In-band signal-to-noise ratio monitor for an FSK relaying system
AssigneeWestinghouse Electric Corp.
InventorMichael J. Leib
Life of this patent
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Abstract
An improved in-band signal-to-noise ratio monitor is used in conjunction with the receiver of an FSK relaying system. The improved monitor measures the signal-to-noise ratio both prior to and after the receiver input signal is filtered by a narrow bandpass filter. The magnitudes of the measured ratios are compared and, if all signal-to-noise ratio permissives are not satisfied, the tripping function of the relaying system at the receiver or local station is blocked or inhibited.
Claims8
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.
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.
Dependencies are inferred from the claim text.