74 Chapter2
Making Measurements
Example 4: Harmonic Distortion
Figure 2-20 Second Harmonic Displayed in dBc
Percent of Harmonic Distortion
The total percent of harmonic distortion of a signal is also measured
frequently. For this measurement, the amplitude of each harmonic
must be measured in linear units (for example, volts) instead of dBc. To
display amplitude units in volts, press
AMPLITUDE, MORE 1 OF 3,
AMPTD UNITS, and VOLTS. The amplitude values of these signals are
used in the equation below to compute total harmonic distortion:
1. Where:
A
1
= the amplitude of the fundamental frequency, in volts
A
2
= the amplitude of the second harmonic, in volts
A
3
= the amplitude of the third harmonic, in volts
A
4
= the amplitude of the fourth harmonic, in volts
A
n
= the amplitude of the nth harmonic, in volts
If the signal amplitudes are measured carefully, as in the previous
example, this procedure measures percent-of-harmonic distortion very
accurately.
A
2
()
2
A
3
()
2
A
4
()
2
.... A
n
()
2
+ + + 100×
A
1
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