Tone systems used in amateur radio
There are two tone systems used in amateur radio: Continuous Tone Coded Squelch System (CTCSS) and Dual Tone Multi Frequency (DTMF).
CTCSS tones are sub audible (cannot be heard) and are primarily used on repeater systems to prevent non-amateur radio emissions from operating the repeater’s receiver. If a device causes interference to the repeater’s receiver then the repeater will ignore the interference since it does not have the CTCSS tone present.
DTMF uses audible tones. These tones are the ones you hear when dialling a number on your telephone. The tones are used to connect and disconnect (link) repeaters in an ad-hoc manner to extend the range of communications; for example, with the IRLP system.
DTMF tones can also be used to control and interrogate a repeater’s operating parameters. Repeater equipment can be remotely polled to report on its power, temperature, etc.
Repeaters and repeater radio links must only transmit when either receiving a signal on the input frequency or transmitting their identification.
Repeaters and repeater radio links must transmit their call sign every ten minutes of operation.
A Foundation or Standard station must not use a repeater which transmits on frequencies they are not authorised to use – for example, a Foundation station can not use a repeater that transmits on 52 MHz, even if it receives on a band the Foundation station can use, like 146 MHz.
If repeaters are operating cross band, they must incorporate an access control system to prevent Standard and Foundation licencees being retransmitted on bands they are not authorised to use.
The access control system normally uses CTCSS.
Internet linking of repeaters is permitted provided the operators of the service take measures to prevent non-unauthorised (non-amateur) users e.g. DMR, Echolink.
Repeater stations may only be operated portable for 7 days.
A beacon station must transmit its call sign every 10 minutes.
Beacon stations may only be operated portable for 7 days.