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7
Tutorial
Modulation
Modulation is the process of modifying a high-frequency signal (called the carrier
signal) with low-frequency information (called the modulating signal). The carrier
and modulating signals can have any waveshape, but the carrier is usually a sine
waveform.
The two most common types of modulation are amplitude modulation (AM) and
frequency modulation (FM). These two forms of modulation modify the carrier's
amplitude or frequency, respectively, according to the instantaneous value of the
modulating signal. Pulse width modulation (PWM) is provided for pulse
waveforms only. In PWM, the pulse width or duty cycle of the pulse waveform is
varied according to the modulating signal.
The function generator will accept an internal or external modulation source. If
you select the internal source, the modulated waveform is generated by a
secondary DDS synthesizer. If you select the external source, the modulated
waveform is controlled by the signal level present on the function generator's
rear-panel Modulation In connector. The external signal is sampled and digitized
by an analog-to-digital converter (ADC). With either modulation source, the result
is a stream of digital samples representing the modulating waveform.
Amplitude Modulation (AM)
The function generator implements a form of AM called "double-sideband
transmitted carrier." This is the type of modulation used by most AM radio
stations.
Amplitude Modulation
360
Modulating Signal
Modulated Carrier
(100% depth shown)
Keysight 33210A User's Guide
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