Chapter 5 297
Concepts
Analog Modulation Concepts
AM Depth Measurement Concepts
Purpose
AM Depth measures the amount of AM on an RF carrier. Modulation depths to
99% can be measured.
Measurement Technique
Amplitude Modulation (AM) of a sine or cosine carrier results in a variation of the
carrier amplitude that is proportional to the amplitude of the modulating signal that
contains information. AM is a linear process. The modulating signal varies the
amplitude of the resultant modulated signal, therefore, changing power of the
carrier.
A quantity which describes the amount of the AM depth (usually expressed in %)
is defined as:
Equation 5-2
where:
VP = the peak amplitude of the AC component, and
VT = the trough amplitude of the AC component. See Figure 5-10 on page 297.
Figure 5-10 Amplitude Modulated Carrier
%
AM
V
P
V
T
–
V
P
V
T
+
-------------------
100%×=
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