Any help with concepts about BFO and TX offset alignment?

[John H Farmer]

Hello all,

I'm progressing on my build of K1 #2822 and I've hit a conceptual block in my understanding of an aspect of the alignment process.  I apologise if this has been discussed  before on this list.  I've read through the archives and can't find a very clear explanation. I'm hoping someone can help out.

It relates to what I'm actually doing when adjusting the Tx offset with C13.

This is what I understand to be true:

I've chosen 600hz as my sidetone and the audio tone  I want to hear receiving CW.  I need to adjust the BFO frequency to be 600hz above the carrier frequency of the received signal, in order to hear that 600hz beat tone.  If the BFO offset is set 600hz above the received carrier, then when I hear the 600hz tone on receive,  I know that I'm "zero beat" with that station and that the frequency indicated on the K1 display will be that station's carrier frequency and also MY transmit frequency, key down.  I adjust this BFO offset as described in the manual,  using C20 and the K1's generated 600hz sidetone as the reference audio signal.  This sets the BFO frequency at 600hz above the carrier.  I've got a good musical ear, so doing that is not a challenge for me.

What I don't understand is what I'm actually doing in the next step -  adjusting Transmit offset, with C13?  I think I understand the concept of the BFO offset, but I don't  know why I also need to alter my transmitted carrier frequency.  I see that C13 is pulling up/down the crystal oscillator frequency @ the Tx mixer.  

In the end, when properly configured,  I want the frequency displayed on the K1 to indicate the carrier frequency of my transmitted signal.  I want to hear 600hz audio when I'm tuned to the carrier frequency of a station I'm receiving.

So, why is it necessary to adjust my Transmit/carrier frequency with C13?  

Sorry if this is a naive question, but I'm new to all this and have never had to think it through before.  

Many thanks to all,

John
VK7JB




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[Don Wilhelm-4]

John,

Spectrogram helps, so go to www.n0ss.net and read the details.
Do the following steps in order:
1) set the BFO frequency to position the center of the FL3 passband at
your chosen sidetone pitch (600 Hz in your case)/
2)Then with Spectrogran still active, set the switch on the bottom of
the K1 to the TEST position and adjust C13 to produce a peak response at
your chosen sidetone pitch (600 Hz).
That is all there is to  aligning the TX offet to your chosen sidetone
pitch.  Set the switch on the bottom of the K1 RF board to OPER and go
on with the other alignment procedures.

If you choose not to use Spectrogram, then follow the instructions in
the manual - both will produce the correct results - Spectrogram does
provide a visual display that many find easy to use.

After those alignments, you should do the CAL OPF on each band to make
the received frequency correct on the K1 display.  The order of these
adjustments is important, attempting to do the CAL OPF before aligning
the BFO passband and adjusting the TX offset will lead to frustration.

73,
Don W3FPR



Dr John H Farmer wrote:

> Hello all,
>
> I'm progressing on my build of K1 #2822 and I've hit a conceptual block in my understanding of an aspect of the alignment process.  I apologise if this has been discussed  before on this list.  I've read through the archives and can't find a very clear explanation. I'm hoping someone can help out.
>
> It relates to what I'm actually doing when adjusting the Tx offset with C13.
>
> This is what I understand to be true:
>
> I've chosen 600hz as my sidetone and the audio tone  I want to hear receiving CW.  I need to adjust the BFO frequency to be 600hz above the carrier frequency of the received signal, in order to hear that 600hz beat tone.  If the BFO offset is set 600hz above the received carrier, then when I hear the 600hz tone on receive,  I know that I'm "zero beat" with that station and that the frequency indicated on the K1 display will be that station's carrier frequency and also MY transmit frequency, key down.  I adjust this BFO offset as described in the manual,  using C20 and the K1's generated 600hz sidetone as the reference audio signal.  This sets the BFO frequency at 600hz above the carrier.  I've got a good musical ear, so doing that is not a challenge for me.
>
> What I don't understand is what I'm actually doing in the next step -  adjusting Transmit offset, with C13?  I think I understand the concept of the BFO offset, but I don't  know why I also need to alter my transmitted carrier frequency.  I see that C13 is pulling up/down the crystal oscillator frequency @ the Tx mixer.  
>
> In the end, when properly configured,  I want the frequency displayed on the K1 to indicate the carrier frequency of my transmitted signal.  I want to hear 600hz audio when I'm tuned to the carrier frequency of a station I'm receiving.
>
> So, why is it necessary to adjust my Transmit/carrier frequency with C13?  
>
> Sorry if this is a naive question, but I'm new to all this and have never had to think it through before.  
>
> Many thanks to all,
>
> John
> VK7JB
>  

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