A Wireless Phasor Measurement Unit (Wireless PMU) includes a coil for magnetic field transduction measurement of phasor data in a transmission line having a widely variable current. The coil output is amplified by a two stage, high gain, selectable gain ratio amplifier that maintains a substantially constant order of magnitude in the amplifier output as the current varies. A digital low pass filter of a third order Butterworth configuration substantially reduces deleterious anomalies appearing in the amplifier output. Shielding is provided to further reduce anomalies. Phasor data is calculated by a processor, and is at least as accurate as phasor data from a PMU using transformers to measure the same electrical characteristic.