I mentioned this in another thread, but it would be nice if the axis setting dialog for dBr which has 'set peak to 0db" also had an option to ‘always keep peak at zero’ so that regardless of if the amplitude is changed, the peak always remains at 0.
Yes, good idea, added to QA402/issues on github
Hi @ttako, yes, there’s something that could be done here for sure. There is a side project using RC notch (like on QA480) and RC notch for a resonator that is being studied for getting THD+N to -125 dB or so to measure some of the newer class D amps that have THDN around -118 dB or so. Some of the requirements are listed at the link below. Soon there will be an update. If it works at 1 kHz, then the question becomes if it’s useful to test at other frequencies and a tracking notch as you mention becomes interesting for sure.
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Thanks Matt, That looks great! I just can’t wait to see progress here 
I would like to see a “dBr Avg” setting which would put the dBr 0 point at the average of the waveform(s) making it much easier to see the +/- variation (I am thinking frequency response) more readily. You would probably need to select which channel you would want to be used as a reference…
Hi @blurpy, yes there is something here that needs attention for sure. Changing of FFT while running can sometimes cause a state where part of the UI thinks it’s acquiring and another part thinks it’s stopped.
For web interface, is it possible you are sending a POST Acq before the last one had finished?
Hi @matt
I don’t think the issue happens during just acquisitions. I am not entirely sure when it happens actually, because it’s been random, and not very often. But I think it happens when changing settings in the web interface, where it sends all the different settings at once.
It sounds like it could be the FFT issue you mention. Maybe it also applies when changing the FFT at the same time as other options?
Hi- I got back and the web interface worked well on my benchtop PC. It does not look like you can change the windowing though- it is stuck on Hann- that that changeable? Thanks!
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Good to hear it’s working!
Windowing wasn’t available in the API until recently, but it is now so I have updated the web interface. Download the latest development version again and you should be able to change windowing, if you also have the newest QA402 software running
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I tried your latest code (THX!) and I could toggle the windowing and attenuation in “Acquire”, but they do not change in the “window information display area”:
For the QA402 software, it would be nice to have the dBr offset value displayed on the trace like it does the attenuation input gain offset. Also, the ability to add a note/ title to the trace would be helpful 
It looks like you are currently in run mode.
I also see that the active settings displayed to the right of the result table are different from what you have currently in the sidebar (Acquire section).
Since changing settings while it’s acquiring has been error prone, I disabled that ability. So the way I usually set this up is I have it stopped, then make my changes, click “Set” and then “Single acquire” to see the result. If I’m happy I click “Run”, if not I repeat.
Does that make sense?
That makes perfect sense and will try it tomorrow and report back…Thanks again!
I tried the Set and single acquire method and still get an error, though some of the data changes, but not all (ext gain):
You are good at finding things 
Never seen that message before. Did you get it when clicking set or single acquire?
The message comes from the QA402 software. Maybe @matt knows what’s going on?
My guess is that some setting you have enabled in the QA402 software is incompatible with the settings used in the web interface. What state is the app in - is it loaded with default settings, or have you tweaked a lot?
If you are not in a default state you can try to start from that, or potentially undo 1 and 1 change to find out which one might create this error.
I was kind of in a hurry and thought maybe it did not like the load being a different value or the external gain being different- it worked before but now I was “cranking up” the amp and needed the external gain in. I will play with it today some more and report back what I find. I wished I knew how to program with this code more, but it is not my forte- I like simpler things like HP/Agilent/Keysight VEE 
Load and gain are options handled by the web interface directly, so they should not interfere with the QA402 software at least. I don’t think that is related to the error you got.
Played with it some more and it did not give me an error if I only changed one parameter and then did SET & Single Acquire. I think I found another problem in that the power is not being calculated correctly, even though it shows the external gain as -12dB. Here is the Web version showing ~203w:
and the QA40x display showing the correct power for the -12.3dB input gain (~12w, and this has A weighting on and 8.25ohms for the loads):
Glad it’s now working
The power calculation looks correct based on the data the web interface receives from the QA402 software.
As you can see from the input row in the result table, the measured voltage is 20 dbV. Then you specify that the signal has been attenuated by 12 dB (ext. gain -12dB), so the calculated output signal from the DUT is 32 dBV. 32 dBV / 40 Vrms is 200w into 8 ohm.
The measured input signal of 20 dBV / 10 Vrms is 12.5w into 8 ohm, which is what you see in the QA402 software. However, that value seem to be calculated based on a specified attenuation of 12 dB in the QA402 software, so the real measured signal is 8 dbV. It looks to me like the QA402 software reports the calculated value and not the measured value to the web interface. So the result is double the attenuation (24 dB) when looking at the web interface. If you set ext gain in either the QA402 software or the web interface to 0, then I think it will look correct.
I am not aware of an API that can be used to synchronize this attenuation value between them, so I don’t think there is any way of handling this better for now.
It worked if I did what you suggested- just use the QA402 software for the external gain settings and now it seems to be happy!