K2 off freq on 10 meters

[Aaron-8]

Hello all,

I finished my K2 about a month ago without any issues. The radio is  
spot on with all bands except 10 meters. If I dial up 28.400.00 I am  
off freq. To be on I need to dial to 28.400.17. Any ideas on this or  
how to correct it?  All other band are right on the money. I have  
installed the SSB, NB, and KPA100 if that helps at all.

Thanks in advance,

KC8MXW
s/n 6187


Aaron Beatty

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[David Woolley (E.L)]

Aaron wrote:
>
> I finished my K2 about a month ago without any issues. The radio is spot
> on with all bands except 10 meters. If I dial up 28.400.00 I am off
> freq. To be on I need to dial to 28.400.17. Any ideas on this or how to

There is nothing, other than corrupt firmware/faulty EEPROM, that could
cause this result on a recent K2.  Even then, it would be difficult to
imagine firmware errors that would result in a selective failure on 10m,
as there is no reason why it would need to do a table lookup, based on
band, when setting the synthesizer ratio.

Older K2's needed calibration of the reference oscillator tweaking (CALL
PLL) on different bands, but modern ones just proportion the corrections
from those on 40m.  I suppose it might still construct seperate tables
for each VFO range, and one of those may have been corrupted.

The only user tweakable factor that might cause an apparent band
sensitive error would be a wrong calibration of a filter.  However, that
would affect all bands, although the fault would switch between LSB and
USB when you pass the point where the IF inverts, but there is only one
place where that happens.

> correct it?  All other band are right on the money. I have installed the
> SSB, NB, and KPA100 if that helps at all.
>

--
David Woolley
"The Elecraft list is a forum for the discussion of topics related to
Elecraft products and more general topics related ham radio"
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[Julian, G4ILO]

David Woolley (E.L) wrote

Older K2's needed calibration of the reference oscillator tweaking (CALL
PLL) on different bands, but modern ones just proportion the corrections
from those on 40m.  I suppose it might still construct seperate tables
for each VFO range, and one of those may have been corrupted.

I think you have hit the nail on the head there, David. The K2 does not generate its VFO steps with synthesizer accuracy. It guesstimates the voltages needed to tune the PLL to specific frequencies in between the coarse synthesizer steps.

If the VCO voltage is not within the range it should be then the voltage/frequency curve will be very non-linear and this could account for the error Aaron is seeing. I would check this first, and remedy it if necessary - I can't recall how, exactly, but it's probably a matter of adjusting the turns on the appropriate inductor - and then re-do the calibration procedure.