594 Keysight InfiniiVision 4000 X-Series Oscilloscopes Programmer's Guide
24 :MEASure Commands
:MEASure:FFT:THD
(see page 1610)
Command Syntax
:MEASure:FFT:THD <tracking>[,<fundamental_freq>][,<source>]
<tracking> ::= {AUTO | MANual}
<fundamental_freq> ::= in NR3 format, required if <tracking> is MANual
<source> ::= {FUNCtion<m> | MATH<m> | FFT} (must be an FFT waveform)
<m> ::= 1 to (# math functions) in NR1 format
The :MEASure:FFT:THD command installs an FFT analysis Total Harmonic
Distortion measurement on screen.
Total Harmonic Distortion (THD) is the ratio of power in the fundamental frequency
to the power contained in the rest of the harmonics and noise. THD is a measure of
signal purity.
Total Harmonic Distortion (THD) measures the power contained in the bands
surrounding each harmonic and compares it to the power in the band surrounding
the fundamental frequency. The width of the bands measured is the same for the
fundamental frequency and each harmonic. That width is 1/2 of the fundamental
frequency.
You can either enter the fundamental frequency as a measurement parameter and
have the fundamental frequency and harmonics be tracked manually, or you can
allow the fundamental frequency and harmonics to be tracked automatically,
where the highest peak is assumed to be the fundamental frequency.
When this measurement is tracked with cursors, the cursors show the band
surrounding the fundamental frequency that is being measured (at ±1/4 of the
fundamental frequency).
Query Syntax
:MEASure:FFT:THD? <tracking>[,<fundamental_freq>][,<source>]
The :MEASure:FFT:THD? query returns the measured Total Harmonic Distortion
value.
Return Format
<return_value><NL>
<return_value> ::= total harmonic distortion ratio percent in NR3 format
See Also • ":MEASure:FFT:ACPR" on page 591
• ":MEASure:FFT:CPOWer" on page 592
• ":MEASure:FFT:OBW" on page 593
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