[Elecraft] Any help with concepts about BFO and TX offset alignment?
Dr John H Farmer
wabi.sabi at bigpond.com
Tue Jan 26 21:45:48 EST 2010
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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