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  #11  
Old 06-04-2021, 12:53 PM
bjdecker's Avatar
bjdecker bjdecker is offline
 
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 800
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Quote:
Originally Posted by Flyingleap View Post
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
Potential RMI/EMI from the LNA in GPS35.
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Retired Firmware Guy and Airplane Builder

2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.
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  #12  
Old 06-04-2021, 01:00 PM
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bjdecker bjdecker is offline
 
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Location: Georgetown, TX
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Quote:
Originally Posted by BobTurner View Post
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....
More likely to run into a forced error (i.e. GPS "testing" at WSMR or Kingsbay) than a geometry problem given the size of the constellation these days...

But, your point is well taken. Good scientific method should be applied, generate a hypothesis, test, create repeatable/verifiable data, make a determination thusly...
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Brian Decker
Retired Firmware Guy and Airplane Builder

2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.
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  #13  
Old 06-04-2021, 01:06 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,562
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Quote:
Originally Posted by Flyingleap View Post
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
Ever see a (old fashioned) TV antenna up on a roof, with lots of horizontal aluminum elements with no wires attached (except to one)? Those aluminum pieces are sized to resonate near the TV signal; they pick up the signal, re-radiate it with a phase off-set. Net effect is to make the antenna directional. Same thing can happen with two gps antennas too close to each other. In some directions reception will be better, but in others, worse.
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  #14  
Old 06-04-2021, 03:20 PM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
Posts: 1,578
Default Thanks

Quote:
Originally Posted by mburch View Post
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/

Thanks for the picture. I will do the same thing, but might forgo the doublers and just use a strip of z-channel bonded to the inside. It is very strong up there since it is between the longerons. i will have to see.

I wish I would have seen this picture a year ago; then I would have put the doublers in when I did the ELT doubler.
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WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

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  #15  
Old 06-09-2021, 01:45 PM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
Posts: 1,578
Default Full Circle

I really like Matt Burch's picture.
It forced me to actually measure the clearance between the canopy and the GPS antennas.
I have mounted mine on the top of the fuselage, just like Matt's.
Thank you, Thank you, Thank you.
Did i say how happy I am with the feedback?
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John S

WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

Dues paid 2021, worth every penny

RV9A- Status:
90% done, 90% left to go
Firewall Forward 5% in work
Fiberglass 0%, thought i was building in metal?
www.pilotjohnsrv9.blogspot.com

Last edited by PilotjohnS : 06-09-2021 at 01:48 PM.
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  #16  
Old 06-09-2021, 01:48 PM
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wirejock wirejock is offline
 
Join Date: Oct 2005
Location: Estes Park, CO
Posts: 4,540
Default Supertracks

If you plan the Supertracks, measure the additional length of the canopy slider. It's about an extra 12"
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Estes Park, CO
wirejock at yahoo dot com
Donated 01/01/2021, plus a little extra.
RV-7A #73391, N511RV reserved (2,000+ hours)
Empennage, wings, fuse, finishing kit, now FWF
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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  #17  
Old 06-09-2021, 02:04 PM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
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Default Actually

Quote:
Originally Posted by wirejock View Post
If you plan the Supertracks, measure the additional length of the canopy slider. It's about an extra 12"
Actually, i have the Supertracks slider track installed. I mount the two antennas on either side of the track, one forward and one towards the back of the first "bay".

I have about 14 inches between them.

I made the Garmin doublers and used them to hold the nut plates, but didn't rivet them to the skin. they should be OK.
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John S

WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

Dues paid 2021, worth every penny

RV9A- Status:
90% done, 90% left to go
Firewall Forward 5% in work
Fiberglass 0%, thought i was building in metal?
www.pilotjohnsrv9.blogspot.com
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