[Elecraft] K2 working on 40M

[Don Wilhelm]

Garry and all - at least those who are building new K2s.

Yes, the filter setup is a bit "tricky", especially when using filter 
widths wider than 1.00 kHz.  The reason is in the varactors that have 
shipped with the more recent K2 kits.  What that means is that a filter 
width that is indicates as 2.00 kHz wide on the K2 may actually be 2.5 
kHz wide (this is not exact, it all depends on the varactors).  The 
result of this is that the LSB filter settings listed in the manual will 
be about right, but the USB settings will be way off.  In other words, 
the manual settings will give you a workable filter for the lower 
sideband response, but will not work for the upper sideband (USB, RTTYr, 
and CWr) settings. (NOTE: the OP1 filter width is not affected by the 
varactors - there are no varactors on the KSB2 board).

The only cure I know is to use Spectrogram or another audio spectrum 
analyzer to measure the actual width of the filter (in LSB or CW - not 
CWr -  or RTTY - not RTTYr).  When you use LSB, CW or RTTY, you should 
be on the lower sideband, and you can change the width without much 
movement of the lower end of the passband frequency.  After getting the 
filer width as you like it, then refine the low frequency end of the 
lower sideband filter (by changing the BFO setting) and then set the USB 
BFOs to properly place the sideband.

If you want specifics on how to set the filters, look at part 3 of the 
article on K2 Dial Calibration at my website www.w3fpr.com (while you 
are there, you may just want to go through the entire K2 Dial 
Calibration procedure which includes adusting the filters.
I have not yet updated the webpage information to include how to handle 
this "varactor problem", but since you can see the passband width on the 
Spectrogram display, it should be obvious.  Just adjust the width of the 
filter until the actual width is what you want, and use the K2 display 
only as a relative indicator.

73,
Don W3FPR

2rGarry wrote:
> Congrats on the K2 receiving on 40.  It's only a month or so back that I
> finished mine so easy for me to remember the thrill of hitting the switch
> and having it come up working.  I used mine on cw for a week or so then went
> on to the ssb board which allows digital modes as well as phone.  Still
> using it qrp here and may never buy and build the power amp as I have been
> having a blast with it even on qrp.
>
> If you chose the ssb option perhaps you will find as I did that the
> directions for setting up the filters are somewhat confusing however it will
> all fall into place eventually.
>
> Cheerio, maybe hear you on the air sometime.
>   
>