QA402 - Separating Function Generators, speed and plug-in help

I’m trying to roll the 402 into my product reviews and put myself in a weird scenario.

Is there a way to run two completely independent tests simultaneously? I have a five-channel amp on the bench. I’d like to monitor one of the full-range channels at 1kHz for THD_N/SNR/Amplitude and the other channel at 60Hz. I didn’t see a way to dedicate the output of the function generators to only one channel.

Second, and maybe I’m just a newb, but is there a way to increase the speed of the measurements? I am used to the QA401 and really like it. The 402 is taking 10x longer to acquire and process.

Last, I tried using the THD vs Amplitude plug-in, and it seems to change the input attenuator back to the lowest setting.

Hi @Dave_MacKinnon,

I think the 40x software should be faster than the QAAnalyzer (for the QA401) because less data is moved around. I just ran a test of THD vs In/Out with a small FFT (video below). The FFT size has an big impact on the test time. But in this case, I did a 1K FFT just to check the speed of things when you had to wait a minimum of time for the actual acquisition. It runs through 30 tests in 7 seconds. Every so often, you’ll see a 250 mS pause–that is due to some additional time needed for the relays to settle.

So, in short, for the same FFT size and same test, I think the QA40x should be just a bit faster. Please try and compare and let me know if you are still seeing something odd.

The automated tests (aka plug-ins) will attempt to wrestle the attenuator settings away from you if you have the Autoset Input Range checkbox checked. If it is, then a first test will be run to learn the setup gain, and subsequent tests will adjust the input attenuator based on the Input Range Adder (dB) that is specified. So, if you are outputting a signal at -20, and your DUT has 20 dB of gain, then the input signal will arrive at 0 dB, and with 18 dB of input range adder specified (for example), the target input level will be +18 dBV.

There’s not a good way right now to run different tests on different channels. Unfortunately…

Thanks as always Matt! I’ll run some tests first thing in the AM.

I think I missed the AutoSet radio box option… Will check that as well.

So, I decided to race the 40X against the 401. As you can see, the 40X is much slower. There is no difference if the 40 isn’t connected and the computer is booted freshly.

Hi @Dave_MacKinnon, got it will study. From your vid, it looks like 402 USB transfer speed is slower. I will report back this week, thanks!

Hi again @Dave_MacKinnon …I think it’s your sample rate. With the QA401, your sample rate is 192K, so a 256K buffer takes 256/192 = 1.33 seconds to fill. On the QA402, your sample rate is 48k, so a 256k buffer takes 256/48 = 5.33 seconds. Double check if my understanding from your vid is correct or not. But with comparable sample rates and FFT sizes, I think you’ll find the QA402 might even be faster (less data is being moved around internally)