"** Best set the level of the second generator to not more than say 10% of the main one, so the auto-nulling system is not confused.

..... Phil "

Hmmm.

I just sent an email to my partner on this, thinking about going up to 25 %.. If I let it lock, or tun or whatever, would I gt away with those higher levels ? Or are you talking about different units or something.

This is askable because this thing has a scale to read up to 100 % THD.

The way I am reading this fromm you is that the tracking circuit may be upset by frquencies too cloes. Would phase locking them help ? I can fuly understand a 1.4 KHz square ave assauling the tracking circuit, that is obvious..

But then, IF that freqquency rsponse of the detector is realy flat it doesn't matter what I put in there as ong as it is far awat fro the fundamental. What if I use 1 KHz for the fundamental and 5 KHZ for the induced signal ? (from the external oscillator) Surely that should not confuse it.

What's more, ou probably don't want a test " pollutin" frequency any closer than second harmonic. I can see that if you are testing the veracity of the filters themselves, but for most THS measurements doesn't matteer. However I intend to beat on the thing.

We got scopes, and I might just be using them all when this happens. In fact it might be a nice to have a high Q 1 KHz tuned circuit to eliminate any THD in the HP oscillator. I am not holding my breath.

We'll see how it goes. I am finally up on working the thing and next we scrutinize. For the audio business, when I test something on it, usually I can just compare channels. But it is nice to have at least a semi-accurate set of absolutes.