[amsat-bb] Re: Diplexer

Anthony Monteiro aa2tx at comcast.net
Sat Apr 9 08:15:04 PDT 2011

Dear Friends,

Perhaps this will help clear up the confusion.

A "diplexor" is a passive device that lets you split
and/or combine signals based on their frequencies.
It does not matter whether the frequencies are close
together or on different bands nor does it matter if
you are using it for transmitting or receiving.

A diplexor is commonly used in radio and TV broadcasting
to allow two transmitters on different frequencies
to share the same antenna.

A "duplexor" is a device that allows both transmitting and
receiving over the same transmission line or antenna. It
may or may not be a passive device and it may or may not
be frequency selective.

In WWII RADAR systems, a duplexor was used to allow
the transmitter and receiver on the same frequency to
share the same antenna. The duplexor was a waveguide
device that had special gas-filled tubes to quickly
switch the signal direction.

A typical ham radio cavity duplexor is used in FM repeater
stations to allow the transmitter and receiver to share
the same antenna. Since it is a passive frequency-based
multiplexor, it is also a diplexor.

If you used the exact same device to instead connect
two transmitters to the same antenna, it would no longer
be a duplexor but it would still be a diplexor.

Tony AA2TX

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