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I went flying last weekend and when I was turning crosswind, my Garmin 430W indicated the "Loss of GPS navigation - Dead Reckoning" message. I usually see this when I bank too much in a turn, so I assumed this was the case here. I acknowledged the message and kept on flying. A few minutes later I noticed my GPS location was not updating and the 430W still did not have valid GPS signals.



It was entirely too cold to debug the issue last week. 25 degrees in the wind is not my idea of fun. I had ForeFlight running on my iPad to get me back home and the airplane tucked in the hangar. During this past week I read about other people who have had similar issues. On VAF, Brantel had this intermittently happening to him and the end solution was a new antenna.

Today I got around to debugging the issue. Luckily I was easily able to reproduce it on the ground. The first thing I noticed was the signal strength for the satellites the 430W was picking up were quite weak. It reminded me of my first Magellan GPS 300 I had for my boat (too about 30 minutes to lock onto GPS). I checked the cabled ends to the antenna and the GPS unit and all looked fine. I was starting to get worried I would need to send my 430W into Garmin for expensive maintenance or buy a new antenna.



I was finished working on the plane and started switching off all of the devices. I turned off the Master, leaving just my auxiliary battery devices enabled (GRT EFIS's and the Garmin 430W). All of the sudden I saw my GPS signal strength increase significantly.



There were only a few non-switchable devices connected to my main bus - my Engine monitor and a second GPS. I disconnected each one and found the second GPS was interfering. I have it mounted right next to my Garmin 430W antenna, which I know Garmin warns against, but up until this point I haven't had an issue.



I tried to move the culprit antenna further away from the 430W antenna, but I still had a lot of interference even at a couple feet away!



So my theory now is this second GPS antenna (cheap Chinese Ebay antenna) has either been slowly releasing more interference over time or had an issue and crapped out all of the sudden (although it still does work). I've already placed an order for a Garmin 18x antenna to replace it. When it gets here, I will test the mounting locations to see the amount it interferes.

Thought I'd share my issue in case anyone else runs into it. I am very happy it seems to be a $60 fix instead of a $800+ fix!

Mike,

Sounds like your well on your way to a fix.

In my case my 430W antenna would kill everything else.

I am starting to think that the engine compartment is not a good place for these antennas....

Let us know how it goes....

Brian,

I agree that the temps in the engine compartment probably cooked my GPS puck. The specs for the Garmin 18X gps call for operating temps up to 176 degrees F, which I believe would be exceeded in the engine compartment. Strangely I could not find operating temperatures for the Garmin GA 35 antenna. The installation manual doesn't mention temps at all.

I am thinking about mounting my new GPS antenna on a shelf in the wingtip for a few reasons. First and foremost the temperature and environment would be better suited for the antenna. Secondly, if the Garmin 430W does malfunction and decide to take out other GPS's in the general vicinity, the new antenna would be far enough away so it wouldn't be an issue.

The new antenna is installed and it works perfectly. I decided on a Garmin 18x LVC. It was a little over $60. I was thinking about mounting it on the wingtip, but being only 25 degrees in the hangar, mounting it where the old one was sounded like a better decision!



The performance of the new antenna is awesome. 10 satellites acquired quickly. Also, I really liked how the GRT EFIS displayed the GPS name and software version.



Also, no interference was seen on the Garmin 430W. The airplane is buttoned back up and ready to go!

Mike,

I have been seeing deterioration in satellite acquisition too. Where did you get the new antenna?

Hi Bret,

GPSCity.com had the lowest shipped price I could find of $59.95:

http://www.gpscity.com/garmin-gps-18x-h ... y-lvc.html

However, I bought mine for $63.84 via Buy.com through EBay in order to use PayPal (I dislike giving my CC number to vendors I use one-time). Here is the Ebay link:

http://www.ebay.com/itm/NEW-Garmin-GPS- ... 5d3a297e27

Buy.com ships from the IL area for this item. Also, the Ebay item is the antenna with 5 meters of wire attached to it. Others ship with 3 meters.

Thanks Mike,

I assume the connector is the same as the stock 430W GPS antenna. I was hoping to just replace the antenna and re-use the cable.

Bret,

The Garmin 18x antenna is a self contained received - it has about a half dozen wires which are used for 5V, Ground and the NMEA data stream. Sounds like you need a different antenna. If you are looking to replace the Gamin WAAS antenna for the 430W, you will need a GA 35 antenna. They are quite a bit more expensive!