On 05/28/2011 11:09 PM, Bud Yerly wrote:
> First check and ohm out your radio connections and coax attachment to
> your antenna. Check out the coax that the center wire and outer shield
> have no continuity.
All too complicated and not necessary. Just borrow an SWR-meter, and see
what it says. Broken wires, shorts, resonance problems, everything shows
up with this simple test.
There are many radio amateurs, find one and he probably loves to look at
the installation of a real airplane.
If there is anything else than the Europa recommended halve wave antenna
in the tail closeout, I would scrap it and arrange such a halve wave
antenna. Contradictory to common believe fed by marketroids, there is
nothing that beats a simple halve wave dipole for this application. No
antenna can have any gain over a dipole without introducing losses in
some area's. It is just like a light bulb, any gain you derive with
reflectors and lenses will introduce dark spot in other directions. A
half wave is close to omnidirectional and only has two small "dark
spots" straight up and straight down. Fortunately if you are overhead an
ATC facility the "dark spot" is of no consequence as you are pretty
close anyway.
There is another reason to stay with a dipole: A dipole has a certain
impedance and it is exactly this impedance (50 ohms) that became the
standard for the coax and output of the transmitter. Of course this is
no coincidence as the manufacturers know that the dipole is the best
solution. Other antennas might have a different impedance, need a
matching network (often built in and invisible to the user), and often
this matching network (consisting of coils and capacitors) breaks down,
causing all sorts of problems.
Just my 2 cents,
Frans
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