[minima] Re: Progress report - Debugging and tuning the minima
- From: "Steve VK2SJA" <vk2sja@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Tue, 18 Feb 2014 18:39:24 +1100
Hi Thomas,
> First, a few questions:
> - How do you tune the emitter voltage on q1/q2 in the KISS mixer?
Took some digging but I remembered seeing Farhan's answer to the same
question in the archives:-
"...the fet has to be biased such that it is half way between being on and
pinch off. You are right that fets like J310 don't have a different
behaviour if you swap the two ends.
I adjust it for minimum LO leak to rf port.
- f"
There may be other ways to do this.
I should also mention that Joe W3JDR mentions that while playing with
Spice simulations he found that there might be a way to re-arrange the
circuit so that it becomes self-adjusting. See:-
//www.freelists.org/post/minima/Kiss-Mixer-Analysis
Could well be worth an experiment.
> - How do you tune the two BFO capacitors? I have used a frequency meter
> to
> place both around 20mhz. Right now I have the LSB BFO at 20.006 and the
USB
> BFO at 20.002. I am not sure what exact values I should aim for...
I'm guessing that the exact values will vary for each filter being built.
Different crystals from different manufacturers will have slightly
different centre and slopes. So your USB/LSB position (BFO) will have to
move accordingly (how much variance there is in the real world remains to
be seen). I suspect that a similar alignment procedure to this one for the
Elecraft K2 may work well:-
http://www.elecraft.com/Apps/new_fil_docs/k2_ssb_gram.pdf
Where you align while looking at the spectrum output of audio frequencies
ideally with a RF noise generator hooked up to the RX. This may be as
"good as it gets" without a real RF Spectrum Analyzer. This of course
still requires a PC and software (Linux people can use Baudline to do the
same trick. http://www.baudline.com)
Of course I guess it's probably just as good to tune in a known good
quality LSB signal and adjust it to ear. So that it sounds good! And then
make the USB tone sound the same by switching back and forth between LSB
and USB while listening to white noise.
But there is a lot of guessing here ;-) More experienced constructors will
know more I'm sure!!
As for the rest, I'll have to let others answer.
Great progress BTW.
73, Steve
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