Noise blanker

Lore & Background

The noise blanker is typically implemented as a network in the intermediate frequency (IF) section of the receiver. When a pulse of noise passes through the IF amplifiers, it is usually of greater amplitude than the desired signal. The noise blanker circuit momentarily reduces the gain of the IF stage during the impulse. More complex noise blankers may use a secondary IF stage and have adjustable threshold and timing characteristics to reduce the noise passed through to the audio stages.

Reader's Guide

The noise blanker is best applied before any narrow-bandwidth filters in the signal path, so as not to introduce ringing and distortion in the filtered signal. It is most useful with amplitude modulation or single sideband signals. Frequency modulation receivers generally include a signal limiter stage that tends to reject noise pulses, making a noise blanker less necessary in such designs. In cases where there are strong signals on frequencies near the desired frequency, a noise blanker circuit may be ineffective and may reduce the quality of the received signal. Its significance lies in improving intelligibility of signals in environments with impulse noise, though it has limitations with continuous noise or adjacent-channel interference.

Did You Know?

• A noise blanker is only effective on impulse-type noise such as from lightning or automotive ignition systems.
• Noise blankers are best applied before narrow-bandwidth filters to avoid ringing and distortion.