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  #11  
Old 11-14-2018, 10:26 AM
rocketman1988 rocketman1988 is offline
 
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Default which antenna

What antenna did you use for the array?
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  #12  
Old 11-14-2018, 11:23 AM
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Paddy Paddy is online now
 
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Default Inside Console Antenna

Inside the console, I have 2 Garmin GA-26C and one Gilsson equivalent.
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  #13  
Old 11-14-2018, 02:18 PM
BobTurner BobTurner is online now
 
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Default

Quote:
Originally Posted by Paddy View Post
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.
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  #14  
Old 11-14-2018, 03:07 PM
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Paddy Paddy is online now
 
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Default 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.
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  #15  
Old 11-14-2018, 07:57 PM
BobTurner BobTurner is online now
 
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Quote:
Originally Posted by Paddy View Post

.... 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.
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  #16  
Old 11-15-2018, 01:04 PM
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Default Overhead Console

Good to know - thanks.
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  #17  
Old 11-15-2018, 07:53 PM
MConner MConner is offline
 
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Location: Snead Island, Florida
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Default 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
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