Abstract: A quadrature demodulator for a phase shifted input pulse signal. The demodulator produces a four state digital code word on two output lines dependent upon the phase of the input signal. The input signal may have a phase shift, from the phase of the carrier signal, of zero degrees, +90.degree., -90.degree., or 180.degree.. The demodulator includes a clock-driven counter having an output signal at a fundamental frequency substantially identical to the carrier frequency of the input pulse signal. The counter produces additional output signals at frequencies which are multiples of the carrier frequency. The counter is synchronized with the input signal during a reference interval of zero phase shift, and a strobe circuit combines the various counter outputs to produce strobe signals to detect the phase shifted input signal.

Abstract: Protected objects are connected together to form an antenna. Preferably, the cabinet for the detector circuitry is also included in the antenna. The antenna is excited by a voltage controlled oscillator (VCO). The capacitive reactance of the antenna changes when an intrusion occurs. This causes the frequency of the VCO signal to undergo an instantaneous change. A phase comparator compares the phase of the VCO signal with the phase of a reference oscillator signal. An instantaneous change in the frequency of the VCO signal due to a change in the capactive reactance of the antenna when an intrusion occurs is reflected by a shift in phase between the VCO signal and the reference oscillator signal. This causes the phase comparator signal to change.

Abstract: An intercom system for remote banking which facilitates communication between a teller terminal and a remotely located customer terminal. A two-way speaker is provided at the customer location and a separate microphone and a speaker are provided at the teller location. An amplifier in the communication path linking the two stations is connected such that normally its input is responsive to the customer two-way speaker with its output feeding the teller speaker, permitting the customer to talk to the teller. When the teller speaks into the microphone, and assuming certain conditions are met, the amplifier automatically switches to connect the teller microphone to the amplifier input and the customer two-way speaker to the amplifier output, permitting the teller to talk to the customer.