http://elecraft.85.s1.nabble.com/BFO-resets-itself-after-cal-fil-K2-tp7511681p7513238.html
> Aha! Then I did not fully understand the inner workings of the K2.
> I just looked att the schematics and noticed the BFO and the mixer. Out of
> that I made the conclution that the BFO value must change the pitch.
>
> So what you are saying is:
> During filter setup, it is normal for the pitch to change but when I press
> XFIL the save-routine inside the K2 is compensating for the change and
> restores the pitch to its original position?
> Is that correct?
>
> Which in practice means that I cannot adjust the pitch manually (like on an
> old radio), it's up to the K2 routine to set the pitch.
>
> ./Erik
>
> 2012/4/29 Don Wilhelm<
[hidden email]>
>
>> 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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