July 2002
Intermediate to advanced
344 pages
8h 37m
English
Content preview from Newnes Radio and RF Engineering Pocket Book, 3rd Edition
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195
16.2 In-band tone and digital signalling
16.2.1 Dual tone multi-frequency (DTMF)
Developed for telephone work, dual tone multi-frequency signalling
has crept into some radio systems but is slow to operate compared
with other in-band systems. Two tones are transmitted simultaneously
to represent each digit. In the UK they conform to the MF4 code
(Table 16.3 ).
Table 16.3 MF4 code of DTMF tones
Digit Frequencies (Hz)
1 697 1209
2 697 1336
3 697 1477
4 770 1209
5 770 1336
6 770 1477
7 852 1209
8 852 1336
9 852 1477
0 941 1336
∗
941 1209
# 941 1477
Some push button telephones signal to the local exchange by gen-
erating a combination of two frequencies. Each row
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