Tim,
I think I now understand the offset you were referring to.
That's a good point, and this might be key to Gerald's problem
of hearing different audio on USB than LSB.
The answer, I think, is to keep the 2000 hz slice of the signal we are receiving
centered on the passband of the 45mhz filter.
As described in post 44182, the original uBitx code moves that slice by 4khz when we
switch from LSB to USB, rather significant given that in some versions the 45mhz crystal filter
can have a 3db passband of +/- 3.75khz.? ?Post 44182 proposes new values for clk1
that should fix the issue.
I first wrote a much longer version of post 44182, spelling out exactly where the
carriers and sidebands wind up at each stage in the rig for both LSB and USB cases,
and how and when and why the sidebands get inverted by the two mixers.
If 44182 gets vetted here in the forum, I'll post that longer version of what I think is going on.
And someday I should dig out my uBitx and see if my solution works.
Maybe even get it on the air.? ?;-)
Jerry, KE7ER
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On Sun, Mar 11, 2018 at 09:40 am, Jerry Gaffke wrote:
You state:
>? Does the ubitx software maintain a CLK0(USB) and a different CLK0(LSB)?
No, the BFO is always below the 12mhz filter passband, if above then harmonics beat with an oscillator on the Nano.
As stated in post 44182.
>? If not then changing the BFO (CLK0) by itself will result in an
>? asymmetric USB and LSB since the actual suppressed carrier freq now has
>? an offset.
I guess this agrees with what I was saying in post 44182, though it's not terribly clear
exactly what asymmetry or exactly what offset you are referring to.
There's a bunch of contenders here.
Yes, changing only the BFO when trying to listen to a signal is generally a bad idea.
