[Elecraft] K3 Questions and gripes

[Wes Stewart]

If you look at the K3 schematic you can see that the noise blanker takeoff point is at the output of the first post mixer amplifier.  The bandwidth here is necessarily wide.  In the blanker itself, there is a double-tuned bandpass filter at the input of the noise amplifier(s).  I don't know what the bandwidth of this is, but to minimize the effects on the risetime of noise pulses, it should be as broad as possible.

There are then a couple of opportunities for mischief.

1) Strong signals get into the noise amplifier and overdrive the first stage

2) Any signal getting into the noise amplifier that is strong enough to exceed the blanking threshold looks like noise and generates blanking pulses.  

That is simply the nature of the beast.

Wes  N7WS

--- On Sun, 12/12/10, David F. Reed <w5sv.dave at gmail.com> wrote:

> Hi folks;
> 
> Yes, I really love my K3 in spite of my questions and
> gripes; here they are:
> 
>    1. During the 10 meter contest, I was up
> around 28.400 operating SSB
>       with the NB on, when I noticed that I
> was getting a strong CW
>       signal pumping my AGC (or so it
> seemed).
> 
>       In doing a little research, I found
> the cw station responsible was
>       down at 28.023, at about S9+40 db; by
> call, I know the station and
>       that he is about 3 miles away. 
> Far enough and weak enough that I
>       should not be receiving this sort of
> interference I think, given
>       there are no key clicks, etc.
> 
>       I turn off the NB, and it clears up
> completely, even 500Hz away,
>       let alone 300 or 400 KHz
> away.   I go back up, no problem except I
>       want to use the NB; turn it back on,
> problem re-appears.
> 
>       This seems to be an artifact of how
> the NB is implemented,
>       rendering it useless under these sorts
> of circumstances.
> 
>       Am I missing something, out of
> adjustment, or ???
> 
>