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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com