Noise suppressor, squelch, NS. Glossary of radio communication terms and abbreviations

The noise suppressor (NS) of a radio station (transceiver) is a system that disables the AF amplifier in the absence of a useful signal. The noise suppressor automatically switches off the speaker when the input signal level is below the squelch activation threshold (noise). When the threshold is exceeded (useful signal present), the noise suppressor activates the speaker (the squelch opens).

The noise suppressor can be manually opened to receive weak signals — those at the noise level. Excessive closing of the noise suppressor leads to a reduction in radio communication range.

Types of Noise Suppressors

Noise suppressors are of two types: spectral and amplitude.

The amplitude (threshold) noise suppressor is simpler to implement and is used in most imported and domestic radios, both handheld and vehicle-mounted (stationary). Its operating principle is to detect the input signal taken from the last IF stage, with the signal level then compared to a threshold set by the squelch control.

The spectral noise suppressor does not detect the absolute level of the mixture of useful signals and noise. Its main task is to evaluate the ratio of noise level to the useful signal, the spectrum of which is close to speech. When this ratio becomes greater than the preset value, the AF amplifier is switched on, and when it becomes lower — it is switched off. The threshold itself is adjusted by the squelch control.

The spectral noise suppressor is considered the most complex to implement. However, it effectively filters out false triggers (when there is no useful signal). This is particularly relevant in the 27 MHz (CB) band, where interference levels can vary greatly over time or with the operator's location. External noise may change due to industrial interference, solar activity, atmospheric noise, and other phenomena.

The automatic noise suppressor (ASQ) continuously monitors the presence of a useful signal among the variety of background noise during the entire operation of the radio and maintains the squelch opening level at an optimal point relative to the "signal-to-noise" ratio.