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  #51  
Old 02-13-2021, 10:05 AM
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byoung byoung is offline
 
Join Date: Mar 2011
Location: Remond WA
Posts: 35
Default Why wouldn’t aft of the canopy be the default position?

Seems to me that aft of the canopy on top of the airplane would be best spot for the GPS antenna. Other then running the coax back there, what would be the downside? Getting the necessary separation from the com antenna that will likely be back there also shouldn’t be an issue.
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  #52  
Old 02-13-2021, 10:49 AM
Jimzim Jimzim is offline
 
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Location: Arvada, CO
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Default Another option

I mounted mine on top of the crossbar which supports the seat backs in the RV 7. In other words, just aft and inboard of the pilots right shoulder. You’ll see the spot. Hope that makes sense. Great performance and easy install, FWIW.
Jim
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  #53  
Old 02-13-2021, 04:45 PM
Flying Canuck Flying Canuck is online now
 
Join Date: Jan 2015
Location: Red Deer, Alberta, Canada
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Default

Finally braved the cold (still around -22C) and went out to the hangar to decide on my antenna mounting location. I've decided to mount it on top of the left front access panel. Will make for an easy installation and check all of the boxes from Garmin's recommendations. I'll install it on Monday along with my GPS 175. Already mounted my SV-ARINC-429 module. Then comes the documenting for the purpose of removing the VFR only operating limit.

Thanks for the lively discussion here, it was very interesting. Not quite primer wars, but close.
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  #54  
Old 02-18-2021, 11:23 PM
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RV7A Flyer RV7A Flyer is offline
 
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Location: US
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Default

Quote:
Originally Posted by Jimzim View Post
I mounted mine on top of the crossbar which supports the seat backs in the RV 7. In other words, just aft and inboard of the pilots right shoulder. You’ll see the spot. Hope that makes sense. Great performance and easy install, FWIW.
Jim
If it works, it works, but it seems like a really big chunk of sky would be masked by the aft top skin, rear bulkhead, and a bit of the sides where the skins curve downwards. Which antenna? The SV-250 or -2020?
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  #55  
Old 02-18-2021, 11:28 PM
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RV7A Flyer RV7A Flyer is offline
 
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Location: US
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Quote:
Originally Posted by olyolson View Post
With the old non WAAS antenna for the GNS 400 I used to have I never had an issue with GPS reception. As stated in my earlier post, I have been getting GPS dropouts occasionally with the new WAAS antenna for the new GTN 650. Based on what someone said about needing some rearward view of the WAAS antennas for gps reception I looked at my antenna mount. Yep- the WAAS is mounted butted right up against the firewall and actually sits a little underneath the mounting lip for the top cowl.

Thanks to Ironflight, “I suffered lots of drop-outs due (I was told by experts) to the fact the view of satellites to the rear was obstructed by the firewall”- this is exactly what happened to me.

I think I’ll leave it on top of the engine bay just under the top cowl but modify the bracket and move it forward.

Thanks for the as always great info from the forum
When you guys say "dropouts", do you mean loss of all signals? Or degradation of position accuracy? The raw GPS position calculation only needs 4 satellites to get XYZt. I suppose maybe the rearward mask might block the view to a WAAS satellite, which could mess it up, but I'm having trouble envisioning why the GPS solution as a whole would "drop out". Even if you masked a sizeable chunk of the rear view, there are always plenty of GPS sats in view overhead, forward and to the sides to get a fix...

Just piqued my curiousity a bit....
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  #56  
Old 02-19-2021, 08:21 AM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by RV7A Flyer View Post
When you guys say "dropouts", do you mean loss of all signals? Or degradation of position accuracy? The raw GPS position calculation only needs 4 satellites to get XYZt. I suppose maybe the rearward mask might block the view to a WAAS satellite, which could mess it up, but I'm having trouble envisioning why the GPS solution as a whole would "drop out". Even if you masked a sizeable chunk of the rear view, there are always plenty of GPS sats in view overhead, forward and to the sides to get a fix...

Just piqued my curiousity a bit....
In my case “dropouts” include everything from a message on the IFD 440 saying “GPS Integrity Lost” with continued good position data for the pilot to complete loss of GPS signal and the IFD going into “Ded Reckoning” mode. Now to be completely up front, this most often happens when I have done something that the FAA “system” didn’t expect, like going upside down, which is perfectly legal, but the guys who designed ADS-B didn’t;t appear to anticipate.....

Paul
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  #57  
Old 02-19-2021, 08:55 AM
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bjdecker bjdecker is offline
 
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Quote:
Originally Posted by Ironflight View Post
... like going upside down, which is perfectly legal, but the guys who designed ADS-B didn’t;t appear to anticipate.....
Nor the guys who designed GPS.
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  #58  
Old 02-19-2021, 09:00 AM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
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Quote:
Originally Posted by Ironflight View Post
In my case “dropouts” include everything from a message on the IFD 440 saying “GPS Integrity Lost” with continued good position data for the pilot to complete loss of GPS signal and the IFD going into “Ded Reckoning” mode. Now to be completely up front, this most often happens when I have done something that the FAA “system” didn’t expect, like going upside down, which is perfectly legal, but the guys who designed ADS-B didn’t;t appear to anticipate.....

Paul
Wait, are you saying that if I fly inverted I can go into ADSB "private" mode and still be legal? Time to sell my 9 and buy a 7. Inverted cross countries, now there is a trick.
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  #59  
Old 02-19-2021, 09:19 AM
Flying Canuck Flying Canuck is online now
 
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Quote:
Originally Posted by Ironflight View Post
... going upside down, which is perfectly legal, but the guys who designed ADS-B didn’t;t appear to anticipate.....

Paul

This here is the best case for installing your antenna on the underside. Simple defense... because I was inverted.
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Claude Pitre
RV-9A #91081, C-GCPT
Dynon SkyView HDX, IO-320 and WW 200RV C/S. Flying as of August 6, 2018

Added GPS 175 and authorized for IFR April 1, 2021

Interactive map of all of my flights here
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  #60  
Old 02-19-2021, 10:16 AM
jnmeade jnmeade is offline
 
Join Date: Mar 2013
Location: Iowa
Posts: 181
Default

Some thick paint (not just metallic paint) and even dirty rain when just sitting on the ground can detune these narrow-band antennas. Dirty rain is not a problem in the air because it washes off. So says a personal friend who was an antenna design engineer for Rockwell Collins for 30 years.
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