Amateur Radio Repeaters

An amateur radio repeater is an electronic device that receives a weak or low-level amateur radio signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation. Many repeaters are located on hilltops or on tall buildings as the higher location increases their coverage area, sometimes referred to as the radio horizon, or “footprint”. Repeaters are similar in concept to those used by public safety entities (police, fire department, etc.), businesses, government, military, and more. Amateur repeaters may even use commercially packaged repeater systems that have been adjusted to operate within amateur radio frequency bands, but more often amateur repeaters are assembled from receivers, transmitters, controllers, power supplies, antennas, and other components, from various sources.

In amateur radio, repeaters are typically maintained by individual hobbyists or local groups of amateur radio operators. Many repeaters are provided openly to other amateur radio operators and typically not used as a remote base station by a single user or group. In some areas multiple repeaters are linked together to form a wide-coverage network.

Equipment

The most basic repeater consists of an FM receiver on one frequency and an FM transmitter on another frequency usually in the same radio band, connected together so that when the receiver picks up a signal, the transmitter is keyed and rebroadcasts whatever is heard.

In order to run the repeater a repeater controller is necessary. A repeater controller can be a hardware solution or even be implemented in software.

Most repeaters typically have a timer to cut off retransmission of a signal that goes too long. Repeaters operated by groups with an emphasis on emergency communications often limit each transmission to 30 seconds, while others may allow three minutes or even longer. The timer restarts after a short pause following each transmission, and many systems feature a beep or chirp tone to signal that the timeout timer has reset.

Services

Services provided by a repeater may include an autopatch connection to a POTS/PSTN telephone line to allow users to make telephone calls from their keypad-equipped radios. These advanced services may be limited to members of the group or club that maintains the repeater. Many amateur radio repeaters typically have a tone access control (CTCSS, CG or PL tone) implemented to prevent them from being keyed-up (operated) accidentally by interference from other radio signals. A few use a digital code system called DCS, DCG or DPL (a Motorola trademark). In the UK most repeaters also respond to a short burst of 1750 Hz tone to open the repeater.

In many communities, a repeater has become a major on-the-air gathering spot for the local amateur radio community, especially during “drive time” (the morning or afternoon commuting time). In the evenings local public service nets may be heard on these systems and many repeaters are used by weather spotters. In an emergency or a disaster a repeater can sometimes help to provide needed communications between areas that could not otherwise communicate. Until cellular telephones became popular, it was common for community repeaters to have “drive time” monitoring stations so that mobile amateurs could call in traffic accidents via the repeater to the monitoring station who could relay it to the local police agencies via telephone. Systems with autopatches frequently had (and still have) most of the public safety agencies numbers programmed as speed-dial numbers.

Networks

Repeaters may be linked together in order to form what is known as a linked repeater system or linked repeater network. In such a system, when one repeater is keyed-up by receiving a signal, all the other repeaters in the network are also activated and will transmit the same signal. The connections between the repeaters are made via radio (usually on a different frequency from the published transmitting frequency) for maximum reliability. Some networks have a feature to allow the user being able to turn additional repeaters and links on or off on the network. This feature is typically done with DTMF tones to control the network infrastructure. Such a system allows coverage over a wide area, enabling communication between amateurs often hundreds of miles (several hundred km) apart. These systems are used for area or regional communications, for example in Skywarn/CANWARN nets, where storm spotters relay severe weather reports. All the user has to know is which channel to use in which area.

Repeaters may also be connected to over the Internet using voice over IP (VoIP) techniques. VoIP links are a convenient way to connecting distant repeaters that would otherwise be unreachable by VHF/UHF radio propagation. Popular VoIP amateur radio network protocols include D-STAR, Echolink, IRLP, WIRES and eQSO.

Central Ontario Area Repeaters

DMR Repeaters

DMR repeaters each have the capability to provide local, regional and worldwide repeater coverage. Much more than that though, the network allows two completely separate QSOs at the same time, a unique feature made possible using Motorola’s “Time Division Multiple Access” (TDMA) technology. This enables a TDMA repeater to divide transmissions into two discrete and pre-selectable “talkgroups”, routing them appropriately to others monitoring the same group anywhere around the world. Effectively, this means two completely separate voice channels are possible within one standard 12.5kHz frequency allocation – highly efficient use of the spectrum!

Time-Division Multiple-Access (TDMA) preserves the full channel width and divides it into alternating time slots that can each carry an individual call. Motorola maintains that two-slot 12.5 kHz TDMA-based systems, providing 6.25 kHz equivalency, are the better choice for most large organization/enterprise radio users. This means that two seperate conversations can be handled by the one repeater, on the same frequency but a different “channel”.

TDMA technology for narrowband 12.5 KHz (6.25 equivalent-6.25e) organization/business radio users, provides advantages of feature flexibility, lower equipment costs, longer battery life, future-readiness, and the proven ability to increase spectral efficiency without risking increased congestion or interference.

For more DMR information and repeaters, see Digital Mobile Repeaters

D-STAR Repeaters

D-STAR (Digital Smart Technologies for Amateur Radio) is a digital voice and data protocol specification for amateur radio. The system was developed in the late 1990s by the Japan Amateur Radio League and uses frequency-division multiple access and minimum-shift keying in its packet-based standard. There are newer digital modes (Codec2, for example) that have been adapted for use by amateurs, but D-STAR was the first that was designed specifically for amateur radio.

Several advantages of using digital voice modes are that it uses less bandwidth than older analog voice modes such as amplitude modulation, frequency modulation, and single sideband. The quality of the data received is also better than an analog signal at the same signal strength, as long as the signal is above a minimum threshold and as long as there is no multipath propagation.

D-STAR compatible radios are available for HF, VHF, UHF, and microwave amateur radio bands. In addition to the over-the-air protocol, D-STAR also provides specifications for network connectivity, enabling D-STAR radios to be connected to the Internet or other networks, allowing streams of voice or packet data to be routed via amateur radio.

All D-STAR compatible radios are manufactured by Icom, Kenwood, and FlexRadio Systems.

For more D-Star information and repeaters, see D-Star Repeaters