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VHF kills GPS reception

Old 01-31-2007, 11:21 PM
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Default VHF kills GPS reception

After reading the thread on radar interference with GPS, I did an experiment. I went to the signal page on my Garmin chartplotters, and keyed the VHF. After about 4 seconds, satellite signals went from full strength on 10 satellites down to no reception. I have an 8' antenna on the t-top and it was in the up position. I don't talk on VHF much, so I'm not too worried, but in the event of a distress call, I can imagine a problem if I am not the one making the call. My GPS antennas are flush mounted on the t-top, 8 feet below the top of the VHF antenna, but the antenna cables run down the same pipe on the t-top as the GPS cables. It also knocks out my stereo, actually powering it off. Any ideas for a fix, maybe some type of inline filter like used in car stereos to reduce interference?
Old 02-01-2007, 12:30 AM
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Default RE: VHF kills GPS reception

it sounds to me like a power issue. are you able to disconnect power to your vhf, and try to run it off a seperate battery from the rest of the electronics temporarily? key up the mic after you have switched power sources and see if the rest of the electronics still drop out.
Old 02-01-2007, 12:17 PM
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Default Re: VHF kills GPS reception

If it is not a DC power problem, you may want to install better coax to the VHF and put some ferrite beads on the GPS cables. Something like Double Shielded RG8X.
Old 02-02-2007, 09:23 PM
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Default RE: VHF kills GPS reception

Your test was a good idea. I think many may find they have the same problem.

It is very poor design to locate a receiving antenna (GPS) near a transmitting antenna (VHF). You should separate them as far as possible. Even thought the frequencies involved are quite different, a strong RF field from a nearby transmitter can create problems for a receiver.

My GPS antenna is about 12-feet aft and 6-feet lower than my VHF antenna. I haven't noticed any interference, although I have not performed a test to check. I will next time I get the opportunity.
Old 02-02-2007, 10:15 PM
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Default RE: VHF kills GPS reception

From your sig pic it looks like the antenna separation is probably ok. A 1 or 2 ' VHF antenna mount extension (to get the GPS below the VHF) may take care of it. Had a similar problem with Raymarine Raystar 120 & 125 - except the GPS cut VHF reception.
Old 02-03-2007, 09:10 AM
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Default Re: VHF kills GPS reception

I added a lowrance 111c hd and have the gps antenna about a foot in front of my vhf, I have the same problem. My old Garmin antenna is about 4 feet away from the vhf and I never had a problem. I plan to also try the different power source to see if it cures the problem. Let me know if it works for you.

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