"rip" wrote in message
. com...
Actually, I think most GPS antennae do receive DC through the coax to
power the preamplifier in the antenna.

Rip

You are correct. My Garmins do exacly that.


Don Tuite wrote:
On Sun, 15 Feb 2004 05:08:30 GMT, Jay Smith
wrote:


Bob Chilcoat wrote:

Recently one of my partners reported that the compass (standard whiskey
compass, not a vertical card) on our Archer was reading 20-25 degrees
off of
runway heading at departure. Today a new partner was up with an
instructor
for his sign off and reported the same thing. I hadn't noticed, but we
seem
to have a definite problem. Nothing has changed in the plane for a
long
time. We recently replaced the old Garmin GPS with a Lowrance AirMap
300
(which has its antenna on the top of the glare shield near the
compass), but
the first incident was before that substitution was made. Any idea how
something like this can happen?


Move the antenna and you will observe the compass swing. Although the
antenna cable is theoretically shielded (?), the leakage of the electric
field affects the adjacent magnetic field, thereby affecting the
magnetic compass.


Doubtful. No DC. A screwdriver in the glove box is more likely.

Don