ARC 400 loud humming noise

ARC 400 loud humming noise

I have an old ARC 400 COM/NAV (RT-428a) which I have tried to hook up in the hangar to listen to the airfield frq. However, all I get from it is a load humming noise. It's as if it replaces the actual audio with humming - when I squelch it it stops, but when it receives a transmission it just hums in the same pattern as the voice of the person talking??? Does the same thing when I un-squelch it to listen to the static.

Any ideas?

Input much appreciated.


J

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Re: ARC 400 loud humming noise

I assume that , since this application is in a hanger, it is powered from an AC wall plug through some sort of transformer and not from a battery.  If so, the noise may be a power line hum at a frequency equal to the 120 Hz frequency of the power line.  If so, try hooking it to a battery instead. If the noise goes away, that will verify that it is power line noise.  A filtered power supply may be required to eliminate this problem.  Otherwise, hooking the radio to a battery and using a small charger to keep the battery charged may work as a filter.

mkaylor
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