| 摘要 |
PURPOSE:To reduce the number of used parts by using a balanced modulator and a low-pass filter for spectrum inversion for transmission as well as reception in a spectrum inverting privacy transmitter-receiver. CONSTITUTION:When an audio signal from a transmitter 111 is detected by an audio detecting circuit 149, switches 141-144 are switched to positions 1, and the audio signal is subjected to spectrum inversion by a balanced modulator 131 and an LPF3 and is transmitted through an FM transmitter 113. At this time, a reception signal is demodulated by a receiver 121 and is given to a receiver 123 as it is. When the audio signal from the transmitter 111 is not detected by the audio detecting circuit 149, switches 141-144 are switched to positions 0, and the reception signal is demodulated by the receiver 121 and is subjected to spectrum inversion by the balanced modulator 131 and the LPF122 and is inputted to the receiver 123. In this transmitter-receiver, signals received during transmission are not subjected to spectrum inversion. |
