[Elecraft] K2 CAL_FIL and the BFO

[Bill Coleman]

On Jul 26, 2009, at 7:37 PM, Stephen Rector wrote:

> Qusetion 1: Is that pitch change directly due to the offset I have
> dialed in during the filter calibration?

Mostly. If you pick the right offset, you can get it real close. One  
tip is to try calibrating one count in either direction to see if it  
is any better.

The BFO DAC does have a minimum resolution -- but you should be able  
to get the filters to all be within 20 Hz or so of each other.

> 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.

Could be, do the best you can.

> 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.

The K2 synthesizer inverts the sidebands above 20 MHz, so the sideband  
is inverted as well. You're still listening to LSB on CW, but it is  
using the USB filter settings because of the inversion. The signals  
also tune backwards from the lower bands. If it bothers you, you can  
switch to CW reverse, which is USB but tunes like LSB on the lower  
bands because of the inversion.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901