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IFR WAAS GPS Antenna Location

jmbueller

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I know this subject has been talked to death somewhat, but who is using their GPS for IFR approaches including vertical guidance, and where have you located your antenna?

I'm getting ready to install a Garmin GTN 635, and I intend to use it IFR in my RV-7. Currently, I'm vacillating between just aft of the canopy, on the fuselage just aft of the firewall in front of the windshield, on the glare shield, and under the engine cowl just forward of the firewall.

I'm leaning towards either on the fuselage just aft of the firewall or just aft of the canopy to get the best view skyward. Heat and the dirty RF environment are a concern for under the cowl. On the glare shield works fine for my 795 handheld antenna, but WAAS is another thing.

I'd appreciate any thoughts on the subject from people with successful WAAS approach capable installations.

Thanks in advance!
 
I have two Dynon WAAS antennas on my glareshield (one ADSB-2020 and one GPS-250). IF you opt to put them there, paint them black or mount with some kind of dark cover to avoid reflection/glare on the windshield.

Otherwise, great location for reception and zero drag.
 
I would suggest that for optimum GPS and IFR performance, use the Garmin install manual's antenna location recommendations. I have dual Garmin WAAS systems and have located both antennas IAW Garmin install guidance aft of the canopy on my RV-9.


Antennas occasionally go bad, so the aft fuselage is easiest to access on my slider.
 
Thanks guys for the quick replies.

I've been going through Garmin's 450 page installation manual for the GTN 635. Clearly they wrote it with something like a Kingair in mind--6 feet between com antennas--sheesh.

Raymo, how far aft of the closed canopy and to the side of the slider rail did you mount yours? My ELT antenna is located just aft of the open canopy, so I'd be something like a canopy length away from that, which I assume is ok. My com antennas are both on the bottom of the fuselage.

Also, how critical is separation of the antenna wire from other wires do you think?

Thanks again!
 
Below is a photo of my glare shield install. They are currently covered with some black felt material to avoid a reflection on the windshield. I plan to pull the gray material and paint it all a dark color (didn't do black due to heat in the south). My ELT antenna is in the next photo with the tip just barely tucked into a hole in the side support bracket.

I only have one COM, at the moment. Its antenna is mounted under the CP seat in the second bay inward. Once I can do the GTN-650, or similar install, the second COM will be opposite the first, under the pilot seat.

I agree with Dan B that you should, when possible, follow MFG recommendations but, as you said, it is often not possible.

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These are the parameters that I was concerned with:

"c. no closer than 12 inches (center to center, 9 inches minimum) from other antennas, including passive antennas such as another GPS antenna or XM antenna. This will minimize the effects of shadowing at 5? elevation angles."

"5. For multiple GPS installations, the antennas should not be mounted in a straight line from the front to the rear of the fuselage."
 
Thanks again gentlemen. For my situation, I'm gravitating towards aft of the canopy to the left of the canopy rail. The other antenna will remain on the right side of the glare shield.
 
Dan B, I meant this question to be for you: How far aft of the closed canopy and to the side of the slider rail did you mount yours? My ELT antenna is located just aft of the open canopy, so I'd be something like a canopy length away from that, which I assume is ok.

Raymo, thanks for the photos--nice looking installation.
 
Dan B, I meant this question to be for you: How far aft of the closed canopy and to the side of the slider rail did you mount yours? My ELT antenna is located just aft of the open canopy, so I'd be something like a canopy length away from that, which I assume is ok.

If you are interested, PM your email and I will send photos.
 
I have mounted them forward the firewall, just under the cowling. This has worked well for a number of years on two or three different airplanes. It may not work if you use a metallic paint.
 
FWIW, I have a Garmin antenna feeding a 430W *and* a Dynon SV-GPS-2020 on a shelf mounted on the forward firewall, basically next to each other, and after 600 hours I've had zero issues with either antenna (now that I say that, of course, one or the other or both will go wonky on my next flight ha ha!). Signal strength on both is always great, no dropouts, no problems. Even have an XM antenna that I stuck under the cowling so I could listen to SiriusXM on XCs. Everything is copacetic.

YMMV.

Oh, and I do recall reading something about not painting GPS antennae. I believe it's in the Garmin install manuals.
 
FWIW, I have a Garmin antenna feeding a 430W *and* a Dynon SV-GPS-2020 on a shelf mounted on the forward firewall, basically next to each other, and after 600 hours I've had zero issues with either antenna (now that I say that, of course, one or the other or both will go wonky on my next flight ha ha!). Signal strength on both is always great, no dropouts, no problems. Even have an XM antenna that I stuck under the cowling so I could listen to SiriusXM on XCs. Everything is copacetic.

YMMV.

Oh, and I do recall reading something about not painting GPS antennae. I believe it's in the Garmin install manuals.

Same here, with the Dynon GPS2020 and Garmin 430W antennae sitting next to each other on a small shelf under the cowling just forward of the firewall, works great.
 
Yet....

People put them under painted fiberglass cowls...??

Just thinking there is a disconnect.

R.
 
The "do not paint" comes from the very real instances of people painting the antennas with paint that is not absolutely RF-transparent. One CAN paint antennas. It is inadvisable unless one is very familiar with the RF transparency characteristics of the paint.
 
And it's fine under the cowling as long as you use non-metallic pigments in the paint.
 
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