| 摘要 |
PURPOSE:To prevent the drop of a C/N accompanied with the fluctuation of the number of channels by decreasing the gain of a gain variable amplifier accordingly as the number of channel data are decreased. CONSTITUTION:In a second transducer (optical-to-electrical transducer) 2, the gain variable amplifier is constituted of an amplifier 21, PIN diode variable attenuator 22, and amplifier 23. One part of the output signal of the amplifier 21 is branched, demodulated by a demodulator 71, and the number of channel data are decoded. A relation between the number of channels and the gain of the gain variable amplifier is stored in a memory 72. The relation is set so that the amplification factor can be decreased in proportion to the decrease of the number of channels. The attenuating of the PIN diode variable attenuator 22 is controlled by a gain value read from the memory 72. As the result, the signal level of a signal outputted by the amplifier 23 in a prescribed channel becomes equal to a prescribed reference level. |
