DTMF

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DTMF Dual Tone Multi Frequency

DTMF is used in ham radio in applications such as IRLP and Echolink, as a means to dial outside numbers via phone patch and as a means for repeater owners to configure the system remotely. It is sometimes known as tone dialling and allows the user to send a series of tones that activate or disable a remote repeater or service.

Why DTMF?

The DTMF system was developed to encompass as wide a range of potential signals as possible. In practice today, most hams will only use the numerical combinations. For example, to open IRLP 6556, the operator will press the talk button on the microphone and then press the digits 6556 also on the microphone.

Each letter and number is allocated a pair of tones, a high tone and a low tone, using the same DTMF frequencies as on telephone land lines.

The following table shows the pairs of signals used for the digits 0 - 9, letters A - D and characters * and #

DTMF keypad frequencies
1209 Hz 1336 Hz 1477 Hz 1633 Hz
697 Hz 1 2 3 A
770 Hz 4 5 6 B
852 Hz 7 8 9 C
941 Hz * 0 # D
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