RADIO RECEIVING DEVICE FOR SERVICE SIGNALS TRANSMITTED AT FIXED FREQUENCY Russian patent published in 1997 - IPC

FIELD: burglar alarm systems; call systems; systems of warning about deviations from normal conditions under control. SUBSTANCE: device has an antenna, an input unit, and a first gated high-frequency amplifier with its output connected to the input of a quartz resonator and to the input of a second gated high-frequency amplifier. The second amplifier output is connected to the input of a detector whose output serves as the output of the device. Control inputs of the first and second amplifiers are connected respectively to the first and second outputs of a gate generator which switches alternately the first amplifier or the second one to circuit at intervals (pauses). Both amplifiers operate at the frequency of a signal picked up by the antenna. Working frequency of the device is determined by the resonator natural frequency. High Q-factor of the resonator and the generator switching frequency chosen so that during the operation of either of the amplifiers the resonator oscillation amplitude has no time to change considerably allow the signal received by the detector to be amplified as compared with the input signal with a gain factor close to the product of the gain factor of the respective amplifier only at the working frequency. EFFECT: reduced minimum discernible signal comparable with that of a superheterodyne receiver having an intermediate-frequency filter with the same bandwidth as that of the used quartz resonator, which is provided by time separation of amplification and use of the quartz resonator simultaneously as a frequency setup unit and a filter without transforming the frequency of received signal. 2 cl, 3 dwg