[Elecraft] N0SS CW Filter Alignment

[frastephen@comcast.net]

From: <RMariutto@aol.com>
> >
> > Subject: N0SS CW Filter Alignment Using Spectrogram
>
> I think my problem is that I am trying to do two things at the same time:
1)
> adjust the filters 2) set the K2 to the proper receive frequency.

Right, work on getting the K2 on frequency first, then adjust the filters.
I think you want to make sure you are adjusting C22 with the widest filter
you have...


>I noticed
> that my receive frequency was about 200 hz lower than indicated on the
> display.  In the manual there is a proceedure for adjusting a variable cap
> that corrects this, boy is that cap touchy.

Yes, it is!!!  I found that it was helpful to give it a few twists to loosen
it up a bit before I made the adjustment -- took a little of the
"stickiness" out of it, and also I understand that sometimes these trimmer
cap plates do not seat properly sometimes unless you turn them a bit before
you try to adjsut them.


>I noticed that the 500 & 600
> hz tone markers don't line up exactly with the respective marks on the
> Spectrogram when I shift from usb to lsb or (cw & cw reverse) .

Hmmm, I just tried it again on Spectrogram on 10 MHz and both sidebands come
out exactly the same....   Curious...

Don't forget that the 500 Hz and 600 Hz tones basically alternate .... when
you see the big spike at 1000 Hz and 2000 Hz it will shift to the other
standard frequency for that minute.


>In other
> words, if I put the tone on 500 hz on lower sideband then shift the K2 to
> upper sideband it is sort of close to 500 hz, if I try I can't get both on
> 500 hz . For instance on 10 mhz lower sidband displays 999982 & upper
> displays 999977.  On 15 mhz lower displays 1499973 & upper displays
1499967.
> Both about 50 hz off but different.  Does this make sense?

No....

>I feel that I
> should get the frequency to display correctly before I set the filters ,
is
> this right?

Yes!

Interesting how the LSB frequency is HIGHER than the USB frequency....

Here are a few ideas.

Did you do the rough alignment of the filters per p. 86?
I would make sure that is roughly OK before you proceed with the fine
adjustments.

It sounds like the filters maybe are set to the wrong side of the passband.
Perhaps if you had these backwards that would account for the problem you
are experiencing.  Remember when you followed Tom's instructions you found
the center of the passband and marked down the DAC count for that place
(probably around 170 or so)?  The CW filter should be set to a DAC count
LOWER than the center and the CW REV should be set to a DAC count HIGHER
than the center.  Make sure the rough cut as described on p. 86 is in place
before you do these fine tuning adjustments.

I would stick with one sideband as you go through this procedure.  When you
get one sideband correct the other one naturally falls into place.  That
might be all you need to do.  Keep working with USB until you get it dead on
and then verify your effort with LSB.  Also, you will probably have to run
through this procedure several times, getting closer each time, until you
are right on!  It took me three iterations of the procedure to get within
the theoretical limit.

When you are following the instructions to adjust C22 to calibrate the VFO,
make sure you do the step where you move the counter probe back to TP2 then
start up CAL FIL, change the BFO control parameter for the current filter at
least one count, then move it back to the original setting (e.g.
126-->127-->126) then tap MENU to exit -- this forces the K2 to re-measure
the BFO frequency.

Also, don't forget that the specification VFO accuracy is +/- 30 Hz.   The
display shows down to 10 Hz.  I am finding that the K@ stays within +/- 10
Hz over time since I made the fine adjsutment.



Does that help????

Let us know how you do!

Peace & 73
Stephen
W3SMK
K2 #2644