| 摘要 |
PURPOSE:To make it possible to demodulates an FSK signal even when D/U is less than one, by providing LPF with a fixed band at the output side of a frequency discriminator. CONSTITUTION:An input signal is supplied to broad-band frequency discriminator 13 via amplitude limiter 12 and its demodulated signal component is supplied to LPF14. Then, LPF14 attenuates greatly a component higher than a carrier freqency, but never attenuates a component lower than the carrier frequency and twice the band width of the input signal. The output of LPF14 is detected by detector 15 and then outputted by way of LPF16 that permits only the detection signal component to pass through it. In this case, an influence of a quadratic higher harmonic when D/U approximates to one can be removed by setting the cut-off frequency of LPF14 four times more as much as the band width of the input signal. |
