What is a repeater?
A repeater is a station that receives incoming signals and retransmits them on a different frequency. The main purpose of repeaters is to extend the operating range of mobile stations, or stations in lower-lying areas or remote locations where simplex communication is not normally possible. They can also be used as calling channels for initial contact before switching to a simplex frequency.
Repeaters also provide a very valuable service for emergency communications.
Repeaters can be linked together to extend their range even further. This linking can be done by link transmitters and receivers installed at the repeater. It can also be done by landline or Internet connection.
Most repeaters are designed for voice operation, using FM or digital voice modes such as D-Star or APCO P25. There are also repeaters for modes such as ATV.
Repeaters must be licensed by the FCC.
10 Metre Repeaters
10 metre repeaters can provide not only local, but also national and overseas coverage. There are four internationally agreed repeater channels between 29.5 and 29.7 MHz.
6 Metre Repeaters
On the 6 metre band, repeaters provide local coverage but interstate contacts also happen quite often during times of high solar activity. There are 18 repeater channels on this band, with output frequencies beginning at 53.550 MHz.
2 Metre Repeaters
2 metres is the main band for repeater activity. There are 16 channels between 146.625 and 147.000 MHz, and 15 channels above 147 MHz. Some additional frequencies have also been allocated for special purposes.
70 cm Repeaters
The 70 cm band is the other major band for repeater activity. A new standard repeater offset of 7 MHz was adopted in 2015, with inputs at 431 MHz and outputs at 438 MHz.
23 cm Repeaters
There are also repeaters on the 23 cm band, with 39 channels available. Repeaters on this band transmit between 1273 – 1274 MHz with input frequencies at 1293 – 1294 MHz.
Repeaters can be linked together to extend their coverage. When repeaters are linked, a signal received by any one of the linked repeaters is retransmitted by all of them, so the user of the repeater is able to cover a wider service area. This kind of linking is especially useful in areas where repeater coverage is limited by terrain, or in areas where there is a small amateur population.
Linked repeaters may operate in the same band, or on different bands. This allows repeater users to operate on one band but still be able to communicate with users on other bands.
Repeaters may be permanently linked, or they can be controlled by access tones so that the user can activate the link if it is required.
A new development in amateur radio is the use of Internet VoIP links. These links allow connections between repeaters anywhere in the world. The two most popular Internet linking systems are IRLP and Echolink.
Most repeaters use a pair of frequencies, receiving on one frequency and transmitting on the other. But it is also possible to add a simplex gateway to an existing split frequency repeater. This is a simple way of allowing a repeater to operate on more than one band.
A number of repeaters use access tones. The most commonly used system is subaudible CTCSS tones, which can be used to activate links to other repeaters. Tone access is also useful if repeaters suffer from interference from non-amateur sources. The access tone prevents the repeater from transmitting unless it is receiving an access tone from an amateur station.
Repeaters for specialised modes
Most repeaters are for normal voice operation, but there are also repeaters for other modes including SSTV and digital voice or data. On 70cm and higher bands, there are also ATV repeaters.