radio noise

On Fri, 26 Nov 2010 11:41:37 -0800 (PST), et
wrote:

On Nov 26, 9:18Â*am, Orval Fairbairn
wrote:
In article
,

Â*et wrote:
I have a radio question. Â* Glasair 1TD with Icom radio, older headset.
When the engine is running and charging 14.5 volts the radio howls
when I transmit. Â* Engine off, battery voltage, no noise. Â* Â*If I put
a small screwdriver in the small hole in the headset and turn it down
1/2 turn, no noise. Â* If I then take the headset and plug it in my old
Cherokee, it won't transmit until I turn it back up.

Are all headsets this voltage sensetive? Â* Or just older ones? Â*Is
there a fix?

thanks

Ed

You need a capacitor between the alternator o/p and ground, to suppress
noise. All the aviation supply houses sell noise suppressors.

It's not that kind of noise, it's a loud howl when I try to transmit,
receives great. It will also howl after I shut down the engine,
until the battery voltage drops a little, then it transmits great.
Never does it when receiving.

Ed




Lots of radios are sensitive to overvoltage. Try putting a diode or 2
in series with the power lead and see what happens. Most work just
fine as low as 10.5 volts or so - so even a good voltage regulator
(low dropout) could do the job - but I'd recommend a couple of silicon
rectifier diodes - minimum 24 volt and 50% more than the rated
current, better yet 50 volt and double the transmitter current.