Passive Locating - Power & Radio; Passive Frequencies - Milwaukee M12 2580-20 Operator's Manual

6 Passive Locating - Power & Radio
6. Passive Locating - Power & Radio

6.1 Passive Frequencies

Passive locating refers to the process of detecting signals that "naturally" occur on pipes
and cables. These tend to fall into two categories, radio signals, and power signals.
Sources of passive locate signals
Power signals are 50/60Hz signals created by power transmission cables. When electrical
power is distributed throughout the network, some of the power finds its way back to the
power station via the ground. These stray currents can jump onto pipes and cables and
also create power signals. Note that there has to be electrical current flowing to create a
detectable signal. For instance, a live cable that is not in use may not radiate a detectable
signal. Also, a very well balanced cable, i.e., the same amount of current flowing in live and
neutral, will cancel out and may not create a signal. In practice, this is unusual as there are
usually enough imbalances in the cable to create a good detectable signal.
Radio signals are created by low-frequency radio transmitters that are used for broadcasting
and communications. When the signals cross a long conductor such as a pipe or cable, the
signals are re-radiated. It is these re-radiated signals that can be detected by the RF mode.
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