System and method for locating underground utilities carrying passive signals
In a method of identifying a passive electromagnetic signal emitted from an underground utility, a portable above-ground antenna is disposed at a location at which the passive electromagnetic signal is expected. Measurement signals are received from the antenna corresponding to electromagnetic signals received by the antenna. The measurement signals are measured at a plurality of different frequency bands within a measurement frequency range expected to include a frequency of the passive electromagnetic signal, and at least one of the plurality of frequency bands is selected based on a predetermined criteria applied to the measurements.
1. A locator for identifying a passive electromagnetic signal emitted from an underground utility, said locator comprising:
a portable housing;
an antenna disposed within said housing;
a control circuit;
a frequency bandpass circuit disposed operatively between said antenna and said control circuit so that said bandpass circuit receives measurement signals from said antenna corresponding to electromagnetic signals received by said antenna and passes to said control circuit a first portion of said received measurement signals within a frequency pass band; and
a frequency filter circuit disposed operatively between said antenna and said control circuit so that said filter circuit receives said measurement signals from said antenna and passes a second portion of said received measurement signals within a frequency range,
wherein said control circuit sequentially sets said bandpass circuit to a plurality of different frequency pass bands within a measurement frequency range expected to include a frequency of said passive electromagnetic signal, receives said measurement signal first portion corresponding to each said frequency pass band set by said control circuit and selects at least one of said different frequency pass bands corresponding to said frequency of said passive electromagnetic signal based on a predetermined criteria applied to said corresponding measurement signal first portions; and
wherein said control circuit sequentially sets said filter circuit to a plurality of different frequency ranges so that, at each first frequency range of the plurality of frequency ranges, said measurement signal second portion excludes a harmonic frequency pass band defined by the bandpass circuit at one or more frequency pass bands to which the bandpass circuit is set when the filter circuit is set to the first frequency range.