| 摘要 |
PURPOSE:To evade a DK use PLL circuit from being locked even with the effect of multi-path or the like by decreasing the sum of a lock range of a PLL circuit for demodulating an SDK signal and a lock range of a PLL circuit for demodulating a DK signal than the difference between the maximum frequency of a BK signal and a frequency of the DK signal. CONSTITUTION:A subcarrier (SK signal) used as a 1st identification signal representing a broadcast station for traffic information is amplitude-modulated by a BK signal representing it that traffic information is the information of any district and a DK signal representing it that the traffic information is on-air, the subcarrier (SDK signal) amplitude-modulated is frequency-modulated onto a main carrier, the resulting broadcast wave to be sent is detected by an FM detector 4, the SDK signal is extracted through a filter 6, fed to a PLL circuit 7, where the SDK signal is demodulated and the result is fed to a PLL circuit 10 to demodulate the DK signal. The condition of (DK-BK)>(DELTAfSK+DELTAfDK) is satisfied, where DELTAfSK is the lock range of the PLL circuit 7, DELTAfDK is the lock range of the PLL circuit 10, BK is the maximum frequency of the BK signal and DK is the frequency of the DK signal. |
