Anon wrote:
"What are the functions of each of these?"

My dictionary says:
"Diplexer - "A coupling unit which allows more than one transmitter to
operate together on one antenna."

The first AM broadcast plant I worked in did this with stations on 950
KHz and 1320 KHz. It was faultless.

Duplexer - "A radar device which, by using the transmitted pulse,
automatically switches the antenna from receive to transmit at the
proper timwee"

I`ve seen gas tubes used for this in radar sets in the navy and company
owned boats I worked on. Again, it worked like a charm.

Combiner - "A circuit for mixing video, trigger, and scan data from the
synchronizer for the modulation of the link."

Obviously definitions depend on applications. For example, I`m familiar
with combiners used to select the best signal from multiples in
diversity reception.

Best regards, Richard Harrison, KB5WZI