fuel pump radio noise only when alt field is on
 

New installation. I'm getting loud static in my gtr 200 radio from my AFP fuel pump. It only occurs when the alt field switch is on. The engine isn''t running. I've tried locally grounding it as well as grounding directly to the battery, engine, and forest of tabs. Any ideas? Thanks

Try a filter capacitor
 

rvmv-

May not hurt to try installing a filter capacitor close to the fuel pump and see if that helps with the noise issue you are experiencing.

If you are running a 12 volt electrical system try finding a 22,000 uF capacitor rated at 25 volts and attach the + lead on capacitor to the 12 volt power wire to the pump (try to make this connection as close to the pump as possible). Attach the - lead on the capacitor to a good ground point near the pump.

You could try playing with the capacitor size ... but guessing 22,000 uF would be in the ball park for what you are trying to accomplish. Others may chime in on what has worked well for them.

Electrical noise can be tough to eliminate ... it is almost black magic ... trial and error.

Good luck.

Is there fuel in the pump/lines? Bat voltage >12v?

headset jacks? intercom?
 

How are your headset jacks installed? Do you have a shield grounded on one end, and have you ensured that the jacks themselves are not grounded to the airframe? Just wondering if the sound is actually coming from the radio - do you have an intercom?

Solved
 

Turns out it was the 12 volt power supply I was using. When I switched to a regular battery the static went away and all is quiet now. Why it only showed up when the fuel pump + alt field were on and no where else I haven't got a clue. Thanks for the replies. mv

Never a good idea to run avioinics off a "cheap" power supply, a switching power supply makes plenty of RF noise even idle but the more load you put on it (alt field can typically pull 5 amps) the more noise they usually generate.