So the last time I measured noise I used an analog multiplier (AD734, I was going to say ~$20, but now $35!
So I'm thinking about methods to measure single channel noise (V^2, V**2) and two chan. correlations V_a(t)*V_b(t)
0.) Digitize everything and do it in software. This is not my strength, so someone else's box would be my starting place. I must admit a fast (10 MHz) two channel digitizer sounds like everyone's cheap DSO.*But I'm looking for ideas.. one problem with cheap scopes is the record length. You can save so much and then have to down load it.
1.) Some switched gain thing like cheap lockin's But I'd be doing Va(t)*sgn(Vb(t)) (where sgn is the sign of the voltage wrt gnd.) or Vb*sgn(Va). Well it's not all that clear how this relates to the correlations.. you get some sort of measure if Vb and Va are the same size. (I'll just note that Va*sgn(Vb) = Va*Vb/|Vb|)or some other silly ideas...diode mixer?
I'm going to order a spendy AD734 as a reference.
George H.
*Does my cheap rigol do A*B? hang on... Yeah it does.. I really need the average of A*B