K2 PLL click educational opportunity

[lstavenhagen]

Hi all,
Sorry if these are dumb circuit-detail questions, but my K2s (the one in use as well as the one on the bench being built) are sort of my self-education laboratories. Yesterday while out /p in the mountains, I discovered the 5khz PLL "click" in my #1 K2, which led to researching it in the reflector archives, which led to learning how PLL synthesizers work which led to the K2 schematic......

Which led to...whew...lol... my current question about the 4.000mhz reference oscillator on the control board. My question is, it looks like the 4.000mhz osc. is the clock osc. for the main K2 CPU (U6), is that right?

And, I would assume that adjusting it to exactly 4.000mhz is what yields the correct dial reading because that adjusts the main CPU's clock frequency?

Just curious and apologies if my questions are a little dense...

Tnx es 73,
LS
W5QD

[Don Wilhelm-4]

LS,

The "PLL click" is usually caused by running CAL PLL with the bottom
cover off.  Install the bottom cover and do it again.

The setting of C22 at exactly 4.000MHz will not usually result in the
best dial calibration.  That 4 MHz oscillator is not used dynamically -
it is only used during the run of CAL PLL and CAL FIL.

The best dial calibration will be obtained by following the instructions
on my website www.w3fpr.com K2 Dial Calibration article.

In short, the procedure is to tune *exactly* to WWV (15 MHz is
preferred) - or other AM station with a known frequency in SSB mode and
using CAL FCTR measure the difference between the VFO (TP1) frequency
and the BFO (TP3) frequency and setting C22 to produce exactly the
difference equal to the station's frequency (15000.00kHz in the case of
15 MHz WWV).
Then run CAL PLL followed by CAL FIL.
Check the results by tuning to WWV again and make slight corrections if
necessary (do it again).

73,
Don W3FPR

On 4/3/2016 10:56 AM, lstavenhagen wrote:

> Hi all,
> Sorry if these are dumb circuit-detail questions, but my K2s (the one in use
> as well as the one on the bench being built) are sort of my self-education
> laboratories. Yesterday while out /p in the mountains, I discovered the 5khz
> PLL "click" in my #1 K2, which led to researching it in the reflector
> archives, which led to learning how PLL synthesizers work which led to the
> K2 schematic......
>
> Which led to...whew...lol... my current question about the 4.000mhz
> reference oscillator on the control board. My question is, it looks like the
> 4.000mhz osc. is the clock osc. for the main K2 CPU (U6), is that right?
>
> And, I would assume that adjusting it to exactly 4.000mhz is what yields the
> correct dial reading because that adjusts the main CPU's clock frequency?
>
> Just curious and apologies if my questions are a little dense...
>
> Tnx es 73,
> LS
> W5QD
>
>
>
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[lstavenhagen]

Hi Don,
Ah, ok, thanks for the info. Interesting on the 4.000mhz osc, just curious what it's actual function was in the circuit.

Oh and as for calibrating the osc, I tried the N6KR procedure, but it turned out that after several different iterations though the different methods, I ended up with the best result from the 2nd option listed on P63 of the manual. I used my K3, which has the 1ppm TCXO in it and is zero beated to WWV to the gnat's rear end lol.

As for the clicks, when I last reran CAL PLL, I hadn't let the K2 warm up for long enough. So I'm going to rerun it again here in a bit (fully assembled) to see what result I get...

Not a problem, just a great learning opportunity - Having a great time with these lol!

Thanks kind sir,
LS
W5QD

[lstavenhagen]

PS: re-tweaked the 4mhz osc with my K3 and reran CAL PLL and CAL FIL - I'm about where I was, within 20 or 30 hz of WWV on 10mhz, well down in the noise of overall drift and well good enough for me. I'll see if the ticks are mitigated out in the mountains where the bands are super quiet later today...

73,
LS
W5QD

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