[TenTec] NB verses NR
n4py3 at earthlink.net
Sun Dec 14 12:51:20 EST 2014
Ken's description does not apply to how noise blankers work with DSP
systems. But the idea is the same. In DSP systems the audio path is
muted for a few milliseconds when the sharp pulse is detected. But in
all systems it is very important for the pulse detection to occur before
sharp filtering in order to preserve the sharp pulse spike.
I know that in the 1950's Collins did actually use a separate blanking
detection receiver that ran on 9 mhz with its own antenna. I never used
one but it must have been good.
The main point of all this was to try and explain the difference between
NR and NB as there seems to be a lot of confusion on this subject.
Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
On 12/14/2014 12:31 PM, Ken Brown wrote:
>> 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.
> DE N6KB
> TenTec mailing list
> TenTec at contesting.com
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