| 摘要 |
PURPOSE:To prevent effectively overmodulation distortion without spreading a demodulation band to an overmodulation at a transmission side by applying accurately expansion and correction to a demodulation signal demodulated while the degree of modulation is limited by means of a nonlinear circuit identical to the circuit used for the limit of modulation. CONSTITUTION:An FM signal 1 is demodulated by an FM receiving and demodulating circuit 11 and becomes a demodulation output 9. The amplification factor is almost zero up to demodulation output levels + or -V1 to a normal FM modulation degree (m) and the amplification factor is increased to the demodulation output 9 exceeding the + or -V1 in the characteristic of the nonlinear amplifier 5. Thus, the demodulated output 9 is led out to an output terminal 10 with respect to an FM wave having the normal modulation degree (m). As to an FM wave in excess of the modulation degree (m), a component of the demodulated output 9 exceeding the + or -V1 is fed back negatively to a local oscillator 6 in the FM and no overmodulation distortion is produced. On the other hand, a component exceeding the + or -V1 among the demodulated outputs 9 has a low demodulation sensitivity and nonlinear distortion is produced, the output of the nolinear amplifier 5 is adjusted by a level adjusting device 8, the result is added to the demodulated output 9 and the distortion is corrected.
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