| 摘要 |
PURPOSE:To receive always radio waves with an antenna of good radio conditions to copy with the variance of a pratical field intensity by detecting the fall of the reception level of an antenna by a receiver to switch selectively this antenna to the other. CONSTITUTION:The antenna of a diversity device is switched to an antenna 2 or 3 by an antenna selecting circuit 1, and the reception signal is amplified and detected by a front end circuit 4 and an IF amplifier 5. The output of the amplifier 5 is applied to a low frequency amplifier 6 and a level detector 7. The output of the amplifier 5 is applied to a buffer 11 of the detector 7, and the output has the voltage divided by (a resistance R1)/(a resistance R1+R2), and this divided voltage and a voltage obtained by allowing the output to pass a time constant circuit consisting of a capacitor C and a resistance R3 are applied to a comparator 12 to detect the fall of the reception level. The pulse for the fall of the reception level from the detector 7 has the waveform shaped by a waveform shaping circuit 8, and a toggle FF9 is triggered by the output of the circuit 8, and switching between antennas 2 and 3 in the circuit 1 is controlled by the output of the FF9. |
