http://elecraft.85.s1.nabble.com/BFO-resets-itself-after-cal-fil-K2-tp7511681p7513799.html
it. :$ :-)
> Erik,
>
> Yes, that is why you cannot use a single signal (tone) when aligning the
> filters.
> The use of a broadband noise source and an audio spectrum analyzer
> application running on the computer soundcard will make K2 filter setup
> easy and uncomplicated.
>
> 73,
> Don W3FPR
>
> On 4/30/2012 2:49 AM, Erik Linder wrote:
>
>> 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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