K2 filter alignment question

[lstavenhagen]

Hi all,
Not meaning to add to the wealth of info already on this topic, but I have a specific question about the "setting up your CW filters for the tonally challenged" article on the elecraft website.

Specifically, part of the instructions in it to read the BFO frequencies after audibly finding the passband centers for each filter width. It instructs you to switch to Rev to get it to display the BFO freq. rather than the BFx number. My question is, why not just hit Display which shows the freq. already? I see the article was written in 1999, was there not the Display capability in the older K2's?

Reason I ask is I decided to revisit my filter alignment (partly for an educational exercise to learn how this all works) and after fighting with a spectrum analyzer (iSpectrum on the mac, which just got me way off each time) I abandoned ship and tried this method. I was all set to put Spectrogram on my work machine and use that instead to try again but this seems to work far better.

By doing it with the displayed frequencies, I got the filters utterly nailed in both normal and reverse simple as pie (after once doing the math wrong and aligning each one on the wrong side hi hi, like I said a great learning experience). If I want to change the pitch of the sig, I just push a pencil on the numbers and viola I have all the settings....

Just wondering if this is too easy and I'm doing something wrong hi hi?

73,
LS
W5QD

[Don Wilhelm-4]

LS,

That method works, but it suffers from the fact that finding the actual
filter center frequency is difficult to do.  As the filter width is
changed, the lower and upper skirts do not change at the same rate  -
that is the main problem.  Yes, you are correct that in 1999 tapping the
DISPLAY button did not display the BFO frequency.

There were many attempts back in 1999 to figure out a god way to align
the K2 filters with better precision.  Then one day, someone mentioned
Spectrogram - the visual displays provided by Spectrogram gave better
results with less difficulty than any other method that had been tried
before.  After several passes using Spectrogram in different ways over
the next year or so, the current methods for using Spectrogram were
evolved.  The latest information is on the Elecraft website documents
(mostly by Tom Hammond N0SS), and Tom has a lot more information on his
website www.n0ss.net.  The K2 Dial Calibration article on my website
attempts to pull this information together along with the procedure for
setting the K2 Dial Calibration - take a look at www.w3fpr.com for details.

73,
Don W3FPR

lstavenhagen wrote:

> Hi all,
> Not meaning to add to the wealth of info already on this topic, but I have a
> specific question about the "setting up your CW filters for the tonally
> challenged" article on the elecraft website.
>
> Specifically, part of the instructions in it to read the BFO frequencies
> after audibly finding the passband centers for each filter width. It
> instructs you to switch to Rev to get it to display the BFO freq. rather
> than the BFx number. My question is, why not just hit Display which shows
> the freq. already? I see the article was written in 1999, was there not the
> Display capability in the older K2's?
>
> Reason I ask is I decided to revisit my filter alignment (partly for an
> educational exercise to learn how this all works) and after fighting with a
> spectrum analyzer (iSpectrum on the mac, which just got me way off each
> time) I abandoned ship and tried this method. I was all set to put
> Spectrogram on my work machine and use that instead to try again but this
> seems to work far better.
>
> By doing it with the displayed frequencies, I got the filters utterly nailed
> in both normal and reverse simple as pie (after once doing the math wrong
> and aligning each one on the wrong side hi hi, like I said a great learning
> experience). If I want to change the pitch of the sig, I just push a pencil
> on the numbers and viola I have all the settings....
>
> Just wondering if this is too easy and I'm doing something wrong hi hi?
>
> 73,
> LS
> W5QD
>  
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>  

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[lstavenhagen]

Hi Don,

Yeah, I've actually discovered that this is not very effective for the wider filter bandwidths such as in SSB. I got them spot on in CW with the narrower widths I use (1.40, .700, .400, .200) but in SSB I can't find the midpoint very well at all.

I've decided, tho, to leave my K2 as-is as CW-only anyway (that's its true brilliance) and just get a K3 for everything else. Another trial run with unhooking the K2 to put it in the portable bag and then back out onto the op table has convinced me I want a second dedicated base station anyway hi hi.

73,
LS
W5QD (probably ordering the K3 this weekend)

[Bill Coleman-2]

On Mar 18, 2010, at 9:44 AM, lstavenhagen wrote:

> Reason I ask is I decided to revisit my filter alignment (partly for an
> educational exercise to learn how this all works) and after fighting with a
> spectrum analyzer (iSpectrum on the mac, which just got me way off each
> time) I abandoned ship and tried this method. I was all set to put
> Spectrogram on my work machine and use that instead to try again but this
> seems to work far better.

iSpectrum should work just as well as Spectrogram. Using the CocoaModem Config window works well, too. There is quite a bit of eye-balling to the filter setting. Of course, if you don't pay attention, you may find yourself on the wrong side of the passband.

The final step that I put into my filter calibration is to use my ears and cycle between opposite sidebands (using CW REV) and make sure the settings sound reasonable with each other, and they look good on the spectrum display. If one of them sounds off, I'll jog the BFO frequency one tick one way or the other and cycle through again. Doing it this way, I'm managed to get the filters within 20 Hz or so of each other.

I've got a blog entry that has a bit more information on how I set up my filters:
http://boringhamradiopart.blogspot.com/2010/02/configuring-elecraft-k2-crystal-filters.html

I don't use the variable bandwidth filter much more than 1 kHz wide, because it starts to get asymmetric and makes for pretty harsh listening. I use the OP1 filter on SSB and use the DSP for high-QRM situations like in contests. (Of course, I'm using KI6WX's "1.9" SSB filter, which is about 2 kHz wide, but has less ripple than the original KSB2 2.0 kHz filter)

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
           -- Wilbur Wright, 1901

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