[Elecraft] KNB2 diagnosis

[Ron D'Eau Claire]

Ha, ha! No "fix". It's  a way of generating noise to demonstrate that the
KNB2 is working. It produces the sort of high-impulse, short duration noise
the KNB2 is designed to handle. 

A lot of operators note that it doesn't do much for random QRN with fairly
wide pulses at varying intervals. That's not what a "noise blanker" is best
suited for suppressing. Blankers do a wonderful job on repetitive spikes
such as those produced by cheap lamp dimmers, auto ignition, etc. The
"scratch" is just a way of testing it if one doesn't have a suitable noise
source handy. 

Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Stan Rife
Sent: Wednesday, December 26, 2007 4:19 PM
To: elecraft at mailman.qth.net
Subject: RE: [Elecraft] KNB2 diagnosis


	 I'll admit that I am pretty gullible, until I prove otherwise, but
scratching the top of a transistor as a fix???? Ha ha ha ha....c'mon now. 


Stan Rife
W5EWA
Houston, TX
K2 S/N 4216


-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of johnfm1 at optonline.net
Sent: Monday, December 24, 2007 11:18 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] KNB2 diagnosis


Chris,
I installed a KNB2 in my K2 a few months ago. I didn't think it worked until
I tried the scratching of Q21 as recommended.
 
With the top off and background noise coming from the speaker, I toggled
from NB1 to NB2 to OFF while I scratched the case of Q21. It worked. I saw a
definite difference. 
 
With the NB on I then toggled between both threshold levels and heard the
difference also.
 
Give this technique another try. Use a small screwdriver to scratch with. 
 
Good luck.
 
John N2YC
 
I've never been convinced that my KNB2 worked as planned. I have the K2 open
today to install the K160RX, and decided to work on the KNB2. 

I found the archive messages about "scratching" Q21. I can only get any
noise out of this with the pre-amp on - don't know if that's as expected or
not. No setting of the NB changes the audio through the headphones. 

I can tap Q21 and get a pulse on my scope, or rub the case back and forth to
get something a little more continuous (but still hard to capture on the
scope - despite being quite evident in the headphones). 

Some of the time, my pulses just die at the output of R8, which goes to
ground via L1. I'm not sure exactly what I do differently when the pulse
gets past - perhaps just how hard I'm tapping? 

If I have the NB turned off, the signal stops at pin 4 of U1 - I see pulses
there, but not at pin 1. 

If I have the NB turned on, pin 4 is biased and pin 1 is biased even higher
- but I don't see the pulses at either pin. 
Help? Feeling stuck here.73 de chris K6DBG
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