[Elecraft] K3 Noise reduction question

[GW0ETF]

Chris Meagher-2 wrote:
> 
> Hello,
> When I hold NR button to adjust noise reduction, I get levels F1, 1 to 4,
> then F2 1 to 4, up to F4.
> Clearly, 1 is least, 4 is most, but what do the F's represent? (Can't find
> any reference to this on page 24 of the manual.)
> I wondered if F refers to filter, if so then why not 5?
> 
> Thanks for any answers.
> 
> By the way, installed latest beta firmware, and so far so good.
> 
> Chris  VK2LCD
> K2 3666
> K3 685
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> 


Chris,

The link below is useful but Lyle provided a full explanation last December.
Can't yet find a way of referring back to a particular message so have
copied the text below also..

Have fun, 
Stewart Rolfe, GW0ETF (K3 145)


<<<<Start of quotes....

http://www.zerobeat.net/mediawiki/index.php/K3_DSP

by Lyle KK7P Dec 22, 2007; 03:31pm :: 
The NR has changed with time and may continue to do so.  As a result,
the manual is general in its treatment.  The overall rule is "more is more."

NR is more properly Signal Enhancement rather than Noise Reduction.  The
distinction is subtle but important if you wish to understand how it
works and how to best apply it.  If ti were noise reduction, the
implication is that it passes everything until it figures out what is
more likely to be noise, which it then attempts to suppress.  Since it
is signal enhancement, it tends to pass nothing until it figures out
that which is more likely signal, which it then attempts to pass.

With this understanding there is one more concept I must explain:
correlation.  This is the degree to which a signal is similar to itself;
conversely, it can be used to figure out how noise is dis-similar to
itself (more random).  This is the basis on which NR works.

In the current implementation of the K3, we have four (4) basic NR
filters.  These are displayed as F1..F4.  F1 is the gentlest, F4 the
most aggressive.  Recalling that the filters tend to suppress everything
until they can sort out what is probably a signal, there is some time
delay involved in their application.  Further, especially with voice
signals, some components of the signal may not be recognized as well as
others.  THis gives rise to distortion.

So, we added a second field to the NR.  This is the -1..-4 which
specifies a certain amount of "bleed through" of the original signal.
This reduces the apparent distortion and delay, but limits the ultimate
S/N improvement.  -1 provides the least distortion but limits the S/N
improvement on weak to moderate signals to about 6 dB.  -4 provides no
"mixing" whatsoever and can result in dramatic S/N improvements, but at
a cost of slight time delays and increased distortion.

NR is not appropriate for very weak signals, so a -1 or -2 is best if
you wish to hear them.

Having saids al this, the correct way to use the NR is to listen and
adjust it for the best compromise between noise reduction and
distortion.  Everyone is different in this regard.  Some tolerate noise
better than others, while some don't tolerate distortion very well at all.

I live in a quiet location, and use NR1-2 as my most common setting.
This is low in distortion, allows me to hear weak signals, and shows no
apparent delay as I tune through the bands.  On the rare occasions when
things get noisy here, I crank it to higher values.

Probably a much longer answer than you wished.

Merry Christmas,

Lyle KK7P

......end of quotes>>>>>>>

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