A minor C22 question

[Howard W. Ashcraft]

Last night I redid my C22 reference oscillator adjustment using WWV on 10mhz as the zero beat reference.  This is the third time I have adjusted C22 and each time I am able to adjust C22 to a precise offset balancing TP1 and TP2.  However, when I put the cover back on the K2/100 I find that WWV zero beats a few tens of hz off.  (After last night's adjustment, the zero beat was 10000.03)  One should expect to be +- 10 hz as that is the finest resolution of the VCO, but it would be nice to get a little closer.  

The unit was thoroughly warmed before adjustment although there may be some temperature difference between having the cover on and having the cover off.

This is hardly a big deal, but I wonder whether others manage to get an exact setting or whether this is a process that you repeat until you finally nail the adjustment.

HOWARD W. ASHCRAFT, Jr.  W1WF
Direct Dial: [phone]
[hidden email]
HANSON 333 Market Street, 23rd Floor
BRIDGETT San Francisco, CA 94105-2173
MARCUS   Direct: [phone]
VLAHOS Main: [phone]
RUDY, LLP Fax: [phone]


_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Stuart Rohre]

The cover on vs. off naturally changes overall circuit capacitance as well
as temperature.  What you do is see how much you are off with cover on, and
adjust with cover off, in a direction to bring the circuit right on with the
cover on.  In other words, you overcompensate the setting for the final
cover on case.   A few iterations should give you a hint on how much change
is needed to be right on.   marking the slot position with cover off, vs.
cover on, when the frequency is right on should give you the range.  Then
set the slot halfway and see if that is not the optimum.  It may be less
than the slot width, so a deft touch is needed.
GL and 72,
Stuart
K5KVH


_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Rich Lentz]

Did you re-run CAL PLL, ** AND ** XFIL on ** ALL ** Modes (USB, LSB, CW,
CWR, RTTY, & RTTYR)
** AND ** when running CAL XFIL you MUST change the number (up or down at
least on digit and then back to the same number) so that the MCU knows that
it needs to re-store the frequency settings for the BFO.

Otherwise you have changed nothing but the frequency of the reference
oscillator.  For a long explanation see W3FPR's discussion.  The short one
is that the MCU stores a digit representing the voltage necessary to make
the frequency.  This is "number" determined by the Reference oscillator
whose accuracy determines the repeatability and accuracy across all bands.
In other words the 4.0 MHz oscillator is only used for the frequency
measurement.  It only measures the frequency when you run the CAL FILL and
CAL XFIL.  After that it does nothing.  

Rich,
KE0X
 
---------------
Last night I redid my C22 reference oscillator adjustment using WWV on 10mhz
as the zero beat reference.  This is the third time I have adjusted C22 and
each time I am able to adjust C22 to a precise offset balancing TP1 and TP2.
However, when I put the cover back on the K2/100 I find that WWV zero beats
a few tens of hz off.  (After last night's adjustment, the zero beat was
10000.03)  One should expect to be +- 10 hz as that is the finest resolution
of the VCO, but it would be nice to get a little closer.  

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Ron D'Eau Claire-2]

HOWARD W. ASHCRAFT, Jr.  W1WF wrote:
Last night I redid my C22 reference oscillator adjustment using WWV on 10mhz
as the zero beat reference.  This is the third time I have adjusted C22 and
each time I am able to adjust C22 to a precise offset balancing TP1 and TP2.
However, when I put the cover back on the K2/100 I find that WWV zero beats
a few tens of hz off.  (After last night's adjustment, the zero beat was
10000.03)  One should expect to be +- 10 hz as that is the finest resolution
of the VCO, but it would be nice to get a little closer.
--------------------------------------

You are probably fighting the resolution limits of the digital-to-analog
converters (DAC's) used to convert between the analog tuning voltages for
the BFO and PLL reference oscillator and the digital values stored in
memory. Since they convert the analog voltage into a binary number, and use
that binary number to recreate the voltage later as you tune in a signal and
choose the filter setting you want, they are never exact.

Sometimes one is closer than 10 or 20 Hz, sometimes not. At that level it's
a matter of "luck".

That's the source of often hearing a small step in the frequency of a CW
beat note when switching between filters too.

Ron AC7AC


_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Mike Harris-9]

G'day,

Not really an issue.  Get C22 right with the cover off and right away do
the "cal pll" before putting the cover on.  After that it doesn't matter
what happens when the cover is replaced 'cos it has no effect whatsoever
on calibration.

Regards,

Mike VP8NO

| The cover on vs. off naturally changes overall circuit capacitance as
well
| as temperature.  What you do is see how much you are off with cover on,
and
| adjust with cover off, in a direction to bring the circuit right on with
the
| cover on.  In other words, you overcompensate the setting for the final
| cover on case.   A few iterations should give you a hint on how much
change
| is needed to be right on.   marking the slot position with cover off,
vs.
| cover on, when the frequency is right on should give you the range.
Then
| set the slot halfway and see if that is not the optimum.  It may be less
| than the slot width, so a deft touch is needed.
| GL and 72,
| Stuart
| K5KVH

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Don Wilhelm-3]

Mike,

I don't have any measurement data to support it, but I do believe that the
oscillators (BFO, PLL, VCO) can be influenced by temperature and the
proximity of objects to the frequency determining components - the
difference should be slight, but could account for 10 to 30 Hz in the end.

Also, remember that CAL FIL must be run to for the results to be correct.
Even if the filters are already correct, each BFO must be moved a notch and
then moved back for the new values to be written.  Failure to do that will
look like your calibration efforts 'just didn't work right'.

You are correct in saying that once the values are written into EEPROM, the
reference oscillator is out of the picture - but those values only represent
voltages which SHOULD produce a specific frequency - if the conditions
around the frequency determining components of the oscillator are not the
same as when the values were written, the resulting frequency may be a bit
different.

Now, I must admit that the differences are slight - but for those who would
struggle to get things 'right on', you should realize that these factors
will influence your results.

73,
Don W3FPR

----- Original Message -----
>
> Not really an issue.  Get C22 right with the cover off and right away do
> the "cal pll" before putting the cover on.  After that it doesn't matter
> what happens when the cover is replaced 'cos it has no effect whatsoever
> on calibration.
>
> Regards,
>


_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com