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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
AMPTD UNITS
used in the equation below to compute total harmonic distortion:
----------------------------------------------------------------------------------------------------
1. Where:
If the signal amplitudes are measured carefully, as in the previous
example, this procedure measures percent-of-harmonic distortion very
accurately.
74
, and
VOLTS
2
2
2
(
)
(
)
(
)
(
A
+
A
+
A
....
+
2
3
4
A
1
A
= the amplitude of the fundamental frequency, in volts
1
A
= the amplitude of the second harmonic, in volts
2
A
= the amplitude of the third harmonic, in volts
3
A
= the amplitude of the fourth harmonic, in volts
4
A
= the amplitude of the nth harmonic, in volts
n
AMPLITUDE
. The amplitude values of these signals are
2
)
×
A
100
n
,
,
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