Topband: K3 & some interesting noise lessons in the ARRL 160.

[Shoppa, Tim]

I have used the K3 noise blanker in several different environments, sometimes with great success, sometimes with less success.

I know the word "null", which many will take to be a subtractive linear process, does not apply to the traditional impulse-noise blanker. The traditional noise blanker is in fact quite nonlinear and more accurately a "multiply signal by zero during a noise pulse" function. But it is not unusual to find a magic frequency where the NB settings and the noise phase characteristics and antenna characteristics all interact to yield "good place on the band" vs "bad place on the band" and that can be hugely important during a test.

I'm not sure anyone needs to disqualify themselves for CQ'ing in a DX window in a contest, but discussions about the DX window and noise environments are very relevant to me and I like hearing them.

Tim N3QE

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Greg
Sent: Monday, December 16, 2013 6:30 AM
To: 'TopBand List'
Subject: Re: Topband: K3 & some interesting noise lessons in the ARRL 160.

Why would the NB null be frequency dependent?  Why does it change?  Why would a different antenna make any difference unless you pick up different noise sources with the two different antennas?  73, Greg-N4CC

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Guy Olinger K2AV
Sent: Sunday, December 15, 2013 8:59 PM
To: Richard (Rick) Karlquist
Cc: TopBand List
Subject: Re: Topband: K3 & some interesting noise lessons in the ARRL 160.

>>I am confused about "1831.5 being occupied."

That's 1831 was UNoccupied, so I used it as a run frequency. No one else was using it as a run frequency.

The noise blanker, at that time, with aforementioned settings, was producing a very effective null in the noise at 1831-1833.  There were vacant frequencies in that range, vacant at various times, and I used them, in the process breaking the dx window rule.

The combination of NB settings and the 250 Hz width (with 250 8 pole
filter) on the K3 was NOT being falsed by nearby frequencies, nor was it "mushing" the noise over weak signals, that discovered by a few hours messing with settings.

If I turned OFF the K3 NB, the buzz noise at 1831-1833 drowned out all but loud signals.

Tonight the noise null using the NB on the TX antenna is around 1826. On the TX antenna the noise goes up over 16 dB when I turn the NB off. On the RX ant the null is at 1838 and the noise goes up 17 dB when I turn NB off.
These are less pronounced than on the contest night when the diffs were in the low 20's, and the noise was S9.

73, Guy


> 1.  The NB works well on the noise, but gets falsed by nearby signals 
> on a crowded band in the contest.  IOW, the NB would have worked fine 
> during non-contest times.  The NB on my FT-1000 is like this (I have 
> the W8JI NB mod).
>
> or
>
> 2.  The local noise was lower on 1831.5, but you still needed the NB.  
> QRM from other stations was not an issue.
>
> I don't own a K3, but an considering buying one.
>
> Rick N6RK
>
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