Digital communications
Figure 1: Error vector magnitude
Error vectors are helpful in characterizing the quality of a transmitted signal.
They are a natural measure of the noise in a communications channel, but they
can also help identify defects of a transmitter, such as ampli
fi
er compression or
an IQ gain imbalance.
Modulation techniques
There are a number of modulation techniques used by the generator. They are
described below.
ASK (amplitude shift
keying)
ASK is a modulation technique in which digital symbols are encoded in the
amplitude of the RF. The phase is ignored. ASK is implemented by only
modulating the I channel and forcing the Q channel to zero.
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.
TSG4100A Series RF Signal Generators User Manual
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