DTMF (Dual-tone multi-frequency)
mode is included into the software MULTIPSK by
Patrick F6CTE, there is the
description of this mode and its variants as well as the specifications
coming from his software :
Duration of the symbol :
variable, in general between 40 to 100 ms for the carrier and 20 to 60
ms for the silence which follows the carrier. In Multipsk, the carrier
is 60 ms long and the silence 40 ms long (100 ms for the whole
Note : to a symbol (of 4 bits) corresponds a character.
Modulation : MFSK, two groups of 4 tones with 2 tones send in the same time (which give 16 possibilities)
Reception mode : FM in VHF, otherwise USB is recommended in HF
Character set : 0..9 * # A B C D
Shape of pulse : rectangular
Tone frequencies : 1st group: 697, 770, 852, 941 Hz and 2nd group: 1209, 1336, 1477, 1633 Hz
For example: "1" is composed of the tone 697 Hz and the tone 1209 Hz
Bandwidth : about 1000 Hz
Demodulation : non-coherent,
Correction code : no
Convolution code : no
Interleaving : no
Automatic Frequency Correction : no (frequencies are fixed),
Pmean/Ppeak : 1 (about 0.5 if the necessary silences between characters are integered)
Lowest S/N : about 2.5 dB (to avoid false detections)
In Multipsk, a DTMF code is supposed finished after 2 seconds of silence.
is added a specific character which is the carriage return / linefeed.
This one adds 2 seconds of silence. This permits to finish the sequence
of DTMF characters which constitutes a definite code. This character is
not useful for only one code but can is useful to separate different
codes as, for example:
"mode" is used for telephone (to dial the phone number) but also in VHF
and UHF for different uses as, for example, activation of repeaters by
Recommanded frequencies for DTMF(FM in VHF and UHF and USB in HF)
1) In FM, on the repeaters frequencies (144,500 to 144,794 KHz and 145,194 to 145.593 Khz).
For example in France: "http://f5ad.free.fr/ATV-RES_%20Tableau_des_frequences.htm"
2) In USB (HF), anywhere but on the frequencies reserved to digital modes (bandwidth >= 1 KHz).
as DTMF frequencies are fixed, the chosen frequency will be a multiple
of 2 KHz, as for example: 14102, 14104, 14106 KHz... on 20 meters.