Amateur Radio Repeater

Amateur Radio Repeater
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.
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 at .
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.
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.
Repeaters may also be linked together or connected to over the Internet using voice over IP (VoIP ). Echolink > allows hams with computers to connect to repeaters anywhere around the world and the Internet Radio Linking Project (IRLP ) and App rpt/Asterisk allow for direct repeater linking. In addition, communications satellites called OSCARs have been launched with the specific purpose of operating as spaceborne amateur 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
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 most 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. In the two-meter band, the standard is a 600 kHz shift, but some non-conforming oddball-split repeaters can be found in various places. 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 with 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 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 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.
Standard repeaters require either the use of two antennas (one each for transmitter and receiver) or a diplexer (also 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).
Most repeaters are remotely controlled through the use of audio tones on a control channel

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