7703 is a 2-channel 5KV impulse winding tester and able to measure inductance down to 0.5uH as well as magnify high-frequency harmonics to prevent shorts between the layers of windings. Mild corona occurring between coils would create harmonics with small amplitude and high frequency (>10MHz) which cannot be detected by a regular impulse winding tester that can only observe mild amplitude without actually identifying the fault. MICROTEST 7703 deploys “High-frequency harmonics analysis HARM “technique to magnify high-frequency harmonics then display them on screen then identify each mild discharge between layers and ensure the quality of each component coil.