Amateur radio repeater

An amateur radio repeater system consisting of a 70cm repeater and a 2 meter digipeater and iGate.

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 not limited to amateur radio (ham radio), they are in use by a wide range of users - public safety (police, fire, etc.) business, government, military, and more.

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 which covers most of western Michigan, or the Western Intertie Network System ("WINsystem") that covers most of California .

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 squelch tone (CTCSS 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 or DPL (a Motorola trademark).

In many communities, the repeater has become the on-the-air gathering spot for the local amateur radio community. Local public service nets may be heard on these systems and many are employed 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.

Repeater networks

Repeaters may also be linked together or connected to over the Internet using voice over IP (VoIP) techniques. Echolink allows hams with computers to connect to repeaters anywhere around the world and the Internet Radio Linking Project (IRLP) allow for direct repeater linking. In addition, communications satellites called OSCARs (Orbiting Satellite Carrying Amateur Radio) have been launched with the specific purpose of operating as spaceborne amateur repeaters.

UK repeaters

In the UK, repeaters are managed by the Emerging Technology Co-ordination Committee of the Radio Society of Great Britain and licenced by Ofcom the industry regulator for communications.

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.

Ham repeaters are found mainly in the VHF two meter (144 - 148 MHz) and the UHF 70 centimeter (420 - 450 MHz) bands, but can be used on almost any frequency pair above 29 MHz. Note that different countries have different rules; for example, in the United States, the two meter band is 144-148MHz, while in the United Kingdom and most of Europe) it's 144-146MHz.

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. 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 146.34MHz and listen on 146.94MHz (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 146MHz, so that the display will read "146.82" (the output frequency), and the radio is set to transmit "down" 600kHz on 146.22MHz.

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 time restarts after a short pause following each transmission, and many systems feature a beep or chirp tone to signal that this has taken place.

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, then plays back the recording over the transmitter on the same frequency. A common name for them is a "parrot" repeater.

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).

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 2m and a second on 440MHz 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 setup 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.

Cross Band Repeater

A repeater that converts the original band of frequencies of the received signal to a different frequency band for retransmission after amplification. 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 duplexer's to achieve the required rejection for same band repeating.fact

Source: from Federal Standard 1037C and from MIL-STD-188

Operating Terms

Kerchunking is a term used in ham radio that refers to the act of transmitting a momentary signal to check a repeater without identifying. 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.

See also

Replexer

External links

• http://www.repeater-builder.com - a free information web site devoted to those that build repeaters of any type: amateur, commercial, GMRS, public safety, etc.
• http://www.usrepeaters.com - list of over 23,000 repeaters in the United States and elsewhere
• http://k5ehx.net/repeaters/ - Display repeaters on map
• http://www.arrl.org/ - The USA national association for amateur radio.
• http://daytonfmgroup.googlepages.com/ Dayton Ohio 220 MHz open repeater.
• http://www.W3AHS.com - W3AHS Repeater Worldwide via Echolink - Williamsport,PA
• http://www.KB3AWQ.com - KB3AWQ Dot Com Williamsport, PA