Re: Duo and WSJT audio

Neil Smith G4DBN

I can't follow how running split doesn't chnage the result David? When you run Fake-It and try to use a 1kHz tone, the program drops the TX frequency by 500Hz and sets the tone to 1500Hz, so in theory, that puts the second harmonic outside the filter. With Fake-It running (and using the DUO driver, not the TS480!) and a tone of say 2200Hz, do you see any unwanted products? (rig should TX oin the base frequency and send 2200Hz). Now try a 400Hz base tone and try again (rig should send 1900Hz and QSY down 1.5KHz on TX).

Now try 400Hz without fake-it split.  Any change?

Do you get a completely pure signal when you set the DUO to TUNE using the front panel button?

How about if you generate a clean sine wave in Audacity and send that to the DUO?

Are you using an external reference to lock the DUO?  If so, does anything change when you don't?  Does anything change if you use a different supply for the DUO?  (I had a nasty one where where an SMPS started putting out ripple and I was getting some VERY weird products via the 10MHz lock input).

In some of the WSJT-X modes, you can type @1200 or @1800 to get a tone of that frequency transmitted from WSJT-X, when you do that with various different tones from say 500 to 2500Hz, what happens to the unwanted products?

Is the level of the unwanted tones directly proportional to the main tone as you reduce the audio power slider in WSJT-X?

Are you using VAC or anything between WSJT-X and the DUO?

Do you have a way to examine the sound card output from your PC to ensure the products aren't being generated somewhere before it hits the USB driver?  Maybe a VAC and some sort of spectrum analysis app like Spectrum Lab or Audacity?

Lots of things to try sorry!

Neil G4DBN

On 13/07/2020 18:57, david via wrote:
Hello All,

I'm looking for guidance (or reassurance) with the setting up of my Duo for
WSJT-X. Let's say for FT8.

I have followed the Elad Application note, and have picked up snippets from
old messages here, although I didn't pay much attention in the past as I
have only recently obtained the Duo.
The set-up is fine - no hitches with most of the settings. But I am most
concerned to put out a clean signal, and that is where I need your help. I
can transmit into a dummy load and 'sniff' the signal using a Perseus SDR.
When I use the 'tune' button in WSJT (which produces a 1kHz tone), I see my
fundamental signal exactly where I would expect it. But there are harmonics
1kHz either side of it.
These harmonics are about 50dB below the fundamental. No changes I make to
the audio drive level in WSJT make a difference to the relative levels. If I
go down low enough in drive level to remove the harmonics, the fundamental
disappears, too. I've tried 'fake-it', 'none', and 'rig' without removing
the harmonics. Is there something else I should try? Or is 50dB down
something I simply shouldn't worry about?

Best Wishes
David, GM8XBZ

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