| 摘要 |
PURPOSE:To prevent the deterioration of a signal-noise ratio S/N by providing a control circuit to control an attenuator which detects the reception power levels of two antennas and attenuates each reception wave according to the detected levels. CONSTITUTION:An antenna circuit of an in-phase synthetic space diversity system contains filters 6 and 7 which extract reception waves, level detectors 8 and 9, attenuators 10 and 11 and a control circuit 12. The attenuation values of attenuators 10 and 11 are set at zero in a normal mode. Then the attenuation degree of the attenuator 10 is increased in case the reception power of an antenna 1, for example, is lowered by fading and then the detection level of the detector 8 is lowered less than a standard level by >=50db. Then the circuit 12 works to give virtually no noise power to a synthesizer 3. Thus the synthesizer 3 does not synthesize the reception wave received through an antenna 2 and noises. This prevents the deterioration of the S/N. |
