Agilent X-Series Signal Generators User’s Guide 347
Custom Digital Modulation (Option 431)
Using the Arbitrary Waveform Generator
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. Figure 13- 25 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 Figure 13- 25 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.
Figure 13-25 STAR QAM Diagram and Table
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