BFO Cal for low pitch CW and narrow filters

[ni0c]

I am pleased to report that K2 s/n 5853 is in the transmitter alignment phase, and all is going well.  Work was interrupted for a few days because we lost power in Thursday's ice storm here in STL.  The house was down to 50 deg. F, when power was finally restored.  

Christine at Elecraft does a superb job at stuffing those parts bags.  At one point, I relied on her work to provide me with a parity check of sorts on my capacitor installation.  I got suspicious when I had a "561" cap left over but was missing a "560" cap.  I reviewed all the other spots that were supposed to receive  a"560," and sure enough I found I had made an error.  I was able to remove the misplaced cap and save it too.  

The receiver sounds great, and compares favorably with my Ten Tec Omni 6 loaded with INRAD filters.

When doing the BFO calibration, I followed the recommended settings, which I understand are based on a 600 Hz pitch.  I like to use narrow filters at a 400 Hz pitch.  I'd like to set up for the following filter sequence: 600, 400, 300, 150 Hz bandwidths.  

Is there a formula I can use to calculate the BFO frequencies I need for CW normal and reverse to get the pitch and bandwidths I want?  Have others produced their own charts or lists of customized BFO settings ?  I apologize if I've missed something in the manual or in the list archives.

73,
Chuck  NI0C


   
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[Don Wilhelm-3]

Chuck,

The full 'equation' also depends on your exact filter center IF frequency.
It is better to use Spectrogram which provides a visual display of the
filter passband placement, and you can set things optimally for any pitch
that you desire.  There are instructions within the K2 Dial Calibration
article on my website http://w3fpr.qrpradio.com and also info at the
Elecraft website.  You can download the last freeware version of Spectrogram
from Tom Hammond's website www.n0ss.com - that version has more than
adequate capability for setting the K2 filters and BFO frequencies.

If you want to try a 'formula', I would suggest 2 steps - to change the BFO
frequencies by 200 Hz, for each CW/CWr pair of frequencies, increase the
lower frequency by 0.2 kHz and decrease the higher frequency by 0.2 kHz -
then as a second step - If your crystal set was marked 3.6 (the most
common), do nothing, but if it was higher (3.7 or 3.8), reduce all the
frequencies above by 0.1 or 0.2 kHz and if your crystal set was 3.4 or 3.5,
increase all the frequencies above by 0.1 or 0.2 kHz.

Even so, you may be off by up to 100 Hz since the real center frequency will
vary from crystal set to crystal set - Elecraft matches the crystals to 10
Hz, and the markings on the crystal bags are only to the nearest 100 Hz.
Note that you can achieve better filter passband placement with Spectrogram
than with just using the frequency settings listed in the manual for this
reason alone.

By far, the easiest and most accurate is to use Spectrogram after you
complete the K2.  At the point where you can receive 10 MHz WWV, you can
accurately set the 4 MHz reference oscillator and all the filters so you
achieve not only proper filter settings but good dial calibration as well.
My website article tells you how to achieve all that with no equipment other
than a computer with a soundcard, a stereo cable to connect the K2 to the
soundcard and the K2 internal frequency probe.

Once you have the filter settings correct for your purposes, write down the
settings in case they are ever wiped out (by a Master Reset for instance) -
you can restore the correct settings quickly.

73,
Don W3FPR

> -----Original Message-----
>
> The receiver sounds great, and compares favorably with my Ten Tec
> Omni 6 loaded with INRAD filters.
>
> When doing the BFO calibration, I followed the recommended
> settings, which I understand are based on a 600 Hz pitch.  I like
> to use narrow filters at a 400 Hz pitch.  I'd like to set up for
> the following filter sequence: 600, 400, 300, 150 Hz bandwidths.
>
> Is there a formula I can use to calculate the BFO frequencies I
> need for CW normal and reverse to get the pitch and bandwidths I
> want?  Have others produced their own charts or lists of
> customized BFO settings ?  I apologize if I've missed something
> in the manual or in the list archives.
>
> 73,
> Chuck  NI0C
>

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[Sam Morgan-2]

Don Wilhelm wrote:
> You can download the last freeware version of Spectrogram
> from Tom Hammond's website *www.n0ss.com*
corrected link
http://www.n0ss.net
--
GB & 73's
KA5OAI
Sam Morgan

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