| 摘要 |
PURPOSE:To execute an automatic frequency control which requires no pilot signal by eliminating a high frequency component from an output obtained by frequency-discriminating a PSK modulated wave which brought to frequency conversion, by a frequency discriminator, and thereafter, controlling an oscillation frequency of the receiving local oscillator concerned by the discriminator concerned whose high frequency component is eliminated. CONSTITUTION:For instance, a phase shift keying PSK modulated wave having a spectrum as shown in a figure, which is applied to a frequency converter 20 from a terminal 24 is mixed with an output wave from a voltage control oscillator 21, and brought to frequency conversion, for instance, to an intermediate frequency. A part of the PSK modulated wave brought to frequency conversion is applied to a frequency discriminator 23, and how much a symmetrical property of a power spectrum which this PSK modulated wave has is shifted from the center of this frequency discriminator 23 is detected. That is to say, a voltage corresponding to a difference of the center frequency of the frequency discriminator 23 and a received input frequency is fetched from this frequency discriminator 23. As for this output voltage, its noise component is eliminated by a low-pass filter 22, and thereafter, said voltage is applied to the voltage control oscillator 21, and the oscillation frequency is controlled so that the output voltage becomes ''0''. Therefore, the frequency of the PSK modulated wave brought to frequency conversion by the frequency conveter 20 always coincides with the center frequency of the frequency discriminator 23. |
