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There are a couple of things that you have to consider when using an antenna
for two units.  If they are both receiving units....it's no problem using a
splitter.  A splitter will decrease the strength of the signal about 3db
(approx. 50%).

If you are going to use an antenna for units that both transmit and receive,
then you need to use a diplexer or duplexer and the signal when transmitting
should be attenuated at least 20db or more to ensure isolation between the
receiving unit when the transmitting unit is in transmission.  It would be
safer, in my opinion, because of the fact that the transponder is
transmitting a lot, to use a separate transponder antenna.  Make sure that
the cockpit area is shielded from the microwave transmission of the
transponder.  This can be done by bonding aluminum foil on the bulkheads
between the seating area and the antenna location.  Microwave is not a good
thing to be bombarded with continually......just think about microwave
popcorn.  Our (plastic) airplanes don't provide any shielding from the
transponder transmission.

Curtis Krouse N753K

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Please send your photos and drawings to marvkaye@olsusa.com.