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A duplexer is a radio device that enables someone to transmit messages and receive them over a single antenna. This is done by splitting the receiver and transmitter functions so the two do not conflict with each other during operation. While the two are split, the duplexer will only work properly if the two are tuned to the same frequency; otherwise, problems may occur. Two or more circuit cavities are needed to properly isolate the two signals, and having more cavities generally results in better quality.
A radio normally can only send messages or receive them, and those that can do both have to do so using two antennas or by using a transceiver. With a duplexer, a radio is capable of sending and receiving messages over one antenna, which serves both purposes. This decreases the amount of parts needed for the radio and also makes it easier to carry on conversations or message relays.
If a regular radio attempts to send and receive messages with one antenna, then this can overload and destroy the radio. A duplexer avoids this problem by splitting the two functions, so even though they share the same antenna, the two never interfere with each other. To perform this split, the duplex unit must be able to isolate both functions; otherwise, noise may occur or the radio may not be able to perform both functions.
To split the two, a duplexer uses resonate circuits that are stored in cavities inside the radio. There normally are two different circuits, and each holds information for either the transmitter or the receiver. When one function is used, it is made the dominant one and works until the function is complete or until the other function is required. While only two cavities are needed, having more than this can increase the quality of the transmission and reception by further isolating the two from each other.
Even though the two functions have to be split to work correctly, they must be set up on the same frequency; otherwise, the functions may be isolated too much and the duplexer will not be able to perform both functions. Not only that, but the radio must be able to tolerate the power from the transmitter, which generally is much higher than the receiver. Temperature may be an issue, because high heat can warp the radio’s body, so the body often is made from temperature-resistant metal.