[Elecraft] K2 Crystal Filter Alignment Questions

[Don Wilhelm]

Jeff,

Let me add my 2 cents worth:

First, if you have been attempting to align your filters by trial and error,
you may have the wrong sideband set.

Secondly, a shift of 20 Hz or so is to be expected because of the DAC
resolution - if your shift is any more than 20 Hz, it can be corrected by
proper filter adjustment.

Third, I don't understand why you are shying away from Spectrogram - it is
by far the easiest method of correctly setting the filter passbands.

Forth, If you have been arbitrarily moving the BDO settings 'by ear', it is
quite possible that you have the BFOs set to the wrong sideband.  A good
starting point is the settings in the manual (either the K2 manual or the
KSB2 manual.  Shift the sideband as required from these settings, but do not
go too far - going far from those values will result in the BFO being set to
the incorrect sideband.

I strongly suggest that you download Spectrogram and use that to set your
filters - see the note from Tom Hammond.  Tom's websote contains the last
freeware version of Spectrogram and instructions for setting it up and using
it to align the K2 filters - try it, I assure you that you will not be
disappointed in the results.

73,
Don W3FPR


> -----Original Message-----
>
> On Aug 19, 2006, at 1:52 AM, Jeff wrote:
>
> > Should the pitch of the background atmospheric noise change when CW
> > RV is
> > toggled on and off?
>
> If you get it adjusted right, the pitch shouldn't change (or should
> change very little), however the "color" of the noise might shift a
> bit, depending on the bandwidth, due to a bit of asymmetry in the
> bandpass of the filter.
>
> > Also, I have the KSB2 installed, and the pitch of the atmospheric
> > noise
> > changes greatly when I switch from USB to LSB or vice versa.
>
> You don't have it adjusted right. The pitch should change very
> little, the color will change a bit because of the asymmetry of the
> filter, but if you get it adjusted correctly you'd hardly notice the
> shift.
>
> > Finally, and most irritatingly of all, in CW mode, when I switch
> > from filter
> > FL1 to FL2, the pitch of the received CW signal changes significantly.
> > However, when I switch from FL2 to FL3, or from FL3 to FL4, no such
> > pitch
> > change occurs, which is good.
>
> The K2 design isn't perfect in this regard, because of the way the
> BFO frequencies are determined - but you should be able to get any
> shift down to a few Hz, if that.
>
> It sounds to me like you don't quite have the filters aligned correctly.
>
> > I assume that I inadvertently changed the FL1 BFO setting.  However, I
> > subsequently tried various settings and couldn't get the pitch of the
> > received CW note for FL1 to match that of FL2.
>
> Again, because of the quantization of the BFO frequency, you may not
> be able to get all the filters perfectly aligned on the same
> frequency. Close is good.
>
> > Shouldn't I be able to correct this problem by trial-and-error,
> > without
> > using Spectrogram?
>
> Yes, I've done this. Try moving a filter one step up or down from
> where Spectrogram thinks it should be. See if it makes things better
> or worse.
>
> > Unfortunately, I'm not set up to use Spectrogram to align the filters.
>
> If you can't use Spectrogram, perhaps you can use another piece of
> software that supports and audio spectrum display. This is really the
> best way to align the K2 filters. (I personally use CocoaModem (a
> MacOS X RTTY / PSK application) to align my K2)
>
> > p.s.  Here's a trivia question to which I'm curious to know the
> > answer:  Why
> > is it that the KAT2's relays chatter pleasantly when you turn the
> > K2 on, but
> > make not a peep when you turn it off?
>
> Latching relays. They remember their last state and stay there even
> if no power is supplied.
>
> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
> Quote: "Not within a thousand years will man ever fly!"
>              -- Wilbur Wright, 1901
>
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