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Front page 6/2/2021-Seen at Monk's

PilotjohnS

Well Known Member
On the front page there is a picture of a GPS antenna mount forward of the firewall using an Adel clamp and brace to firewall.
But I noticed there is no ground plane under antenna.
I thought the GPS (or any antenna) needed to be bolted to a ground plane to work well.

Curious if this plane has trouble receiving GPS with no ground plane under antenna?

I plan to make a small shelf forward of the firewall to mount my antennas, FYI.
 

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My 2c, IFR GPS antennas belong outside on the fuselage as designed, excessive heat and limiting sky visibility should be avoided.
 
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Despite what Garmin has in their install manuals, in my experience (and I’m not an engineer) GPS antennas work just fine without a ground plane. That said, like Walt I’m not a fan of FWF installations. YMMV.....
 
Not an electrical engineer so I can only relay my experience-my gps antenna has been mounted in a similar location since 2006 with unwavering service. My brothers RV 7a since 2008 same results. Multiple aircraft built in my old builders club-same result. Is the signal attenuated by the fiberglass-maybe but based on our experience through gps approach checks-not enough to affect accuracy.
However, don’t try this with a carbon fiber cowl-big time attenuation!
As they say
YMMV
Cheers
db
 
What about the GPS antenna cables passing through the firewall apparently via a black rubber grommet?
 

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I did this for awhile with my old Garmin 496 GPS receiver and found that you need to be sure the antenna is well forward of the firewall. Whenever flying in a northerly direction my Sirius weather feed would sometimes take up to 45-60 minutes to update. Not what you want when you are headed into an area with lots of rain and/or low visibility.

I discovered that the weather satellites are generally south of the USA and consequently the airframe and firewall can block the line-of-sight view the antenna can get when headed north.

Better to place the antenna on the panel or the turtledeck where it gets lots of visibility to the sats. Just my experience with this.

Chris
 
What about the GPS antenna cables passing through the firewall apparently via a black rubber grommet?

While many don't like this and I understand why, all of the FW pass throughs called out in the RV10 manual use a plastic grommet with no other sealing. Clearly this is ok with the kit developer, but as always, each of us can make our own risk decision.

There is probably only an 1/8" of rubber between the coax and the SS. Not a lot of fire can pass through a hole that small. Not recommending that approach, but not the same as a 2" hole that will be created when the aluminum heat box melts away. If you have the standard Van's alum heat box, I would be far more worried about that then the tiny rubber grommet.

Larry
 
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Antenna failure

I recently had an antenna failure after 350 flawless hours mounted FWF.. I agree with Walt that if you plan on flying IFR this area probably isn't the best spot. While most of us have multiple redundant systems that make this somewhat of non event, it is probably best avoided.
 
I recently had an antenna failure after 350 flawless hours mounted FWF.. I agree with Walt that if you plan on flying IFR this area probably isn't the best spot. While most of us have multiple redundant systems that make this somewhat of non event, it is probably best avoided.

I originally had the GA-35 under the cowl. Had two GPS losses (~ 5 minutes each), while IFR (luckly just enroute) and subsequently moved it to the top of the fuse and have not had a problem since.

Larry
 
Popcorn is popping

I would love to put the gps antennas on the turtle deck, but I dont have any space with the supertrac mod for the slider. Maybe I will check again if the canopy will pass over the gps antenna, but I am thinking not.

I guess I can use the Vans access covers for the instrument subpanel and then use a fiberglass cover???
 
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I would love to put the gps antennas on the turtle deck, but I dont have any space with the supertrac mod for the slider. Maybe I will check again if the canopy will pass over the gps antenna, but I am thinking not.

I guess I can use the Vans access covers for the instrument subpanel and then use a fiberglass cover???

PM sent...
 
GPS WAAS antenna

Brian, Walt, Chris, Bill P. or any of you smart guys,

I am also concerned about the GPS mount the original builder installed in front of the firewall. Since updating the panel and all the avionics with a WAAS antenna I at least will have to move it about 4-5” forward to get a rear look for the antenna. I would rather have it on the fuselage or the glare shield but wouldn’t relish running cable all the way back to the aft turtleneck of my -8.

The glareshield would be ideal but I don't want a bright white antenna right in front of my face. Is there any approved method of covering the gps antenna with something matte black to avoid glare but still get good reception?
 
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Brian, Walt, Chris, Bill P. or any of you smart guys,

I am also concerned about the GPS mount the original builder installed in front of the firewall. Since updating the panel and all the avionics with a WAAS antenna I at least will have to move it about 4-5” forward to get a rear look for the antenna. I would rather have it on the fuselage or the glare shield but wouldn’t relish running cable all the way back to the aft turtleneck of my -8.

The glareshield would be ideal but I don't want a bright white antenna right in front of my face. Is there any approved method of covering the gps antenna with something matte black to avoid glare but still get good reception?

Paint...just make sure that it's non-metallic, and 0% graphite...

Cover/wrap the antenna with painters tape, spray with paint of choice and then observe satellite reception/constellation...If it works, remove tape and paint for real.
 
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Fabric

Paint...just make sure that it's non-metallic, and 0% graphite...

Cover/wrap the antenna with painters tape, spray with paint of choice and then observe satellite reception/constellation...If it works, remove tape and paint for real.

Just wrap the antenna in black fabric.
 
Brian, Walt, Chris, Bill P. or any of you smart guys,

I am also concerned about the GPS mount the original builder installed in front of the firewall. Since updating the panel and all the avionics with a WAAS antenna I at least will have to move it about 4-5” forward to get a rear look for the antenna. I would rather have it on the fuselage or the glare shield but wouldn’t relish running cable all the way back to the aft turtleneck of my -8.

The glareshield would be ideal but I don't want a bright white antenna right in front of my face. Is there any approved method of covering the gps antenna with something matte black to avoid glare but still get good reception?

Run the cable, not that big a deal. A receiver is only as good as it's antenna, compromise on installation and you will compromise performance.
 
Egg on My Face

Run the cable, not that big a deal. A receiver is only as good as it's antenna, compromise on installation and you will compromise performance.

Well, my reason for mounting the antennas under the cowl was because I thought the slider would not clear the antenna if place on the turtle deck. I measured today and it looks like there is enough room so that the slider will go over the antennas without hitting.

If anyone has the Garmin GPS antennas on the turtle deck and the slider slides over them, please let me know if there was a clearance issue.
 
when in doubt, read the manual. from the garmin g3x install manual.

Although no ground plane is required, the antennas typically perform better when a ground plane is used. The ground plane should be a conductive surface as large as practical, with a minimum diameter of 8 inches.

bob burns
RV-4 N82RB
 
Brian, Walt, Chris, Bill P. or any of you smart guys,

... Is there any approved method of covering the gps antenna with something matte black to avoid glare but still get good reception?

While the antenna has a "Do not paint" warning engraved into it, I must confess I painted my original white GPS 56 antenna (mounted on top of the glareshield) with a single coat of matte black from a spray can. That was 15 years ago and I've never had a reception issue. My new GA35 antenna that is connected to my GTX 345 ADS-B is mounted on the turtle deck behind me so I've left it unpainted.

I find it curious that Garmin makes some antennas in white and others, like the one for my AERA 660, is made in black. I would think black would be the better default since most glareshields I see are a matte black.

Chris
 
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