A circuit, system and method for measuring the optimal frequency of transmission and reception for achieving the best possible signal-to-noise ratio (SNR) in low impedance receive systems are provided. In one embodiment, the circuit includes: (1) an antenna that transmits and receives radio-frequency (RF) signals, (2) a receive circuit that is connected to the antenna during a receive mode and a calibration mode, wherein the receive circuit includes an amplifier having a low input impedance, and (3) an impedance switching circuit that places the amplifier in a high input impedance state during the calibration mode.