| 摘要 |
PURPOSE:To reduce the guard bands at both sides of a pilot signal by adding a pilot signal detecting circuit and a controller which receives the detection output of said detecting circuit and scanning the frequency after deviating the oscillation frequency of a variable frequency oscillator. CONSTITUTION:A pilot signal detecting circuit 1 sends a signal showing the absence of a pilot signal to a controller 12 in case the frequency of a received pilot signal gets out of a pull-in range and no pilot signal emerges at the output of a narrow-band filter 4. Here the controller 12 produces the control signal which performs the frequency scan with the prescribed width on the basis of a point where the oscillation frequency of a variable frequency oscillator 8 is deviated from the center frequency of f0 by a prescribed frequency. The center deviation is set at +DELTAf/2 or -DELTAf/2 according to +DELTAf or -DELTAf in consideration of a case where the frequency deviation is set at the maximum DELTAf. Then a frequency range of + or -DELTAf/2 is scanned centering on the frequency of the deviated point. Thus a pilot signal is caught. In such a way, the frequency scanning range is reduced down to 1/2 compared with a conventional case. And also the guard band width is reduced down to 1/2. |
