K2 Noise Blanker Problem

[WD6DBM]

I built my K2 some months back with the KNB2 option.  The noise blanker has never been effective against any type of noise.  The MCU recognizes the blanker, it draws the proper amount of current, but just doesn't seem to do anything.  Before drinking the Kool-Aid (TM) I was pretty much a Kenwood man and was used to ineffective noise blankers so I ended up blowing it off.  I recently built a K1, and the NB in it works FB.  This got me thinking, and besides Elecraft would never release a NB that was useless--it violates the Tao of Elecraft.  Yesterday I built another KNB2 (any excuse) and installed it in my K2.  Same result!  I checked all the solder joints, component values, RF board mods.  It makes no difference whether it is NB1, NB2, HI or LO, the preamp is on or off--nothing.  No change in S-meter reading, no change in audio.  Any ideas, oh mighty brains?  

Thanks, Eric WD6DB(lost in noise) 
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[Don Wilhelm-4]

Eric,

First do a test to see if your NB is working at all.  Remove the
antenna, turn on the Preamp, then tap on the case of Q21 with a
screwdriver.  The taps will create impulse noise in the receiver which
should be blanked when NB1 or NB2 is turned on.  Be careful to
differentiate between the clicks from the impulse noise and the rush of
'antenna/band noise' that happens because the screwdriver shaft can act
as an antenna.

If you find the NB is responding to that test, but it still does not
help with your noise source, you can try widening the gate time a bit -
try adding an additional .001 uF capacitor in parallel with C11 (just
soleder ti to the solder pads for a test - if that helps, you can either
leave the parallel cpacitor in place or change C11 to .002 uF.  Other
values may help as well, so some experimentation may be of help.  If the
noise gate is widened too much you will begin to notice "holes" on the
received signal.

73,
Don W3FPR

eric norris wrote:

> I built my K2 some months back with the KNB2 option.  The noise blanker has never been effective against any type of noise.  The MCU recognizes the blanker, it draws the proper amount of current, but just doesn't seem to do anything.  Before drinking the Kool-Aid (TM) I was pretty much a Kenwood man and was used to ineffective noise blankers so I ended up blowing it off.  I recently built a K1, and the NB in it works FB.  This got me thinking, and besides Elecraft would never release a NB that was useless--it violates the Tao of Elecraft.  Yesterday I built another KNB2 (any excuse) and installed it in my K2.  Same result!  I checked all the solder joints, component values, RF board mods.  It makes no difference whether it is NB1, NB2, HI or LO, the preamp is on or off--nothing.  No change in S-meter reading, no change in audio.  Any ideas, oh mighty brains?  
>
> Thanks, Eric WD6DB(lost in noise)  
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[David Woolley (E.L)]

Don Wilhelm wrote:
>
> First do a test to see if your NB is working at all.  Remove the
> antenna, turn on the Preamp, then tap on the case of Q21 with a
> screwdriver.  The taps will create impulse noise in the receiver which

Has it actually been established that the problem noise is impulsive?
One of the commonest problems with noise blanking is that people don't
understand that it is only suitable for wideband, impulsive noise.

--
David Woolley
"we do not overly restrict the subject matter on the list, and we
encourage postings on a wide range of amateur radio related topics"
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