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question about third order intermodulation product

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jayleung

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intermodulation order

Hi, I have a question about the third order intermodulation product (IP3).

I understand that for two single tone signals at f1 and f2, the IP3 appears at 2*f1-f2, and 2*f2-f1. But if those two signals are modulated, with frequency f1_Low~f1_High, and f2_Low~f2_High, what are the IP3 spectrum?

Do they appear at (2*f1_Low-f2_High)~(2*f1_High-f2_Low), and (2*f2_Low-f1_High)~(2*f2_High-f1_Low).

Thanks.
 

The case of IM3 which appears at 2f1-f2 and 2f2-f1 is valid ONLY for CW signals.

For digital modulated signals, the relation is much more complex and outside of doing a simple math.
 

    J

    jayleung

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You are true vfone but the idea is to guess the likely spectrum it can fall and not wrt to the amplitudes.
In case of CW signals the IMDs are single and equie amplitude.
In case of modulated signal the spectrum gets multiple signal overlaps and the IMD spectrum envelop is not constant, probably it may be triangle fashion.
 

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    jayleung

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