[Elecraft] K2 CAL_FIL and the BFO

[Stephen Rector]

Hi Don:

I will check your article out, and thanks again. Last I checked today,  
the pitch change was slight, so I'll keep an ear on it. And I'll try  
Spectrogram at some point, after the construction is done. Still have  
the PA and KAT-100 to go.... It's nice to have the knowledge base that  
you and others are willing to share.

Cheers,

Steve

On Jul 26, 2009, at 5:16 PM, Don Wilhelm wrote:

> 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
>> ______________________________________________________________