After making the MMM, I was thinking about making a low pass filter to clean it up. But having no toroids kicking around the garage at the moment, I was thinking about building all air core wound on forms.
But then I started thinking how to measure the LPF. I started thinking about noise generators - feed broadband noise into the LPF, and look at the output on the FFT of the oscilloscope. In theory, anyway.
I came across this circuit and decided to build it.
Had several missteps (wrong resistor value, forgot to cut a trace, etc). But after all that it still wasn't working. I noticed in their writeup they mention that they got it from a different site, and when I looked at that one, I noticed they were using slightly different values (including a 12v source). On a whim, I tried the higher voltage, and got noise!
I'm not sure if I'm getting as much noise as I want, though. The output of this seems to be maybe 2v P-P. If I'm reading the FFT right, it looks like the noise is up 30dBVrms. But the FFT doesn't look to be going out as far as I would think. If I'm reading it right, it is only showing me the fft out to around 600 KHz. Strange.
After asking around and playing with the scope, I found that you need to adjust the horizontal time scale *before* you go into the Math function. I also adjusted to use the maximum memory (under the horizontal menu) - not sure if that helped.
I think the next step here is to look at the output signal level and see if I can figure out how to go about increasing that - feels like that will be needed to really see signals when I try to measure filters.
After asking around and playing with the scope, I found that you need to adjust the horizontal time scale *before* you go into the Math function. I also adjusted to use the maximum memory (under the horizontal menu) - not sure if that helped.
I think the next step here is to look at the output signal level and see if I can figure out how to go about increasing that - feels like that will be needed to really see signals when I try to measure filters.
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