Open Loop with QA402

Just got my QA402 and was wondering if there was a timeline for open loop testing to be enabled as I’d like to work on some dacs.

Sorry for my duplicate post. I see DanClark was essentially asking the same question.

Hi @Moto, it should be in the current builds already. I just checked: Open the “Press to Run” context menu (do this by right clicking on button OR touch and hold OR control+click) and then press start and begin playing back the specially created WAV. The name is “triggered acquisition” which is the same as “open loop”


Let me know if you run into any trouble.

Thanks, Matt

Thx Matt. Found it. Is that in documentation anywhere?
Sorry for being dense but isn’t triggering then more or less equivalent to mirroring at least for single tones?

Thx Matt. Found it. Is that in documentation anywhere?

Not yet. The documentation wont’ be updated until the UI is frozen, which I think happened today with the 0.999 release.

Mirroring is for tones. The triggered acquisition is for chirps. So, to use the chirp, you really need to play the specially created WAV. If you just want to capture a tone from a device with no analog input (like a car stereo), you can just play a 10 minute sine file and analyze it as you would any sine.

The challenge with the chirp to sweep frequency response is that the analyzer needs to know how long you are spending at each frequency. If it doesn’t know that, then it doesn’t know if the measured energy is more or less than expected.

So: To analyze a sine wave from any device, just connect it and measure. The timing isn’t important. To sweep a frequency response from a device with an input, you can sweep it directly from the QA402 using the Expo Chirp or White Noise button.

But if the DUT doesn’t have an analog input, then you need to use Remote Trigger. And finally, the mirroring is needed only if you want to step a DAC.

Let me know if not clear!

Thx much. Only question is by stepping dac are you referring to step responses of the dac?

Hi @Moto, sorry for confusion, I was referring to stepping of frequency (eg 100 Hz, measure, then 200 Hz, measure, then 300 Hz, measure). So, you step through discrete tones and make a measurement on each.

I think Mirroring will be added with a checkbox in the Gen1 dialog. When you enable the checkbox, if you set Gen1 to be -10 dBV, then when Gen1 is enabled, it will also play a sine on host Windows machine at -10 dBFS. This is similar to how it operated for the QA401. This will then allow you run automated tests and and instead of stepping just the QA401 frequencies, it can simultaneously step the DAC too.