On Fri, 28 Mar 2008 12:03:30 -0700 (PDT), Lancair IV-P Flyer
wrote:


The handheld radio had no static. However, it gave me an idea to
power up the radios without the engine running to isolate whether it
is alternator based. I can get the static without the engine
running. The alternator switch is off so the VR is not powered up
either so the static is coming from a powered instrument it would
seem. So, why does the static go away when the engine is running and
the alternator switch is turned off?

Hmmm. It is odd that the shutting off the alternator field current
seems to fix the static, but meanwhile you also get the static while
on the ground without the engine running.

I think your idea to pull breakers while on the ground without the
engine running is a good next step.

You mentioned a voltmeter in the plane. Does it oscillate or is it
fairly stable? I don't know if you have access to one, but it would
be really helpful to see an oscilloscope on the main bus when the
static condition occurs.

BTW - where are you based?