Reduction of adjacent channel interference

The method of improving the adjacent channel interference rejection performance of receivers in receiving a monophonic double-sideband signal, said method comprising:

• separately demodulating the upper sideband and lower sideband portions of the signal to produce first and second audio waves, respectively;
• measuring interfering signals in the upper sideband and lower sideband portions to produce correction signals according to the relative effects of the interfering signals on the respective sideband portions;
• feeding the audio waves to circuitry suitable for driving first and second transducers, respectively;
• and
• modifying one of the audio waves relative to the other by means of the correction signals to enhance the intelligibility of desired portions of the audio waves relative to the interfering signals.

The method of improving the adjacent channel interference rejection performance of receivers in receiving monophonic double-sideband signals, said method comprising the steps of:

• isolating and demodulating the wave received in the upper sideband to produce a first audio wave;
• isolating and demodulating the wave received in the lower sideband to produce a second audio wave;
• measuring the level of the received interference in the channel contiguous to and above the upper sideband component of the desired signal;
• measuring the level of the received interference in the channel contiguous to and below the lower sideband component of the desired signal;
• reducing the audio frequency response to the sideband suffering from the greater measured interference level;
• and
• feeding the audio waves produced as a result of the above steps to circuitry suitable for driving separate transducers.

A receiver responsive to an amplitude-modulated double-sideband, monophonic signal centered on a carrier frequency, both of the sidebands of the signal containing substantially equal portions of a desired modulating signal, said receiver comprising:

• input means to receive signals in a frequency band including a selected monophonic signal and an interfering signal offset with respect to the carrier frequency of the signal;
• separation circuit means connected to receive signals from the input means and comprising first and second signal paths receiving lower and upper sideband portions, respectively, of the selected signal, one of the signal paths also receiving substantially more of the interfering signal than the other signal path receives;
• first demodulating means connected to the first signal path to demodulate signals therein to extract, as a first extracted signal, substantially the desired modulating signal;
• second demodulating means connected to the second signal path to demodulate signals therein to extract, as a second extracted signal, substantially the desired modulating signal, one of the extracted signals including the interfering signal in demodulated form;
• first transducer means connected to the first demodulating means to reproduce audible signals based on the first extracted signal;
• second transducer means connected to the second demodulating means to reproduce audible signals based on the second extracted signal;
• comparison circuit means to compare signals extracted by the first demodulating means with signals extracted by the second demodulating means;
• and
• control means connected to the comparison circuit means to be controlled thereby in response to the difference between the compared signals to modify one of the extracted signals relative to the other extracted signal to enhance the intelligibility of the audible signal based on the desired modulating signal portion of the first and second extracted signals relative to the interfering signal portion.