With Bode analysis an active method could work because it is very easy to automatically detect when the signal starts falling apart (wild phase snaps and so on). But one has to place limits or stuff could go kablouie with gusto.
Well, the Bode 100 does:
It has automatic setting for the level, fixed, or whatever shape you want for the envelope over frequency
Cheers
Klaus
The simple method AFAIK is just to measure the swept frequency RMS level on the output. If you have a 5V output, a 50mV level is not going to hurt anything
Regards
Klaus
50mV often isn't enough to overcome the noise. When you raise it towards 200mV things can become dicey. That combined with an aggressive loop ... *BAM*
Well, you need to use time synchronized averaging:
Then the signal appears from the noise, even when burried deep. The network analyzer I have build (slow version due to GPIB and scope speeds) used this approach.
Cheers
Klaus
The speed can be boosted if the time averaging is only used at frequencies with signals of low S/N
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