[K2] Overall adjustment - and a little bit more ..

[Leif Hoffmann]

From: SM4MNC, Leif Hoffmann

 

I have just finished building K2 #7836. A very great pleasure and about a
ton of fun too, and I sincerely hope that this "100% solder kit" will remain
in the future!

My kit was from the summer sale and contained the K2, the SSB- module, noise
blanker and antenna tuner.

Everything went almost flawless: Under Alignment and test, Part 2 there was
absolutely nothing to be heard in the headphones! What now? The problem
solved itself when I found the bag with the surface mount IF-amplifier U12.
The step to mount it was described in the errata and I had just missed that
small detail! When installed, there were no more problems here.

 

I did the initial adjustments, the transmitter and receiver were functioning
- perhaps the filters did not match perfectly, but that was a
"software-problem" to be solved later!

The SSB-unit, noise-blanker, and finally the antenna-tuner were built and
put in the radio, and everything seemed to work as it should. What an
amazing little radio this is!!

 

Two more things:

1.     In my K2 there is absolutely no space between the encoder and the
front panel. Not even the best flush-cutter in the world will give enough
space there. I have read in the Elecraft Archives of paper-bits etc. I have
put on double layers of adhesive tape (tape for electrical purposes) with
the advantage that it doesn't get dislodged when you remove the control
board next time.

2.     During the assembly there were some very small (in value) capacitors,
that in my kit not were similar to the pictures in the parts list, but
thanks to Stephanie, Leony, Johanna and all the other packers of the
subassemblies, I could simply rely on the number of the remaining parts (no
more - no less) and after a little examination of the parts, the problem got
a solution and as the radio is functioning, it seems that I have got all
parts in the right places!

 

Overall I can say that building the hardware actually were "the easy part"
and I have learned a lot in the process. Thanks, Elecraft!

 

BUT: I have read, and re-read many times both in the main manual and the
manual that comes with the KSB2 concerning the adjustments. The envelope
with the filter crystals for the KSB2 were marked E850006 and 3228-1,
180611. I could not recognize any of these as a calibration number between
3.2 and 3.9, so I used 3.6 as described, and when I came to the filter setup
I did exactly as shown in table 3 - with catastrophic result !! The FL1 -
under OP1 and LSB- were so high-pitch that it was practically useless, and
this is the filter-setting that I probably will use the most! With an
antenna and the loudspeaker mounted I adjusted the freq. to more like 4914.1
- 4914.2 than the 4913.5 that comes from the table. The ideal would of
course be to sweep the filters with appropriate equipment - which I have
none!

So that now I have all the filters (both for SSB and CW) adjusted "by ear".
I do have a radio that I can use, even if it's not optimal. It's pleasant to
listen to and a couple of good reports "on air" too. I just wonder: How many
of the previous kit-builders have experienced the same problems - and done
what I have done?

 

Finally: How accurate are the settings over time? The 4 MHz oscillator on
the control board is of course the most critical part here. But - yesterday
evening I had the radio adjusted to within +/- 10 Hz compared to my big
transceiver. When I turned on the K2 today it was about 320 Hz high. I have
- again - re-run the frequency calibration procedure, the CAL PLL and now
again the display shows inside of +/- 20 Hz. Can this be a temperature
problem? It was rather warm in my shack yesterday and pretty cold today when
I came in.

The small capacitor C22 is of course critical here! And a small suggestion:
The adjustment would be much more calm if there were two trim-capacitors.
One 8-50 pF(as C22 is), and in parallel with that another adjustable
capacitor on 1-2 pF for the fine-adjustment.

 

Naturally, I don't expect this little radio to have the same stability as my
big radio, with its X-tal oven and that can zero-in on WWV to within +/- 1
Hz, but on the other hand, I don't know what to expect from the K2. Will it
be within +/- 10 Hz, +/- 100 Hz or perhaps +/- 500 Hz? How will it perform
under field conditions? Actually, it is not that very important, as long as
my #7836 performs "as expected". Can you say anything about what stability I
can expect from a K2?

 

Yours,

 

SM4MNC, Leif

 

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[Don Wilhelm]

Leif,

The temperature stability of your K2 (after a 5 minute warmup period)
should be within 20 Hz if the dial calibration and Filter BFO settings
are correct.

You can easily optimize your filters and calibrate the dial readings on
your K2.
The 4 MHz Reference Oscillator only needs to be correct just before
running the CAL PLL and CAL FIL routines.  At other times, it is not
used dynamically and only serves as a clock for the MCU.
The DAC values for the PLL and BFO are stored in EEPROM and are used in
normal operation for displaying the K2 dial frequency, the 4 MHz
Reference Oscillator is not used, and it can drift substantially and not
cause any variation in the K2 frequency.

The BFO stabilty should be good unless you have mounted L33 in a manner
where the toroid can move with temperature, and the "Thermistor Board"
provides good temperature stability for the PLL Reference Oscillator.
If you experience extreme temperature swings when operating, you may be
able to modify the amount of compensation by changing the value of RA on
the thermistor board.  Download the PLL Upgrade instructions from
http://www.elecraft.com/manual/E740046%20PLL%20upgrd%20old%20K2s%20-%20Option%20Rev%20E.pdf 
for details on how to move the RA value.

Your K2 should be frequency stable within a few HZ, but give it 5
minutes for initial warmup.

There is information about setting the K2 dial calibration on my website
www.w3fpr.com.

For optimizing the filter response, the only equipment you need is an
audio spectrum analyzer running on your computer, and a broadband noise
source feeding the K2 antenna.  Band noise on a portion of the band
without signals can be used if you do not have a broadband noise
generator such as the Elecraft N-Gen.

Information about optimizing your K2 filters can be found both at my
website and at
http://www.mmccs.com/mmarc/n0ss/k2_filters_using_gram_v5r17.pdf

If you are running a Windows computer and need Spectrogram, it is
available on my website www.w3fpr.com.  Scroll down on the opening page,
the links are near the bottom.

73,
Don W3FPR

On 9/3/2018 6:28 PM, Leif Hoffmann wrote:

> From: SM4MNC, Leif Hoffmann
>
>  
>
> I have just finished building K2 #7836. A very great pleasure and about a
> ton of fun too, and I sincerely hope that this "100% solder kit" will remain
> in the future!
>
> My kit was from the summer sale and contained the K2, the SSB- module, noise
> blanker and antenna tuner.
>
> Everything went almost flawless: Under Alignment and test, Part 2 there was
> absolutely nothing to be heard in the headphones! What now? The problem
> solved itself when I found the bag with the surface mount IF-amplifier U12.
> The step to mount it was described in the errata and I had just missed that
> small detail! When installed, there were no more problems here.
>
>  
>
> I did the initial adjustments, the transmitter and receiver were functioning
> - perhaps the filters did not match perfectly, but that was a
> "software-problem" to be solved later!
>
> The SSB-unit, noise-blanker, and finally the antenna-tuner were built and
> put in the radio, and everything seemed to work as it should. What an
> amazing little radio this is!!
>
>  
>
> Two more things:
>
> 1.     In my K2 there is absolutely no space between the encoder and the
> front panel. Not even the best flush-cutter in the world will give enough
> space there. I have read in the Elecraft Archives of paper-bits etc. I have
> put on double layers of adhesive tape (tape for electrical purposes) with
> the advantage that it doesn't get dislodged when you remove the control
> board next time.
>
> 2.     During the assembly there were some very small (in value) capacitors,
> that in my kit not were similar to the pictures in the parts list, but
> thanks to Stephanie, Leony, Johanna and all the other packers of the
> subassemblies, I could simply rely on the number of the remaining parts (no
> more - no less) and after a little examination of the parts, the problem got
> a solution and as the radio is functioning, it seems that I have got all
> parts in the right places!
>
>  
>
> Overall I can say that building the hardware actually were "the easy part"
> and I have learned a lot in the process. Thanks, Elecraft!
>
>  
>
> BUT: I have read, and re-read many times both in the main manual and the
> manual that comes with the KSB2 concerning the adjustments. The envelope
> with the filter crystals for the KSB2 were marked E850006 and 3228-1,
> 180611. I could not recognize any of these as a calibration number between
> 3.2 and 3.9, so I used 3.6 as described, and when I came to the filter setup
> I did exactly as shown in table 3 - with catastrophic result !! The FL1 -
> under OP1 and LSB- were so high-pitch that it was practically useless, and
> this is the filter-setting that I probably will use the most! With an
> antenna and the loudspeaker mounted I adjusted the freq. to more like 4914.1
> - 4914.2 than the 4913.5 that comes from the table. The ideal would of
> course be to sweep the filters with appropriate equipment - which I have
> none!
>
> So that now I have all the filters (both for SSB and CW) adjusted "by ear".
> I do have a radio that I can use, even if it's not optimal. It's pleasant to
> listen to and a couple of good reports "on air" too. I just wonder: How many
> of the previous kit-builders have experienced the same problems - and done
> what I have done?
>
>  
>
> Finally: How accurate are the settings over time? The 4 MHz oscillator on
> the control board is of course the most critical part here. But - yesterday
> evening I had the radio adjusted to within +/- 10 Hz compared to my big
> transceiver. When I turned on the K2 today it was about 320 Hz high. I have
> - again - re-run the frequency calibration procedure, the CAL PLL and now
> again the display shows inside of +/- 20 Hz. Can this be a temperature
> problem? It was rather warm in my shack yesterday and pretty cold today when
> I came in.
>
> The small capacitor C22 is of course critical here! And a small suggestion:
> The adjustment would be much more calm if there were two trim-capacitors.
> One 8-50 pF(as C22 is), and in parallel with that another adjustable
> capacitor on 1-2 pF for the fine-adjustment.
>
>  
>
> Naturally, I don't expect this little radio to have the same stability as my
> big radio, with its X-tal oven and that can zero-in on WWV to within +/- 1
> Hz, but on the other hand, I don't know what to expect from the K2. Will it
> be within +/- 10 Hz, +/- 100 Hz or perhaps +/- 500 Hz? How will it perform
> under field conditions? Actually, it is not that very important, as long as
> my #7836 performs "as expected". Can you say anything about what stability I
> can expect from a K2?

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]