[600MRG] K3s LF Frequency Variations

[Edward R Cole]

One typo:

0.1ppm is 1.0 E-7 and not 10 E-7.

At 02:04 PM 12/7/2015, Edward R Cole wrote:
>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
>http://www.kl7uw.com
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>
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73, Ed - KL7UW
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