[Elecraft] K2 CAL_FIL and the BFO

[Don Wilhelm]

Steve,

There may be a slight change in the pitch of the received signal when 
changing filters, but it should be limited to 20 Hz or less.  If it is 
more than that, you will have to do a good filter alignment.  I 
recommemd using Spectrogram and a noise generator so you can see what 
you are doing, but lacking the wideband noise generator, the same thing 
can be accomplished with band noise.  See my website www.w3fpr.com 
article on K2 Dial Calibration for more information.  Part 3 of that 
article deals with aligning the filters (adjust the BFO frequency to 
shift the passband), and has links to help setting up and using 
Spectrogram.  Even though the latest version of Spectrogram is now 
freeware, I recommend you use version 5.17 (download from Tom Hammond's 
website www.n0ss.net) because the 'how-to' information is written for 
that version - the screenshots may differ for other versions (but are 
similar).

Yes, the K2 places the VCO on the high frequency side of the signal 
frequency for bands up through 17 meters, but at 15 meters and above, 
the VFO is on the low side - that is what causes the sideband 
inversion.  If you prefer to listen to CW in LSB for all the bands, then 
switch to CW reverse for 15, 12 and 10 meters.

Stephen Rector wrote:
> I'm new to the list, with a couple of questions on the K2. My s/n 6770  
> has been running for about a week: this weekend put in the KSSB2,  
> KDSP2 and KNB2. When I select from the four CW xtal filter bandwidths,  
> I get a slightly different pitch on the received CW station.
>
> Qusetion 1: Is that pitch change directly due to the offset I have  
> dialed in during the filter calibration?
>
> The circuit changes the bandwidth of the Cohn crystal filter and, at  
> the same time, I dial in an offset to center that new passband to my  
> desired pitch. So, I'm confused why the pitch changes - maybe it's  
> just calibration error because the tuning step is coarser than my ear.
>
> Question 2 is an observation: CW mode is LSB all the way to 17 meters,  
> then USB from 15M up. This is normal, right? On previous  
> (upconverting) radios it's always been USB from 20M up, so this  
> surprised me.
>
> Thanks for any help with these...
>
> 73,
>
> Steve NU7B
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