|
Amplitude Modulation (AM)
is a
method of modulation wherein the carrier amplitude changes with the
amplitude of the input signal. Simply put, amplitude
modulation generates a signal with power concentrated at its carrier
frequency and its two sidebands. These side bands are bands of
frequencies above and below the carrier frequency. They have equal
bandwidths, and are mirror images of each other.
AM is not
an efficient way to modulate - much of its power is wasted. At
least 2/3 of the power is used by the carrier signal, while the
remaining power is split between the two equal sidebands.
Percent Modulation
M = [(Ec
- Et) / (2Ea)] x 100%
or
M =
[(Ec -
Et) / (Ec+Et)] x 100%
where
M = %
Modulation
Ec =
crest amplitude of the modulated carrier
Et =
trough amplitude of the modulated carrier
Ea =
average amplitude of the modulated carrier
Sideband
Power
Ps = M2Pc
/ 2
where
Ps =
sideband power of an AM carrier, W
M =
%Modulation
Pc =
carrier power, W
Total
Radiated Power
Pt = Ps +
Pc
where
Pt =
total radiated power, W
Ps =
sideband power, W
Pc =
carrier power, W
See Also:
Frequency Modulation Equations; More
Articles
|
