In-band signal-to-noise ratio monitor for an FSK relaying system

Claim 2

In a relaying network having guard and trip signal input means, a trip relay and control circuit means cooperatively coupling said guard and trip signal input means and said trip relay, monitoring apparatus for blocking actuation of said trip relay whenever the signal-to-noise ratio of a transmitted signal exceeds a predetermined value, said apparatus comprising: a. a bandpass filter having an input terminal adapted to receive a transmitted signal and an output terminal adapted to forward a filtered signal therefrom to said guard and trip signal input means; b. first signal-to-noise detecting circuit means connected to said bandpass filter input for generating a first output signal which is a function of the signal-to-noise ratio of the transmitted signal; c. second signal-to-noise detecting circuit means connected to said bandpass filter output for generating a second output signal which is a function of the signal-to-noise ratio of the filtered transmitted signal; d. means for generating a reference voltage signal proportional to a predetermined acceptable value of a signal-to-noise ratio in the transmitted signal; e. level detection means adapted to receive said second output signal and said reference voltage signal for comparing said signals and for generating a third output signal whenever said second output quantity exceeds said reference signal; and f. comparator means, adapted to receive said first, second and third output signals and having an output connected to said control circuit means, for generating a blocking signal usable to block coupling of said trip input means and said trip relay whenever said first, second and third output signals reach a predetermined relationship.

Claim 3

The apparatus according to claim 1 wherein said first and second signal-to-noise detecting circuit means comprise: a. an input terminal adapted to receive a transmitted signal; b. amplifying means connected to said input terminal for generating an output signal which is proportionally related to the logarithm of the signal-to-noise ratio of a received signal; and c. rectifying means connected to receive said output signal of said amplifying means for generating an output signal which is proportional to the absolute value of the signal-to-noise ratio of a received signal.

Claim 4

The apparatus according to claim 2 wherein said comparator means comprises: a. first circuit means adapted to receive said first and second output signals for generating a fourth output signal whenever said first and second output signals reach a predetermined relationship; and b. second circuit means adapted to receive said third and fourth output signals for generating said blocking signal whenever said third and fourth output signals reach a predetermined relationship.

Claim 5

The apparatus according to claim 1 wherein said comparator means comprises: a. first circuit means adapted to receive said first and second output signals for generating a fourth output signal whenever said first and second output signals reach a predetermined relationship; and b. second circuit means adapted to receive said third and fourth output signals for generating said blocking signal whenever said third and fourth output signals reach a predetermined relationship.

Claim 6

A signal-to-noise detector comprising an input terminal for energization by the transmitted alternating voltage, a bandpass filter having an input circuit energized from said terminal and having an output circuit, a first and a second signal-to-noise detecting network having an input circuit and an output circuit, each of said detecting networks being effective to provide an output quantity of its said output circuit which is a function of the signal-to-noise ratio of the voltage supplied to its said input circuit, said input circuit of said first detector network being energized by a voltage supplied from said input terminal to said input circuit of said bandpass filter, said input circuit of said second detector network being energized by the voltage output of said bandpass filter, first and second comparator networks, each of said comparator networks having a pair of input circuits and an output circuit, said input circuits of said first comparator network being individually connected to said output circuits of said signal-to-noise detecting networks, said first comparator network being effective to provide a given logical output at its said output circuit at a first relative polarity of the quantities applied to its said input circuits, a level detector having an input circuit and an output circuit, said input circuit of said level detector being connected to said output circuit of said second signal-to-noise detecting network, said level detector being effective to provide a first logical output when the magnitude of the quantity applied thereto from said second signal-to-noise detecting network is above a predetermined minimum value, said second comparator network having one of its said input circuits connected to said output circuit of said level detector and the other of its said input circuits connected to said output circuit of said first comparator network, said second comparator network being effective to provide a desired logical output at its said output circuit solely when said given and said first logical outputs are applied to its said input circuits.

Claim 7

A signal-to-noise detector comprising an input terminal for energization by the transmitted alternating voltage, a bandpass filter having an input circuit energized from said terminal and having an output circuit, a first and a second signal-to-noise detecting network having an input circuit and an output circuit, each of said detecting networks being effective to provide an output quantity of its said output circuit which is a function of the signal-to-noise ratio of the voltage supplied to its said input circuit, said input circuit of said first detector network being energized by a voltage supplied from said input terminal to said input circuit of said bandpass filter, said input circuit of said second detector network being energized by the voltage output of said bandpass filter, first and second comparator networks, each of said comparator networks having a pair of input circuits and an output circuit, said input circuits of said first comparator network being individually connected to said output circuits of said signal-to-noise detecting networks, said first comparator network being effective to provide a given logical output at its said output circuit at a first relative polarity of the quantities applied to its said input circuits, a level detector having an input circuit and an output circuit, said input circuit of said level detector being connected to said output circuit of said second signal-to-noise detecting network, said level detector being effective to provide a first logical output when the magnitude of the quantity applied thereto from said second signal-to-noise detecting network is above a predetermined minimum value, said second comparator network having one of its said input circuits connected to said output circuit of said level detector and the other of its said input circuits connected to said output circuit of said first comparator network, said second comparator network being effective to provide a desired logical output at its said output circuit solely when said given and said first logical outputs are applied to its said input circuits.

Claim 8

The detector of claim 5 in which each of said signal-to-noise networks includes a log generating means.

Claim 9

The detector of claim 6 in which each of said signal-to-noise networks includes a rectifying network and a low pass filter in series between its said log generating means and its said rectifying network.

Claim 10

The detector of claim 7 in which each of said signal-to-noise networks includes a direct current blocking device in series between its said low pass filter and the said rectifying network.