REFLECTOR: Intercom noise

[sbjknox]

I have been following this thread and also am interested to know what you 
find.

>  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.

As I understand the current situation based on the discussions between you 
and Brian, the noise is *not* caused by:
1) Radiation or conduction from the primary side of either the mag or the 
EI.
     > I've tried turning off the mag, and the EI.  I even disconnected the 
power to the EI.
     > I disconnected the ground and P lead to the mag.
2) Alternator
     >  I removed the alternator belt.

That does not leave much... What  remains is:
1) Secondary ignition (high voltage to plugs).  When you turn off one of the 
ignitions to listen to the other, does the characteristic of the noise 
change (ie., does one sound different than the other)?  If the sound is 
different, then perhaps there is a problem with plug wires (?)
2) Some other source... something else running that is generating noise.
Does the frequency of the noise follow engine rpm?

> Should I consider a mag filter?  (links to two filters, one for P-lead, 
> one for power bus).

Since you have disconnected the P-lead at the mag for no improvement, the 
P-lead filter would probably do nothing for you.  The power line filter 
'might'  help if there is something on the power bus that is generating the 
noise.  On the other hand, if there is something (#2 above), it might make 
more sense to fix the noise source.

How confident are you that the intercom wiring is correct... proper wire 
type (shielded) and shields connected where they should be,  etc...

One thing you said  "It occurs when the engine is running, even while 
starting." that seems odd to me.  I think it is bad practice to have the 
avionics powered-up while cranking the engine.  I'm not suggesting that this 
is related to your intercom noise... just a side observation.

Please keep us informed of your efforts.

Sid Knox
Oklahoma

Velocity  173 RG  N199RS
Starduster  N666SK
KR2         N24TC
W7QJQ