Specifications

132 Chapter 15
Concepts
Harmonic Distortion Calculations
Concepts
Harmonic Distortion Calculations
The analyzer provides a one-button automated measurement for
harmonic measurements (from the second to the tenth harmonic) and
provides a calculation of the total harmonic distortion for continuous
wave signals or complex digitally modulated carriers.
When the harmonic distortion measurement is activated, the analyzer
searches for the fundamental and determines the frequencies of the
harmonics. The analyzer then changes to zero span, and measures the
amplitude of each harmonic. The analyzer calculates the total harmonic
distortion by dividing the root-sum-squares of the harmonic voltages by
the fundamental signal voltage and then provides the result as a
percentage.
Where:
%THD = Total Harmonic Distortion as a percentage
h = harmonic number
H
max
= Maximum Harmonic Value listed
E
h
= voltage of harmonic h
E
f
= voltage of fundamental signal
Example of a THD calculation:
If the number of harmonics selected is 5 (H
max
= 5) and the measured
values are as follows:
then,
%THD 100
E
h
2
h2=
H
max
∑




E
f
----------------------------
×=
E
f
5 dBm 3.162 mW 397.6 mV== =
E
2
42– dBc 37– dBm 199.5 nW 3.159 mV=== =
E
3
26– dBc 21– dBm 7.943 µW 19.93 mV=== =
E
4
49– dBc 44– dBm 39.81 nW 1.411 mV=== =
E
5
36– dBc 31– dBm 794.3 nW 6.302 mV=== =
THD 100
3.159 mV
2
19.93 mV
2
1.411mV
2
6.301 mV
2
+++
397.6 mV
---------------------------------------------------------------------------------------------------------------------------------
× 5.33%==