[Elecraft] [K2] KNB2 vs. electric fence.

[Joe Planisky]

Thanks for the responses, Dale and Vic.

I tried increasing C12 to 0.1uF, no change.

I tried turning on the preamp, again no change.

I did some research on the web and it seems the effectiveness of the  
KNB2 has been the subject of some discussion in the past.  A handful  
of folks even shared my suspicion that their KNB2 was not working at  
all.   I was able to verify that my KNB2 was indeed working by  
connecting a short piece of wire to the antenna jack and scraping it  
against various metallic objects in the shack with the NB on and off.   
(I tried the light dimmer trick, but I must have the worlds quietest  
light dimmer.  Never thought that would be a problem!)

What did seem to help was the mod suggested by DL7MAJ:

http://www.dl7maj.de/KNB2-Mod.pdf

which adds a 0.1uF capacitor between the emitter of Q2 and ground.   
This increases the low-threshold sensitivity.  Before, I never noticed  
any difference between the LEVEL=LO and LEVEL=HI settings.  Now there  
is most definitely a difference and the LO setting takes out at least  
some of the pops.

Thanks again for your responses.

73
--
Joe KB8AP


On Aug 3, 2008, at 2:16 PM, Dale Boresz wrote:
>
> Turn on your preamp, and then try the NB.

On Aug 3, 2008, at 2:07 PM, Vic K2VCO wrote:
>
> Some electric fences produce wide pulses, so you should try using  
> the NB2 setting. If that doesn't work, you might consider increasing  
> one of the capacitors that determines the pulse width in the KNB2;