Supervisory circuit for unattended repeaters

Claim 1

In a carrier current communication system including a pair of terminal stations interconnected by a transmission path and a plurality of repeater stations disposed in said path between said terminal stations, said path having a first frequency band to provide operation power for at least said repeater stations and a second frequency band for transmitting information signals, a system for supervising said repeaters comprising: first means disposed in one of said terminal stations to generate an interrogation signal for transmission over said path in said first frequency band to the nearest one of said repeater stations without interrupting the transmission of said information signals through said repeater stations; second means disposed in each of said repeater stations coupled to said path to extract said interrogation signal for said path; third means disposed in each of said repeater stations coupled to said second means to delay said interrogation signal a predetermined interval of time; fourth means disposed in each of said repeater stations coupled to said third means and said path to inject said delayed interrogation signal into said path for transmission over said path to the succeeding one of said stations; fifth means disposed in each of said repeater stations coupled to said third means and said path responsive to said delayed interrogation signal to produce a response signal for transmission over said path in said second frequency band from the associated one of said repeat stations to said one of said terminal; sixth means disposed in said one of said terminals coupled to said path responsive to a predetermined characteristic of said response signal received from each of said repeater stations; and seventh means disposed in said one of said terminals coupled to said sixth means to generate an alarm when said predetermined characteristic deviates by more than a given amount; said second and fourth means each including power separating filter means to separate said first and second frequency bands; further including a bandstop filter disposed in each of said repeater stations connected between said power separating filter means to prevent the direct transmission of said interrogation signal through each of said repeater stations; said first and fourth means each including eight means to generate direct current pulses, and ninth means coupled to said eighth means to convert said direct current pulses into a wave having frequency components falling within said first frequency band to provide the appropriate one of said interrogation signal and said delayed interrogation signal; said third means including a first monostable circuit coupled to the first of said power splitting filter means extracting said interrogation signal from said path, said first monostable circuit being triggered by said extracted interrogation signal and returning to its original state after said predetermined interval of time, and a second monostable circuit coupled in tandem with said first monostable circuit and to the second of said power splitting filter means to inject said delayed interrogation signal into said path, said second monostable circuit being triggered by the output signal of said first monostable circuit and returning to its original state after a given duration to produce said delayed interrogation signal; and said fifth means including an oscillator means providing an output signal having a frequency falling within said second frequency band, and first switch means coupled to said oscillator means, said second monostable circuit and said first of said power splitting filter means responsive to said delayed interrogation signal to connect said oscillator to said first of said power splitting filter means, said output signal of said oscillator means providing said response signal.