[Elecraft] K2 dial alignment SOLVED!!

[paul]

Hi Don,

The inductor I removed measures 12.9 uH - seems to be in tolerance.  My 
guess is the crystals (X1) had too high Q.  I got two - one with the the 
PLL temp compensation and one in the BFO upgrade.  Tried each of the 
crystals - both had the same dial error result.

You are right that instructions do say that, but I posted the results of 
this test in my original post.  The only messages I got were to set the 4 
Mhz oscillator (using several different methods), run CAL PLL and CAL FIL 
(vary each entry).  None of this addressed the real issue.

I had installed the components correctly and I just could not understand 
what went wrong.  It ends up being a design flaw (component variation 
exceeded the design parameters).  Oh well, I learned a lot even though the 
radio sat idle for a year.  Can't contest or qsl much when you don't know 
what frequency you really are on. :)

Another person on the list had the same problem and mentioned it in a 
single post - which had no response or update to the FAQ list.  That 
post gave a hint that a slightly low VCO frequency was resposible for dial 
error.

Don, I am not picking on you as you have provided help tirelessly to 
hundreds of people on this list (and to me several times).  Thank you.

All I am asking is that Elecraft update their FAQ to include this critical 
info.

Thanks,
Paul
AD5IW


On Wed, 3 Dec 2008, Don Wilhelm wrote:

> Paul,
> 
> The A to B instructions do state that the PLL reference high frequency is
> 'typically 12097 to 12100 kHz'.
> Yours was clearly not in the typical range, and indicated that something was
> awry.
> You are correct that there should be a statement that the upper frequency must
> be above 12096 kHz.
> 
> Incidently, a 12 uHy choke should provide a greater range than a 10 uHy.  I am
> wondering if the 12 uHy choke you received was really a 12 uHy.  I am certain
> it was marked as a 12 uHy - any chance that you can measure it to see if my
> speculation is correct?
> 
> 73,
> Don W3FPR
> 
> paul wrote:
> > Last year, I upgraded my K2 from rev A to Rev B.  Afterwards the dial was
> > off by 12 KHz at 10MHz, even after setting the 4Mhz crystal, doing CAL
> > PLL, CAL FIL more than 30 times.  Yes, I followed every procedure posted
> > and verified the 4 MHz clock accurately.  Prior to the upgrade, the dial
> > was right on.
> > 
> > It turns out that the VCO max frequency must be at least 12096 khz or the
> > dial calibration will be off.  This should be in the FAQ, along with how
> > to fix it in the upgrade instructions.
> > 
> > After making the rev A to B mod, the VCO range was 12084.87 to 19094.44
> > creating the 12Khz dial error - no matter how many alignments attempted.  
> > 
> > Finally I just tried experimenting with the VCO.  I put in another
> > crystal in parallel with X1 (that came with the BFO upgrade) in X2.  The
> > VCO range was 12081.52 to 12098.17 which fixed the dial error, but the
> > VCO was too wide at 17.19 Khz.
> > 
> > I swapped out the 12uH inductor (L31) with the old 10uH inductor and got
> > a VCO range of 12084.87 to 12094.44 - dial calibration was way off (Yes,
> > CAL PLL and CAL FIL were run after each of these changes).
> > 
> > Then I removed the second crystal at X2 that I had temporarly installed
> > two steps above.  VCO range now 12090.70 to 12097.63 - BINGO - the dial
> > is dead on!!!  The VCO is a little narrow at 6.93 Khz, but I have no
> > plans to use 160 meters - so this should be ok.
> > 
> > So the solution was to go back to the 10uH inductor.
> > 
> > I have spent several weekends and nights trying to figure out this
> > problem.  While I have learned a lot doing this, please put this in a FAQ
> > somewhere and save someone else the trouble.
> > 
> > Paul
> > AD5IW
> > 
> > On Sun, 2 Dec 2007, paul wrote:
> > 
> > 
>