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". Amateur radio repeaters are similar in concept to those in use by public safety (police, fire, etc.), business, government, military, and more. Amateur radio repeaters may even use commercially-packaged repeater systems tuned into an amateur radio frequency allocation, but more usually amateur repeaters are assembled from various sources for receivers, transmitters, controllers, power supplies, antennas, and other components.
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, such as the linked system provided by the Independent Repeater Association[1] which covers most of western Michigan, or the Western Intertie Network System ("WINsystem") that now covers a great deal of California, and is in 17 other states, including Hawaii, along with parts of four other countries, Australia, Canada, Great Britain and Japan.[2]
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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 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.
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. Such a system allows coverage over a wide area, enabling communication between amateurs often hundreds of miles (several hundred km) apart. All the user has to know is which channel to use in which area.
In order to get better receive coverage over a wide area, a similar linked setup can also be done with what is known as a voted receiver system. In a voted receiver, there are several satellite receivers set up to receive on the same frequency (the one that the users transmit on). All of the satellite receivers are linked to a voting selector panel that switches from receiver to receiver based on the best quieting (strongest) signal, and the output of the selector will actually trigger the central repeater transmitter. A properly adjusted voting system can switch many times a second and can actually "assemble" a multi-syllable word using a different satellite receiver for each syllable. Such a system can be used to widen coverage to low power mobile radios or handheld radios that otherwise would not be able to key up the central location, but can receive the signal from the central location without an issue. Voting systems require no knowledge or effort on the part of the user - the system just seems to have better-than-average handheld coverage.
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.
In addition, amateur radio satellites have been launched with the specific purpose of operating as spaceborne amateur repeaters. The worldwide amateur satellite organization AMSAT designs and builds many of the amateur satellites. Several satellites with amateur radio on board have been designed and built by universities around the world. NASA and AMSAT coordinated the release of SuitSat which was an attempt to make a low cost experimental satellite from a discarded Russian spacesuit outfitted with amateur radio equipment.
Having two repeaters operate on the same radio frequency is problematic, as they can interfere with each other, even with selective calling methods enabled. To help minimize this issue, regional repeater coordination organizations have been created. In some jurisdictions, coordination may be required by law or regulation. In others, coordination is done on a voluntary basis, but with a regulatory preference for coordinated repeaters.
In the USA, coordination is optional, but Part 97 rule 205(c) prefers a coordinated repeater over an uncoordinated repeater in disputes over interference.[3] Coordination is overseen by the National Frequency Coordinators' Council (NFCC), a non-profit organization that certifies regional coordinators.[4]
In the UK, repeaters are managed by the Emerging Technology Co-ordination Committee (ETCC) of the Radio Society of Great Britain[5] and licenced by Ofcom, the industry regulator for communications in the UK.
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.
Ham repeaters are found mainly in the VHF six meters (50-54 MHz), two meter (144 - 148 MHz), 220 MHz band (222-224 MHz) and the UHF 70 centimeter (420 - 450 MHz) bands, but can be used on almost any frequency pair above 28 MHz. Note that different countries have different rules; for example, in the United States, the two meter band is 144-148 MHz, while in the United Kingdom (and most of Europe) it's 144-146 MHz.
Repeater frequency sets are known as "repeater pairs," and in the ham radio community most follow ad hoc standards for the difference between the two frequencies, commonly called the offset. In the USA two-meter band, the standard offset is 600 kHz (0.6 MHz), but some non-conforming oddball-split repeaters can be found in various places, and for various reasons, usually technical. The actual frequency pair used is assigned by a local frequency coordinating council.
In the days of crystal-controlled radios, these pairs were identified by the last portion of the transmit (Input) frequency followed by the last portion of the receive (Output) frequency that the ham would put into the radio. Thus "three-four nine-four" (34/94) meant that hams would transmit on 146.34 MHz and listen on 146.94 MHz (while the repeater would do the opposite, listening on 146.34 and transmitting on 146.94). In areas with many repeaters, "reverse splits" were common (i.e., 94/34), to prevent interference between systems.
Since the late 1970s, the use of synthesized, microprocessor-controlled radios, and widespread adoption of standard frequency splits have changed the way repeater pairs are described. In 1980, a ham might have been told that a repeater was on "22/82" -- today they will most often be told "682 down." The 6 refers to the last digit of 146 MHz, so that the display will read "146.82" (the output frequency), and the radio is set to transmit "down" 600 kHz on 146.22 MHz.
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.
A type of system known as a simplex repeater uses a single transceiver and a short-duration voice recorder, which records whatever the receiver picks up for a set length of time (usually 30 seconds or less), then plays back the recording over the transmitter on the same frequency. A common name for them is a "parrot" repeater.
Standard repeaters require either the use of two antennas (one each for transmitter and receiver) or a duplexer to isolate the transmit and receive signals over a single antenna. The duplexer is a device which prevents the repeater's high-power transmitter (on the output frequency) from drowning out the users' signal on the repeater receiver (on the input frequency). A diplexer allows two transmitters on different frequencies to use one antenna, and is common in installations where one repeater on 2 m and a second on 440 MHz share one feedline up the tower and one antenna.
Most repeaters are remotely controlled through the use of audio tones on a control channel.
Repeaters can be set up as a "link system" where transmitting on one repeater simultaneously transmits on all repeaters in the system. These systems are used for area or regional communications, for example in Skywarn.[6]
A cross-band repeater (also sometimes called a replexer), is a repeater that retransmits a specific mode on a frequency in one band to a specific mode on a frequency in a different band. This technique allows for smaller size and less complexity of the repeater system. Repeating signals across widely separated bands allows for simple filters to be used to allow one antenna to be used for both transmit and receive at the same time, avoiding the use of complex duplexers to achieve the required rejection for same band repeating. This type of system is used in the OSCAR repeaters.[7]
Contrast with a transponder, which retransmits a range of modes and frequencies from one band to another.
Most dual-band amateur transceivers are capable of cross-band repeat.
Another form of repeater is used in amateur packet radio, a form of digital computer-to-computer communications, and are dubbed "digipeaters" (for DIGItal rePEATERS). These repeaters are used for activities and modes such as packet radio, Automatic Position Reporting System, and D-STAR's digital data mode. The operate in a store-and-forward manner, by receiving and then retransmitting on the same frequency after a short delay.
An SSTV repeater is an amateur radio repeater station for relaying of slow-scan television signals. A typical SSTV repeater is equipped with a HF or VHF transceiver and a computer with a sound card, which serves as a demodulator/modulator of SSTV signals.
SSTV repeaters are used by amateur radio operators for exchanging pictures. If two stations can not copy each other, they can still communicate through a repeater.
To activate a repeater the station must send a tone of frequency 1750 Hz. Then the repeater is activated and sends K in morse code. The station must start sending a picture in approximately 10 seconds. After reception the received image is transmitted on the repeater's operation frequency.
Repeaters should operate in common SSTV modes, but it depends on the software used (MMSSTV, JVComm32, MSCAN). Some repeater are not activated by audio tone, but instead by the SSTV vertical synchronization signal (VIS code).
When there is no activity on the repeater's frequency, it works as a beacon and periodically send a random picture with identification and a timestamp.
Amateur television (ATV) repeaters are used by amateur radio operators to transmit full motion video. The bands used by ATV repeaters vary by country, but in the US a typical configuration is as a cross-band system with an input on the 33 or 23 cm band and output on 421.25 MHz or, sometimes, 426.25 MHz (70 cm band). These output frequencies happen to be the same as standard cable television channels 57 and 58, meaning that anyone with a cable-ready analog NTSC TV can tune them in without special equipment.
There are also digital amateur TV repeaters that retransmit digital video signals. Frequently DVB-S modulation is used for digital ATV, due to narrow bandwidth needs and high loss tolerances. These DATV repeaters are more prevalent in Europe currently, partially because of the availability of DVB-S equipment.
Amateur transponder repeaters are commonly used on amateur satellites. A specified band of frequencies, usually having a bandwidth of 20 to 800 kHz is repeated from one band to another. Transponders may be inverting or non-inverting. An example of an inverting transponder would be a 70cm to 2m transponder which receives on the 432.000 MHz to 432.100 MHz frequencies and transmits on the 146.000 MHz to 146.100 MHz frequencies by inverting the frequency range within the band. In this example, a signal received at 432.001 MHz would be transmitted on 146.099 MHz. Voice signals using USB modulation on the input would result in a LSB modulation on the output, and vice versa.[8]
Timing Out is a term used to describe the situation where a person talks too long and the repeater timer shuts off the repeater transmitter.
Kerchunking is a term used in ham radio that refers to the act of transmitting a momentary signal to check a repeater without identifying.[9] In many countries, such an act violates amateur radio regulations.
The term "Kerchunk" can also apply to the sound a large Amplitude Modulation Transmitter makes when the operator switches it off and on.
| Range | Band | ITU Region 1 | ITU Region 2 | ITU Region 3 |
|---|---|---|---|---|
| LF | 2200 m | 135.7 kHz - 137.8 kHz | ||
| MF | 160 m | 1.810 MHz - 1.850 MHz | 1.800 MHz - 2.000 MHz | 1.800 MHz - 2.000 MHz |
| HF | 80 / 75 m | 3.500 MHz - 3.800 MHz | 3.500 MHz - 4.000 MHz | 3.500 MHz - 3.900 MHz |
| 60 m1 | 5.250 MHz - 5.450 MHz | |||
| 40 m | 7.000 MHz - 7.200 MHz | 7.000 MHz - 7.300 MHz | 7.000 MHz - 7.200 MHz | |
| 30 m2 | 10.100 MHz - 10.150 MHz | |||
| 20 m | 14.000 MHz - 14.350 MHz | |||
| 17 m2 | 18.068 MHz - 18.168 MHz | |||
| 15 m | 21.000 MHz - 21.450 MHz | |||
| 12 m2 | 24.890 MHz - 24.990 MHz | |||
| 10 m | 28.000 MHz - 29.700 MHz | |||
| VHF | 6 m | 50.000 MHz - 52.000 MHz1 | 50.000 MHz - 54.000 MHz | 50.000 MHz - 54.000 MHz |
| 4 m1 | 70.000 MHz - 70.500 MHz | |||
| 2 m | 144.000 MHz - 146.000 MHz | 144.000 MHz - 148.000 MHz | 144.000 MHz - 148.000 MHz | |
| 1.25 m | 220.000 MHz - 225.000 MHz | |||
| UHF | 70 cm | 430.000 MHz - 440.000 MHz | 420.000 MHz - 450.000 MHz3 | 420.000 MHz - 450.000 MHz3 |
| 33 cm | 902.000 MHz - 928.000 MHz | |||
| 23 cm | 1.240 GHz - 1.300 GHz | |||
| 13 cm | 2.300 GHz - 2.450 GHz | |||
| SHF | 9 cm | 3.400 GHz - 3.475 GHz3 | 3.300 GHz - 3.500 GHz | 3.300 GHz - 3.500 GHz |
| 5 cm | 5.650 GHz - 5.850 GHz | 5.650 GHz - 5.925 GHz | 5.650 GHz - 5.850 GHz | |
| 3 cm | 10.000 GHz - 10.500 GHz | |||
| 1.2 cm | 24.000 GHz - 24.250 GHz | |||
| EHF | 6 mm | 47.000 GHz - 47.200 GHz | ||
| 4 mm3 | 75.500 GHz1 - 81.500 GHz | 76.000 GHz - 81.500 GHz | 76.000 GHz - 81.500 GHz | |
| 2.5 mm | 122.250 GHz - 123.000 GHz | |||
| 2 mm | 134.000 GHz - 141.000 GHz | |||
| 1 mm | 241.000 GHz - 250.000 GHz | |||
| THF | Sub-mm | Some administrations have authorized spectrum for amateur use in this region. | ||
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1 This is not mentioned in the ITU's Table of Frequency Allocations, but it is a de facto international amateur radio allocation. |
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| See also: Radio spectrum · Electromagnetic spectrum | ||||
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