My 296 did that the other day also. It was only finding 2 sats. It did this
of and on the whole trip. I have never even and a blip with this unit
before.
wrote in message ...
Flew my 172M today and experienced some truly bizarre GPS behavior.

On preflight my portable GPS (Garmin 296), with external antenna and
aircraft power securely attached, initialized just fine, acquired
several satellites and went right into NAV mode. After runup and right
before takeoff, it showed total loss of satellite signals and even
after cycling power several times, would not pick them up again.

With the utmost confidence in my pilotage skills (sarcasm intended) I
took off and hoped to see valid GPS signals in flight. No dice. we
fired up the copilot's Garmin 195 portable, and with a fresh load of
batteries and the external antenna connected tried to pick up a signal.
Once again, nothing. This persisted on both portable units for a good
10 minutes, including a climb up to 4500' MSL.

I tried individually cycling power on the vast avionics array (dual
ancient NARCOs, King DME, pre-Cambrian ADF and King XPNDR) and lo and
behold, when the transponder was turned off and then back on, both
portable GPS units came to life, acquired multiple satellites and
worked perfectly. Looking back, the 296 probably pooped out when the
transponder went on in the runup area.

On the trip back, there was no problem on either portable unit when the
transponder was turned on.

Has anybody ever seen the 296 (or their own portable) act like this??