Abstract: A station carrier telephone system employing single sideband transmission permits optimal utilization of the available frequency spectrum without requiring individual stable subscriber carrier sources by utilizing a common source signal for all subscriber carriers. The common source signal is received via the common transmission line at each subscriber circuit where it is processed and mixed with the similarly received central office carrier to derive a difference frequency signal which serves as the subscriber carrier. In a preferred embodiment sixteen channels share the common transmission line and employ sixteen adjacent subscriber frequency bands and sixteen adjacent central office frequency bands.

Abstract: A continuous monitoring arrangement for a carrier telephone system utilizes the subscriber carrier at a reduced level when the subscriber set is on-hook. Proper reception of the reduced carrier level at the central office circuit during on-hook condition verifies operability of the carrier frequency circuitry. In a preferred embodiment the central office carrier, which is always present, is modulated by a control tone in the audio range during on-hook conditions. The control tone is detected at the subscriber circuit and modulates the reduced level subscriber carrier whereby reception of the control tone back at the central office circuit verifies operability of all carrier and voice frequency circuits at both subscriber and central office locations.