| 摘要 |
PROBLEM TO BE SOLVED: To transmit two signals of a sound signal and a sensor signal being a binary signal by modulating them with a single FM modulator. SOLUTION: In this FM modulation circuit, the sound signal and the sensor signal are added with each other and frequency-modulated by the FM-modulator 2. The low level of the sensor signal is modulated to a frequency f1 and the high level of the sensor signal is modulated to a frequency f2. Consequently, in the FM-modulated signal, both the shift frequency from the frequency f1 and the shift frequency from the frequency f2 are made correspond to the level of the sound signal. The signal modulated by the FM-modulator 2 is inputted to a filter 3 and a filter 4. The filter 3 extracts and outputs 2nd higher harmonic components in the output signal of the FM-modulator 2, and the filter 4 extracts and outputs 3rd higher harmonic components in the output signal of the FM- modulator 2. Then, the output signal of the filter 3 and that of the filter 4 are added with each other by an adder 5 and outputted to a transmission line.
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