This paper describes the theory and chip measurements of a built-in test technique for RF receivers which uses simple RF amplitude detectors. The method has been used to measure the performance parameters of a 940 MHz RF receiver front-end with a mixer and LNA. The detector has small area overhead with low frequency output. The sampled output waveform is analyzed using an FFT, and the low frequency measurements are used to deduce the conversion gain and Third Order Intercept point (TOI, IIP3) of the receiver. A test chip was fabricated in a commercial 0.18um CMOS process. By using two detectors, both the system performance and specifications of discrete components have been accurately measured. Measurement results show accurate prediction of system and component specifications.