Kenwood TS-480 manual Noise reduction, Demonstrates how ignition noise is reduced by the DNL

First, the input signal is divided into its low- and high-frequency components. Ignition and other pulse noise tends to be concentrated in the latter, from which amplitude variation is output. The attenuation coefficient derived from this signal is multiplied by the input signal. As soon as pulse noise occurs, the attenuation coefficient rises instantaneously, thus damping the amplitude variation in the input signal. Because of this adaptive processing performed by the DNL and based on the amplitude variation, the output signal has virtually none of the “digital feel” that is often the mark of digital signal processing. It is perhaps only natural to associate this DNL with the old “noise limiter” technology, but as explained it works on a completely different principle, performing the sort of advanced processing that is only possible with DSP.

Because the TS-480 will be often used for mobile operations, DNL parameters have been tuned so as to have maximum effect on ignition noise. However, even when used as a fixed station, it can be very effective on irregular, unanticipated noise, so we recommend that you try making use of it, in combination with the noise blanker as well.

Fig.14 demonstrates how ignition noise is reduced by the DNL.

Fig. 14: The effect of DNL on ignition noise

The DNL works in SSB, CW, FSK and AM modes, and it can be used in conjunction with other interference reduction and noise elimination features.

●Noise reduction

There are two methods available for noise reduction: NR1 and NR2. NR1 is a line enhancer that employs adaptive filter technology. By shaping a filter that lets through signals with a certain amount of periodicity, as with voice and CW, it can suppress noise that falls outside the passband. NR2 employs what is known as SPAC (speech processing by auto correlation) technology. What results from looping one cycle of the RX signal’s autocorrelation coefficient is then output as the received audio. What this means is that only periodic signals found in the received audio emerge. In principle this approach can result in a small amount of noise at the “seam” where the periodic signal is looped together, but in practice it proves extremely effective at noise compression.

NR1 is a good choice for SSB and other audio signals, while NR2 is especially effective when used with single frequencies, as with a CW signal.

Figs. 15~17 demonstrate the effect of applying NR1 and NR2. For comparison purposes, the same weak sine signal was received, with the audio output monitored by an FFT analyzer.

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