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

[Brett Howard]

Are there a set of mods for the KNB1 similar to this?  My TS450Sat had a
very effective noise blanker and the K3 works wonders on the noise at my
home QTH but the K1 blanker could really use a bit more work.  Not sure
what it needs ATM but it could be fun trying to find it.. 

~Brett


On Wed, 2009-07-08 at 00:17 -0400, Don Wilhelm wrote:
> Steve,
> 
> I suggest that you build the KNB2 first and see if it is effective for 
> the noise you have to deal with.  Normally, the gating level is not the 
> problem, but the blanking pulse width can be varied (G3ULB mod) to 
> handle other noise pulses.
> 
> The stock KNB2 is quite effective for impulse noise of the automotive 
> ignition type.  Yes, if you have other types of noise sources that you 
> must deal with, try either (or both) of these mods to see if it helps in 
> your situation.  Similarly, your proposed change for Q3 may make a 
> difference too, so try it out.  There is nothing wrong with a bit of 
> experimentation.  What I am encouraging you to do is build the KNB2 as 
> "stock" first, and then experiment from there.  The actual beta of 
> several 2N2222As that I have measured is in the range of 100, so your 
> proposed transistor change may make no difference.
> 
> 73,
> Don W3FPR
> 
> NU7B wrote:
> > Joe:
> >
> > I just ordered a KNB2 and looked at DL7MAJ's modification. In looking at the
> > schematic, it seems like the shortest time constant for the one-shot is
> > above 10 µs. The DL7 mod noted that Q2 was being loaded by the base of Q3 -
> > possibly there is a load transient associated with charging C11,12. The
> > 2222A has a fairly low beta, and Q3 has no RE, so its base current could be
> > fairly high. Raising the beta seems like it would reduce the loading on Q2.
> >
> > I'll measure the beta on what comes with the KNB2. I've got 2n3904 (B=100)
> > and 2n5089 (B=400), so I may substitute. The 5089 has a lower fT of 50 MHz,
> > but for a 10µs pulsewidth, it should be fine.
> >
> > Steve NU7B
> >   
> >
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