Frequency selective signal presence detector

Claim 1

A signal presence detector selective over at least a frequency range of a first frequency F L to a second frequency F H where F H ≧ F L , said signal presence detector comprising: a. first means comprising means responsive to amplitude variations in an input signal for developing a timing signal comprising a series of timing indications whose occurrences are dependent at least upon the amplitude of the input signal such that for a sinusoidal input signal of frequency F X the frequency of said timing signal is CF X where C is a predetermined scale factor; b. second means comprising means for generating a periodic clock signal comprising a series of clock indications; and c. third means comprising means responsive to said timing indications and said clock indications for (i) providing a time window following and associated with each timing indication, each of said time windows, as measured in time from its associated one of said timing indications, opening no later than T H /C and closing no earlier than T L /C, where T H and T L are respectively equal to 1/F H and 1/F L , and (ii) detecting time coincidence between a first time window and a second timing indication, said first time window being associated with a first timing indication and said second timing indication comprising the timing indication succeeding said first timing indication.