GB1501706A - Multi-frequency signal receivers - Google Patents

Abstract

1501706 Tone receivers COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 21 April 1975 [24 April 1974] 16335/75 Heading H4K A multifrequency tone receiver of the type having a number of detecting circuits connected in parallel to an input comprises in each detecting circuit a signal generator, the output of which is modulated with an incoming tone to produce a heat frequency which is common to all the detecting circuits. Each detecting circuit further comprises a filter to separate out said heat frequency and the output of each detecting circuit is coupled to common logic circuitry which enables a signal to be produced at an output corresponding to the frequency content of the incoming tone. The signals to be detected are 2 out of 6 multifrequency tones comprising 15 combinations a 1 -a 15 of the frequency as 700-1700 Hz arranged in 200 Hz steps. In addition a single tone of 1900 Hz used as a control signal is to be detected. In one embodiment the receiver comprises nine parallel detectors each including a respective square wave signal generator G1-G9. Generators G1-G6 have respective frequencies 900-1900 Hz arranged in 200 Hz steps and generators G8 and G9 have frequencies of 500 Hz and 700 Hz respectively. Each detector further includes a 200 Hz filter F1-F9 and the tone frequencies w and generator frequencies w0 are such that each single tone w will produce an output at at least two of the filters F1-F9, and three of the tones 1300 Hz, 1700 Hz and 1900 Hz will each produce outputs at three of the filters because of a significant w-3w0 frequency component due to the use of square wave generators. The logic arrangement of Fig. 3 enables unique outputs to be produced for the 15 dual tones a 1 -a 15 , and the control signal ac. A no tone present output S = D2 + D3 + D8 is also produced. A further arrangement using 800 Hz filters and a set of seven generator frequencies from 700-2100 in 200 Hz steps excluding 1300 Hz is described, which enables the logic of Fig. 3 to be simplified. Fig. 4 (not shown) illustrates an arrangement using 600 Hz filters wherein one of the square wave generators is coupled to two detecting circuits. The devices T1-T9 used for modulation may be F.E.T.'s.