Bends and Junctions (HI and LO Mode)
A variation of the two-line, single-lobe identification problem just described, occurs when the line being traced has a
bend or junction. As the receiver is brought near a bend or junction, the tracing signal becomes difficult to interpret.
When this occurs, walk a 20-foot circle around the spot where the signal becomes confusing to detect the null that will
indicate the line’s new direction. However, to be certain that it is the new direction and not a junction, complete the
circle to check for a second null that will indicate if the line has a branch.
Figure 5-6. Identification of Bends and Junctions
Signal spreading (HI Mode)
Target lines that are poorly insulated from ground such as gas pipes, water pipes and anode strings may cause signal
spreading to occur over long distances from the transmitter, even when the tracing signal is being applied conductively.
This condition is prevalent when ground water is present. The signal also spreads to nearby lines and into the soil itself.
When this situation is encountered, the transmitter must be moved closer to the section of the line to be traced and the
signal must be applied conductively if possible.
Signal spreading can also occur even when lines are well insulated. The tracing signal can travel into buildings via the
ground or the shield of a line and transfer to the shields of other lines leaving the building. Signal spreading can be
minimized by placing the transmitter as far as possible from the building.
Magnetic (MAG) Mode Aids in Interpreting Ground Clutter
The MAC-51Bx has a unique feature designed to help you unscramble underground clutter. It is the option of switching
to the MAG mode for a different indication of what other category of targets are in the immediate vicinity. In this mode,
Schonstedt Instrument Company
5-4
NOTE
If the target is a continuous metal conductor,
such as a cable, you can eliminate most signal
spreading by conductively applying the tracing
signal and using the receiver in the LO Mode.