[Elecraft] K3 Questions and gripes

[Scott Ellington]

The K3 noise blanker bandpass filter appears to have a bandwidth of about 400 kHz, so any strong signal within that bandwidth will affect its operation.  This is a problem with all noise blankers of this type, as  they can't detect noise pulses smaller than the strongest signal within the filter bandwidth.  Some use a narrower filter, perhaps 15 kHz, to minimize the chance a strong signal is in its passband.  That, of course, us usually still far too wide during a contest, and the noise blanker just won't work with a narrower bandwidth.  One solution is the "Evasive Noise Blanker", which essentially uses a second receiver to detect noise pulses at a slightly different frequency, for example, just outside the ham band.  I may someday investigate trying to do that with the K3.

I'm just guessing, but it seems Elecraft took a different approach in using the very wide bandwidth.  This increases the peak amplitude of the noise pulses, allowing them to be detected at a higher threshold while, under crowded band conditions, the strongest signal remains about the same.  

By the way, many have noticed, I'm sure, that noise blankers are at times much more effective than at others, even if the characteristics of the noise are the same.  Generally, they work great when there are no strong signals around.  When there are strong signals in the NB filter passband, the noise detection threshold goes up as a result of NB AGC action, and the same noise pulses may not be detected at all.  That can happen even when the obvious distortion from the NB isn't present.

73,

Scott  K9MA


On Dec 12, 2010, at 9:59 AM, David F. Reed 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 ???
> 
>   2. The power switch - early serial number (1476); my power switch -
>      well the rubber / plastic part you press on - is starting to look
>      like a mouse has nibbled on it, with little divots falling off
>      along the top and right side edges.  It is looking quite ragged. 
>      Has anyone else had this, or know if I can replace just the
>      rubber/plastic part, or do I need to replace the entire switch
>      assembly?
> 
> Thanks and 73 de Dave, W5SV
> ______________________________________________________________
> 

Scott Ellington
Madison, Wisconsin
USA