Repeater site pictures
Our repeaters use one common cabinet, which stands about six feet tall, with a single power supply powering both repeaters.With the power supply at the bottom, the two meter repeater is in the lower half, and the 440 repeater and its duplexer are in the upper half.
Two transmitters are fed in to one feedline, and share the same antenna, while two receivers are simultaneously using the same antenna, without being burnt to a crisp by the transmitters. We use duplexers and diplexers to accomplish all of this.
A duplexer consists of resonant cavities to separate the transmitter output from its companion receiver. A cavity acts as a series-tuned circuit, to pass RF from the transmitter to the antenna with increasing loss to frequencies away from the transmit frequency, while another one similarly passes RF from the antenna to the receiver, at the receive frequency. Other cavities serve as parallel-tuned circuits to reject RF between the transmitter and receiver, with maximum rejection points tuned to the transmit frequency and to the receive frequency. Such a system is called a bandpass-band-reject duplexer.
We originally used a four-cavity duplexer for the 147.12 repeater, but now are using a six-cavity unit. While it has more insertion loss to the desired signal than the old unit, it has proved to more than make up for it by removing much more transmitter noise from the receiver input, and the system is more responsive as a result.
A diplexer is a unit which isolates one repeater from the other. It does not need to be as large and cumbersome because of the wide separation of frequencies involved between the 147 MHz band and the 444 MHz band.
A diplexer is used to separate your dualband radio's two-meter section from its companion 70 centimeter section, when using the same antenna. it is built in to the radio if there is one antenna port for both bands. Also, a TV splitter is a diplexer, separating the VHF and UHF signals for the TV. Modern TV sets have this feature built-in, as there is only one antenna port on the rear of the set.
