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  #1  
Old 08-10-2018, 01:06 PM
Bavafa Bavafa is offline
 
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Default Sharing G3X GPS antenna with G5

Just wondering if anyone has shared the same GPS antenna from a G3X with G5 successfully. I was thinking of using a splitter to extend the GPS antenna to the G5 instead of yet another antenna so it can work all independently which is it sole purpose to be my back up instrument.

I highly doubt that the internal antenna in the G5 will receive any signal considering that it has lots of metal above it.
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  #2  
Old 08-10-2018, 02:45 PM
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Ed_Wischmeyer Ed_Wischmeyer is offline
 
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Default

The G5 works just fine in the panel of my RV-9A.
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  #3  
Old 08-10-2018, 02:53 PM
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uk_figs uk_figs is offline
 
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Default another data point

I do not have the G5 but have had the 796 in my panel for years and did not wire up the external GPS puck, I have never had an issue with GPS reception with the internal antenna, also drives the GDL39 3D with no errors or problems.
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  #4  
Old 08-10-2018, 02:54 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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Default

Quote:
Originally Posted by Bavafa View Post
Just wondering if anyone has shared the same GPS antenna from a G3X with G5 successfully. I was thinking of using a splitter to extend the GPS antenna to the G5 instead of yet another antenna so it can work all independently which is it sole purpose to be my back up instrument.

t.
This is not a trivial question. These days most GPS antennas have a pre-amp inside them, powered by dc coming up the coax. You need to:
Make sure the dc gets by the splitter.
Make sure the dc power in the two boxes donít fight each other.
Make sure the pre-amp gain is compatible with both boxes.

Since these are both Garmin, G3Expert can probably answer your question.
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  #5  
Old 08-10-2018, 03:09 PM
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RV6_flyer RV6_flyer is offline
 
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Location: NC25
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Quote:
Originally Posted by Ed_Wischmeyer View Post
The G5 works just fine in the panel of my RV-9A.
Both G5 GPS in my RV-6 Slider work find without external antennae except for when doing step pitch and or bank maneuvers.

One typically should try to avoid sharing GPS antenna with more than one GPS receiver.
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  #6  
Old 08-10-2018, 05:02 PM
Bavafa Bavafa is offline
 
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Thank you folks, I am still months away but just finishing the wiring and thought if it would make sense to add an antenna feed to the G5. I will try it without and see if it works OK with its internal GPS.
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  #7  
Old 08-10-2018, 06:22 PM
jump4way jump4way is offline
 
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Location: Coolidge, AZ
Posts: 285
Default Rs-232

I believe you can share rs-232 position data from a gtn or G3X. Itís worth looking in to at least. Itís one wire to run.
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  #8  
Old 08-10-2018, 06:41 PM
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g3xpert g3xpert is offline
 
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Post

Quote:
Originally Posted by Bavafa View Post
Just wondering if anyone has shared the same GPS antenna from a G3X with G5 successfully. I was thinking of using a splitter to extend the GPS antenna to the G5 instead of yet another antenna so it can work all independently which is it sole purpose to be my back up instrument.

I highly doubt that the internal antenna in the G5 will receive any signal considering that it has lots of metal above it.
Hello Mehrad,

We don't recommend GPS antenna splitters, but you have lots of options to consider for the G5.

First and best is to enable the internal WAAS GPS receiver and have an external antenna (glareshield or top of aircraft) connected to the G5. This gives you the most independence and provides the best performance when everything else is unavailable or load shed in a power emergency.

If you want to see how well your internal antenna, glareshield, or externally mounted antenna is working with your G5, you can pull your aircraft outside and use the GPS Configuration page in config mode to tell you if your installation is adequate. Note that this test is only for those using the G5 internal WAAS GPS receiver.

The G5 has a very sensitive WAAS GPS receiver, and will almost always have enough signal to receive a 3D or 3D Differential fix to be able to determine and display the basic track and ground speed information, but having the high quality signal necessary for the G5 to use GPS data to improve the attitude measurement is something quite different.

Here is an example of a poor installation that would still provide the basic GPS data on the display.



The G5 can operate without a GPS (see below), but for the best performance, you want to have a 3D or 3D Differential fix with a green check mark shown next to the fix type. If you do not see this green check mark on this page, your installation needs improvement.



You can also disable the internal GPS receiver on the G5 and rely on GPS data provided by the G3X/G3X Touch system (over the CAN bus), or the connected WAAS GNS/GTN using MapMX over RS-232. These are not quite as good as the external antenna since you are reliant on one of these data sources being available at all times for the best performance.

Also keep in mind that in the worst case scenario when the G5 has no GPS data of any kind to use, it falls back to degraded mode operation using air data to correct for attitude sensor drift.

When we fly the 2+ hours of degraded mode flight tests to satisfy DO-334 TSO requirements, we disable the internal G5 GPS receiver, and shut down any external MapMX data being provided by GTX/GNS/GTN and also disable G3X provided GPS data. The DO-334 maneuvers are designed to challenge an ADAHRS while it is using an alternate means of aiding (in this case air data).

Whew, long answer to a simple question.

Thanks,
Steve
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Last edited by g3xpert : 08-11-2018 at 10:28 AM.
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