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Duplexers. What are they?

18 November 2015

A Duplexer is a device that allows a Repeater to be equipped with a single antenna for both transmit and receive purposes.

It is a passive mechanical device with three ports (connections) Antenna, Transmitter and Receiver and has two internal tuned filters.

A repeater can be set up with two antenae one to transmit and the other to receive but these aerail need to be separated by some distance to vaoid co-interference and require cable feeders to each antenna. So in most installations a duplexer makes for a lower cost, simpler and more reliable installation.

It works as follows.

  • The transmit port is connected to the antenna port. But transmit frequencies are blocked from reaching the receiver port.
  • The receiver port is connected to the antenna port. But receiver frequencies are blocked from reaching the transmitter port.

The duplexer has to be manually tuned to both the transmit and receiver frequencies and special equipment is used to do this as frequency precision is essentially for good performance.

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