glider_rider
Well Known Member
Did anybody place the GA35 GPS antenna on the top forward fuselage skin under the canopy? Any reception issues?
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GA35 GPS antenna under the canopy
- Thread starter glider_rider
- Start date
Southern Pete
Well Known Member
It will probably work but the STC install manual requires a clear view of the sky ...
I know we don't have to comply with the STC but how important is good nav data when flying in poor weather?
It is probably only when the skin/canopy is wet that reception issues will be discovered.
I know we don't have to comply with the STC but how important is good nav data when flying in poor weather?
It is probably only when the skin/canopy is wet that reception issues will be discovered.
If you are running something like a GTN-650 make sure you add enough coax to provide signal attenuation (see install instructions). This is a known issue with the GTN-650, the added line is needed to attenuate RFI induced into the GPS receiver when transmitting on the GTN comm. If you do this still watch GPS signals as you transmit on the GTN to verify satellite reception is not degraded.
I just installed this antenna on a doubler right behind the cabin fiberglass top. Good location and it meets the install restrictions.
Carl
I just installed this antenna on a doubler right behind the cabin fiberglass top. Good location and it meets the install restrictions.
Carl
My GA35 is currently just forward of the firewall under the cowl. It worked fine with my previous 430W and now works fine with my IFD440. My EFIS GPS#2 antenna is on the glareshield. Not sure how the GA35 ended up there...original builder placed it on the turtle deck and would be under the canopy when it's open. Either he or the second owner re-located it.
I often mount GPS antennas under the fiberglass cowl. Have also seen antennas located under the windscreen.
Make sure the location is not shadowed by a metal component, ie. canopy frame, or too close to the firewall if under the cowl.
In years past metalic paints blocked the signal. Today almost all metalics use mica and doesn't interfere.
glider_rider
Well Known Member
What I'm worried about is steel center cabin brace. Not sure if shadowing would be a factor?
I had exactly the same idea but my plans changed, I intend to place the starling mini over there.
glider_rider
Well Known Member
Right, space is not a concern over there. At 100W Starlink mini is a relatively powerful transmitter and I have no idea if / how it would interfere with the GA35
On the other hand I've got a GPS antenna on the dashboard in my 14. No issues whatsoever. That's why I want to copy that configuration to the 10.
cjohngraham
Member
Any issue with high temperature under the cowl? I just got a GPS 175 with included GPS antenna. Per the specs, upper temperature limit for the latter is 85C (176F).
My maximum temperature reading at the antenna shelf located upper FWF under cowling is 125 F in flight and 135 F 5 minutes after shut-down. Florida summers. I've measured hotter skin temperatures behind my canopy. RV-14A with a IO390. 5 years no issues. GA-35 and 26.
This pre-dates the GTN series. The GNC 4xxW/5xxW also had the 2meter minimum/10meter maximum limitation. (1.5dB loss minimum to 7dB loss maximum). A number of us just used inline attenuators instead of the roll of coax.
And it's not for comm interference; the gain from the amplified GA antennas exceed the WAAS receivers front-end for the L1 frequency. The 12th and 13th octave issue is still there, regardless of the loss introduced by the cable.
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Nope. I watched all the satellites go away on the display when transmitting on the GTN comm so yes, it was Comm induced RFI into the satellite receiver. I can only assume the cause was comm transmit harmonics falling into GPS frequencies, aggravated by the GPS antenna pre-amp.
Carl
2 different issues.
1. The adoption of WAAS in the 4nnW/5nnW receivers required the additional loss to avoid issues with GPS reception.
2. The 12/13th issue is still there, and was there in the GPS 155 days - causes problems for a large number of receivers. This is why the TED filter exists (notch filter).
Edit: I think it's a terrible user experience to have a multi-thousand $$$ GPS/COMM/NAV solution that needs an additional $130 notch filter to work.
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Yup, did the same thing with a remote antenna for my Trimble Flightmate -- mounted the antenna up on the center post in my Mooney 231.
I know I've seen more than one RV-8 with the Garmin GPS antenna mounted under the canopy back on the turtle-deck.
Notch filters and com antenna interference aside, how many are flying with the GA35 under the canopy, either back on the turtle-deck or up on the glareshield? For those that are (or have), how well (or poorly) does it work for you?
Notch filters and com antenna interference aside, how many are flying with the GA35 under the canopy, either back on the turtle-deck or up on the glareshield? For those that are (or have), how well (or poorly) does it work for you?
glider_rider
Well Known Member
could you post a photo of the mount / installation?
Haven's had any issues with heat. Have installed, and seen other installs with GTN and G3X antennas under the cowl. No one has had issues.
As far as the 15' min coax length for Navigators; rather than having a coil of wire cluttering the space behind the dash I put the antenna under a wing tip. My current -8 is configured this way. The G3X antenna is under the cowl. Been that way for 6 years, no issues.
I had that installed under the cowl on my 6A. I had at least three loss of signal issues with that configuration. Finally moved it to the top of the plane and has been problem free for the last 1200 hours. I fly a fair amount of IFR, so was unwilling to accept the risk any longer. My GRT GPS antenna is still under the cowl and has never had any problems.
From my reading here over the years, I am definitely not the only one who has had issues.
Probably depends on installation. (shadowing, length of antenna cable run, etc.) It's easy to look at signal strength cowling on and cowling off rotating 360 degrees. I saw zero difference cowling on and cowling off before and after paint (metal flake paint used) and temps I monitor. (See post 10) Never an issue with signal loss.
I agree that most people get away with it. But when I see statements like no one has issues with it, I think it's important that people with problems speak out.
