[Elecraft] Auto Notch Filter Freeze

[wa9fvp]

In January and October of 1992 I wrote two QEX articles on a project that
another Ham and I worked on called the "Hamblaster". We developed a DSP
based
sound card that used filter programs for noise reduction and auto notch.

A feature that we added proved to be quite interesting in some respects and
corrected problems where the DSP was outside the AGC loop. First of all the
Hamblaster had its own AGC loop that maintained an optimal baseband level.

There was an on screen option to freeze filters. My theory was "Why design
an
auto notch that continuously adapts". You only need to converge on the
interfering carrier once. After that, there's no need to re-adapt.  If the
interfering 
carrier changes, to readapt, you can press the auto notch button again.

Because everything was done in software, we added buttons on the PC screen
where
you can set a parameter to automatically freeze the auto notch after a given
time or you can manually freeze it. This worked well and after the notch was
locked to carrier, there was no distortion.

We even added a freeze button on the noise reduction. I noticed that when
the
filter adapted to ones voice. The LMS algorithm was, for the most part, was
optimized to the person's voice characteristics and the filter was optimal
for
the whole QSO. The drawback was that it took several tries to get it right. 
Some times the filter lock on the high frequency elements of speech and
other
times on the low frequency components but it reduced noise to a certain
degree
without the usual artifacts in the noise floor.

I thought that this would be an interesting feature to add to the K3 in the
next
firmware upgrade.

Jack WA9FVP
Willco Electronics.








-----
Jack WA9FVP

Sent from my TRS-80 :-)
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