Keysight EXG and MXG X-Series Signal Generators User’s Guide
387
Custom Digital Modulation (Option 431)
Using the Arbitrary Waveform Generator
By modulating the carrier to one of several predetermined positions in the I/Q plane, you can then
transmit encoded information. Each position or state represents a certain bit pattern that can be
decoded at the receiver. The mapping of the states at each symbol decision point on the I/Q plane
is referred to as a constellation diagram. You can create a unique signal by mapping your
constellation diagram into the I/Q table editor, shown in
. The table editor also has a
display feature, which provides a quick visual check of the expected I/Q constellation.
Figure 16-24
I/Q Table Editor
Utilizing this I/Q mapping flexibility, you can create unique modulation schemes. For example, a
circular constellation arrangement called a STAR QAM is easily implemented and saved for later
recall with the real-time I/Q baseband generator.
shows that the STAR QAM has 16
states or symbols. Four data bits define each symbol. Thus, the diagram and the table are
equivalents.
Create a STAR QAM Modulation Scheme
1.
Press Preset on the signal generator.
2.
Press Mode > Real-Time Custom Modulation > Modulation Setup > Modulation Type > Define
User IQ.
3.
Enter the values shown in
for I and Q using the numeric keypad and arrow keys.
Press Display IQ Map to check your entry and adjust any entry errors.
4.
Press Return > Store To File > Clear Text.
5.
Turn on Custom Modulation. Press Return > Return > Return > Real-Time Custom On.
6.
Name the file STAR and press Enter.
7.
Load the file. Highlight STAR and press Load from Selected File > Confirm Load From File.
8.
Turn on Custom Modulation. Press Return > Return > Return > Return > Real-Time Custom On.
9.
Set the Frequency and Amplitude to the desired values.
10.
Press RF On.
For details on each key, use key help
as described on
.
Mode > Real-Time Custom Modulation > Modulation Setup > Modulation Type > Define User I/Q
