[Elecraft] K2 Filter Alignment

[W3FPR]

Jim,

I agree partly with you.  The K2 RX sounds fine on SSB, but only if the 
TX filter is used.  That filter width can vary between 2.1 kHz and 2.6 
kHz if the filter capacitors are changed to the vales specified for 
those widths.  The 2.1 kHz width is a bit constrained, 2.4 is quite 
usable, and 2.6 kHz is quite good.
Those widths are fixed and not switchable, only fitting the KSB2 with 
the proper capacitors can the width be changed.  early KSB2 boards came 
with only the 2.1 kHz filter, but later ones used the 2.4 kHz width.

The narrower SSB filter widths created using the CW filter require 
careful placement of the BFO frequency so the slope of the low end of 
the filter at 3 dB down is as close too 300 Hz as possible. That will 
provide SSB copy in difficult band conditions, but fidelity is not to be 
expected.  It is better (but not perfect) in K2s later than SN 2560 or 
those updated with the newer filter crystals.

There are also 2 freeware versions of Spectrogram on my website 
www.w3fpr.com - version 1.6 is the older one.  I suggest using the newer 
one, but the setting of the markers is different, and the window size is 
changeable.  IMHO, it is a very useful and accessible audio spectrum 
analyzer for ham projects.  YMMV.

73,
Don W3FPR

On 12/22/2025 4:25 PM, Jim Brown via Elecraft wrote:
> On 12/22/2025 10:00 AM, Bruce Beford via Elecraft wrote:
>> I strongly suggest you learn to do the alignment yourself. It's not 
>> difficult. You will gain knowledge and experience, and appreciate the 
>> radio that much more.
>
> I owned and used a K2 that I bought used, and carefully did the SSB 
> filter alignment using Spectrogram. The results were not wonderful, 
> thanks to the extreme phase shift of the stagger-tuned filters, which 
> made speech hard to copy. The radio only sounds good on receive at 
> full bandwidth, which uses the transmit filter.
>
> It's a very nice CW rig, but NOT great on SSB except at full RX 
> bandwidth. It's the nature of the design, which started out as a QRP 
> CW rig, and morphed into much more. But the SSB part of the morphing 
> didn't turn out all that great.
>
> If you want to attempt the alignment, the last version of Spectrogram 
> is on my website, k9yc.com/publish.htm  But it's GIGO -- garbage in, 
> garbage out.
>
> 73, Jim K9YC