| 摘要 |
PURPOSE: To surely detect frequency deviation by making a local oscillation frequency nearly equal to a calling frequency and to attain efficiency in the utilization of a frequency band and high speed transmission by reducing the detection margin of frequency deviation. CONSTITUTION: The signal I of the reception signal FSK of a carrier frequency fc and a transmission signal from a local transmitter 20 which is nearly equal to the signal I are mixed by a mixer 13 and removed of a carrier wave signal through LPF 14 to obtain a frequency shift signal. On the other hand, the signal with π/2 phase difference from the local transmission signal is mixed to the signal Q of the signal FSK by a mixer 15 and removed of a calling frequency signal through LPF 17 to obtain the frequency shift signal Q including frequency deviation components. This is π/2-phase-shifted by a phase shift circuit 81 and mixed with a reference frequency from the local oscillating circuit 20 by a mixer 82 so that the frequency shift components are taken out through LPF 83 and detected by a detection circuit 84 and inputted to a voltage control oscillator 85 to make an oscillation frequency equal to the carrier wave frequency fc. Thereby, the detection margin of frequency shift is reduced to narrow an interval between the calling frequencies of respective radio equipments. |
