Transponder Antenna Location

Ken Kochanski wrote:
We have been researching transponder installation options for our
ASW-27B (carbon fuselage) and have seen or heard about antenna
installations on the bottom of the fuselage in front and behind the
gear ... on top of the deck ... and with internal or external ground
planes ... and without ground planes. All appear to work, although I
have not seen any hard empirical data or testing results that shows
one type of installation is marginal ... or another superior.

Is a ground plane required on a carbon fuselage ... I understand some
German manufacturers don't install GPs during the factory install.

Start off with a query to the dealer, and if that doesn't work, ask the
factory directly. They install antennas routinely. On the ASH 26 E, they
install it about 2" behind the left gear door, no ground plane, and the
carbon fiber fuselage is apparently satisfactory. I installed one on my
ASH 26 behind the other gear door because it was easier to route the
cable to it. Seems to work fine.

If a GP is required, should it be outside the fuselage ... or will it
also work as well if it is inside?

Will the transponder system work satisfactorily with the antenna on
the top of the fuselage? ... understanding that the radiation pattern
would not be ideal for the ground based interrogation systems.

I don't know specifically about 27s, but people have put them there on
other gliders, and on top of the instrument cowling, so it appears to
work. I read Knauff put one on top behind the canopy on his Duo Discus.

On my 26, there is plenty of clearance between the antenna and the
trailer, and it won't hit the pavement in a gear up landing. I use the
cheap "ball on a stick" type that bends easily, rather than damage the
fuselage, if something does hit it.

I know a fellow that mounted a dipole inside the nose (which is
fiberglass) of his 26, and says it works well. A clean install, if you
don't mind having the antenna transmitting so close to you.

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Eric Greenwell
Washington State
USA