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As the test name implies, you need two tones, that is two signal generators
and a combiner. Now, you need to be careful here. There can be various ways
to combine two signals. Resistive combiners can be the simplest thing, but
due to poor isolation, two signal generators sometimes "fight each other" to
generate IM distortion. Hybrid combiners usually offer 20dB or better isolation.
You will need to confirm the distortion level after combining.
Connect your spectrum anlyzer after the combiner, and confirm your test
signal's IM level is far below your UUT spec.
These days, some signal generators are capable of generating multitone signals
in a single instrument. Again, its DSP circuit has a certain limit, and I found
their two tone IMD is about -60 to -70dBc.
Your spectrum analyzer set up is important. Adjust attenuation, so that your
SA's mixer is not generating IM.
Regards,
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