Interference Evaluation of Overhead Medium-Voltage Broadband Power Line Systems

We analyze the radio interference from a broadband power line (BPL) system operating between 2 MHz and several tens of megahertz. The overhead medium-voltage power line is modeled as a three-phase set of parallel wires above a lossy earth. A near-exact solution, based on previous approaches for infinitely long lines, is presented for the fields from arbitrarily long lines. A closed-form approximation is then derived for the far (radiation) field using the saddle-point method. Emissions are computed by considering a BPL section of specified length between repeaters, and the maximum allowable excitation voltage versus frequency is computed by assuming compliance with Federal Communications Commission (FCC) field strength limits. These calibration results are used to study the interference to terrestrial, airborne, and ionospheric services. We show, based on our power-line model, that 1) terrestrial interference can be significant under FCC compliance; 2) interference into airborne receivers is potentially significant, and therefore, current rules prohibiting BPL use at selected frequencies in the 2-50 MHz band and at 75 MHz are appropriate; and 3) there is no threat from BPL deployments to high frequency and very high frequency ionospheric channels.