20-01-2012, 12:42 PM
Amplitude &Frequency Modulation
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Modulation Methods
In the modulation process, some characteristic of a high-frequency
sinusoidal carrier is changed in direct proportion to the instantaneous
amplitude of the baseband signal. The carrier itself can be
described by the equation
Zero Span and Markers
One possibility, if the percent modulation is high enough, is
to use the analyzer as a fixed-tuned receiver, demodulate
the signal using the envelope detector of the analyzer, view
the modulation signal in the time domain, and make
measurements as we would on an oscilloscope.
The Fast Fourier Transform (FFT)
The maximum modulating frequency for which the
FFT can be used on a spectrum analyzer is a function
of the rate at which the data are sampled (digitized);
that is, it’s directly proportional to the number of data
points across the CRT and inversely proportional to
the sweep time.
