Posted by
Don Wilhelm-4 on
Apr 29, 2012; 9:01pm
URL: http://elecraft.85.s1.nabble.com/BFO-resets-itself-after-cal-fil-K2-tp7511681p7511796.html
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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