Agilent Technologies E8247C PSG CW - Manual (Page 194)

184 Chapter 9
Two-Tone Waveform Generator
Creating, Viewing, and Modifying Two-Tone Waveforms
To Minimize Carrier Feedthrough
This procedure describes how to minimize carrier feedthrough and measure the difference in power between
the tones and their intermodulation distortion products. Carrier feedthrough only occurs with center-aligned
two-tone waveforms.
This procedure builds upon the previous procedure.
1. On the spectrum analyzer, set the resolution bandwidth for a sweep rate of about
100-200 ms. This will allow you to dynamically view the carrier feedthrough spike as you make
adjustments.
2. On the signal generator, press
I/Q
>
I/Q Adjustments
> I/Q Adjustments Off On to On.
3. Press I Offset and turn the rotary knob while observing the carrier feedthrough with the spectrum
analyzer. Changing the I offset in the proper direction will reduce the feedthrough level. Adjust the level
as low as possible.
4. Press Q Offset and turn the rotary knob to further reduce the carrier feedthrough level.
5. Repeat steps 3 and 4 until you have reached the lowest possible carrier feedthrough level.
6. On the spectrum analyzer, return the resolution bandwidth to its previous setting.
7. Turn on waveform averaging.
8. Create a marker and place it on the peak of one of the two tones.
9. Create a delta marker and place it on the peak of the adjacent intermodulation product, which should be
spaced 10 MHz from the marked tone.
10. Measure the power difference between the tone and its distortion product.
You should now see a display that is similar to the one shown in Figure 9-4 on page 185 . Your optimized
two-tone signal can now be used to measure the IMD products generated by a device-under-test.
Note that carrier feedthrough changes with time and temperature. Therefore, you will need to periodically
readjust your I and Q offsets to keep your signal optimized.