"due to progressive attenuation of the harmonics. "

Seems you have answered a question I have not yet asked. Like, if the reading is to be considered valid there has to be a specified bandwidth otherwise you are excluding the meaningful or including the useless. Like, you do not need to know the content at 4.8 GHz.

So 100 KHz is the cutoff then ? I never checked. Seems reasonable, that would be the fifth harmonic of 20 KHz. If anyone can hear that we should all line up to kiss their ass and give them time to advertise the tickets.

Anyway, my buddy took it home today. It is his actually, but we just umm, don't care which place a certain piece of equipment is at all the time.

But now I want to get more specific on this mixing a square wavee into the sine wave thing to do an ersatz calibration check. Right now it is reading pretty high distortion on its internal oscillator, and actually reading lower on my Wavetek. I haven't been to all the ranges of the internal oscillator yet, nor on the Wavetek. At 1 KHz, the Wavetek read like 0.48 %. the internal oscillator was like 27 %. This does not seem right, maybe a ground problem or bypass caps or something because it just doesn't seem all that likely. I would like to have a distortion meter to check the oscillator on this distortion meter. Yup.

The wavefoprm looks alright by eye. I did not try nulling it with the Wavetek nor doing the Lissajous thing to see if I oculd get a decent circle. but it looked alraght and back then I did see a decent sine wave. the high distortion reading came after it had an all night burn in.

Then, unfortunately it was time to go.

He has to learn how do run the thing. Hey, I didn't know initially. I know the theory behind it but operation is another thing. I got it figured out pretty much and next will come the finer points. Like, yeah it measures, but does it measure accurately ?

Next question. This thing FILTERS, not really nulls out the fundamental. this allowws it to accurately measure through a system that has phase shift. Otherwise an OP AMP would make the best distortion meter. So it gets lovcked to that frequency by something that resembles a PLL at least remotely.

Now, if I have 1 V P-P sine going in there at 1 KHz, if I took another generator, not locked or anything to the fundamental one, and injected a 2 KHz sine wave into it, the distortion meter should read that accurately, correct ?

I mean I am putting in a controlled amount of the second harmonic, but it is not locked in any phase relationship and in fact is not even frequency locked.

WILL THAT WORK ?

That thing wiht the mixing a square wave with the sine wave, I want to try that. But the ratio, is it RMS voltage or P-P ? A sine wave makes it easy because it is the same as the fundamental. Adding it at the second harmonic at 10 % the amplitude clearly should read 10 % on the meter, correct ?

In fact, now that I think of it I shold be able to add ANY frequency to it not at the fundamental and the meter should read that. Read the dB scale or the percentage, whatever snokes ya up. (yeah, I hear some are starting to describes THD in -dB instead of percent)

Anyway, now that I think of it, all I need is a second generator.

Interesting.