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  #1  
Old 06-04-2021, 09:00 AM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
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Default GPS Antennas Mountings

OK, there have been great debates in other forums about mounting GPS antennas to various surfaces. Most of these discussions are off track from the original thread topic. So here is my question:

With an RV7(a) / 9(a) slider, will the Garmin antennas fit on the rear fuselage skin so that the slider can slide over them?
Or do the Garmin GPS antennas need to be located aft of the rear of the slider when fully opened?
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  #2  
Old 06-04-2021, 09:21 AM
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mburch mburch is offline
 
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Default

There's plenty of room on the F-7112 top skin for multiple antennas, as long as you don't mount them too far forward: https://www.rv7blog.com/2009/10/31/gps-antennas/

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  #3  
Old 06-04-2021, 10:22 AM
DavidHarris DavidHarris is offline
 
Join Date: May 2018
Location: Upland, CA
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I built an RV-7A with a slider and SuperTracks. I placed an Avidyne GPS antenna, a Dynon GPS antenna, and the ELT antenna on the top of the rear fuselage close to the vertical stabilizer, with reasonable spacing between the components to limit interference.

I don't think the canopy would have slid over my GPS pucks if they were further forward.

David
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  #4  
Old 06-04-2021, 10:49 AM
Flyingleap Flyingleap is offline
 
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Location: Cincinnati,Ohio KHAO
Posts: 145
Default Garmin GPS antenna mounting

Garmin install manual of GPS 35 antenna:

"To maintain a constant gain pattern and limit degradation by the windscreen, avoid mounting the antenna closer than three inches from the windscreen"

I believe that includes the canopy. John
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  #5  
Old 06-04-2021, 11:37 AM
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bjdecker bjdecker is offline
 
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Quote:
Originally Posted by Flyingleap View Post
Garmin install manual of GPS 35 antenna:

"To maintain a constant gain pattern and limit degradation by the windscreen, avoid mounting the antenna closer than three inches from the windscreen"

I believe that includes the canopy. John
Gotta ask "Why?" -- Probably because the aircraft that was used in the certification process had a heated windscreen and that caused some reception issues...(as a wag.)

Otherwise, I don't understand how a micro-stripline/ceramic antenna is going to be adversely affected by the canopy.

We're experimental; so experiment with it.
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  #6  
Old 06-04-2021, 11:57 AM
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bruceh bruceh is offline
 
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I'm looking into adding a Garmin GPS175, and it uses the GA-35 antenna. The install instructions suggest outside on the top of the fuselage is best. I already have my Dynon GPS antenna up there and the new GA-35 antenna would have to be 6" from that, and not on the same centerline. I thought about mounting it under the cowling, but I don't really have the room there, and it will bake. The installation instructions don't preclude putting it in a wing tip, so I think that is going to be my solution. The right wing tip has plenty of space, no other antennas, and can be kept cool. I just will need to fabricate a mounting bracket and get the antenna leveled and be at least 3" away from the wing skin.
The only downside I can see is my approaches might be 14' off of the centerline to the left.
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  #7  
Old 06-04-2021, 12:12 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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Quote:
Originally Posted by bjdecker View Post

We're experimental; so experiment with it.
Experimenting is great; just be careful to account for all the variables before reaching a conclusion. e.g., a lot of folks throw the antenna somewhere, say ‘it works’ and move on. Then comes the day where the satellite geometry isn’t great, there’s a lot of sunspot activity, and they don’t understand why the gps fails....
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  #8  
Old 06-04-2021, 12:25 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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Quote:
Originally Posted by bruceh View Post
I'm looking into adding a Garmin GPS175, and it uses the GA-35 antenna. The install instructions suggest outside on the top of the fuselage is best. I already have my Dynon GPS antenna up there and the new GA-35 antenna would have to be 6" from that, and not on the same centerline. I thought about mounting it under the cowling, but I don't really have the room there, and it will bake. The installation instructions don't preclude putting it in a wing tip, so I think that is going to be my solution. The right wing tip has plenty of space, no other antennas, and can be kept cool. I just will need to fabricate a mounting bracket and get the antenna leveled and be at least 3" away from the wing skin.
The only downside I can see is my approaches might be 14' off of the centerline to the left.
Do the installation instructions specify a maximum allowed length of RG400?
Do you have a strobe light out there? Might check it for interference (Look at signal strength page, strobes off. Turn them on, see if any signals go down).
If you use this gps for adsb-out position, you do have to enter the offset in your set-up table.
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  #9  
Old 06-04-2021, 12:35 PM
Flyingleap Flyingleap is offline
 
Join Date: Nov 2012
Location: Cincinnati,Ohio KHAO
Posts: 145
Default Garmin 35 install

Garmin GPS antenna 35 to another 35: "spacing less than 9 inches center to center results in unacceptable antenna pattern degradation."

Not sure why. John
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  #10  
Old 06-04-2021, 12:44 PM
Flyingleap Flyingleap is offline
 
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Location: Cincinnati,Ohio KHAO
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Default RG400 length

Garmin GPS 35 length: The maximum Db loss must be calculated to be
1.5Db to 6.5Db. It cannot be less than 1.5Db. A 13ft RG400 with connectors is about 2.77Db, within specs in loss. A 14ft wing (9) and 6ft additional length
should be less than 6.5Db for the antenna mounted on the wing. I think max length is 35ft (RG400) with a minimum ground plane radius of7.5inches. John
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