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Analog Modulation
38
Frequency Modulation Example
Figure 36 shown below is a 2 MHz carrier being frequency modulated by a 100 kHz
square wave with a 1 MHz deviation. In this example of Frequency Shift Keying (FSK)
the carrier frequency is being rapidly switched between 1 MHz and 3 MHz.
The top trace is from the rear panel Modulation Output BNC which shows the 100 kHz
modulating waveform. The middle trace is the front panel BNC output, whose amplitude
was set to 1 VPP. The bottom trace is from the front panel Type N output, whose
amplitude was set to 2 VPP.
Figure 36: FSK Modulation
Phase Modulation
The phase modulation can use either the internal modulation generator or an external
source. The internal modulator can generate sine, triangle, ramp, square, noise, or user
waveforms.
The phase of the output traverses the specified deviation at the modulation rate. For
example, with a frequency of 1000 MHz (1 GHz), and modulation rate and deviation set
to 10 kHz and 45 degrees, respectively, the output will be a fixed frequency with its
phase traversing ±45 degrees at a 10 kHz rate.
Stanford Research Systems
SG390 Series RF Signal Generators