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AMfone's Online AM Handbook => Hints and Kinks => Topic started by: Steve - K4HX on February 16, 2014, 01:32:37 PM

Title: Calculate THD
Post by: Steve - K4HX on February 16, 2014, 01:32:37 PM
Attached is an MS Excel Spreadsheet from Al, W1VTP. Use this file with the following test procedure.

Input an audio tone to the transmitter under test at the desired percentage or modulation.

Using a spectrum analyzer or SDR, measure the sideband level (relative to the fundamental sidebands) of the harmonics of the modulating tone. Example, if the input tone was 1 kHz, there would, of course be sidebands at plus and minus 1 kHz relative to the carrier. There will also be sidebands at 2, 3, 4... kHz, depending on the amount of distortion.

Measure the level of these harmonic sidebands relative to the sideband at either plus or minus 1 kHz.

Enter the measured levels into the appropriate cells (marked in yellow) in the attached spreadsheet.

The sheet will then calculate the total harmonic distortion (THD).

If you make measurements at several frequencies, the sheet will produce a plot of the THD versus frequency.
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