[Elecraft] K3(s) main oscillator calibration

[Wes]

If you look at my earlier message in this thread, you'll see the link to nabble 
and my post from 11 years ago where I describe this method. :-)

Wes  N7WS

On 6/7/2020 6:03 AM, Randy Farmer wrote:
> The best way I've found to calibrate the K3 reference oscillator is to use the 
> 500 Hz and 600 Hz audio tones transmitted by WWV. I put the line out audio 
> through a sound card and look at it with SpectrumLab. Tune in WWV in USB or 
> LSB mode and tweak the reference trim until the tones are correct when you 
> switch sidebands with the dial at precisely XX.000 000 MHz. I've found that 
> you can't get precise agreement between sidebands, probably because of 
> quantization limits in the synthesizer, but it will certainly be less than a 
> couple of Hertz. This is plenty accurate for amateur (or probably any other 
> kind) of service.
>
> 73...
> Randy, W8FN
>
> On 6/6/2020 10:20 PM, Bob McGraw K4TAX wrote:
>> From my take, it is "ham radio" therefore +/-1 Hz. should be good enough for 
>> most operations.  After all, the K3S resolution is 1 Hz., +/-1 count as I see 
>> it.   I can keep mine +/-2 or 3 Hz on most bands.
>>
>> I use WWV with the radio in CW mode and CWT on, tune close to WWV and press 
>> SPOT.    If it settles on the WWV frequency that's good.  If it is off a few 
>> Hz, then I tweak the REF CAL up or down a few Hz until I get the accuracy I 
>> wish by repeating the process several times.  Still I find +/- 1 Hz is about 
>> it, even with the high stability TXCO and very adequate warm-up time of about 
>> 2 hrs.
>>
>> If one needs something more accurate, then Don is correct, test equipment is 
>> the way to go.  And expect to spend big bucks for good quality equipment that 
>> IS traceable to NIST.   If the NIST document or calibration is more than 1 
>> year old, the results will be questionable.
>>
>> I wrote an article which was published in QST, Sept 2015.   It deals with 
>> "Transmit and Receive On Frequency".  It shows that digital readouts are just 
>> that, readouts,  and they are not frequency determining or measuring 
>> circuits.    And when it is accurate on one band it may not have the same 
>> accuracy on another band.
>>
>> 73
>>
>> Bob, K4TAX
>>
>>
>> On 6/6/2020 5:20 PM, Don Wilhelm wrote:
>>> With the main K3 fine tuning at 1 Hz steps, I don't know that 0.1Hz or even 
>>> 0.25Hz doppler shift will matter much in the final result.
>>>
>>> My frequency counter is good to 10 exp-9 which equates to +/-0.1 Hz at the 
>>> TCXO frequency, so the WWV method provides as good or better accuracy, even 
>>> considering the doppler shift possibility.
>>>
>>> The main problem is chasing the beat note down to a stable solid note. You 
>>> usually can't truly get there, but you can get close enough that you hear 
>>> about 10 or 20 seconds between peaks. Close enough for me.
>>>
>>> It can be quite expensive to obtain stability better than the K3S in an 
>>> analog oscillator.  My HP8640B signal generator will do that, but it takes 
>>> at least a 3 hour warmup before it becomes stable.  Yes, all the internal 
>>> enclosures in my '8640 have covers with all the screws installed - that 
>>> helps.  OK, that is 'old iron', but I am not going to spend several $10,000 
>>> for something better.  I have better things to do with my money, and no 
>>> longer have access to modern lab quality equipment to achieve that kind of 
>>> stability.
>>>
>>> We have a ham band transceiver - not a precision lab instrument. As long as 
>>> we can stay inside our ham bands, that is all that matters to me.  I would 
>>> not put a carrier exactly on 7,000.00 kHz with any transceiver.
>>>
>>> 73,
>>> Don W3FPR
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