Clarification on IM3 measurement of high-power amplifiers
I am measuring IM3 in the lab where I applied 2 tones of equal power into our Tx chain. When comparing Pout (total output power) vs IM3, I am unsure if it is against the total output power of the 2 tones
the power of one of the two tones (approx. 3dB minus the total power). In two tone measurements you have other products (F2-F1, 2*F-F2 (IM3), 2*F2-F1(IM3), F1+F2, etc.), that aren't present in a one tone test with a power equal to the total power of the two tones.
Thanks in advance.
Unless requested otherwise, when performing two-tone measurements, I explicitly state that input/output power is "per tone"; I also note the tone spacing and that the IM products are "relative to one of two equal tones X MHz apart". I typically only use total power in efficiency calculations.
Spectrum analyzers typically put their markers on the tones, not the imaginary point 3dB higher, when displaying IM data. Saves a lot of mental math and confusion.
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