Can someone please add whatever is necessary to this LTspice file to measure THD at Vtr. No great precision needed.
I've read several descriptions but stupid here doesn't understand.

 

Add ".four 50 V(vtr)" as a command on the schematic, run the sim, view error log.

 

Thank you - I have got that working.
Now a suplementary question. It gives two values for THD, for instance:
"Total Harmonic Distortion: 0.009663%(0.024211%)"
What is the difference between the two numbers?

 

Sorry, no idea what the bracketed number refers to. Bordodynov would likely know.

 

Thank you - I have got that working.
Now a suplementary question. It gives two values for THD, for instance:
"Total Harmonic Distortion: 0.009663%(0.024211%)"
What is the difference between the two numbers?

The first number is the THD for the number of harmonics selected (the default is 9)
The second number (in parenths) is questionable as to what is represents. Opinions vary.

use the directive .opt plotwinsize=0 on the schematic to ensure LTspice uses all datapoints for Fourier computations.

eT

 

OK, I'll ignore the second number.
Many thanks.