Coupling circuit for a communication system

Claim 1

IN AN EDUCATIONAL COMMUNICATION SYSTEM INCLUDING A PLURALITY OF STUDENT STATIONS, AND MASTER SIGNAL GENERATOR HAVING A PREDETERMINED MEDIUM OUTPUT IMPEDANCE, EACH OF SAID STATIONS INCLUDING A STUDENT AMPLIFIER HAVING AN INPUT PROVIDING A SUBSTANTIALLY UNIFORM LOW IMPEDANCE AND A MICROPHONE HAVING AN OUTPUT OF LOW IMPEDANCE; A COUPLING CIRCUIT COMPRISING RESISTANCE MEANS INDIVIDUALLY CONNECTING THE MICROPHONE OUTPUTS TO THE INPUTS OF THEIR RESPECTIVE AMPLIFIERS IN SUBSTANTIALLY IMPEDANCE MATCHED RELATIONSHIP; HIGH IMPEDANCE RESISTANCE-CAPACITANCE MEANS INDIVIDUALLY INTERCONNECTING THE OUTPUT OF THE GENERATOR AND THE INPUTS OF THE AMPLIFIERS IN SUBSTANTIALLY IMPEDANCE MEANS ISOLATING THE STATIONS FROM EACH OTHER TO MINIMIZE TRANSMISSION OF STUDENT SIGNALS ROM ONE STUDENT STATION TO ANOTHER; AND MEANS INDIVIDUALLY CONNECTED TO THE HIGH IMPEDANCE MEANS AND TO THE GENERATOR FOR SHORTING OUT THE SIGNAL APPLIED TO SELECTED STUDENT AMPLIFIERS WITHOUT AFFECTING APPLICATION OF THE GENERATOR SIGNAL TO THE OTHER AMPLIFIERS.