Hello,
Obviously I don’t know the installation in question, but let me offer my
2cents. My day job is as an RF engineer.
A metal ground plane is much better than paint. But it doesn’t have to be
any significant thickness. Foil, or sticky back foil or tape is ok.
The reason for needing a ground plane is because the structure is non
conducting. Effectively the structure is not there as far as the radio signal is
concerned, so it’s just as good to put the ground plane on the inside, which is
a bit easier.
Follow that logic through and you come to the idea that the whole antenna
can be inside, providing you can set up a suitable ground plane or
equivalent.
The difficulty comes if the aircraft structure is partly conducting, rather
than insulating, and therefore absorbs radio energy instead of being transparent
to it. This is where there’s a gap in my knowledge – I don’t know the electrical
characteristics of carbon fibre. I suspect it can be treated as an insulator,
but maybe someone can confirm that.
Nick Long
Sent: Tuesday, November 5, 2013 1:36 PM
Subject: [LML] Re: TXPDR antenna
John, I'm trying to figure out how a xponder antenna would be between
the rudder pedals and the firewall.
Paint works at first but can fracture.
A physically robust connection to the ground plane is best.
If it were me I would take the antenna off (assuming it's outdoors like it
should be), grind through all the filler down to the carbon, install a small
sheet metal ground plane, provide a good strong contact area, reassemble, and
then bodywork over the remaining visible ground plane.
Colyn
On Nov 5, 2013, at 7:46 AM, John Barrett wrote:
Hello all,
Behind the rudder pedal the antenna for the transponder can be ID'd by the
brown Rg cable.
ATC sometimes loses my squawk and I am thinking I need to add a ground
plane. Question for the group is if I can paint conductive paint around
the antenna and under neath the hydraulic lines as much as possible. Will
the Jeffco tank sealer interfere with effecitveness? Do I need to remove
the antenna or can the hub be painted to provide continuity?
Any suggestions welcome.
Thanks,
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