[Elecraft] KNB2 Performance

[Scott Prather]

It has been my experience that the KNB2 is one of the least effective noise
blankers that I've used on a current-production radio.  At night, I have a
high noise level produced by malfunctioning street lights (this has been
true for the 10 years I've lived here), and the KNB2 is completely
ineffective in blanking this noise while other radios such as my Ten-Tec
Paragon II or Drake TR-7 eliminate it completely. As a result, I cannot use
the K2 at night.

In an effort to understand why this is the case, I've looked at the received
noise with a spectrum analyzer.  I found that, while the noise sounds
continuous across the amateur band, it actually has large peaks and valleys,
in some cases varying up to 20 dB across the band.  Other noise sources,
such as electric motor noise (which the KNB2 blanks well, depending upon the
pulse repetition rate) are typically of nearly equal-amplitude across the
bandwidth of the RX front end.

About a year ago I spent a lot of time trying to improve the performance of
the KNB2, but my attempts were in vain, as any improvement in blanking
effectiveness caused a corresponding decrease in performance in some other
respect.  I finally gave up this effort, in my opinion the entire KNB2 needs
to be re-designed in order to meet the expectations of those of us who
really need it.

While I understand that there are folks on the reflector that claim the KNB2
does an excellent job of blanking this or that specific interference type,
in general I've found that such instances are relatively rare.  I have seen
the KNB2 work very well, there's no doubt in my mind that it can under the
proper conditions.  However, I agree with those on the reflector who see the
NB performance as a major impairment to an otherwise excellent receiver.  As
someone suggested, even if a portion of an updated NB had a surface-mount
aspect, that wouldn't be any different than what we had with the KDSP2, and
in my opinion, it's much more important.

Until a better design comes along for the NB, my K2 will continue to sit
unused in the evening when the blanker is needed.

Scott
N7NB