----- Original Message -----
From: "Paul McAllister" <paul.mcallister@qia.net>
Subject: Europa-List: Transponder issues
<paul.mcallister@qia.net>
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| Hi all,
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| I posted a similar note on the avionics list if anyone has some ideas
please contact me. I have UPS SL70 mounted in my composite Europa. Up until
recently it has operated faultlessly, but I a recent trip between Wisconsin
and Arkansas I had several complaints from ATC that they could not see my
transponder, even at 9000'.
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| I am unsure if I have a problem or not, the antenna is mounted in the
baggage bay, it is a simple "spike" type mounted on a piece of 6 x 6
aluminum. The cable run is fairly short and it is RG400. I have reseated
the transponder, the connection to the coax and to the antenna and I can't
spot any obvious problem.
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| During the times that ATC were complaining I was seeing a solid reply to
there integrations so the receiver seems to be working fine. I'd appreciate
anyone's input on things to check or trouble shooting ideas. I'd also like
to know what installations people have out there that are working fine. I
am thinking that maybe I have to mount the antenna on the belly of he
aircraft with a ground plane.
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| Thanks, Paul
Paul,
I think that piece of 6x6 alu IS the ground plane. You didn't say
whether it hung from the ceiling or sat all alone. That might be a
difference. The only way to increase the radiation is to turn the flat disc
of alu into a cone at up to 45deg from the axis of the 'spike'. this might
tune the antenna more closely to the 50ohm characteristic of cable and
spike. You should not have to place the spike on the exterior to improve it.
Good luck,
Ferg
PS: - maybe the metal nearby 'blanked' your reply - try changing direction
if you get a complaint. The Vampire was a wooden jet with metal wings. We
used to have to 'waggle' the wings for the radar base to read us side-on.
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