You are here: Home » Amateur Radio » What are Repeaters?
What are Repeaters?
When using a radio on UHF or VHF from a car or from a hand-held transceivers, signals can be affected by obstacles, such as high ground and buildings. This means they have a short range. Also, the antennae tend to be lower and not as effective.
The range can be greatly improved by the use of a repeater. They tend to be located on a hill or a tall building, which receives transmissions from a wide area and re-transmits them on another frequency. Everyone who can hear the repeater can communicate with everyone else who can hear it, thus greatly increasing their range.
Amateurs repeaters are usually on the 2m and 70cm bands, but there are also several on the 23cm and 6m bands. The range of amateur television transmissions can also be improved by repeaters and there are television repeaters on 1.3GHZ and 10GHZ. Repeaters are built, maintained and financed by local groups of u use a repeater frequently, you should find out how to make a donation towards it upkeep.
It is extremely difficult to use a repeater where the transmit signal is on the same frequency as the receive frequency so repeaters use separate transmit and receive frequencies. These are 500 KHz apart on 6m, 600 KHz apart on 2m and 1.6 MHz apart on 70cm. Even with this frequency spacing, a repeater's transmitter can interfere with its receiver, even if separate antennae are used. To reduce this effect,' filters are placed between the radio equipment and the antenna; in the transmitter lead to filter out any noise which may be on the receive frequency, and in the receiver lead to filter out the transmitter signal which would otherwise overload it.
Amateur repeaters have control equipment, known as the "logic", which generates its callsign in Morse every few minutes (GB3 plus two letters) and handles the audio connection between the receiver and the transmitter. The logic also produces a 'beep' or Morse 'K' a second or two after each person stops talking. You should always wait for this 'beep' before transmitting to allow others to 'break in'.
In order to ensure that the only stations relayed by a repeater are those intended to use it, a short 1750Hz tone must be sent by the user to 'wake the repeater up'. The repeater will then stay on air whilst it is being used but will close down if it 'hears' no-one on its input frequency for several seconds. Alternatives are now used; a CTCSS tone. This is a tone sent all the time you are transmitting, but it doesn't interfere with your speech as it is extremely low in frequency. It is so low that humans can not hear it. Repeaters in different areas are allocated their own tone and use of CTCSS prevents well-located stations accidentally activating two repeaters on the same channel at once. All 6m repeaters must use CTCSS to access them as they do not use the 1750Hz tone.