Codan Radio Radio Repeater Systems Training Guide - Manual (Page 32)

TRAINING GUIDE | RADIO REPEATER SYSTEM
Chapter 3: Repeater System Equipment Page 24
DUPLEXERS, MULTICOUPLERS AND COMBINERS
Band-pass and band-reject duplexers allow use of the same antenna for transmitting and receiving.
Multicouplers and combiners are an arrangement of band-pass and band-reject cavities which permit
use of the same antenna by a number of receivers and transmitters respectively. Additional duplexers
can be required in such a system.
Duplexers, multicouplers and combiners have the following characteristics which are important to your
system design:
a) the unit(s) must match the frequency range, temperature range, impedance, and termination type
(coaxial fi ttings) of the rest of your equipment;
b) the manufacturer’s data sheet fi gures noting frequency separation and isolation must match your
requirement. For example, if your frequency separation is 5 MHz, there is no need to purchase a
duplexer that has a minimum frequency separation of 0.8 MHz. On the other hand, conditions at
your site (frequencies used by others) may require better than the usual 50 to 90 dB isolation;
c) ensure that the power output of the transmitters / power amplifi ers does not exceed the specifi ed
power rating of the unit. The VSWR should be as low as possible, but this item is controlled by
the construction of the unit and is nearly always less than 1.5:1.0;
d) insertion loss must be noted for your later calculation of signal levels, and;
e) the mechanical specifi cation of the unit by the manufacturer must be noted to ensure space in
your enclosure. As a rule of thumb, the less the minimum frequency separation and the higher
the isolation, the larger and heavier the unit.