[Elecraft] Question about KNB2 Noise Blanker

[VR2BrettGraham]

W3FPR added:

>>W3FPR replied to KH6AT that gated noise blankers cannot be expected
>>to work when the noise pulse is insufficient to reach the gating threshold
>>& that more signal might improve performance when blanking weak
>>noise.  Sounds reasonable, but...
>>
>>I believe my other radios have gated noise blankers.  They behave far
>>better than the KNB2 in my K2 - even on noise that presumably is what
>>the KNB2 was designed for (chain saws, dirt bikes & similar stuff that
>>might be encountered by backpackers) - regardless of strength.
>>
>>Outside of the type of noise the blanker is tailored for, why would it
>>be that a number of folks using one particular radio with a gated noise
>>blanker (K2 with KNB2) find the performance to be lacking compared to
>>other radios also with gated noise blankers?
>
>OTOH, many have reported that the K2 blanker is better.  I don't know the 
>real answer, but I can guess that the gain of a particular receiver ahead 
>of the noise blanker would make a big difference.  Multi-conversion 
>receiver designers have a lot more places to put the noise blanker (and 
>more control over the gain at that point) than is possible in a single 
>conversion receiver like the K2.  Try the K2 NB with the preamp set on to 
>see if that makes any difference, you may be surprised.

My impression is that whenever there is mention of the KNB2, there are
more posts about its ineffectiveness than anything else, as is the case
with this current thread.

I cannot recall any other rig using anything other than a gated noise
blanker, including those with single conversion receivers, such as the
TS-820.  I do not have an 820 here, but from my recollection of using one
with a vertical in an urban W7 environment, its noise blanker performed
better overall than the KNB2 in my K2/100.

Combinations of PREAMP & NB LEVEL settings on the K2 here tends
to have one of two results: no effect on noise, or totally trashing the
receiver.  My current QTH is in the middle of a mixed residential/industrial
area, with garages & work yards just next door doing plenty of arc welding
& other unsociable electromagnetic activities going on all around me - the
KNB2 is useless on most of it & even my lowly IC-706 does better.

I would suggest it is more a matter of the design of the KNB2 than the
fact that the K2 is a single conversion receiver.  I would agree with you
that variation in gain between K2s may be part of the problem, though
that really comes back to the design in the first place (consistency,
repeatability & ease of assembly & alignment being desirable in any
product, even a kit).

I also suspect that there are other factors that are involved or at least
aggravate things, as I find the KNB2 to be especially useless during
times that the AGC is responding to out of band energy (the EU 17m
problem recently noted in a post here by a bloke in NA - I experience
this on 15, 17, 20 & sometimes 30m).

But as the KNB2's performance continues to surface here from time
to time, there must be something behind it - we have enjoyed far
better performance from noise blankers in products with single, double
or however number of conversions in the receiver for decades.  I for
one hope that in any future products, Elecraft can improve upon this
& other attributes of their products that are lacking in comparison to
others on the market.

73, VR2BrettGraham