Repeaters are simply automatically controlled amateur radio stations that simultaneously re-transmit on one frequency what it received on another frequency.
Their purpose is to extend the range of radio communications beyond normal line of sight propagation in the VHF and UHF spectrum, or to enhance local communication in low-lying areas or where there are many obstructions and/or hills.
For maximum range and performance, repeaters typically have efficient antennas placed high above ground so they are often located on hills, towers or tall buildings. They also transmit at greater power levels than the average ham uses to provide a stronger signal. Repeaters usually have back-up power sources to provide functionality during a momentary or sustained power interruption.
The practical result is that a repeater enables a ham on the ground with a low-power radio and poor antenna to communicate clearly with people many miles away. Repeaters make hand-held and mobile communications practical and fairly reliable.
Because repeaters must use separate transmit and receive frequencies, the radios have to support this arrangement to work properly. Fortunately most modern radios are designed for repeater operation with appropriate frequency configuration and other related settings.
Direct radio communications (non-repeater) is termed simplex operation. In simplex mode both radios operate on the same transmit and receive frequency.
Conventional repeaters operating in Frequency Modulation (FM) mode are by far the most common. However, some repeaters support other modulation types. Others repeat on a different frequency spectrum (cross-band) and some are designed for satellite operation or digital modes. Some repeaters are linked together for very wide-area coverage.
Wherever you are located you can find a listing of area repeaters and their characteristics in a repeater directory. These directories are found online, in a smart phone app, or in printed books and are the best source of information for repeater location, features, and settings.
VHF/UHF repeaters are found worldwide. Most cities have at least one repeater; many cities have multiple repeaters. In metropolitan areas there can be so many repeaters that they start to interfere with each other. To address this issue, repeater frequency and location are often managed by a repeater coordinator to minimize problems.
Repeaters are most popular on the 2m band, then on 70cm and 1.25m. 33cm and 23cm repeaters are also taking root in certain areas There are repeaters on lower frequency bands but these are not as common; 6m repeaters can be found in some locations and there are a number of 10m repeaters.
The ARRL’s QST magazine had an excellent article on understanding repeater operation. It is well worth every ham’s time to read this comprehensive yet easy to understand explanation of how repeaters work and how they are commonly used: Analog FM Repeater Overview ARRL Learn about transmit & receive frequencies, duplex vs. simplex, offsets, coordination, access tones, squelch, courtesy beep, timeout, linking and more.
This article is copied from QST magazine, February 2015, pages 82-83. A direct copy is located here. You must be an ARRL member to access the e-magazine but if you’re a US ham you are strongly encouraged to be a member for many other good reasons.