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06-02-2014, 03:07 PM
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Join Date: Apr 2009
Location: Sammamish, WA
Posts: 208
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GTN-650 problem
Hey Guys,
I am having a really funny thing happen to my GTN-650. Not sure if others have seen it. For a while now that the weather is getting warmer on taxi out to the runway I would always loose GPS for about 30 seconds. Didn't think much about it, but one day I was taxiing without my headset on.
The GTN Fan Kicked on and boom, lost GPS. So it has been happening with the warmer temps, when the fan kicks on I loose GPS for a short time.
This seems really scary to me for a TSO'd IFR GPS, any thoughts on this problem? Has this happened to others?
Thx
__________________
Chad
Sammamish, WA
RV-7 Standard Build - Tip UP
Flying ! As of 032913
Superior IO-375, WW200RV, Single Lightspeed, SkyView, GTN
http://www.704ch.com/
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06-02-2014, 05:29 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,642
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I have noticed the fan kicking on a lot more lately, but I have yet to see it take out the GPS signal.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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06-02-2014, 07:48 PM
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Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
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Never noticed any issues with the fan and GPS signal.
I would check your antenna, antenna connections, antenna location etc.
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06-03-2014, 05:23 AM
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Join Date: Feb 2010
Location: Boston
Posts: 37
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I've had the same issue twice inflight, in an R44 helicopter. Didn't think of heat, but that could well explain it.
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06-03-2014, 05:47 AM
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Join Date: Sep 2011
Location: Edgewater, FL. KSFB
Posts: 1,116
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I believe there have been other conversations about the antenna getting hot and loosing reception. Funny that it happens for you at the same time as the fan.
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06-03-2014, 06:28 AM
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Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,165
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I wonder if the motor on the fan is creating interference with the GPS signal. How far is the antenna from the fan? Turning on the AFS 4500 near our 696 reduces signal strength in half. It does not take much EMI to disrupt a GPS signal.
George
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06-03-2014, 07:23 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,642
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In addition to the antenna placement, do you have the specified antenna cable length, and is it coiled up under the boot cowl?
As a point of reference, my antenna is on my canopy, right at my shoulder. The cable snakes around a little bit in an attempt to use up the excess length, but it isn't coiled on itself anywhere.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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06-03-2014, 01:05 PM
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Join Date: Aug 2009
Location: Goodyear, Arizona
Posts: 875
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My antenna is firewall forward under the cowl on a shelf next to my Dynon antenna. The Dynon GPS has never lost a signal, but the Garmin occasionally loses lock and takes a minute or two to re acquire. I never considered temperature as a cause. Is there something in writing from Garmin on this topic??
__________________
Karl, Goodyear, Arizona (KGYR) ATP, CFII
RV-14A, Flying
Extra 330LX, Flying
RV-8, Sold
RV-7, Sold
Bearhawk 4-Place, Sold
=VAF= donor 2020
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06-03-2014, 01:33 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,642
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The TSO requires something like a 60 inch minimum (don't quote me) antenna lead, AND a 3 sq ft ground plane. I just ran across the ground plane requirement in the installation manual the other night. With so many roll bar and engine mounted GPS antenna's (no ground plane), I had not considered this before.
Don't know if this is a factor or not, but it may drive me to move my antenna if I ever get serious about IFR flying.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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06-04-2014, 03:29 PM
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Join Date: Jan 2005
Location: Olney, Texas
Posts: 143
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No problem with mine, yet.
__________________
Brent Colvin VAF#147
RV 7 0-360 CS Flying
Comm, Multi, Inst. 
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