GPS Satellite Reception Dropout
 

A good friend and fellow pilot (RV-9A) and I both bought 396's at Oshkosh in 2006. And we both have had similar problems...occasionally the GPS just quits, with a message that says something like "Lost Satellite Reception." I have noticed that mine always drops out on the way to my favorite grass airport, Moontown, 3M5, near Huntsville, Alabama.

I mentioned this to Paul Dye a few months ago who is also using a Garmin 396 with XM Weather. He said his always drops out near a certain "antenna farm" near Houston.

Hmmm....looking at my usual trip to Moontown through Huntsville (HSV) Class C airspace, I notice that I travel BETWEEN two hilltops with lots of TV and RADIO ANTENNAs on top of them. This last Saturday I also had the dropout on the way to Moontown, but on the way back I avoided going between the hills and chose rather to go around them on the north side, and I had continuous satellite coverage. More hmmm...

My friend is more frustrated than I am as his 396 refused to acquire satellites during a 30 minute flight around the local airport (DCU) last Saturday. We both have updated the software from the web site and I believe we are operating the latest version.

So the question is "Is anyone else having similar problems with their 396 (or 496's)?"

If there is a preponderance of such satellite reception dropouts across the country, I am wondering if we could have a map of "thumbpins" showing where they are. More importantly, I am wondering if Garmin has a problem that has been reported by many of us but has not fixed the problem. I also recently had a momentary dropout near Dayton, Ohio, so I am beginning to suspect my 396 may not be as reliable as I thought it was.

My friend is planning to call Garmin and expects to send his 396 back to them for a thorough checkout. I'm not ready to do that yet.

Also, do Lowrance or other brands of handheld GPS's have the same occurrence?

Obviously, my friend and I should do a side-by-side test on the Moontown trip but he is so aggravated that he is ready to send his back to Garmin.

Any similar experiences out there?

Don

Garmin only, or general GPS problem?
 

Don, I am sorry to hear that you have these problems. However, to me this is very strange.

Imagine, I use a GPS in my Lexus for more than 6 years now (back than GPS?s were not as sophisticated as they should be now!) In all this time of driving around a very congested Europe (Belgium, Holland, Germany, UK, Austria, Switzerland, etc.) with lots of industry, antennas and the like, I have not had one ?lost satellites? message or anything similar, ever, unless I was in an underground parking or a tunnel (but the moving map in the Lexus still keeps working on memory and input from the steering and the wheels), really.?. not ones, even between the mountains of Austria, or in a build up city like Frankfurt!

I use an Avmap EKP-IV for flying (so far as a knee-pad moving map in C-152/172,s), again never had any ?lost satellites? messages. In an other thread I mentioned that I tested the EKP-IV in my car trying to hide the antenna under my seat, but it still kept on going!

If the Garmin is skipping, is it because some of the satellites were out of order at the time? Or is it really only in certain spots, as you describe? What sort of signal could mess-up the GPS-reception?

I am really interested to hear what the problem is and if it could upset any GPS or if it is only a Garmin problem. Keep us posted.

Regards, PilotTonny

Thanks for your reply, Tonny.

I usually try to do an internet search before posting, but with a feeling of trying to help my friend as well as share my experiences, I went ahead and published my original post.

I just now did a Google search, and found the following. This is interesting reading and is even cause for more alarm, as it indicates some RF interference can originate from onboard avionics. As one poster on another group said, a 396 should be able to do handstands!

Here's one post I clipped from another discussion group. It sounds like the answer is from Garmin. Sure makes me wonder why a panel mount like a 430 doesn't have this problem. Maybe I need to go to an external antenna.
Here's the post and answer I found:

<SNIP>...
"The same reason my 196 loses reception, from Garmin's support database

"
Question: Why is my GPS losing satellites in the middle of my flight?
Answer:


Portable GPS units have the ability to experience loss of satellite
reception as a result of RF interference caused by a variety of
sources. These sources can be as simple as a portable MP3 Player used
for in flight entertainment to a ground based air traffic control
radar antenna on an airport. When these devices are powered on and are
in close proximity to the portable GPS or antenna, the GPS may lose
satellite acquisition as a result. Another common source of RF
interference is aircraft communication and navigation radios. When
certain radios are tuned to a specific frequency there is the
potential for enough RF interference to be released that the Portable
GPS unit will experience loss of satellite reception as though the
signals were being jammed. An article in the Aviation Consumer, dated
February 15th, 1994 has outlined a list of aviation communication
radios and frequencies that may cause a portable GPS unit to lose
satellite reception in the aircraft. This information is listed below.


Radio Frequencies That May Jam GPS Receivers.


Transmit 131.285 and 121.186 Receive


Narco MK 12D/E Com 810/811, Nav 824/825 Com 131.220 and 119.285 Nav
115.464 and 109.672


King KX 155/165 Com 131.820 and 119.885 Nav 116.128 and 109.564


King KX 170/175 Com 122.285 and 130.186 Nav 113.651


Collins Microline Com 132.720 and 120.785 Microline Nav 116.028 and
109.464


Notes: KX 155/165 transmitting on 118.15 ws shown to jam an external
mounted antenna. Narco MK 16 tuned to any 115 or 109 Nav channel was
shown to jam a hand held GPS. Narco MK 12D/E and Nav 824/825, if not
wired with memory keep alive, will default to 115.5 MHz in the active
channel and will jam any GPS receiver. "...<SNIP>

Don

Info.
 

My 496 seems to work as expected.
My friend just sent his 396 back for a warranty repair.
He could only get one sat. even after changing the antenna, yet his GX60 was working just fine. He call Garmin and was told to send it in for a free repair.

Kent

I would expect electronics in airplanes to be more susceptible to interference from transmitters on towers than automobiles on the ground. The antenna is usually up high on the tower and has gain such that the strong part of the signal would tend to shoot over a ground vehicle that is near the antenna. That same gain might shoot right at an aircraft, especially at lower altitudes.

I can't see where one brand/type of GPS should be more or less affected than another, BUT I have had no dropouts in over 100 hours flying my RV with and AvMap IV, nor ever with it in other aircraft before finishing the 9A. I did have dropouts with a 196 in a Cessna 180 and the owner said to just switch off the alternator for a moment and it would come back. Very strange. There are things we aren't meant to understand...

Bob Kelly

Antennae
 

If you are using the 396/496 with it's built in antenna, you might experience much better reception with an external amplified antenna.

There is no gain in the attached antenna. One of the non-WAAS antennae being removed from 430/530 installations that are being upgraded might improve things. These GA-56 antennae are amplified.

In general, bigger is better for antennae...:) ...and if you can't make it bigger, add gain....:)

gil A

GPS Question to Dan Checkoway
 

Dan,
I hope you are following this thread. I'd be interested in knowing if you ever have any "Lost Satellite Reception" messages with your antennas mounted below the fiberglass panels you fabricated.
Thanks,
Don

Thanks for the reply, Gil. I'm not using the attached antenna but rather the one that has the length of cable for mounting on the glareshield. I have it velcroed in place.

I notice the GA-56 lists for $385 but is available for $100 on ebay. I'm still interested in using what Garmin supplied with my GPS.

Don

Deep South Mystery
 

Hmmm... My wife and I were on vacation week before last, driving on the interstate between Mobile and Montgomery, Alabama. My PDA based road nav system dropped out several times. The drops were around 10 minutes at freeway speeds. I noticed the satellite reception signal LED on the receiver was not showing a singnal.