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. 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 [http://www.w8hvg.org Independent Repeater Association] which covers most of western Michigan, or the Western Intertie Network System ("WINsystem") that covers most of California [http://www.winsystem.org A series of linked, or Intertied, UHF (440 MHz, or 70 cm) repeaters] .

ervices

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 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.

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 repeater nodes setup to receive on the same frequency. The repeater node with the strongest signal will be the one that actually triggers the central repeater transmitter to begin transmitting with its signal. Such a system can be used to widen coverage to low power amateur transmitters that would not be able to key up the central location, but can receive the signal from the central location without an issue.

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 Echolink, IRLP, WIRES and eQSO.

atellite repeaters

In addition, communications satellites called OSCARs (Orbiting Satellite Carrying Amateur Radio) 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.

Repeater coordination

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.

USA coordination

In the USA, coordination is optional, but Part 97 rule 205(c) prefers a coordinated repeater over an uncoordinated repeater in disputes over interference. [cite web|url=http://www.metrocor.net/faq.htm#q1|title=MetroCor FAQ: Why do systems need coordination?|accessdate=2008-08-06|publisher=MetroCor] Coordination is overseen by the National Frequency Coordinators' Council (NFCC), a non-profit organization that certifies regional coordinators. [cite web|url=http://www.arrl.org/nfcc/nfcc.htm|title=What is the NFCC?|publisher=NFCC|accessdate=2008-08-06]

UK repeaters

In the UK, repeaters are managed by the Emerging Technology Co-ordination Committee (ETCC) of the Radio Society of Great Britain [http://www.ukrepeater.net Emerging Technology Co-ordination Committee] 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.

implex repeater

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.

Cross-band repeater

A cross-band repeater (also sometimes called a replexer), is a repeater that converts the original band of frequencies of the received signal to a different radio 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.

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

ame-band 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 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. [http://k5ehx.net/repeaters/qrepeater.php?tag=TARCUHFLINK An example of a linked repeater system]

Digipeater

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.

TV repeater

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.

Transponder

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. Some transponders may be inverting or non-inverting. This means that a 70 CM to 2 M transponder which repeats 432.000 MHz - 432.100 MHz to 146.000 - 146.100 MHz would take a signal at 432.001 MHz and repeat it to 146.099 MHz; vic versa. [cite web | url=http://www.arrl.org/tis/info/HTML/p3d/ | title=Phase 3D Satellite Primer]

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. [cite web | url=http://www.arrl.org/FandES/ead/materials/Repeater.ppt | title=The New Ham's Guide to Repeaters] 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.

References

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://www.arrl.org/ - The USA national association for amateur radio.