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[November 11, 2020]


All of my GPS antennas are in a tight cluster in front of my firewall, under my cowl. Recently I have started to have GPS degradation issues with the Garmin GTN650 - it would lose GPS signal on nearly every flight. Some people claim the antenna gets too hot under the cowl and it shortens the life. My plan is to relocate the antenna to the top of the fuselage.


Before I got to the GPS antenna relocation project, my oil temp sensor has been acting up. GRT said it is a known issue, and they do have a new temperature sensor which fixes these having a short life (250 hours). However, the new sensor requires a $250 upgrade to the EIS. New compatible sensors cost me $50 each every 4-5 years, so that's a no brainer!


To put my Garmin GPS antenna on the rear deck of the fuselage required me to run a new RG400 coax run. That is a lot of work and a lot of inspection panels that need to be removed. I came up with the idea of reusing the marker beacon antenna wiring I had out to the right wingtip. I clipped the end of this cable off and pulled it back through the wing into the fuselage.


Here is the other end at the audio panel. I clipped the end off of this also and put a TNC connector on it and had it connected to the back of the GTN650 GPS receiver.


I wanted to make sure this wire and my connections were good so I put a temporary end on the cable and connected it to the antenna.


Good sign, the GTN saw some birds in the sky.


Hmm, this is interesting. My PFD's screen was all garbled. It resolved itself after a reboot.



I decided to put the GPS antenna on the rear deck, about 3" back from the aft canopy. There is already a doubler here. I couldn't mount the antenna centerline, as the 5/8" hole for the TNC antenna connector would run into the webbing of the rib. So I needed to offset the centerline by 1/16"


All of the measurements drawn and triple checked.


The edge distance between those two rivets and the GPS passthrough hole is a little close.


Here the antenna is installed. Turned out really really well if you ask me. It's almost on centerline - 1/16" offset due to interference under the skin.


Wow, look at all of them birds! Reception seems to be great. If I was smart, I would of done a complete comparison of before and after. Oh well, let's hope this resolves the issues I have been having with losing GPS reception.

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Last Modified: November 11, 2020