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Re: REFLECTOR: Antennas



Al Gietzen wrote:

> Many months ago (before the fuselage top was on) I installed the VOR antenna
> into the top.  Now I find as I install the carbon beams behind the doors on
> the elite that the tips of copper ribbon at the forward end of the "V" go
> just under the ends of the beams.  There is no direct contact as there is a
> fine BID over the ribbon and there will be a some additional thickness of
> microglass.  Graphite isn't like metal, but I'd appreciate opinion on
> whether there may be some inductive coupling to worry about that could
> effect antenna performance.

Al,

I apologize for my Very Tardy response. I am way behind in responding to my e-mail.

Insofar as antennas are concerned, carbon fiber has the same effect as metal.
Ideally, carbon fiber should be several feet from your Nav and Comm antennas.
While a small piece of carbon will not make much difference, a piece similar
in size to your antenna is a No-No. 

With the carbon as close as you describe, it will definitely have some
detuning effect on your antenna. It's impossible to know just how bad it is
until you test the antenna. My best advice is to take the airplane outside and
check the antennas with an Antenna Analyzer or SWR meter. If the SWR is below
2:1 across the band, you're fine. If it goes above 3:1, I'd install a new
antenna somewhere else. 

Keep in mind that in spite of the general rules of antenna installation,
antennas always involve a good deal of black magic. The best way to ensure
yours is working properly is to use an Antenna Analyzer to observe the effect
of slight changes in location and length of the antenna. 

Best,
Dave Black