Niels Kock a crit :
> ...
> It may well be an antenna/screening problem. But why does this problem
> arise after a some years' impeccable service, and
> then seem to increase?
>
> Can anybody help with an explation which even I might grasp, and a
> solution?
>
Niels,
Please remember that shielding is not a one-size-fits-all solution to
audio noise problems. It only works for specific cases. Many many times
it has something to do with proper grounding.
The appearance after some time may indicate a wiring related issue.
Are all your grounds properly connected at a unique point of the firewall ?
Is your intercom corrrectly wired ?
Why do you have a long coax run for the radio ? Why not shorten it and
(at least) gain on the signal attenuation ?
Are your antennas sufficiently remote from each other ?
Have you tried running each of the suspected device from a completely
separate power source (battery), to ascertain the radiated or conducted
origin of the problem ?
Since the noise seems to be related to some specific frequency ranges,
have you considered adding a notch-filter to your radio ? The Garmin
400-series call for a check of the VHF entire frequency range and the
addition of a 1.547 GHz notch filter at the rear of the radio in case of
interference problem.
Regards,
Gilles Thesee
Grenoble, France
http://contrails.free.fr
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