Characterization of 100-kHz noise in the lightning current derivative signals measured at the CN tower

Successful simultaneous measurements of the current derivative, the generated electromagnetic field, and the channel characteristics of CN Tower lightning strikes have been performed since 1991. A noise component in the lightning current derivative signals, oscillating around 100 kHz, has caused substantial limitations on the use of recorded lightning current data. The characterization and identification of noise has become necessary for its removal and possibly avoiding it altogether in future installations. This paper proves that this noise corrupting the current waveforms is the Loran-C signal. Loran-C is a radionavigation system using the frequency band of 90-110 kHz. Although it is known that lightning is the main source of noise in the reception of Loran-C, it is shown here that Loran-C signals are the source of a low-frequency noise corrupting the lightning current derivative measured at the CN Tower. This finding is a major contribution not only for the CN Tower lightning project but also for any other research related to the measurement of the lightning current at tall structures.