| 摘要 |
In AM radio receivers it is desirable to operate the automatic gain control so that strong signals are actually heard louder than weaker signals. This means that when AM stereo is incorporated into the radio, using a limiter and phase demodulator to recover the L-R stereo information, some means must be provided to cope with the variable L+R signal level. Typically this is done by using a gain control characteristic that eliminates the desired variable sound level. In the invention an absolute value detector is employed as an AM demodulator, the d-c output of which is related to the L+R signal content. A multiplier is coupled between the phase demodulator L-R output and the matrix in which the L+R and L-R signals are combined to produce the separate L and R signals. The multiplier is biased by the d-c component at the AM detector. Thus, as the L+R level varies, the L-R out of multiplier is varied to match. Additionally, the multiplier is provided with an electronic control port which can act to reduce the L-R signal below optimum, thereby producing stereo blend.
|
