| 摘要 |
PURPOSE:To improve S/N ratio, by detecting the IF level from DC signals responded to the signal level of SHF radio wave and by changing the band width into the BPF which lowers the threshold by compressing the band width through the detected DC voltage level. CONSTITUTION:BPF4 contains BPFA and BPFB. This BPFA is used for normal reception and set to a band width of 26-30MHz. On the other hand, since BPFB is used when SHF wave receives a considerable amount of rain attenuation, it is set to a compressed band width. At IF level detector circuit 7, the 2nd IF signal is converted into a DC signal responded tothe signal level of SHF radio wave, and the AGC voltage is obtained. This voltage is level detected at DC level detector circuit 9, and controls switching circuit 5. By this, BPF4 is changed over into BPFB, the band width of which is compressed by circuit 5, and S/N ratio is improved by lowering the threshold. |
