| 摘要 |
A system enabling the frequency, and if desired, phase control of an oscillator which generates a standard signal useful as a carrier which is modulated by modulation signals. A multiplicity of such oscillators and associated transmitters may be used in a simulcast transmission system which covers a large area, for example in paging applications where the transmissions must be of the same frequency or with predetermined frequency offsets and be matched in modulation in order to prevent interference and distortion in areas where the transmissions from different transmitters overlap. The transmissions originate from a station which may be remote from the transmitters. The station has a system controller and the transmitters have transmitter controllers. For frequency control a reference signal generated in the system controller is transmitted over the same link and band width (e.g. the voice band width) with the voice modulating signals to the transmitter controllers of all of the transmitters. This reference signal may be corrupted by noise and other error signals. It also may be transmitted or received intermittently during periods when transmissions are quiet and traffic is light. At the transmitter controllers, multiplicities of phase measurements are made a plurality of times, each time during an interval of predetermined length and at predetermined rates. From these measurements statistical values of phase, deviations and times of occurrence are collected and used to provide error control signals in terms of the ratio of phase difference to time, notwithstanding that the reference signals may jitter in phase and amplitude due to noise and other errors and also notwithstanding that the phase measured at various of the times may include a multiplicity of phase wraps (the phase difference being greater than one cycle or 360 DEG .) A frequency error may be offset, or if offsets are not used, the frequency errors may be applied to the standard oscillator to lock the phase thereof in predetermined relationship with the reference. For modulation control, each transmitter is keyed with modulation calibration signals. These signals are transmitted to the system controller where they are correlated, and codes representing deviations from matched correlation characteristics (delay, gain and frequency spectrum) are transmitted to each transmitter where modulation signal correction circuits are conditioned to process the modulating signals so that the transmissions from each transmitter will be matched in modulation characteristics. |
