Tauno Voipio wrote:
: It still has the smell of a ground loop if the intercom
: power supply filtering is OK.

: Maybe a ground loop between the intercom and the radios
: (audio panel)?

Now you're talking. Like I said, I don't know the particulars on the SPA-400,
but many intercom models are simple single-ended... a ground is a ground is a ground.
The intercom *does* connect to the audio panel, which connects to the nav, com, dme,
adf, radio, anklebone, etc, etc.

I suspect if you *truly* were to disconnect absolutely everything that could
re-ground the intercom (and thus render most of the avionics stack useless), float the
case and all jacks, you won't hear any whine.

As far as the pilot/copilot side being worse, remember that only the bus
(+14V) goes to the battery on a dedicated line (I don't recall what plane you're
talking about... if it's composite, I'm wrong). The alternator current meanders
through the aircraft structure somehow and eventually makes it to the battery. The
structure could very well favor more of this current on the copilots side and generate
a few more mV of alternator-induced IR drop there.... or rather where "there" is the
distance between where the intercom and some other avionics is grounded.

-Cory


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************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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