Mixer / Amp IP3 Calculator

The third-order intercept point concept was developed in the 1960s as cable-TV amplifier cascades revealed the practical importance of intermodulation distortion. Long amplifier chains with moderately-strong signals produced distortion products that landed on top of adjacent channels — the IP3 metric quantified how much headroom each amp provided before such products corrupted the signal.

RF receiver designers adopted IP3 as a primary spec in the 1970s-80s as two-way radio and cellular systems grew dense. A receiver had to tolerate strong nearby transmitters (adjacent-channel and intermodulation interferers) without generating its own spurs in-band. Modern SDRs are often IP3-limited in dense RF environments rather than sensitivity-limited.

Modern GaN and GaAs pHEMT amplifiers routinely achieve IIP3 > +30 dBm with gain 15-20 dB — performance that would have been impossible with 1980s-era bipolar technology. This has enabled cellular receivers to coexist with 1+ W GSM/LTE emitters in the same handset without a hardware duplexer.

Enter the two-tone input power (each tone, in dBm), the amp gain, and the IM3 level (how many dBc below the fundamental tone the 3rd-order intermodulation product sits). The tool computes IIP3 = P_in + ΔIM3/2 (the classic two-tone extrapolation) and OIP3 = IIP3 + Gain.

SFDR = (2/3)·(IIP3 − MDS) — the dynamic range where intermodulation products stay below the noise floor. 80+ dB is excellent for SDRs; 90+ dB is audio-grade. For cascaded amp chains, use the cascade IIP3 formula; earlier stages dominate because subsequent gain amplifies their distortion. Everything runs client-side.