What is a Repeater
By placing a repeater in a central or high location, radio communication range for VHF and UHF can be extended. This is very useful for handheld radios. This article is mainly about VHF FM voice repeaters. The type that is used on the Far West Repeater system. Other types of repeaters exist, but is not the focus of this article.
Repeaters are radio systems that transmit and receive at the same time. The easiest way to do this is to use two radio frequencies. One for transmit, and one for receive. This specialized service puts extra requirements on the radio equipment that would not be necessary under normal radio operations. In the United States, a standard of 600 KHz has been established for the difference or split between transmit and receive on VHF frequencies. This is only an agreement and not an FCC rule. This 600 KHz split gives a reasonable separation between transmit and receive signals that, with proper filtering and other engineering practices, minimizes interference the receiver gets from the transmitter.
Antenna systems also have to be specialized for repeater operations. The Far West repeaters use a single antenna with a very sophisticated filter (duplexer) to connect the transmitter and receiver to the single antenna. Other antenna configurations are possible. All antenna systems associated with a repeater system needs special consideration.
Transmitters in repeater service need to have a very clean radio signal. The generation of a radio signal inherently generates more than you want. All transmitters, repeater or not, need internal filtering to reduce the transmission of unwanted radio energy. Standards as well as rules and regulations describe the required attenuation of these extra radio emissions. Repeater transmitters are usually in close proximity to the repeater receiver. This adds an extra burden on design criteria. Tight filtering circuits and extra RF shielding is employed in critical areas and on power and other wiring entering the transmitter housing.
Receivers in repeater service also require special consideration above and beyond a standard receiver. As with the transmitter, extra shielding and filtering reduce the chance of interference. With the receiver needing only to receive one frequency, the bandwidth of front end circuitry can be adjusted to maximize weak on-channel signals while rejecting unwanted radio signals that are usually prevalent at highly populated repeater sites.
The transmission line, connectors, grounding, and mounting hardware all play a critical role and should be of utmost quality and installed by knowledgeable personnel. Regular testing and maintenance keeps repeater systems in top operating condition.