Everyone is clear on what a filter is, but there exists a lot of
confusion over what is the difference between a duplexer and a
diplexer. As you might expect, there are a lot of opinions - even
between manufacturers. Traditionally, duplex communications implies
the ability to transmit (Tx) and receive (Rx) on the same channel
simultaneously. doing so requires a means of separating the
transmit and receive paths in a manner rendering them independent
of each other, i.e., isolation. Thus, a duplexer
is used. One method is to use a circulator for routing signals
from the transmitter to the antenna while routing singles from the
antenna to the receiver. If the Tx and Rx operate at different
frequencies, the job can be accomplished by a set of filters with a
common feed point. A diplexer
is usually thought of as a set of filters, again with a common
feed point, that is used to combine or split signals travelling to
or from an antenna, respectively, while providing isolation between
the two independent paths. If more than two independent paths are
required, the name for both usually changes to a common term:
multiplexer.
