On Monday, February 26, 2018 at 6:28:31 AM UTC-8, Dan Marotta wrote:
This may or may not be related, but...

I mentioned GPS dropouts to my avionics technician since I had several
GPS pucks under the fiberglass glare shield on my Stemme. They were
mounted directly under my Flarm antennae so I moved them to the top of
the glare shied and to the canopy frame up front. This took care of most
of the dropouts but there is still an occasional dropout.

The tech said he's seen this on power planes as well and he thinks it's
a failing GPS antenna.Â* He said that one antenna failing could
(apparently) transmit interference which could take out others.Â* He
suggested disconnecting my antennae one at a time and flying with that
system down and see if there are problems with the others.Â* It might be
less painful simply to get another GPS antenna (they're cheap) and swap
it around the cockpit from system to system and see if that fixes the
problem.Â* ...Or maybe an antenna combiner...

OBTW, there should be no problem with mounting an antenna underneath a
fiberglass cover.

On 2/25/2018 7:44 PM, Dirk_PW wrote:
I'm doing a little housekeeping with instrument panel this winter with the intent to eventually install an ADS-B solution (whatever that may be). The panel is quite cluttered right now. I'm considering one option of moving the FLARM GPS antenna (and eventually a ADS-B GPS antenna) back behind my head somewhere in the baggage area. I'm curious if anyone has done this and has had any problem acquiring a GPS signal (on a fiberglass glider). I'm currently having no problems acquiring a signal with the GPS antenna under the fiberglass front panel. Thanks.

--
Dan, 5J

Check for electrical noise on your mains. In my case it was caused by switching power supplies for the Oudie and Colibri II. I was seeing occasional dropouts in my IGC traces. Liberal use of ferrites stopped the problem cold.