I was wanting to use the AWG on my SDS2000X Plus to generate a waveform to make two tone tests of an SSB HF transmitter. This is a learning experience in a few respects. I haven’t generated arbitrary waveforms before and I haven’t used the scope's FFT function before although I am comfortable with FFT theory to a certain extent. I don’t normally use the scope FFT because I have a SA but it doesn’t go down to these low frequencies, hence the use of the scope.
I am referencing the process described here
https://siglentna.com/application-note/easywave-two-tone-arbitrary-waveform/ . Note that there are no particular spurious signals on the screenshot in the article, just the general noise floor at some 60 dB down from the two tones (700Hz and 1900Hz).
So I have generated an arbitrary waveform with 7 cycles of sine wave added to 19 cycles of sine wave and uploaded that to SDS internal AWG. I’ll leave aside that sending it over then network doesn’t work, no error message, EasyWave seems to do its bit, but no file arrives. So I used a USB stick which was fine.
The result is as shown in the first screenshot. I can clearly see the two wanted frequencies but there are spurii some 37-39dB down.
That is not what is shown in the article where they are using the “proper” SDG.
As a matter of interest I tried my FY6900 and got the results shown in the second screenshot. The spurious signals are better than 50dB down
Question(s)
1 Is my FY6900 really so much better than the AWG on my Siglent ? If so, is that a bit embarrassing ?
2 Is my application of FFT on the scope correct? - I normally use an SA but it doesn't go down to these frequencies and this is my first time playing with the Scope FFT Math function.
3. Would I get better results using both channels of the FY6900 running them as sine waves and then using electronics to sum the two waves ?
I’m not sure that I actually need any better performance than I can get from these methods just to check the ballpark linearity of the SSB transmitter. There is no spec I am measuring against anyway, I just want to see that it looks ok-ish and isn’t likely to create a huge amount of IMD.
Siglent Spurii
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FY6900 Spurii
Regards
Eloso
Edited to use proper descriptive name for the second screenshot.