| 摘要 |
<p>The cosine correction factor of a receiver for compatible AM stereo reception is controlled by the amount of high frequency energy present in the demodulated signal. Large amounts of such energy indicate a low signal-to-noise ratio and cosine correction under such conditions is then not desirable. During periods of excessive high frequency energy, a filter circuit output causes a switching circuit to remove the derived cosine correction factor and cause division of the demodulated signal by a factor of one instead. The output of a cosine phase detector (24) is coupled to a divider (25) through the switching circuit (27). The output of the detector (24) is also coupled to a high pass filter (29), an output of which is coupled to a first control input of the switching circuit (27). A second control input (30) provides a reference signal. When the S/N ratio of the received signal is low and thus the output of a limiter, which contains only the phase information of the received signai, contains large amounts of high frequency energy, the high pass filter (29) provides to the switching circui; (27), a control voitage sufficient to disconnect the output of the detector (24) from the divider (25) and to substitute therefor the reference voltage which is such as to cause the divider (25) to effectively divide the dEmodviated signal (L-R) cos ø signal by a factor of one.</p> |
