[Elecraft] K3 Auto Notch distortion

[Jim Brown]

On 1/26/2012 11:08 AM, Nate Bargmann wrote:
> I have had bad distortion using the Auto Notch onSSB.

ANY filter, whether it uses analog components or DSP (which is a 
simulation of analog components) has a phase response associated with 
the amplitude response, and the greater the amplitude response changes, 
the greater will be the phase response changes. These changes in 
amplitude and phase are simply another form of  DISTORTION, and the 
greater the distortion, the more likely we are to HEAR it.  For example, 
when the crystal filters in the K2 are aligned for narrow SSB bandwidth, 
the amplitude response is QUITE bumpy, and the resulting phase 
distortion makes it hard to listen to.

Now, it is POSSIBLE to detect a single frequency and reproduce it, then 
carefully add it precisely equal in amplitude and 180 degrees out of 
phase with the interfering signal without adding distortion.  I don't 
know what method(s) Elecraft is using.

Another point.  NO audio stage is ideal -- there is SOME distortion, 
which consists of harmonics and even intermod products -- and a strong 
heterodyne can produce fairly strong harmonics. If the fundamental is 
there, it MASKS the harmonics (within our ear/brain) so that we don't 
hear them, but if the fundamental is removed, they can be quite 
audible.  Audio engineers have learned to recognize various kinds of 
distortion products by listening to the distortion output of a 
distortion analyzer, which is essentially a notch filter.

Bottom line -- ALL notch filters have audible artifacts. I use the notch 
only when I need it, and leave it off when I don't.

73, Jim Brown K9YC