Actually, I did try a few tests. When switching to my second com and
transmitting, it did the same thing. Down to zero on every sat.
Relocating the GPS antenna to the back seats near the window or anywhere
else made no difference when transmitting. It did seem a little better
for reception on the right side of the glareshield (opposite side from
the XM antenna). Turning off all the radios and the complete electrical
system had no effect. I still had flaky reception.

Once I have my other GPS units side by side with this one, I should be
able to isolate whether it is a plane/radio or specific GPS problem.

Thanks to all for suggestions,
Mike

Very possible... He needs to get out of the airport area and turn off
thenav/com radios and the transponder and see what happens... If that
is no good, then turn off the master switch and the alternator... If
still no good, then it is the 396...

denny