Garmin GpsMap 396 - Flight Test

Mike Spera wrote:

30 seconds after take off, lost
the GPS sat lock. Took about 15 seconds to regain it. In the next 5
minutes, it lost lock several more times. I'm thinking, external antenna
is loopy.



Mike,

For what its worth...

I just flew my Arrow around the country and experienced the same
problem (with my brand spank'n new 396) that you described. Most of the
occurrences were in the takeoff or landing phase of the flight. I had
my old Lowrance airmap 100 on the copilot yoke and it never lost lock
once during the flight. The 396 was connected to the remote antenna
which was sitting on the glare shield, the airmap 100 was using it's
built in antenna.

-Bernie

My fly-about http://www.iperformax.com/flyabout/flyabout.html

Too early to reach a conclusion. As I said, I will try the Airmap 1000
and Apollo 920 side by side with the Garmin and see if I can isolate it.

At least I don't feel quite so crazy since yours does it too. Funny
thing, I never mentioned any problems in landing in my post, but it did
indeed almost lose its lock in both descents I made during testing. I
had maybe 2 sats at minimal strength for 30 seconds or so one time.
Another descent had the thing completely checking out for 1 full minute
(no sats at all).

Thanks,
Mike



Thanks,
Mike

An off the wall thought - you lose lock and signal during periods of
high-rpm (takeoff and climbout) and low-rpm (landing), but mid-range
seems to work okay. Could there be some hypersensitivity to voltage
fluctuations that the 396 has? Voltage might also drop during
transmitting if there is a resistance in the bus supply.

You've moved the antenna, around and even switched back and forth
between powered external and stubs. If it isn't the 396 then what other
common denominators are there? (Even if it is voltage fluctuation, the
396 shouldn't be that sensitive -- none of your other avionics are.)



-----Original Message-----
From: Mike Spera ]
Posted At: Tuesday, July 04, 2006 14:17
Posted To: rec.aviation.owning
Conversation: Garmin GpsMap 396 - Flight Test
Subject: Garmin GpsMap 396 - Flight Test


Mike Spera wrote:

30 seconds after take off, lost
the GPS sat lock. Took about 15 seconds to regain it. In the next 5
minutes, it lost lock several more times. I'm thinking, external
antenna
is loopy.



Mike,

For what its worth...

I just flew my Arrow around the country and experienced the same
problem (with my brand spank'n new 396) that you described. Most of
the
occurrences were in the takeoff or landing phase of the flight. I
had
my old Lowrance airmap 100 on the copilot yoke and it never lost
lock
once during the flight. The 396 was connected to the remote antenna
which was sitting on the glare shield, the airmap 100 was using it's
built in antenna.

-Bernie

My fly-about http://www.iperformax.com/flyabout/flyabout.html

Too early to reach a conclusion. As I said, I will try the Airmap 1000
and Apollo 920 side by side with the Garmin and see if I can isolate
it.

At least I don't feel quite so crazy since yours does it too. Funny
thing, I never mentioned any problems in landing in my post, but it
did
indeed almost lose its lock in both descents I made during testing. I
had maybe 2 sats at minimal strength for 30 seconds or so one time.
Another descent had the thing completely checking out for 1 full
minute
(no sats at all).

Thanks,
Mike



Thanks,
Mike

I picked up a 396 on Friday and it was fine all the way from Phoenix to
Santa Fe, but lost it's sat signal during landing in Chandler....
Strange, but it seems I am not alone.


--Dan


wrote:
Mike Spera wrote:
30 seconds after take off, lost
the GPS sat lock. Took about 15 seconds to regain it. In the next 5
minutes, it lost lock several more times. I'm thinking, external antenna
is loopy.


Mike,

For what its worth...

I just flew my Arrow around the country and experienced the same
problem (with my brand spank'n new 396) that you described. Most of the
occurrences were in the takeoff or landing phase of the flight. I had
my old Lowrance airmap 100 on the copilot yoke and it never lost lock
once during the flight. The 396 was connected to the remote antenna
which was sitting on the glare shield, the airmap 100 was using it's
built in antenna.

-Bernie

My fly-about http://www.iperformax.com/flyabout/flyabout.html

By the way, this was with firmware version 2.8 which is what came on
the unit. I am planning to upgrade to 3.2 soon.

--Dan


Dan wrote:
I picked up a 396 on Friday and it was fine all the way from Phoenix to
Santa Fe, but lost it's sat signal during landing in Chandler....
Strange, but it seems I am not alone.


--Dan


wrote:
Mike Spera wrote:
30 seconds after take off, lost
the GPS sat lock. Took about 15 seconds to regain it. In the next 5
minutes, it lost lock several more times. I'm thinking, external antenna
is loopy.


Mike,

For what its worth...

I just flew my Arrow around the country and experienced the same
problem (with my brand spank'n new 396) that you described. Most of the
occurrences were in the takeoff or landing phase of the flight. I had
my old Lowrance airmap 100 on the copilot yoke and it never lost lock
once during the flight. The 396 was connected to the remote antenna
which was sitting on the glare shield, the airmap 100 was using it's
built in antenna.

-Bernie

My fly-about http://www.iperformax.com/flyabout/flyabout.html

On 07/03/06 17:59, Doug Vetter wrote:
Mike Spera wrote:
snip
Not exactly confidence inspiring. This unit may be a bad one. It
happens, I just wish it were a complete failure instead of this
intermittent crap.

I'll report on its progress.

Mike

Funny you should mention this. My 396 GPS reception has been flaky
lately too. Normally, the stick antenna would give me 4-5 sats indoors,
which is pretty good, while the external (powered) antenna would lock 8+
sats at higher signal indications in the same location (understandable
since it has a preamp that's powered through the coax).

Shortly after I upgraded to firmware 3.0 or 3.1 (can't remember exactly)
I took a trip to SC and had the external antenna just completely crap
out on me. No sat reception at all. I replaced it with the stick and
that got me three sats...enough for 2D positioning.

I initially attributed it to poor satellite positioning (there are times
when all the sats are behind the aircraft and the aircraft structure
shields the yoke/glareshield area), but it didn't comfort me to realize
that the Garmin 430 in the panel was locked to 10 sats with signals
pegged high.

Uhhhh, but where is the antenna for the GNS 430 mounted?
.... it's not near the yoke/glareshield, right?


Just today, after upgrading to 3.2, the problem isn't as bad, but the
external antenna doesn't seem to be doing the same job as it used to.

The release notes for the last several releases mention that they've
been screwing with reception issues for the XM receiver, but I wonder if
they messed something up with the GPS component firmware.

So, who wants to open a case with Garmin? If I can find two seconds to
rub together, I just might...this thing WAS running beautifully in the
2.x firmware days. I'm almost tempted to downgrade and test my theory.

-Doug

--------------------
Doug Vetter, ATP/CFI

http://www.dvatp.com
--------------------



--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA

Dan Luke wrote:
"Mike Spera" wrote:


I'm thinking this unit has an internal antenna connection defect.


Or it could be RF interference from some source in the airplane: the
symptoms sound like it. This is exactly what one of my Cessna ARC-385
radios used to do to my portable GPS. Try tuurning off all emitting devices
one at a time the next time it happens. As a last resort, try turning off
the master. You might also try a new location for the remote antenna.

The garmin 196 I had before the 396 used to lose lock whenever my KX-155 was
tuned to certain VOR frequencies.

Dan Luke wrote:
"Jonathan Goodish" wrote:

,
john smith wrote:


You know, with the reception problems I am reading about here, I think I
will stick with my GPS 195 a while longer. I always get a lock with a
minimum of six to eight sats.

I don't have reception problems...


Nor I. I get the same reception performance--or better--with the 396 as I
have with all my previous Garmins.

ditto.


I do remember that my 195 had trouble locking if activated while in motion.
The 396 is not bothered.

Yes, the ol' 196 would take noticeably longer to initialize if powered up
somewhere other than where it went to sleep, even a few feet. Not so the 396.

So I set up my other 2 GPS units in the cockpit and put their external
antennas right next to the Garmin. The Lowrance Airmap 1000 and an old
Apollo 920+ showed 5-9 sats up near the 80%. The Garmin showed 8+ sats
pinned at the top and one or two more at 50%. Immediately after liftoff
the Garmin marched down to zero on all sats and lost its lock. The other
2 units stayed strong. The Lowrance got better reception in flight than
on the ground.

After leveling, the Garmin reacquired a lock. 10 seconds later, WAAS
locked. Hit the transmit button and the Garmin again marched down to
zero on all sats and immediately popped back up when the mic button was
released. The 2 old units never blinked the entire time during
transmission.

Take up a SE heading, the Garmin goes to zero on all sats and stays
there until I turn to some other direction. The other 2 units keep a
strong lock.

Tried every possible position in the cabin and the Garmin still blanked
out. The other 2 had different sat bars but never went below 80% with 6+
sats. Unplugged all units from ships power and tried the tests on
batteries. Same result. Flew outside the Mode C veil and shut off the
electrical system. Same results. Tried different power settings and it
did not seem to make any difference

When powered back for landing with the nose pushed over, the Garmin
again went out to lunch. The other 2 remained locked and strong.

Brought the whole box o' stuff back to JA Air center after calling them
to obtain agreement for a swap. They swapped the unit and external
antenna and kept the rest of the accessories for the new unit. Made
sense. They did try to talk me into upgrading the software before
agreeing to a swap. I said I would upgrade AFTER we swapped if the
problem remained. After the swap, I would have confidence it is not one
particular bad unit. So, I am not chasing a gremlin that turns out to be
a defective unit.

I would love to go up tonight and try the new unit, however, the
President found it necessary to bung up not one, but 2 30 MILE TFRs FOR
HIS FREAKIN BIRTHDAY PARTY! FOR 24 HOURS! Lovely.

I never did check the SW level of the old unit. I missed that one bit of
data. I will try the new one and check the SW level. If it performs like
the old one, I will upgrade and try again. If it still does not work
after the upgrade, I'll give Garmin a call before taking the unit back
for a refund.

I really d0 love the weather data. I am hoping I can find the gremlin
and keep it.

Will report back late Friday or Saturday.

Mike

I inquired to Garmin Tech support about our problems and got the
following response about clearing the almanac. Probably worth a shot.

--Dan


========================
Problem:
I had a problem with satellite reception over the weekend. In
disucssing this with other GPSMAP 396 users, including one who recently
upgraded to firmware 3.20, it seems they are experiencing similar
problems as well.
(i.e. intermittent GPS satellite loss) I have a GPSMAP 195 and have
never had a satellite signal issue. Is this a known problem? Will there
be a firmware fix?
===============================
Thank you for contacting Garmin.

As the GPS uses a satellite almanac of data to track the satellites,
corruption of this almanac will cause the unit to drop the satellite
signals. To correct(erase) the almanac, turn the unit off. Press and
hold the OUT button while turning the GPS on. When the GPS powers on,
release the buttons and let it acquire the satellite signals to start
rebuilding the almanac.

If you have any other questions, please let me know.

Best Regards

===================
Thanks. Would this likely resolve intermittent outages, or is this
only in the case of being completely unable to get a satellite lock at
all?

--Dan

================
Thank you for contacting Garmin.

As the unit contains data on all of the satellites and cycles between
all ones available, corruption of even one satellite's data could cause
the unit to have brief outages as it cycles through the list.

If you have any other questions, please let me know.

Best Regards
















Dan wrote:
By the way, this was with firmware version 2.8 which is what came on
the unit. I am planning to upgrade to 3.2 soon.

--Dan


Dan wrote:
I picked up a 396 on Friday and it was fine all the way from Phoenix to
Santa Fe, but lost it's sat signal during landing in Chandler....
Strange, but it seems I am not alone.


--Dan


wrote:
Mike Spera wrote:
30 seconds after take off, lost
the GPS sat lock. Took about 15 seconds to regain it. In the next 5
minutes, it lost lock several more times. I'm thinking, external antenna
is loopy.


Mike,

For what its worth...

I just flew my Arrow around the country and experienced the same
problem (with my brand spank'n new 396) that you described. Most of the
occurrences were in the takeoff or landing phase of the flight. I had
my old Lowrance airmap 100 on the copilot yoke and it never lost lock
once during the flight. The 396 was connected to the remote antenna
which was sitting on the glare shield, the airmap 100 was using it's
built in antenna.

-Bernie

My fly-about http://www.iperformax.com/flyabout/flyabout.html

Awwww right! I learned something here.. Who says Usenet is useless...

denny