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The current methodology for EM tracking of PIGs, SmartBalls and Pipe divers looks for an increase in the average amplitude in a very narrowband filter. This provides an directly interpretable curve and is simple to implement however it is extremely susceptible to environmental noise. Because a constant 22Hz tone from the transmitter is indistinguishable from the constant 22Hz component of environmental noise (which can be modulated by unpredictable factors to rise and fall in about the same timeline as a PIG passage). Using a GPS-synchronised chirp (linearly increasing frequency with time over the burst period) or a FSK/QPSK encoded message would permit removal of constant environmental signals, and provide a signal that is much more unique and much less likely to be present in environmental noise.