K2: Spectrogram and BFO/filter calibration

[VK7JB]

Hi Group,

K2 #6998 is alive and listening on 40m.

I'm no expert in all this, so I have a basic question about using Spectrogram
for BFO alignment.

I've been using Spectrogram to align BFOs/filters for CW and SSB, having read
some tutorials about how to do this.  On CW, I'm adjusting the BFO settings so
that my sidetone frequency lies in the centre of the bandpass of each filter.  
For SSB, I'm adjusting the BFO settings so that the bandpass of the filter
lies centred between the upper and lower frequency cut-off marker lines for
the filter:  for example- for a 2.4khz filter width, centering the bandpass
between 300 and 2700hz.  I hope that understanding is correct.

Now, my question is this:  how is the "bandpass" defined, visually, using the
Spectrogram trace on my screen?  Is it enough to get the trace symmetrically
oriented around the sidetone frequency (CW) or between the upper and lower
frequency markers (SSB). Or are there other points of significance on the
visual trace that I need to use to ensure correct placement of the BFO offsets.
Also, what degree of precision is required?  Do I need to get obsessional
about this and measure the width of the bandpass , however defined, precisely
and then adjust the filter response around the markers using actual
measurements.  Or is "eyeballing" all that's required here?? I'm not sure how
type A I need to be.

Thanks for your advice.  I also have a question about the AGC, but I'll leave
that for another time...

73,
John
VK7JB




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[Don Wilhelm-4]

  John,

For the OP1 filter, drop the high frequency marker to 2600 Hz and center
between the 2 markers.
Remember that what is important is for the low frequency "corner" (-3 dB
point) of the passband be placed quite near 300 Hz.  That is also
important for the more narrow SSB filters as well.

For CW, you are doing it correctly - EXCEPT - if you try to center a
wide filter (say the FL1 filter is either the default 1.50 or 1.20
width), centering it will cause a response on the opposite sideband.  
Move that filter higher so you can see a drop down to the noise level on
the low frequency slope - that will likely place the low frequency
"corner" at about 200 Hz.

Refer to the K2 Dial Calibration article on my website www.w3fpr.com for
more information.

73,
Don W3FPR

On 10/10/2010 11:01 PM, [hidden email] wrote:

> Hi Group,
>
> K2 #6998 is alive and listening on 40m.
>
> I'm no expert in all this, so I have a basic question about using Spectrogram
> for BFO alignment.
>
> I've been using Spectrogram to align BFOs/filters for CW and SSB, having read
> some tutorials about how to do this.  On CW, I'm adjusting the BFO settings so
> that my sidetone frequency lies in the centre of the bandpass of each filter.
> For SSB, I'm adjusting the BFO settings so that the bandpass of the filter
> lies centred between the upper and lower frequency cut-off marker lines for
> the filter:  for example- for a 2.4khz filter width, centering the bandpass
> between 300 and 2700hz.  I hope that understanding is correct.
>

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