[Elecraft] Noise Reduction parameters

[Lyle Johnson]

> Can someone enlighten me about setting up the NR parameters....hope I can
> explain myself ok!

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