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[February 9, 2013]


Last week my dad and I went flying. Right after takeoff, my Garmin 430W gave me a warning message stating it lost GPS. I banked pretty hard on my turn to crosswind, so I assumed that it just lost site of the GPS's for a second and would recover quickly - which it normally does. However, I was flying for a few minutes and noticed my position on the GRT EFIS's map wasn't changing - it was still saying I was over KDMW. I noticed the Garmin 430W didn't recover from losing GPS signal.

Two things disturbed me here - one is my very expensive GPS wasn't working, and the other is why the GRT didn't work with my second GPS puck.

Today I set out to try to figure out what was going on with both issues. I was easily able to reproduce the GPS losing it's signal. With the RV pulled out of the hangar I received this message.


I tried wiggling the GPS wire into the antenna but it seemed secure, and the issue continued. I decided to then pursue why I couldn't navigate with the GPS #2 on the GRT's. I had two issues. One was my GPS2 Flight Plan Source was set to External, so I couldn't use the flight planning feature with it. The other issue was I needed to select GPS2 as my nav source. I simulated the issues I had last week and was able to get things working.


You can see from this picture how weak my GPS signals are. I tried everything and came to the conclusion either the GPS unit needed to go in for maintenance, or I had a bad antenna.


I powered off the master (the 430W runs off of the aux battery which was still on) and boom - the GPS signals quickly came up to full strength. I don't think I've ever seen them this high. I turned on the master and they all disappeared. So something was on the Main bus which was causing interference. My first though was it was the GRT engine monitor. I disconnected it and nothing changed. The only other thing I could think of which is powered by the main bus and not switchable was my second GPS - a puck mounted next to the 430W antenna. Sure enough, when I disconnected the power to it I could flick on the master and the GPS signal was still solid.


My GPS2 is mounted very close to the Garmin 430W antenna - I know Garmin recommends the other GPS antennas be located away, but I didn't know it caused this much interference.


I had a bunch of slack under the panel for this GPS antenna so I pulled it through to forward of the firewall. Even at 2' away, the GPS2 antenna still knocked out the Garmin 430W reception. I think something must have done wrong with this antenna for it to cause this much interference.


Just for grins, the only other GPS antenna I had was in my iPad. I opened up ForeFlight to make sure I had a GPS lock, and placed the iPad right next to the Garmin 430W antenna. No signal degradation was seen on the 430W.

So I am going to replace my GPS#2 antenna with a Garmin 18x GPS puck. Hopefully that will fix my GPS issues.

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Last Modified: September 4, 2017