[Elecraft] CW speed clabration

[David Woolley]

Tom Hammond wrote:
> Fellas:
> 
> There is NO(!) means of significantly re-calibrating the keyer speed... 

I did say the adjustment range would be rather limited!

> and it should not be off by nearly THAT much.

Sorry, I couldn't resist giving a literal reply.  Yes, the keyer speed 
is crystal controlled by the 4MHz clock crystal (which cannot be 
significantly in error without an obvious failure of the VFO 
calibration).  If the speed is wrong,  it is one of:

- a hardware fault in the microcontroller;
- a bug in coding the timer handling;
- a difference in the definition of speed between the firmware
   coder and the user.
> 
> The Keyer speed control IS a POT... the ONLY encoder is the VFO knob.

Physically its a pot, but its function in the K2 is as a shaft encoder. 
  The microcontroller reads the position of the pot as, as a number, and 
uses that number to decide how fast to send the morse.  It is not being 
used to control the R part of an RC time constant as might be the case 
in a non-software implementation of a keyer. I'd therefore say it was a 
poor man's encoder, rather than a pot, in reality.
> 
> C22 is the master oscillator calibration capacitor which sets the 
> calibration for the entire K2. If you adjust C22, you will HAVE to 
> re-run CAL PLL, and then you will probably want to re-run CAL FIL for 
> each of your XTAL filter settings.

If you were to to modify C22 to change the morse speed calibration, 
which would be pretty pointless, as the adjustment range is probably 
only about 100 parts per million, you *MUST NOT* re-run CAL PLL or CAL 
FLTR.  Both of these assume that C22 has been set to make the frequency 
exactly 4MHz.  (You also should not re-run these at a different 
temperature from the one at which C22 was last correctly adjusted, if 
you want maximum accuracy and you have the thermistor board.)

In normal operation, the 4MHz oscillator is not used as a frequency 
reference, for anything except the morse speed.  It is used as the 
primary frequency reference during CAL PLL and CAL FLTR.  As the normal 
reason for adjusting C22 is to make the 4MHz more accurate, the natural 
consequence of changing is that one would want to recalibrate the PLL 
master reference oscillator, which is what sets the frequency reference 
in normal operation, but is trimmed with an electrically, rather than 
mechanically, variable capacitor.  If one compromises its 4MHz accuracy 
to achieve some other aim, it is no longer a good primary reference for 
calibration.

PS I think the reply about individual calibration charts was also tongue 
in cheek.

-- 
David Woolley
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