[Elecraft] Auto Notch Revisited.

[wa9fvp]

It's been 2 years since there were complaints on this forum about the K3
auto-notch.  Apparently it was never fixed.  

The other day I was working a Ham in Tel Aviv when a carrier came on and
covered his signal.  The Auto notch worked well but the guys voice was very
distorted.  To me that's unacceptable.  

This year at the Dayton Hamvention I talked to someone from Elecraft about
the DSP problems and he agreed that the auto notch needs some improvement. 
I think he was a the product manager.

Back in the early 90's I worked with another Engineer on a project we called
"The Hamblaster". I published two articles in QEX (October 1991 and January
1992). We developed a PC based sound card that connects to the receiver's
audio and performed, among other things,  an auto-notch and noise reduction
(NR).  In our DSP software, the auto-notch was generated by summing the
inverted NR output to the input signal.  Whether it's a noise reduction or
an auto-notch we still used a software algorithm called the LMS (Least Means
Square).   

Most Ham transceiver use the same LMS algorithm and I never heard distorted
audio when the notch was engaged.  That's especially true with Yaesu, Icom
or Kenwood. I'm not sure about the other American brands but I bet they are
OK as well.

My second complaint is the K3's NR control.  Most other manufacturers have
an analog like control that simply changes the NR level.  I don't understand
the logic of having several steps from F1-1 to F4-4 and F5-1 (mixed) to F8-4
(mixed).  I would rather have two separate settings.  F0 to F9 for the level
and if you want a to fiddle with the delay, D0 to D9 in the main menu.  I
think the level control on other radios is simply a mix of the input signal
with the NR output and is similar to the K3's mF5-1 to mF8-4 

To me it sounds as if there's a dynamic range problem on the K3 whereby the
numbers in the math are over-ranging when the notch is engaged and is
causing a "flat-topping" in the audio signal.  But that's just a guess!   

I hope someone at Elecraft reads this and gets the ball rolling to fix the
problem!

Jack WA9FVP
Willco Electronics  
repair at willcoele.com




-----
Jack WA9FVP

Sent from my TRS-80 :-)
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