Keysight E8357D/67D & E8663D PSG User’s Guide 257
Multitone Waveform Generator
Creating, Viewing, and Optimizing Multitone 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 can only be observed with even–numbered
multitone waveforms.
This procedure builds upon the previous procedure.
1.
On the spectrum analyzer, set the resolution bandwidth for a sweep rate
of about
100 to 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 end 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
Your optimized multitone 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 the signal
optimized.
