Interference Rejection - Kenwood TS-990S In-Depth Manual

Interference Rejection

Interference signals such as pulse noise and beats may affect the AGC and suppress the desired signals. In that case,
eliminating the interference signals in the preceding stage to the AGC can highlight the signal behind the interference
signals. The interference rejection is a function that is placed before the in‑band AGC processing, as well as the IF filter,
and that eliminates particular interference signals.
For interference rejection by digital signal processing in the TS‑990S, in addition to the noise blanker, the manual
notch filter and auto notch filter, the band elimination filter that can adjust the stopband bandwidth and the amount of
attenuation is newly employed.
● Noise Blanker
The TS‑990S has two noise blankers called the NB1 and NB2. NB1 is the noise blanker for the analog circuit. NB2 is the noise
blanker for digital signal processing. The noise blanker can be selected depending on the type of noise and the receiving
status. Furthermore, NB1 and NB2 are usable concurrently for finer adjustment by tuning their respective effective levels.
NB2 operates with the envelope following system, so that it is effective even if there is a slight signal level difference
between the desired signal and a pulse noise signal that cannot be followed by the past analog circuit as the noise blanker.
This algorithm does not allow you to simply blank the pulse noise from the received signal, unlike the analog‑circuit
noise blanker. With automatic demodulation of the pulse noise following the received signal level and comparison with
the desired signal level other than the pulse noise, the length of time corresponding to the pulse noise is appropriately
attenuated. This is the algorithm that achieves the noise suppression with this system. Hence, this enables you to
process the relatively long pulse noise even with less deterioration of the desired signals.
The "Effect of NB2" graphs show how an audio signal suppressed by AGC operation is highlighted when the pulse noise
is eliminated by NB2.
NB2 affects the noise that cannot be processed by the analog circuit; however, there may be a case where it cannot
suppress the noise depending on the strength of the desired signal and characteristics of the pulse noise. In such
a case, by using noise reduction together, the receiving status may be improved. Also, use of a narrow roofing filter
bandwidth may change the noise component that deteriorates its effect: flexible use of NB1, NB2 and noise reduction
according to the situation provides you with more variations.
NB2 OFF
Time (S)
NB2 ON
Time (S)
Fig. 62 Effect of NB2
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