[Elecraft] KNB2 Noise Blanker Not Working

[Gregg R. Lengling]

Yes you should see the pulse there.  I had the same problem when I built 
mine a few years back and ended up right where you are, but what I found was 
that I had a bad connection on C8 the coupling cap on the output of Q5.  The 
result will also look like a bad Transistor with no pulse showing on the 
collector.

Good hunting.

Gregg R. Lengling, W9DHI, Un-Retired
K2/100 SN 3075
http://www.milwaukeehdtv.org

----- Original Message ----- 
From: <lfcluff at comcast.net>
To: <elecraft at mailman.qth.net>
Sent: Tuesday, November 15, 2005 8:36 AM
Subject: [Elecraft] KNB2 Noise Blanker Not Working


> I've had my K2 built for about 2 months now.  Everything works except the 
> noise blanker.  I've looked at a lot of archives on this.  What I have 
> done to test it is:
>
> 1.  Scratch the top of Q21 on the RF board to generate noise.
> 2.  Using an oscilloscope, I can trace the noise pulse through Q2-Q4 on 
> KNB2 borad.
> 3.  I do see a  noise pulses on the "GATE" node and at the base of Q5. 
> When I turn off the NB, this pulse goes away as expected.
> 4.  I do not see any pulse on collector of  Q5.  Since the pulse on the 
> base of Q5 saturates Q5, should I see anything on the collector?
>
> I'm not sure if I have a bad Q5.  I am going to replace it today.
>
> Thanks,
> Leon, NE0N
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