[Elecraft] K2 Crystal Filter Alignment Questions

[Bill Coleman]

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