[Elecraft] Calibration of BFO

[David A. Belsley]

Ron:
  This is my experience exactly.

dave

--On Monday, February 4, 2002 8:39 AM -0800 Ron D' Eau Claire 
<rondec@easystreet.com> wrote:

> Dave, K9DC, wrote:
>
>> Actually, I believe the adjustment increment of the BFO is in 20 Hz
>> steps. The VFO steps are 10 Hz. My comment about shifts less than 1 Hz is
>> referring to frequency shifts when stepping through the four filter
>> bandwidths. It can be less than 1 Hz.  It also will drive you
>> nuts getting
>> there. Sometimes just entering the filter alignment mode, making a change
>> then returning back to the same setting and exiting will get it right on,
>> sometimes it makes it worse. I've not discoverd the key to getting it
>> right except to keep repeating the procedure... and then don't mess with
>> it once you get it right.
>
> As I recall a discussion a couple of years ago, the 12-bit Digital to
> Analog Converters (DAC's) used in the K2 permit a 10 Hz resolution. That
> is, they can't come up with a control voltage that will set the
> oscillator any closer than that.
>
> If you get lucky, the DAC will pick a value that hits closer, but it's
> purely a matter of luck. The system can't tell the difference. And if you
> do anything at all to make it store the value again, it may easily store
> a new value that translates into a frequency error of up to 10 Hz.
>
> I've always assumed that the reverse would be true when operating the rig.
> Whenever the digital value representing a frequency was recalled from
> memory, it would be translated into an analog voltage by the DAC, but only
> with an accuracy that would place it within 10 Hz of the original spot. So
> it would not be possible to store a value that would always be more
> accurate than 10 Hz. I've always noted a 10 Hz step in at least one
> filter.
>
> Sometimes when setting up the filters they sounded and looked 'exactly on'
> but when I operated the rig later the 10 Hz frequency error would be back.
> Never more than that, but it's always been there no matter how often I did
> the alignment.
>
> Ron AC7AC
> K2 # 1289
>
>
>
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----------------------------
David A. Belsley
Professor of Economics