Sri International

Commtech International

William R Rambo

An FM diversity receiver system and method are disclosed which include two antennas and a switch for switching the receiver from one antenna to the other. A fade control signal is produced which is related to the received FM signal, in which fade control signal both multipath and non-multipath disturbances are manifested. Disturbances in the fade control signal are compared with a threshold voltage and, when the disturbance exceeds the threshold voltage, antenna switching is momentarily prevented to prevent antenna switching in response to electrical noise impulses, such as ignition noise, which are shorter than the period during which antenna switching is momentarily prevented. If the fade control signal disturbance continues to exceed the threshold voltage after the momentary period of disablement, the threshold voltage is reset to a level related to the maximum level of the fade control signal disturbance, after which antenna switching takes place. Antenna switching then is again momentarily prevented; this time to prevent antenna switching in response to switching transients produced during the antenna switching operation.

Switched diversity method and apparatus for FM receivers

A system for enhancing the quality of a signal received by a mobile FM transmitter by reducing the adverse effects of multipath transmission to the receiver. A pair of antennas is provided, and each antenna is arranged to receive transmitted signals that traverses a different path. The signal produced in the receiver by one antenna is compared with a reference threshold and when the amplitude of the signal falls below the reference threshold, the receiver switches to the other antenna. The signal amplitude is sensed in a high frequency portion of the receiver, i.e. before detection or demodulation, so that switching between antennas occurs rapidly and is normally not perceived by the user of the receiver. Sensitivity to switching is dependent on the rate of change of the received signal amplitude and on the modulation frequency of the received signal so that the system responds both to an overall reduction in received signal strength and to reduction in the strength of the high frequency portions of the received signal.

Growing community of inventors

Stanford, CA, United States of America

William R Rambo