GB1369946A - Noise-muting device for telegraphy receivers - Google Patents

Abstract

1369946 Muting telegraph receivers MEL EQUIPMENT CO Ltd 10 May 1973 22403/73 Headings H4L and H4P Muting apparatus for a telegraphy receiver comprises : means for detecting incoming signal elements of less than a predetermined duration; means for deriving a number representative of the number of such elements received during a given time; and means for providing a signal for muting the receivers if the representative number exceeds a predetermined number. The demodulated signal, comprising pulses less than 5ms. width characterizing noise and pulses greater than 5 ms. width characterizing wanted signal elements, is applied to monostable circuits 25, 26 to produce, on line 32, a pulse at each transition of the input signal. These pulses are applied to the reset input of a counter 33 which is arranged to fill and produce an output of line 35 only if the pulses are more than 5 ms. apart. The output pulses from counter 33 set bi-stables 36, 38 to hold bi-stable 39 in its reset state. If the pulses are less than 5 ms. apart bi-stables 36, 38 remain in their reset states, and the pulses on line 32 clock bi-stable 39 to fed logical " 1 " pulses into an eight stage register 42. The contents of the register is then read out into a counter 45 which counts how many of the eight stages contain a "1". The number counted is then fed to a comparator 46 where it is compared with a reference number to produce on line 47 a signal which mutes the receiver when the number exceeds the reference.