Noise suppression circuit for HF heterodyne receiver - has low-pass filter which separates noise from intermediate frequency signal and whose output is converted into switching signal

摘要

The noise suppression circuit can be used in sensitive FM personal call receivers. A switching voltage is derived from the IF and used to activate an auxiliary circuit suppressing the useful signal when noise appears. A wideband amplifier (4) is used as the IF amplifier. Its output is connected to a low-pass filter(8) whose pass-band is below the IF signal frequency and/or below the IF sideband frequencies. The low-pass filter(8) output signals are applied to a rectifier(11) generating the switching voltage. A band-pass filter may be connected between the LP filter and the rectifier having a frequency range in which preferred noise signals appear.