Part 1 – Repeaters: What They Are and How to Use Them

Curated from ARRL – 

More hams use frequency-modulated (FM) voice than any other communications mode.  Most hams have an FM rig of some type. They use it to keep in touch with their local friends. Hams often pass the time during their morning and evening commute talking on the air. In most communities, amateurs interested in a specialized topic (such as chasing DX) have an FM frequency where they meet regularly to exchange information. At flea markets and conventions, hand-held FM units are in abundance as hams compare notes on the latest bargain.

Generally, it’s a good idea to use VHF or UHF for all local communications. The HF bands should be reserved for longer-distance contacts to reduce interference on the HF bands.

VHF and UHF FM voice operation takes two forms: simplex and repeater. Simplex operation means the stations are talking to each other directly, on the same frequency. This is similar to making a contact on the HF bands.

FM voice operation is well-suited to local VHF/UHF radio communication because the audio signal from an FM receiver is not affected by static-type electrical noise. Car engines and ignition systems produce quite a bit of static electrical noise, and many hams like to operate their FM radios while they are driving or riding in a car. (This is called mobile operation.) An AM or SSB receiver is affected much more by static-type electrical noise.

The communications range for VHF and UHF FM simplex is usually limited to your local area (5-15 miles). If you live high on a mountain and use a high-gain directional antenna, you may be able to extend your range considerably. Unfortunately, most of us do not have the luxury of ideal VHF/UHF operating conditions. Often, we want to make contacts even though we live in a valley, are driving in a car or are using a low-power, hand-held transceiver.

Enter repeaters. A repeater receives a signal and re-transmits it, usually with higher power and from a better location, to provide a greater communications range. Often located atop a tall building or high mountain, VHF and UHF repeaters greatly extend the operating range of amateurs using mobile and hand-held transceivers. If a repeater serves an area, it’s not necessary for everyone to live on a hilltop. You only have to be able to hear the repeater’s transmitter and reach the repeater’s receiver with your transmitted signal.

A repeater receives a signal on one frequency and simultaneously retransmits (repeats) it on another frequency. The frequency it receives on is called the input frequency, and the frequency it transmits on is called the output frequency.

To use a repeater, you must have a transceiver that can transmit on the repeater’s input frequency and receive on the repeater’s output frequency. The input and output frequencies are separated by a predetermined amount that is different for each band. This separation is called the offset. For example, the offset on 1.25 meters is 1.6 MHz. A repeater on 1.25 meters might have its input frequency on 222.32 MHz and its output on 223.92 MHz. Repeater frequencies are often specified in terms of the output frequency (the frequency you set your receiver to listen on) and the offset.  Your transmitter operates on a frequency that is different from the receive frequency by the offset amount.

Most transceivers designed for FM repeater operation are set up for the correct offset. They usually have a switch to change between simplex operation (transmit and receive on the same frequency) and duplex operation (transmit and receive on different frequencies). So, if you wanted to use the repeater in the preceding example, you would switch your transceiver to the duplex mode and dial up 223.92 to listen to the repeater. When you transmit, your rig will automatically switch to 222.32 MHz (1.6 MHz lower in frequency), the repeater input frequency.

When you have the correct frequency dialed in, just key your microphone button to transmit through (“access”) the repeater. Most repeaters are open — that is, available for use by anyone in range. Some repeaters, however, have limited access. Their use is restricted to exclusive groups, such as members of a club. Such closed repeaters require the transmission of a continuous subaudible tone or a short “burst” of tones for access. These are called CTCSS (continuous tone-coded squelch system) or PL (Private Line PL is a Motorola trademark) tones. There are also some repeaters available for use by everyone that require the use of special codes or subaudible tones to gain access. The reason for requiring access tones for “open” repeaters is to prevent interference from extraneous transmissions that might accidentally key the repeater. If you wish to join a group that sponsors a closed repeater, contact the repeater control operator.