[Elecraft] Noise blanker [was: K2 battleplan?]

[Ron D'Eau Claire]

Mike AB3AP wrote:
I've noticed the majority of K2s seem to be built with the NB.  I don't have
it, and since I don't seem to be having any man-made noise problems I've
been wondering when & where the NB is useful.  Is it mainly for presumably
noisier urban and suburban areas?  Without it would something like
Spectrogram show continual spikes at certain frequencies?  And finally,
would the DSP board have any substantial effect on the sort of man-made
noise the NB addresses?  Thanks!

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The noise blanker is designed to suppress noise consisting of a train of
high-intensity pulses with a regular interval between them. Good examples
are the raucous buzz most cheap incandescent lamp dimmers produce or the
staccato pops produced by poorly-shielded automobile ignition systems,
especially on the higher frequencies.

If the noise does not have pulses that occur with very fast rise times and
at regular intervals, the noise blanker won't be able to identify it from
regular QRN or it won't able properly time the action to suppress the
pulses. 

It does a wonderful job on the proper sort of noise but, like all such noise
blankers, it does it at some expense in performance. The blanker actually
shuts off the i.f. strip for the duration of each pulse. Instead of a train
of loud pops coming through the second detector and down the audio channel,
you have a chain of 'holes' where there is no output. 

The problem is that process of switching the i.f. strip on and off quickly
also turns the i.f. into an unintentional frequency mixer. With the noise
blanker on, strong signals can mix with each other in the i.f. producing
spurious artifacts that sound like everything from normal QRN to actual
spurious signals on the band. That's why the noise blanker has an on/off
switch. The noise blanker should only be turned on when it's needed.

I don't have the DSP unit in my K2 so I can't compare them. The sorts of
noise the noise blanker is designed to produce are more likely to be
encountered in a urban environment, although sources capable of drowning out
the bands might also be in your own home. The noise from cheap lamp dimmers
usually doesn't travel very far, for example. The troublesome ones are
usually very close by. 

Ron AC7AC