GB1384336A - Telegraphic receiving apparatus - Google Patents

Abstract

1384336 Digital transmission; signal testing ITT CREED Ltd 3 Nov 1972 50695/72 Heading H4P An arrangement testing whether a received signal is not spurious measures the signal and accepts it as genuine only if it has a minimum length but disregards fading if it is of less than a certain duration. The arrangement comprises a counter driven by a clock which is released on appearance of a transition, and which provides an output signal at the end of a first determined period indicating a valid signal, with a second counter reset and held at zero at the first transition and released on failure of the signal when the second counter, also driven by the clock at a second determined count resets the first counter to zero. The first counter is also reset by the appearance of a second received signal within the first determined period. Applied to a telegraph circuit, appearance of a space (mark) signal sets toggle 3 to A and applies an inhibit reset of counter 4, also starts first counter 5 driven by clock 7. If a determined count is reached the signal is considered genuine. If the signal fails, although counter 5 continues, inhibit is removed from counter 4 and if a second determined count is reached counter 4 gives a pulse on line 10 which resets toggle 3 to B and resets counter 5. If however, a space signal is not received before counter 4 times out this is reset and counter 5 on reaching the first determined count provides a "valid" signal on line 9. The arrangement may alternatively monitor mark signals.