[600MRG] K3s LF Frequency Variations

[Edward R Cole]

Paul,

I was a beta tester on the Elecraft K3 EXREF board.  As you state it 
uses an external high stability 10-MHz reference to keep the TCXO-3 
on frequency.  My understanding the ckt checked frequency against the 
Reference about every 4-seconds and if an offset was detected the 
EXREF ckt wrote a correction word to the TXCO controller which 
brought the TCXO back on frequencty.  Drift rate between comparisons 
to the reference is the standard drift of the TCXO which is actually 
about 0.5 ppm.  Adding the EXREF lowers the drift to 0.1ppm as the 
TCXO does not get to drift very long between  checks.  So there will 
be a small ramp function assuming drift is in one direction.

0.1ppm = 10 E-7 and F = 480 KHz = 4.8 E+5 Hz so the maximum value of 
drift should not be more than 4.8 E-2 in Hz, or 0.048 Hz.  If you are 
seeing drift higher than 1-Hz the system is not working right.

At 28-MHz I only see 2-Hz drift on my K3 using EXREF and OCXO 10-MHz 
reference (5 E-12).

Drift of the TCXO is a function of temperature change so if running 
at 1mw for 630m operating there is little to warm up in Tx.

73, Ed - KL7uW

At 09:11 AM 12/7/2015, Paul Signorelli wrote:
>i have been testing my K3s on 480 kHz.
>Lots of guys have seen a ripple or sawtooth wave on my signal on QRSS30.
>i see the frequency corrections as a saw tooth wave correcting every 
>1 to 8 minutes.
>If there is little temperature change there are fewer corrections.
>i am using the High Stability TCXO (+/- 1 ppm).
>i see the frequency variations on my ARGO also.
>i told the K3s design team about the output variations and they said:
>The behavior is normal.
>     The KSYN3A uses a frequency (not phase) locked loop to keep 
> the    output exceptionally clean in terms of phase noise.  The 
> loop will    occasionally perform a small, typically sub-Hz 
> frequency correction    of the synthesizer output based on 
> comparison to the internal (or    external) frequency reference to 
> maintain frequency accuracy.
>     This means that the same behavior will be there whether or not 
> a 10    Mhz external reference is used.
>Maybe i could put the TCXO in a small oven.
>Paul   wa2xrm
>
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73, Ed - KL7UW
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