About Repeaters:

VHF and UHF radio signals from vehicle-mounted or hand-held transceivers, have short range which is affected by obsticals, such as high ground. Their range can be greatly improved by the use of a repeater. This is a radio station located on a hill, or with its antenna on a tall mast, 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 incresing their range.

Amateur repeaters can be found mainly on the 2m and 70cm bands, but there are also several on the 1.3GHz and now the 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 amateurs and if you use a repeater frequently, you should find out how to make a donation towards it upkeep.

Because it is extreemly difficult to re-transmit a signal on the same frequency used to receive it, repeaters use seperate 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, it is easy for the repeater's transmitter to interfere with its reveiver, even if seperate atennas are used. To reduce this effect, vary 'sharp' 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.

In addition to the radio and the filters, amateur repeaters have control equipment, known as 'logic', which generates its callsign in Morse every few minutes (GB3 plus two letters) and handles the audio connection between the reveiver 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. Recently, it has been possible to use an alternative, 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 extreemly low in frequency - less than 100Hz. Repeaters in different areas are allocated their own tone and use of CTCSS prevents well-located stations accidently activating two repeaters on the same channel at once. All 6m repeaters must have a CTCSS tone to access them, they do not use the 1750Hz tone burst.