"Bret Ludwig" wrote in message
ups.com...

Arny Krueger wrote:
"Bret Ludwig" wrote in message
oups.com...

Arny Krueger wrote:
snip

(1) Bret doesn't seem to know how to set up a scope that views the
output
of
a distortion analyzer
(2) Bret doesn't seem to know what to expect to see on a scope that
views
the output of a distortion analyzer
(3) Bret doesn't seem to know how to analyze what one sees on a scope
that
views the output of a distortion analyzer.

How clear does it have to be?

Silly me.

No, inexperienced you, Bret.

BTW, watching skilled techs run a THD analyzer, or reading magazine ads
which is all you've provided evidence of Bret, isn't what Graham and I
are
talking about.

Here I thought you hooked a BNC cable from the residual out of the
distortion box to a channel input of the scope and set the time/div
knob so each bump took a graticule or so and the volts/div to where the
height was about right. GOD, how STUPID could I have been?!

Arny, please educate us on your SUPERIOR method!

BTW, it's not my method. It's how it is done by everybody with a clue.

Two words: X/Y mode.

BTW, X/Y mode does not change the vertical calibration of the 'scope, so
you
can still estimate the peak distortion from the 'scope.

What X/Y mode does do is cause the 'scope's display to remain stable
without
further adjustment as you change the test frequency. Just another little
convenience that anybody who actually has significant hands-on time with
a
THD analyzer knows.

Wow Bret, when you expose yourself to be a poser, you really do a bang-up
job!

Bull****. If there is any amplitude to the signal at all the scope
will trigger properly,

Of course but that isn't the same as "no further adjustment as you change
the test frequency", is it?

although you will have to adjust to keep the
display size of the waveform to a sensible figure.

Bret, thanks for conceding that your alternative is on the face of it,
highly suboptimal.

One other benefit if the X/Y approach is that it can be used to determine
the order of the predominant distortion. The magic word is "Lissajou".

Here's a simulation:

http://galeb.etf.bg.ac.yu/~milosr/ja...u/Lissajou.htm