[TenTec] NB verses NR
ken.d.brown at hawaiiantel.net
Sun Dec 14 12:31:24 EST 2014
> Noise Blanker (NB) is a classic function that goes way back to at
> least the early 1950's. What it does is look for a very sharp leading
> edge on noise and actually blank out audio for the duration of the
> steep noise spike.
This description is essentially correct. However there are a lot of
variations in how it is done. The variations are in how the blanking
trigger is obtained, the timing of the blanking and in where the signal
chain the blanking is performed.
In the Ten-Tec Omni VI the noise spikes that trigger the blanking are
detected before the first narrow filter and then the blanking of the
signal (and noise) path occurs later in the IF. So yes the audio is
blanked, but it is blanked by interrupting the IF signal path before the
signal becomes audio.
In some systems a completely separate noise receiver (maybe with a
separate antenna) is used to generate the blanking trigger. The blanking
can occur anywhere from the antenna port to the headphone jack of the
receiver being "noise blanked." There are good reasons to do it earlier
in the signal path. The timing of the blanking can also be varied. How
soon after the trigger does the blanking start, and how long does the
blanking last. Another option is to use the AC mains as the trigger and
synchronization of the blanking, which is effective when most of the
noise is caused by the power distribution system.
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