REFLECTOR: Intercom noise

[Brian Michalk]

Does the noise stop when that mag lead is grounded?  What about when you 
disconnect the mag wire altogether?  Try easy tests first, don't try to 
fix anything yet.  Take your hypothesis and test it.

Is it shielded twisted pair, or coax?  Does the mag P-lead return back 
to a ground at the mag(correct), or through some other ground path(wrong)?

What is the frequency?  Mags will hum at 1/2 the RPM.  an Alternator 
will hum at 3X of the alternator RPM, which is several multiples above 
engine RPM.  Can you eliminate based on that frequency?  If it's the 
alternator, disconnect battery and field (or belt) and test again.  If 
it is the alternator, do you have a ground strap from that case to your 
starter ground cable ... or at least a very good confirmed electrical 
connection?

On 01/05/2011 06:30 PM, aminetech at bluefrog.com wrote:
> I'm still trying to eliminate noise on my intercom.  It occurs when 
> the engine is running, even while starting.  My mag wire going to the 
> switch is in the overhead duct along side the wires for the headset 
> jacks.  Can this close proximity be the problem?  The mag wire is 
> shielded.
> John
>
>
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