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GPS Antenna Inside Overhead Console

rocketman1988

Well Known Member
Does anyone have any photos of GPS antennas mounted inside the overhead console?

If you have been flying with install, how is the antenna performance?

Deciding on interior or exterior mount for my -10...

Thanks!
 
Here are a few of my install in Aerosport overhead using 90 deg fittings , have about 140 hours, get good signal, sometimes get signal in the hangar with door open.

2itggk.jpg



drfew2.jpg



24uyj5t.jpg
 
Thanks!

Knew there had to be at least 1 out there...

Is it actually mounted to the access panel?
 
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Yes puck to spacer block, block to access panel. The afs puck is narrower to fit in the rear access but the navigator puck was thicker and had to fit in the forward taller space, all worked out. Coax and wiring run through forward cabin bar.
 
I don't have a dog in this fight but I'm pretty sure most folks don't have the ability to measure/determine antenna performance other than ancedotal evidence "it works ok".

Personally I suggest that antennas be mounted for best performance and not cosmetics, which usually means as close as possible to the install requirements called out in the install manual.
I consider IFR navigator antennas as critical items and treat them as such.
 
and...

The Garmin install manual doesn't prohibit antenna installation beneath a composite skin.

I wanted to see if anyone who had done this has had any issues, that's all.

In reality, it is not a big problem because if the antennas do not perform mounted IN the overhead console, they get removed and mounted on the exterior of the cabin top in the same location...no need to change any wiring.

From what Garmin has said, a metallic paint job would pose more of a problem than the fiberglass cabin top. I don't have the equipment to verify it but that is what I was told...

Think I will give it a try as there is nothing to lose if it doesn't work...
 
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Just FYI stuff from the GA35 IM...

2.4 Antenna Grounding

The antenna is grounded through the mounting hardware. The mounting hardware (washers and nuts) and doubler plate should make contact with an unpainted surface ensuring proper antenna grounding.

It is very important to have good conductivity between the coaxial shield and the ground plane. This is ensured when all the fasteners properly ground the antenna base to the skin of the aircraft.
 
and...

"...23.3.5 Antenna Grounding Plane
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. To use an antenna in aircraft with fabric or composite skin, a ground plane is recommended. It is usually installed under the skin of the aircraft, below the antenna, and is made of either aluminum sheet or of wire mesh..."

It is funny reading the install manual, there are places which seem to contradict each other.

I really have to laugh at the GMU position requirements. If you were to follow every recommended distance to determine the best mounting location, it would appear that the magnetometer needs to be flying about 10 feet outside the aircraft but in close formation...

Obviously, that isn't the case but it is funny...:D

In the antenna example, they talk about grounding the antenna to the ground plane but in another section, it states that the ground plane is not required...

I intend to mount the antenna on an aluminum plate within the overhead console, and ground that plate to the airframe.
 
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Antennae

Bob,
I have the GA-35 antenna mounted on the outside of the cabin top between the doors and another 3-antenna GPS array mounted inside the overhead console on the rear aluminum panel. They all work reliably, in fact the 3 inside acquire faster than the one outside, but that is probably due to differences in the software between the G3x and the GTN. I don't have a way to measure signal strength other than to observe that they all acquire a full constellation inside the hangar with the door closed and have been reliable in flight.
 
Ground Plane

If you ask a truly knowledgeable person at Garmin, they'll tell you that the GA-35 antenna was designed such that the metal baseplate of that particular antenna is sufficient ground plane to be mounted directly to a non-conductive surface such as the cabin top, without further ground plane requirement. This probably isn't the case for some other antennae.
 
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Inside Console Antenna

Inside the console, I have 2 Garmin GA-26C and one Gilsson equivalent.
 
If you ask

I intend to mount the antenna on an aluminum plate within the overhead console, and ground that plate to the airframe.

It is important to connect the coax shield to the plate, but it is not necessary to otherwise ground the ?ground plane?.

The 430, and I think other Garmin gps boxes, have a signal strength display on the top right display page. It would be interesting to compare those pages between two similar aircraft, one with an internal, one with an external, antenna.

As a side note, I recently did experience a GPS failure. On a vfr approach, the gtn650 first downgraded from LPv to LNAV, then, as we touched down, downgraded further to no gps. External antenna. It would have been informative to have had a similar but internal antenna plane nearby.
 
Bonding vs Grounding

I'm no expert in this area, so please correct me if my seat-o-the-pants physics assumptions are inaccurate.

If you're going to have a separate ground plane in addition to the antenna base, the reason you need to make sure to bond the two with the mounting screws (coax shield is already bonded to the antenna base via the connector) has more to do with having it all at the same potential than anything else.

If all the parts aren't connected together electrically, there's some risk that the assembly becomes a big capacitor, with the non-conductive substrate acting as an insulator between two metal plates. Add the high-speed airstream to excite a charge on the fiberglass and you've got a recipe for instability.

Although I'm not convinced it helped, I added a foil ground plane on the inside of the cabin top, passed the mounting screws through it and strung a wire from one screw to the carbon fiber overhead, so they're all bonded together.
 
.... and strung a wire from one screw to the carbon fiber overhead, so they're all bonded together.

Since it's RF, path lengths matter. So current induced in the ground plane has to be able to flow directly to the coax shield. If the current's path is along the graphite, past the coax connector, to some wire, then back 8" to the connector, it will be all screwed up. It would be best to bond the aluminum ground plane to the graphite at multiple places around its circumference (or use multiple wires, like the spokes of a wheel). That said, since the graphite portion is already a reasonable distance from the aluminum, it probably doesn't matter much.
 
Inside antenna

I have three GPS antennas and an XM antenna, all on my glareshield, and they work flawlessly. I think inches of seleration is plenty for good reception. YMMV
 
I experienced gps losses occasionally with my GNS430W a separate ADI GPS shortly failed thereafter. I switched off the GNS and the ADI gps came back. So either my antenna cable/connectors somewhere jam the ADI GPS or it might be the GA35 antenna. The antenna manual states that the conductivity test should show <10 milliOhms when the cable is disconnected. The GPS is mounted on the cabin top with no further grounding.
It worked flawlessly over years but now lately gps no signal messages appeared.

If I understand correctly I need to ground the antenna itself and can’t rely on the RG400 shield.

Kind regards
Michael
 
You understand incorrectly. Although commonly called a ‘ground plane’ (this dates back to when the earth was used as a ‘ground plane’) there is no requirement that it be connected independently to aircraft ground. But it must be connected to the coax shield.
Some gps antennas with built in pre-amps have suffered electronic failures where the amplifier began to radiate a signal which interfered with other nearby gps antennas. Could this be your issue? (Switch off GNS, ADI comes back).
 
Thanks Bob for the clarification, however there distance between my GA35 and the ADI gps puck is really quite far away (glare shield - cabin top above rear passengers). The other issue which makes me wonder that this is an inconsistent error, some flights are fine on others the failure occurred. I will now check the connectors before I commit to a new antenna.
 
Digging this old thread up since Daves pics are missing.

The XM and GTN650 pucks don't seem to fit in my Aerosport overhead. The space, with 90s is about 7/16" too shallow.

Has anybody fit these in somehow? Pictures appreciated.
 
GTN Antenna

The GTN antenna should to be mounted outside the aircraft in accordance with the Garmin instructions if you're going to use the plane for IFR flight. It might work fine under the fiberglass, but your DAR won't sign off on that if he's on the ball. Besides, as you found, it won't fit inside the Aerosport overhead even with a (very expensive) right angle threaded connector. I do remember a builder who carved out a bay for the antenna out of the cabin top fiberglass and then fitted a plexi window on top of it to make it flush with the outside.
 
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The GTN antenna should to be mounted outside the aircraft in accordance with the Garmin instructions if you're going to use the plane for IFR flight. It might work fine under the fiberglass, but your DAR won't sign off on that if he's on the ball. Besides, as you found, it won't fit inside the Aerosport overhead even with a (very expensive) right angle threaded connector. I do remember a builder who carved out a bay for the antenna out of the cabin top fiberglass and then fitted a plexi window on top of it to make it flush with the outside.

Not sure where this information is coming from, but this is a "flight" issue and has nothing to do with the eligibility of the aircraft to meet 21.191(g). The DAR may caution you that it may not operate well, but he/she should not deny certification on this basis.
It is up to the operator to determine whether or not the aircraft is eligible for IFR operations per the operating limitations for that aircraft.
 
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I have my GPS antenna's both mounted under the overhead console . Below is a picture of one of them. They are both working perfectly. However, even with the 90 degree TNC adapter the cover does not fit without a hole for the connector. I am going to mount my rear headset hangar in that location so the hole will be covered eventually.

20190923_001333206_iOS.jpg
 
I mounted the antenna to the rear cover on my aerosport there is more room behind the roll over bar in the top. It works great. My GTN650 shows the strength of the signals and the are strong.
 
Do you have a pic or two that you could post? My antenna's don't fit - similar to the picture in the above post.
 
Take a look at the top of an SR22, it has a row of antennas, why do you suppose they did that?
 
Take a look at the top of an SR22, it has a row of antennas, why do you suppose they did that?

1. Slavish adherence to the STC/TSO for the antennas
2. They needed a place to put the parachute + rocket motor and straps :)

:D
 
90 degree BNC and TNC connectors

Hello,

I am searching for 90 degree BNC and TNC connectors for my antennas. I will be using RG400 cable. There appears to be several to choose from and they span price from 9 dollars to 90 dollars and these are all AMP products. What is the difference? I prefer all crimp.

There there a difference in performance, reliability. I do not need weatherproof.

Thank you for any additional knowledge.
 
Any pictures, TomSpencer46 (or anyone else)?

Keep in mind that anything you mount inside the Aerosport overhead console reduces the already minimal airflow.

Suggest you mount the antennas on the metal airframe aft of the cabin cover - decent ground plane and minimal drag.

 
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