Waveforms v3.20.1 Amplitude modulation issues

[nanderson]

I was on v3.18.1 previously but updated to 3.20.1 when I got an AD3. Previously, I could set AM settings to 100% Amplitude/index and 100% offset to get a sinusoid to invert fully over the AM period, but now when Amplitude is 100% setting any significant offset makes the waveform freeze for part of the AM period, and when offset is +-100% there is no AM at all.

In addition, when the two channels are set to synchronized, the "Wavegen C1/C2" trigger option in the scope doesn't trigger.

[nanderson]

Actually, it looks like something is very messed up with the Offset option. Setting it around 6% gives me a result close to what I would expect at 100%. The preview in the Wavegen tool is very different than the feedback in the Scope tool. Feeding the wavegen output back to the scope confirms that the feedback in the Scope tool is accurate.

I also seem to remember that the Wavegen trigger source would trigger on modulation periods, not just edge events. Could we get that back as an option? It was very useful.

[JColvin]

Hi @nanderson,

I'm not certain how accurate the plot view in the Wavegen instrument itself is intended to be; I would have to defer to Attila on that and the offset details (I'm unexpectedly at my home office today so I don't have hardware on hand to test this myself).

As for the triggering on periods, this is still here. You will need to change the dropdown within the Wavegen to something other than "No Synchronization" and then setting a finite run time. This is explained a bit more in Help -> WaveForms -> 7. Triggers

Let me know if you have any questions.

Thanks,
JColvin

[nanderson]

Oop yeah, didn't know that was the requirement for triggering on periods, that's working fine still. 

I'm still unable to get the wavegen AM to behave like I expect, though. With offset at -100% I expect to see the waveform fully flipped for half the period, but instead I see that behavior with offset around -6, and anywhere past -10 or so I get no AM at all. 

I have workspace files saved from previous versions of the software that had configuration like the 2nd image but output like the 1st.

 

[attila]

Hi @nanderson

This *16 modulation offset is fixed in the latest version:

Thank you for the observation.

[nanderson]

Thank you for that!

I also have noticed that setting certain values of AM period produces discontinuities in the carrier waveform. For example, at 10khz sine carrier, nearly any period with more than 1 decimal place of precision produces a discontinuity at the start of the period, but that same period value may not produce a discontinuity at other carrier frequencies. 

 

[attila]

Hi @nanderson

Set "No Synchronization" or Run "continuous" or use exact multiple frequencies/periods.

The Auto Run sets the Run time to the longest period, lowest frequency, after which the generator is restarted with the configured initial phases.