconnected? If the noise stays, even with the antenna disconnected, then I'd start at the bus. A commercial filter like this one can sometimes address some of the problems with an acceptable squelch offset voltage:

http://www.digikey.com/product-search/en?WT.z_header=search_go&lang=en&site=us&keywords=schurter+5500.2223&x=0&y=0&formaction=on

This is a desperate band-aid for the problem, though. The problem is usually better solved at the source of the noises...generators, fans, etc. You can diagnose this problem by using a bypass capacitor across the inputs of the offending items. 250 microfarads should really knock things down noticeably if the issue is dirty power (Radio Shack). Be sure to observe polarity when using an electrolytic cap.

Hope this helps. Chasing EMI can be time consuming, and the offending item is usually something trivial but hard to pin down right away.

Some people turn the squelch offset up so far the tower or ATIS won't break squelch even just a few miles away, which is unacceptable.

I had the same issue with my Champ, although I was using a handheld radio. I did notice that the Icom radio was much, much worse than an old King KX99. I tried nearly everything to stop the noise....One of the problems was the shielding on the plug wires. One was slightly loose, and caused most of the 'whine' on the radio.....the best solution was to never turn the radio on.
Good luck chasing the problem down!!!

Hey WW

Where you been!!!! Good to hear from you.

This noise thing is going to drive me nuts. I had all the panels off, radio out, trace all the wires, made sure they were hooked up where they should be. all the grounds in place. Different headset, on and on and on.......
Think I give up and take it to a Avionics shop ...I think there is one in LuVerne.....would like to be able to talk to the Mrs in the back seat.
I was up tonight for 1 1/2 hours the air was perfect.

I'm not familiar with Knipco heaters, but looking them up on-line, seems they use a spark plug with repeating arc to keep the flame going.

The first radio transmitters, "Marconi arc gap transmitters", were able to send a signal across the Atlantic Ocean, so you know electric arcs can radiate significant energy. It's also "broad band", meaning it covers large portions of the frequency spectrum (i.e. whatever frequency you have on your receiver, it's likely you will hear the arc transmission.

So as already suggested, you'll want to find out how the interference is getting into the radio. The most likely way is via the antenna, so as already suggested, disconnect the antenna. If that quiets the interference, then the fix is to adjust the radio squelch, or, if that doesn't solve the problem, repair or replace the radio.

If you still get the noise even with the antenna disconnected, then remove the coax at the radio. If noise is still present, the the noise is coupling in via the power or other wiring. Install ferrites on the wiring and see if that helps.

http://www.amazon.com/Gino-Movable-Inne ... uctDetails

These are available in different sizes, if you have enough wire slack they are almost twice as effective if you can loop the wire through them twice. (Not for coax, which should not be bent tightly in any case.)

The line filter previously suggested will help if the interference is in the audio range such as alternator or generator whine being coupled in on the DC power wires - - this does not sound like your problem, though, as you had the noise with the engine not running.

bumper

Be careful starting up your radio with the antenna disconnected.
Some radios can be damaged in that configuration if you do the wrong thing, e.g. transmit... it will depend on the design I suppose..? I don't know any details about what/how, but I did read this warning in CAPITAL BOLD LETTERS with my new radio.