Re: K1 NB Modification

Posted by Brett Howard on Sep 19, 2009; 9:30pm
URL: http://elecraft.85.s1.nabble.com/K1-NB-Modification-tp3675941p3677327.html

hrm...

I could have swore that there was a set of mods that would allow one to
modify the blanking time and what not a bit...  

I'm finding it ineffective in power line noise and would like to try and
make it more so.  However if I end up with the time to do it I'll
probably not have enough time nor repeatable enough condx to test a
whole lot.

~BTH

On Sat, 2009-09-19 at 12:00 -0400, Mike Morrow wrote:

> >I remember somewhere on the net reading about some mods to make the
> >K1-NB a little bit more aggressive.
>
> I've never come across anything like that in the almost nine years that I've
> had my K1.  I've found the KNB1 to be effective on spark-type noise, but
> not at all effective on local power line noise.  The NB on my old TS-50S is,
> in contrast, very effective on that same power line noise.
>
> The KNB1 has only the OFF, HI, LO noise threshold settings.  Obviously,
> the blanking is *least* effective in the HI setting since the noise magnitude
> has to exceed a higher value to trigger the noise gate, compared to when
> the LO threshold is selected.  The only construction option provided is
> changing D2 from the normal 1N4148 to an LED to raise the threshold in HI
> to require an even *higher* noise pulse magnitude before the the noise gate
> will trigger.
>
> The early KNB1 is identcal to the current KNB1, except that it wasn't
> provided with a 0.01 uF cap between U1 pin 1 and pin 8.  Without that
> cap, gosh-awful noise is generated on some frequencies in the 20m
> band (at least) as the K1 transitions between transmit and receive.
> Anyone whose early KNB1 is without this cap should install it.
>
> Of course, that cap has no effect on setting the noise gate trigger threshold.
> That's determined only by RP1(9-10), RP2(5-6), and D1 when on LO, plus
> D2 when on HI.
>
> BTW, the K1 Quick Reference has for almost a decade now said that the
> KNB1 menu selections are OFF, NB1, NB2 instead of the correct OFF, HI, LO.
>
> Mike / KK5F
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