Garmin 396 Reception Problems - Latest Observations

Mike Spera wrote:
In my previous posts, I described what appeared to be random signal lock
losses with my new 396. Changing everything did not help. I got the
dealer to swap the unit with a new one and I upgraded the software to
the latest level.

It appeared to work well for over 2 months, however, it started fritzing
out again the other day.

Mike,

I took my 396 through another hard reset procedure as Garmin requested,
and that had some effect. Not necessarily more satellites, but those it
did receive were much stronger. Probably coincidence, because if the
almanac is corrupt (as Garmin suggests), it would look for the wrong
satellites (which it wouldn't find) and the signals for those sats would
be at or near 0.

This time, moving the GPS antenna DID make dramatic differences. So, I
was content on knowing that shifting the antenna back a few inches when
it went out to lunch would make it spring back to life.

Never noticed this before. In my case, once the receiver goes deaf,
repositioning of the antenna makes no difference.

However, I had read that certain nav/com freqs (even just receiving)
would give the thing fits.
snip

I was doing some instrument currency yesterday. My safety pilot was
playing with the 396 while I was under the hood and noted:

1) Transmitting on almost any frequency (122.8 most common that day)
caused the 396 to go briefly deaf. It took a few seconds to
reinitialize but the signals eventually came back. I'm usually too busy
transmitting to notice this.

2) We both verified that 115.5 dialed into a Narco slimline nav or (for
example) 119.32 into the comm is like hitting a light switch when it
comes to satellite reception on the 396. I've been hitting that more
lately because it is indeed the frequency to which the Narco nav
defaults if the keep-alive circuit is non-functional, and the keep alive
was accidentally disconnected recently during a wiring overhaul.

The impact of the local oscillator interference is far greater than I
would have expected, but it's not entirely unexpected. Needless to say,
the G430 installed in the panel not 2" away from it is happy 100% of the
time.

3) However, in spite of the Narco interference issue, my 396 still goes
on the fritz once it's been on 1+ hours. It will stay deaf (no sats)
for periods of 10+ minutes and then come back only to hear maybe 3-4
sats at 50% signal or worse, and get stuck in 2D positioning mode. And
here's the kicker -- turning off the offending panel-mount radios
(indeed the master switch) has no effect. There is something else at
work here.

-Doug

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Doug Vetter, ATP/CFI

http://www.dvatp.com
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