| 摘要 |
PROBLEM TO BE SOLVED: To prevent the incoming call of a vehicular communication equipment in specified space by radiating the radio wave of the same frequency as the radio wave used in a vehicular communication and preventing the incoming call from being interfered by a radio wave. SOLUTION: The output signal from a waveform formation circuit 3 is passed through a differentiating circuit 4, the characteristic of a frequency to energy is flatened, the characteristic is converted into a multifrequency signal of a fixed level having the twice frequency interval as many as a basic frequency and the multifrequency of a base band is made. The frequency of a reference oscillator is set to the outside of the band of the multifrequency signal of the base band so that the signal component of the reference oscillator may be leaked into the base band. The multifrequency signal of this base band is mixed with the signal from a local oscillator 7 in a frequency mixer 6, an unnecessary signal is eliminated by a band filter 8 and a local oscillation frequency prevention filter 9, the signal is converted into a multifrequency radio frequency signal and the signal is transmitted from an antenna 10. In the case of using this device, the device is set near a room preventing an incoming call and the antenna 10 is provided at the proper place of the room. |
