| 摘要 |
<p>PROBLEM TO BE SOLVED: To detect the same channel interference by providing a BPF when directly receives the phase of a Q-channel output signal of a synchronous demodulator and comparing the averaged signals passing through the BPF with the threshold. SOLUTION: A synchronous demodulator 14 connected to an IF stage of a receiver that receivers the stereo signals of an AM frequency band outputs a Q-channel single signal. Receiving this signal, a BPF filter 22 transmits the signals having the frequency of about 25Hz, for example. An integrator 24 averages the signals passing through the BPF 22. A high comparactor 28 compares the averaged signals with the high threshold 32 (higher than a desired phase modulation level by 50%). A low comparator 30 compares the averaged signals with the low threshold 34 (lower than a desired phase modulation level by 50%). An AND of outputs of both comparators 28 and 30 shows the presence of the same channel interference. Under such conditions, a stereo mode is canceled.</p> |
