| 摘要 |
PURPOSE:To facilitate the removal of an unnecessary wave, by multiplying the frequency of a receiving signal and passing the same through BPE in a multiplied frequency state. CONSTITUTION:When a transmitter-receiver 2 receives, for example, an unnecessary wave with frequency of 49.0kHz, this unnecessary wave is multiplied to 2,450kHz in its frequency by a multiplier circuit 17 to be sent into a mixer 18 where mixed with a frequency signal of 2,905kHz from a local transmitter 19. The obtained difference frequency of 455kHz is sent into the signal extraction part 20 in the following stage. For example, when the central frequency of BPF22 is set to 450kHz and the band width thereof to 2kHz, only the frequency signal of 449-451kHz is passed and, therefore, frequency of 455kHz does not appear in a detection circuit 23. That is, unnecessary frequency 49.0kHz is removed. |
