I would like to have a convenient tool to measure filters and amplifiers in 20 Hz - 20 kHz frequency range. Currently I'm doing this with a signal generator, an oscilloscope and LibreOffice. It's not the fastest and not the most convenient method, but it gives a nice looking result:
I've tried several software solutions for my primary OS, which is MacOS. The closest things I could find were iSpectrum and Friture, but they don't do exactly what I wanted to. I couldn't find a way to determine a 0 dB reference. I also tried to run several Windows tools using CrossOver - some of them didn't work, some were no better than Friture.
I very much like my Rigol DSA815-TG. But the problem is that it doesn't work well below 9 kHz and is completely deaf below 1 kHz. I tried to use a diode ring mixer to upconvert the frequencies of interest above, say, 10 Mhz. It works, but this mapping turns out to be non-linear. I.e. 1 dB change in DUT frequency response doesn't cause 1 dB change on upconverted frequencies. This is actually to be expected, since audio devices are usually not matched to 50 Ohm. It means that I have to design some sort of compensation network to make this work. This starts to sound complicated.
In theory I could also write a little piece of software for STM32 microcontroller to automate the task.
Basically what I'm looking for is a frequency analyzer, but for low frequencies. Or like HP 35660A dynamic signal analyzer, but for a resonable price.
I find it hard to belive that I'm the first one who encountered this issue. Is there really no software, no open source MCU based project and no upconverter that already make plots like the one shown above?