filter alignment question

[dennis rosenbalm]

I recently acquired K2 #1084 from a friend. I upgraded the radio to Rev. B, added the DSP module and am about half way through the KPA100. As I was aligning the filters I noticed something unexpected. Everything seems to be fine except that as I scroll through the CW XFIL filters, the tone of the test signal changes slightly. Is this to be expected? Is it possible to get the tone exactly the same for every filter setting or is a slight variation normal?
The DSP was in bypass while alignment on the XFIL filters was done.

The K2 is a wonderful little radio. It sits on top of an OMNI 6+. Its a tough decision lately which one to use, hi hi.

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[Don Wilhelm-3]

If the tone pitch change is 20 Hz or less it is because of the quantizing
error in the K2 and nothing can be done about it.  The K2 firmware works to
preserve the pitch no matter where the filters are set as long as the signal
is anywhere within the filter passband.

73,
Don W3FPR

> -----Original Message-----
>
> I recently acquired K2 #1084 from a friend. I upgraded the radio
> to Rev. B, added the DSP module and am about half way through the
> KPA100. As I was aligning the filters I noticed something
> unexpected. Everything seems to be fine except that as I scroll
> through the CW XFIL filters, the tone of the test signal changes
> slightly. Is this to be expected? Is it possible to get the tone
> exactly the same for every filter setting or is a slight
> variation normal?
> The DSP was in bypass while alignment on the XFIL filters was done.
>
> The K2 is a wonderful little radio. It sits on top of an OMNI 6+.
> Its a tough decision lately which one to use, hi hi.
>
>

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[Ron D'Eau Claire-2]

KT5D asked:
Everything seems to be fine except that as I scroll through the CW XFIL
filters, the tone of the test signal changes slightly. Is this to be
expected? Is it possible to get the tone exactly the same for every filter
setting or is a slight variation normal?

----------------

Yes, it is normal to have a slight variation although sometimes you "get
lucky" and it will be zero. What's happening is that when you select a
filter (FL1thru 4) digital data is being recalled from memory that is
converted into an analog voltage that tunes the BFO and VFO to the right
frequencies. The accuracy with which the analog voltage is generated is
limited by the Digital-to-Analog Converters (DACs). The DACs in the K2
provide a resolution of about 30 Hz. That is, the frequency can be as much
as 30 Hz different from the value that was originally set when the filters
were aligned. What you need to do to get it closer, if you can, is to repeat
the filter alignment procedure in the manual. Actually, you don't need to
repeat the whole setup, but simply cause the system to re-store new digital
data for the current settings. Information on now to do this is included in
the Builders Resources on the Elecraft web site.

You may get a closer "match" or, if you are already within 30 Hz, it might
not be quite as good!

Ron AC7AC


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[Vic K2VCO]

W3FPR - Don Wilhelm wrote:
> If the tone pitch change is 20 Hz or less it is because of the quantizing
> error in the K2 and nothing can be done about it.  The K2 firmware works to
> preserve the pitch no matter where the filters are set as long as the signal
> is anywhere within the filter passband.

Well, something CAN be done about it, if you don't mind changing the filter
bandwidth slightly.  For example, suppose that you have set a filter to 400 Hz
bandwidth and located the BFO so that the signal is centered in the filter, and
suppose that the result is that the pitch of the centered signal comes out 10
Hz. high.  Just change the bandwidth to 420 (or 380) Hz., readjust the BFO and
let the K2's magic algorithm do its work.  Chances are it will come out on
pitch.  I have been able to adjust all of my filters so that there is no change
in pitch when I cycle through them.

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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