Steve,
Yes, the "4 MHz" reference may have to be set a few Hz different than
exactly 4.00000 MHz to calibrate the dial accurately.
The best method I know of is to feed the K2 audio into a computer
running Spectrogram. This method compensates out any difference between
4 MHz and the actual required frequency for the reference - one does not
even need to be concerned about the reference frequency with this method.
On the Spectrogram line display, set markers (pointers) for 500 and 600 Hz.
Now tune WWV in LSB (or USB if you prefer) - 10, or 15 MHz, either is OK
- 20MHz requires a bit of a difference in the VFO/BFO calculation due
the the sum of the oscillators rather than the difference.
When you look at the Spectral line display of the WWV transmission, you
will see the carrier (only if you are mistuned), and a transmitted tone
(wait until the do transmit a tone). The tone is normally either 500 or
600 Hz, but there is a 440 Hz tone for one minute each hour and there
are some non-tone minutes. You can look up the transmission format on
the web and it will tell you which minute is which tone - or you can
just wait and watch the tones alternate. The short tone transmitted for
one second at the beginning of each hour is always1000 Hz, so I move the
cursor to 1000 Hz (read the frequency in the lower left box of the
screen) and click to place a crosshair at 1000 Hz too, it is a handy
reference if WWV is weak ir the other tones are not clear.
Now that you have the Spectrogram 'picture' of WWV and have identified
the relevant tones in the audio (the carrier, and one of the transmitted
tones), tune the VFO first listening until the voice sounds rather clear
- then you may see the carrier near zero Hz and the tone near the 500 or
600 Hz marker that you have set. Tune the VFO until the tone is lined
up exactly with the marker. Wait until the next tone minute to be
certain you are tuned correctly and not 100 Hz off.
Enter CAL FCTR, then check to see if the tones are still lined up - you
can fine tune a bit if necessary, but when you have the VFO set
correctly (for the tones, not the dial reading - the dial reading will
not be correct - that is why you are going to all this trouble). Do not
move the VFO after this, you will next be adjusting C22.
Now, you move the probe between TP1 and TP2 until the frequency
difference is exactly equal to the WWV transmitted frequency. Since WWV
transmitts on 0000.000 kHz boundaries, just look for the low order
digits to be the same at TP1 and TP2. If the digits are not the same,
adjust C22 a bit and see if the frequencies got closer. Once C22 is
adjusted correcctly, the low order digits of the BFO (TP2) and the VFO
(TP1) will match exactly, and you can declare that C22 is now set
exactly right - do not touch it again.
Now, switch to 40 meters and run CAL PLL followed by CAL FIL (change
each BFO setting even if it is correct - moving it up a bit and back
down to where it was constitutes a 'change' to the K2.
Once that has happened, you are done.
Tune WWV again as before and note the dial setting - you should find it
no more than 20 Hz off. The DAC limit of tuning varies with frequency,
but averages about 13 Hz, so 20 Hz is within the expected practical
tolerance limits.
It takes a LOT more time to write this than it does to do it - it is
easier to do than to say.
73,
Don W3FPR
Steve Kallal wrote:
Don,
Sorry I didn't fully read your comments before my first reply.
Could you briefly explain how you calibrate with the 500 & 600 Hz
markers? Can it be done in real time while tweaking C22? I can't do
it. I have C22 set exactly to 4 MHz via the 20 MHz WWV method, with a
perfect zero beat. Yet, I am about 40 Hz off on WWV 10 MHz. Apparently
there is more than setting the clock to exactly 4 MHz followed by CAL
PLL/CAL FIL.
If you have some canned document of the 500/600 Hz tones Spectogram
method , let me know.
73,
Steve N6VL
K2/100 #2289
Don Wilhelm wrote:
Steve,
Your steps are correct.
It sounds like you are off by the amount of your sidetone pitch.
Were you receiving WWV in LSB or USB mode? If you used CW mode, that
would explain the difference.
Are you quite certain that you tuned WWV accurately? Do not 'set
the dial at 10,000.00', but instead, ignore the dial and tune until
WWV is received correctly. I use Spectrogram for that with markers
(pointers) set at 500 and 600 Hz for that. When correctly tuned,
you will see the tones alternate each minute from 500 to 600 Hz (yes,
I know there are no-tone minutes, and one minute shortly after the
hour is 440 Hz, but mostly they alternated between 500 and 600 Hz.).
When done correctly (mostly tuning WWV accurately), you results will
be within 20 Hz of WWV. One cannot expect much better than that due
to the DAC resolution used in the K2. I do this most every day, and
it has become 'old hat' to me - use Spectrogram to verify the correct
tuning - ignore the K2 dial display until the last verification step.
73,
Don W3FPR
Steve Kallal wrote:
I was trying to calibrate my K2/100 and had it within 10 Hz
according to WWV 10 MHz. I should have left it alone. Now it is off
by about 700 to 800 Hz on 40 meters. Ouch!
Here are the steps I did so far:
1. I set the C22 trimmer on the Control Board by the N6KR method at
http://w3fpr.qrpradio.com/n6kr_method.htm. I set the dial at exactly
10.000.00 MHz, and alternated between TP1 & TP2 until the readings
CAL FCTR match with about 2 Hz.
2. I ran CAL PLL.
3. I ran CAL FIL on every mode / filter combination, being sure to
change the BFO hex value even if not needed.
I didn't build the K2 in the first place. So I never did the entire
procedure before.
Any help is welcome!
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