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GPS antenna location

T

togaflyer

Well Known Member
Talking to someone at an avionics shop, it was recommended to place the two GPS antennas (one for the GTN 650 and the other for a Garmin EFIS) attached on a bracked, a few inches forward of the fire wall and an inch below the cowling. Just left and right of the center line. Has anyone done this. Any shadowing or degradation in performance. The other sugestion was just aft of the baggage bulkhead, just left and right of the center line.
 
Two RVs now and both have the GPS antennas on top of the glare shield. The RV-10 has a GTN-650 and the Dynon SkyView GPS. I do cover both antennas with a piece of dark gray fabric to prevent glare on the windshield. Performance has been flawless.

Many have done the bracket under the cowl mount but I figured the heat in that area is intense after engine shutdown on a hot day. As these antennas have active components I assume the heat can't be good for them.

Carl
 
Talk to your EFIS manufacture. With the new ADS-B antennas being as sensitive as they are, there is some concern that placing the antennas under the painted surface may not be a good thing.

The top of my glair shield is covered in loop Velcro (it feels like felt) and all my antennas are stuck to that, along with at least one writing instrument.
 
I would find a new shop.
1. As Carl said, it can get hot, especially after shut down, under the cowl. While some have had success there, it cannot be good long term for the solid state electronics.
2. Minimum separation is hard to achieve under the cowl. Some radios radiate the local oscillator signal back out, and can interfere with another antenna/system if they are too close to each other.
3. Are you planning to use the GTN for either IFR, or ADSB-out signal source? If so, you must follow the TSO installation guidelines, or be prepared to show that your installation "meets the performance" specifications of the TSO. Antenna location is in the installation manual, e.g., it's part of the TSO.
 
I ask folks what's more important to them, performance or looks. If you don't care about performance mount it anywhere you want but if optimum performance is your priority then simply follow the installation guidelines. Garmin does an excellent job in their manuals on how to install this stuff.
 
For what it is worth, Vans plans for the RV12 Skyview D1000 system have the GPS antenna FWF under the cowl...
 
Mine (G3X and GTN 650) are mounted externally on top of the cabin between the doors. They are about a foot apart with the forward one to the right of centerline and the rear one left of centerline.
 
Kyle Boatright said:
How do they work?

Also, how'd you get the wires up there?
Click to expand...

They work perfectly. As for the wiring, both antenna feeds run from the sub-panel area up through the cabin brace, into my overhead console and to their respective antenna. To mount the antennas I had to rout out a cavity in the cabin top on the inside large enough to be able install the BNC connectors. I then used flox to reinforce the area around the sides of the cavity.
 
+1 for what Walt said. Why would you want to degrade such an expensive piece of equipment. If you intend to ever fly IFR and also use the GPS as a source for ADS-B, follow the manufactures recommendations. You won't be disappointed.:rolleyes:
FWIW mine are mounted on the top of the cabin cover, spaced accordingly and work flawlessly....
 
If you're installing an overhead console they work well in there. I've put 4 different gps antennas in two overheads and they all worked great.
 
I m not installing an overhead console so center cabin wont work for me. I did read how Vans is now installing one in the cowling, but I do understand the heat issues, which was my concern.
 
I have an RV-6 with a Dynon Skyview with the GPS antenna mounted under the fiber glass cowl using a bracket attached to the upper part of the engine mount and also have a Garmin Aera 560 with the antenna mounted on top of the glare shield. Have not had any problems with either location. Aircraft is VFR only.
 
bob888 said:
What about ground plane when mounting on cabin cover?
Click to expand...

I did not install a ground plane but was prepared to, per the 650 install manual, if any antenna related issues materialized. To this point performance has been within the manual's listed specs. YMMV. ..
 
For the ground plane on composites (Lancair Evolutions) we use the Electrodag products (specialty conductive coatings - basically copper paint). Where possible we paint the inside (overheads), sometimes the outside (wing tips to help with static relief). With thus in mind, I used this product for my RV-10 (taped off and painted the cabin inside where the overhead goes), all equipment works perfect!. Be very careful to space the antennas according to the manufactures specs as best you can.
 
aerhed said:
If you're installing an overhead console they work well in there. I've put 4 different gps antennas in two overheads and they all worked great.
Click to expand...

Any pictures?
Curious to know how you mounted them and how you accommodated the bottom connectors.
Thanks.
Johan
 
From a general RF engineering perspective the under-cowl mount has two strikes against it.
Since all of these GPS antennas have amplifiers built into them, we need to consider the following:

1) electronic component reliability is an inverse function of temperature. Heat is not your friend in this case.

2) amplifier noise figure is a direct function of temperature. Amplifier noise is not good, so we want to keep the amp as cool as possible in order to keep it as quiet as possible (thus allowing our receivers to better pick out that minuscule GPS signal).

I know of at least one GPS antenna which became "flaky" while under the cowl. They're really not made for that environment. Sure, some will work well and will survive there - we've seen plenty of anecdotal evidence here to support that conclusion. But others will fail prematurely. Besides the obvious cost of a replacement antenna, I suspect most of us would not want to lose GPS functionality while in flight.
 
I have two GPS antennas mounted on a shelf I fabricated that is bolted to the top of the firewall, a couple inches below the top cowl. So far they have performed flawlessly. If in 5 years they burn up from the heat, I'll buy new antennas. To me it is worth keeping them hidden, yet fully functional.
 
Bluelabel said:
Did mine on the cabin top. Put in an aluminum plate under the ant and then ran a wire back to the metal airframe. Easy
Click to expand...

You must make sure the coax braided shield is electrically connected, via the connectors/fittings, to the plate. The wire to the metal airframe is not needed.
 
Active GPS antennas seem to want at least 6" spacing between them. I recently helped a buddy install a new GTN-650 in his Lancair and we spaced two antennas (one for the 650, the other for a 496) on an aluminum plate 6" apart mounted behind the baggage area rear bulkhead and they both work very well.

GPS antennas forward of the firewall and under the engine cowl may work too, but are subject to a lot of heat, especially after landing and shutdown. If you decide to place them there, at least show them a little mercy and open your oil door to help the heat escape after shutdown.
 
Just as a data point, in my RV6 I have a bracket from firewall to engine mount with the Garmin GPS antenna mounted about 1 inch under cowl. 11 years and never a signal issue or dropout nor heat issue, although in the 10 I'll be putting 2 antennae in the overhead console.

Dave Ford
Cadillac, Mi
 
Since Im not installing a center overhead, I will be installing the GTN 650 GPS antenna just aft of the bulkhead on the tail. The two antennas for the two G3X, I can install both antennas on the glare shield, or one outside on the tail with the 650 antenna and one inside. For those with the inside antenna on the glare shield, any reception issues. I decided against under the engine cowl. Old school beliefs won out at the end. Thanks for all the input.
 
Reading this thread and I am still trying to determine how or what needs to be grounded when installing antennas on the outside of the RV-10 cabin top.

I will have a overhead so plan on installing the antennas on the cabin top but is a AL plate required? If a plate is used do I need to run a connection to ground or just screw the antenna to the plate (but then where is the ground).

As you can tell, not an antenna expert by any means.

All help (and pictures) appreciated

E
 
If you have an overhead there is no need to mount them externally. They work great inside the cabin top. No ground plane needed either way.
 
ethand said:
Reading this thread and I am still trying to determine how or what needs to be grounded when installing antennas on the outside of the RV-10 cabin top.

I will have a overhead so plan on installing the antennas on the cabin top but is a AL plate required? If a plate is used do I need to run a connection to ground or just screw the antenna to the plate (but then where is the ground).

As you can tell, not an antenna expert by any means.

All help (and pictures) appreciated
,
E
Click to expand...

Just like conventional circuits, antennas are inherently two terminal devices, one terminal connected to the center conductor of the coax, the other to the shield. But the shield is more than a "shield"; it carries just as much current as the center conductor. For long wavelengths it is common to use the earth itself as part of the antenna, and hence the name 'ground'. But there is no need (outside of lightning protection) for this part of the antenna to actually be connected to the airframe ground. OTOH, the coax must be connected to this part of the antenna so that the current can flow. Most simple quarter wave whips require you to furnish a flat conductor perpendicular to the whip, attached to the coax braid (usually the aircraft's metal skin). Some gps antennas have the second part of the antenna inside the box; all you need to do is make sure there is a good electrical connection from the braid to the outside of the connector.
 
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