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  #1  
Old 01-19-2021, 10:29 AM
hpmicrowave's Avatar
hpmicrowave hpmicrowave is offline
 
Join Date: Nov 2007
Location: Fort Walton Beach, FL
Posts: 98
Default When All your GPS systems have No Signal?

Just before my 1st RV8 test flight at the start of a simple ground run all the GPS systems in my RV8 would not boot up (in total I think I have 5?). All the systems showed No GPS satellites and zero signal strength. To me this looked like a severe case of GPS Jamming (and it was)?? After some trouble shooting I found that when I turned off my GNS430W all the other GPS systems suddenly came back to life. I then swapped the GNS430 with one from another plane and same thing happened, all the GPS systems were dead?

Figuring an antenna cable or something went bad I did some testing and as best i could tell the antenna cable checked good, this only left the GA35 GPS antenna. I swapped a hockey puck $15 GPS antenna (I was using with my G5) with the GNS430W's GA35 antenna to the BNC connector on the 430 unit and it booted up normally and all the other GPS systems also. So my first RV8 test flights flew good using the $15 antenna on my 430. When I had my next chance I swapped the GA35 antenna with a GARMIN GA56 teardrop GPS ANTENNA (same hole pattern) using the same GA35 coax cable with a TNC to BNC adapter and again the 430 operated good.

In my GNS430W installation you can't just turn off your 430 NAV/GPS and leave the COM system operational, If I was on the road and experienced this problem and was able to trouble shoot as far as I did just swapping antennas would have been difficult since all my GPS systems use a different coax connector (TNC or SMA). So what would have been the fall back solution would be to just disconnect the GA35 antenna from the 430 (I didn't test this) to allow the Comm Radio to remain functional but not allow the 430 GPS to Jam all the other planes GPS receivers. I would think the VOR/ILS would also remain functional. The GA35 TSO'd GPS antenna currently sell for $309 on Aircraft Spruce. And yes they are the worse performing GPS antennas I have on either of my planes.

I have asked several avionics folks if they had ever seen a Garmin GPS antenna go this bad before and they all said No, so lesson learned is that GPS systems are far from being bullet proof and some of your most expensive trustworthy avionics can turn on you in surprising ways. So take this story as a documented worst case of what can go wrong with your TSO'd Garmin IFR rated GPS antenna and how it can affect all your GPS systems. I've not seen any Garmin published GPS failure mode that addresses this type of failure that will JAM all your GPS systems at once.

I'll let you know if Garmin wants this antenna back to analyze it and adds total GPS systems jamming as a possible GA35 failure mode?
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Cecil "TRON"
RV8 N95CH In Phase 1 !!
RV6A Flying with Son Chris
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Sling 4 TSI Tail Done, Fuselage next
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  #2  
Old 01-19-2021, 10:33 AM
Pdtofly Pdtofly is offline
 
Join Date: Jan 2012
Location: Reno, NV
Posts: 483
Default GA35 antenna’s have gone bad

Cecil,

Years ago, Garmin had a batch of GA35 go bad in different ways. Call them up, and give them the serial number and see if it was in that batch. They were replacing them free for awhile. Never hurts to ask.

Good luck.

Brian

Last edited by Pdtofly : 01-19-2021 at 10:36 AM.
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  #3  
Old 01-19-2021, 10:40 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 5,747
Default

Welcome to the club! I had mine (GA35) go out on the end of an IFR flight plan. Fortunately I was close to the airport and used for flight to get close then cancelled and landed VFR.

Brantel has some posts here about this happening and the failure will emit a jamming signal for other GPS antenna close by - like 18". I don't know the precise distance, but 4 ft is good.

Garmin may be nice to you, but you wont get a new antenna. Just order a new one.
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RV-7
Lord Kelvin:
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cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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  #4  
Old 01-19-2021, 11:00 AM
molson309 molson309 is offline
 
Join Date: Jul 2009
Location: Longmont, CO
Posts: 242
Default

This happened to me a couple of years ago. I replaced the antenna and this solved the problem.

That failure really got my attention - it was disconcerting to have all my GPS receivers go offline at the same time.

Could have been been a high pucker factor failure if flying IFR.
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  #5  
Old 01-19-2021, 05:02 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,180
Default

Yes, this is a known failure mode. This antenna, like many others, contains active electronics, and certain failures can cause them to emit an interfering signal. This is why I recommend not installing them under the cowl (too hot), and keeping gps antennas as far apart as possible. I know, lots will reply that they’ve never had a problem, but it only takes once, at the wrong time/place,...
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  #6  
Old 01-20-2021, 07:52 AM
g3xpert's Avatar
g3xpert g3xpert is offline
 
Join Date: Sep 2010
Location: Olathe, KS
Posts: 2,956
Default GA 35 Antenna

Quote:
Originally Posted by hpmicrowave View Post
Just before my 1st RV8 test flight at the start of a simple ground run all the GPS systems in my RV8 would not boot up (in total I think I have 5?). All the systems showed No GPS satellites and zero signal strength. To me this looked like a severe case of GPS Jamming (and it was)?? After some trouble shooting I found that when I turned off my GNS430W all the other GPS systems suddenly came back to life. I then swapped the GNS430 with one from another plane and same thing happened, all the GPS systems were dead?

Figuring an antenna cable or something went bad I did some testing and as best i could tell the antenna cable checked good, this only left the GA35 GPS antenna. I swapped a hockey puck $15 GPS antenna (I was using with my G5) with the GNS430W's GA35 antenna to the BNC connector on the 430 unit and it booted up normally and all the other GPS systems also. So my first RV8 test flights flew good using the $15 antenna on my 430. When I had my next chance I swapped the GA35 antenna with a GARMIN GA56 teardrop GPS ANTENNA (same hole pattern) using the same GA35 coax cable with a TNC to BNC adapter and again the 430 operated good.

In my GNS430W installation you can't just turn off your 430 NAV/GPS and leave the COM system operational, If I was on the road and experienced this problem and was able to trouble shoot as far as I did just swapping antennas would have been difficult since all my GPS systems use a different coax connector (TNC or SMA). So what would have been the fall back solution would be to just disconnect the GA35 antenna from the 430 (I didn't test this) to allow the Comm Radio to remain functional but not allow the 430 GPS to Jam all the other planes GPS receivers. I would think the VOR/ILS would also remain functional. The GA35 TSO'd GPS antenna currently sell for $309 on Aircraft Spruce. And yes they are the worse performing GPS antennas I have on either of my planes.

I have asked several avionics folks if they had ever seen a Garmin GPS antenna go this bad before and they all said No, so lesson learned is that GPS systems are far from being bullet proof and some of your most expensive trustworthy avionics can turn on you in surprising ways. So take this story as a documented worst case of what can go wrong with your TSO'd Garmin IFR rated GPS antenna and how it can affect all your GPS systems. I've not seen any Garmin published GPS failure mode that addresses this type of failure that will JAM all your GPS systems at once.

I'll let you know if Garmin wants this antenna back to analyze it and adds total GPS systems jamming as a possible GA35 failure mode?
Good Morning,

As mentioned above, this is a known issue with these antennas should they be torqued beyond the recommended 12-15 inch-pounds. Trek reviews some of our history with it in this post. Since the initial investigation and result, our supplier has improved the housing of the antenna, so that even in the event it is slightly over-torqued, this should not happen. When was this antenna purchased? If you email our Product Support group at G3Xpert@Garmin.com we can help get it swapped out.

Thanks,

Justin
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  #7  
Old 01-20-2021, 02:34 PM
Bill Boyd's Avatar
Bill Boyd Bill Boyd is offline
 
Join Date: Sep 2006
Location: Landing field "12VA"
Posts: 1,612
Default

Glad you found the trouble - but in FL these days it could be layers-deep:
https://www.militarytimes.com/news/y...ence-says-faa/
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  #8  
Old 01-20-2021, 11:50 PM
hpmicrowave's Avatar
hpmicrowave hpmicrowave is offline
 
Join Date: Nov 2007
Location: Fort Walton Beach, FL
Posts: 98
Default GA35 Antenna

Thanks Justin, I have contacted Garmin via e-Mail. The malfunction certainly seems to be what you discussed but I don't believe I over torqued the antenna install, this was the 5th GA35 I have installed with no previous issues, and this antenna has been installed and operational on my RV8 for over 3 years during the build process and several ground test runs. Anyway something definitely went bad inside of it.
__________________
Cecil "TRON"
RV8 N95CH In Phase 1 !!
RV6A Flying with Son Chris
Member, FlyOnSpeed Team
Sling 4 TSI Tail Done, Fuselage next
2021 Dues Paid, Home Field 18FD
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  #9  
Old 01-21-2021, 07:09 PM
GalinHdz's Avatar
GalinHdz GalinHdz is offline
 
Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 2,129
Default

Quote:
Originally Posted by Bill Boyd View Post
Glad you found the trouble - but in FL these days it could be layers-deep:
https://www.militarytimes.com/news/y...ence-says-faa/
I am based at St. Augustine, FL and see this happening once in a while even with little to no notice. THAT is one big reason why I made sure my airplane was ILS capable.

FAA Flight Advisory - GPS Interference Testing, Carrier Strike Group Four.


BTW, it has been extended till Jan 27th.

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Last edited by GalinHdz : 01-22-2021 at 06:42 AM.
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