http://elecraft.85.s1.nabble.com/BFO-resets-itself-after-cal-fil-K2-tp7511681p7512596.html
I just looked att the schematics and noticed the BFO and the mixer. Out of
> Erik,
>
> The K2 will preserve the pitch when the BFO is changed. Of course, if
> you move the BFO enough, the signal will no longer be inside the passband.
>
> You must move the VFO to change the pitch, just changing the BFO will
> not do it. The filter passband edges will change, but the pitch of a
> tuned signal will not. That is why it is important to use a broadband
> noise generator (often band noise will do) and some type of audio
> spectrum analyzer (I use Spectrogram) to view the shape of the passband
> - you can see when it is centered at your target pitch. Use no signals
> in the passband when changing the filters, having signals present will
> only confuse your view of the passband shape and positioning.
>
> If you need Spectrogram, you can find it on my website www.w3fpr.com -
> look near the bottom of the opening page.
>
> 73,
> Don W3FPR
>
>
> On 4/29/2012 4:40 PM, Erik Linder wrote:
> > Don, tnx for the answer.
> >
> > Yes, the difference was small. Tnx for the info about 20 Hz, then I now
> the
> > limitation of the construction.
> >
> > Yes I can use the FL1 (open) as both TX and RX (well of course TX is
> alway
> > using FL1). But if I want something more narrow I like to use FL2 - FL4.
> > And now I know that I can get in 20 or so Hz if I work hard enough. :-)
> >
> > But the main problem here is that I cannot adjust my filters at all right
> > now. :-(
> > I can move the BFO (change the pitch) as long as I am in cal fil but as
> > soon as I save the filter and return to listen the pitch has changed to
> > "default". The BFO-value _has_ changed, it _has_ been saved. (I see the
> > display showing BFO freq for a short time).
> > But still - the pitch is where it was before I changed the BFO-value.
> >
> > And I have changed it much - like 50 to 100 units. USB, LSB, CW - the
> mode
> > does no difference.
> >
> > So:
> > Received pitch of the signal transmitted from my 2:nd TRX: 1500 Hz
> > The BFO value is (lets say) 128
> > I change the BFO value too 100
> > I hear (and see on the waterfall) that the pitch is changing.
> > I press XFIL (to save)
> > Display shows BFO freq for a short time.
> > I press XFIL a couple of times to "get round" to FL1 again.
> > The pitch has now jumped back to 1500
> > The BFO-value is at it's saved 100
> >
> > I can now lower the BFO value once more and when I come around the pitch
> > will be 1500 and the BFO is saved with the new value.
> >
> > Isn't it suppose to work like:
> > Change the BFO to get the correct pitch
> > Save
> > Return to the filter and the pitch is where you programmed it to be.
> >
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