Digital communications
Figure 2: ASK constellations
FSK (frequency shift
keying)
FSK is a modulation technique in which digital symbols are encoded in the
frequency of the RF. The amplitude of the carrier is held constant. In the SG390
series generators FSK is implemented using an internal rate generator followed by
cosine/sine tables to convert a phase into its respective I and Q components.
Simple waveforms.
As with analog modulation, the RF may be vector modulated
in frequency with simple waveforms: sine, ramp, triangle, square, noise, and
user waveforms.
Digital constellations.
The generators provide four default constellations for use
with 1-bit, 2-bit, 3-bit, and 4-bit digital modulation. Custom user constellations
can also be downloaded, if desired. The default constellations are summarized
in the following image. Waveforms for digital modulations include PRBS data,
simple patterns, and user data. Frequency deviations of up to 6 MHz are supported.
The con
fi
gured deviation applies to symbol 0 in each of the constellations.
Figure 3: FSK constellations
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TSG4100A Series RF Signal Generators User Manual
