Section IV
Cable and Line Tracing
Theory of Operation
In the Cable and Line Tracing (HI and LO) locating modes, you must use the receiver in combination with the dual-
frequency transmitter which is housed in the carrying case.
As illustrated in Figure 4-1, the transmitter is placed over and in line with any continuous metal conductor. Its two simul-
taneous output frequencies (HF and LF) produce alternating currents that are induced (HF) and conducted (LF), onto the
conductor as tracing signals. The transmitter emits a steady beeping sound to let you know that it is operating. You can
detect the two tracing signals by using the receiver’s HI or LO mode. The receiver emits a siren-like sound ion both
modes that decreases to a minimum pitch when the locator’s tip is directly over the target conductor, and peaks on each
side.
Figure 4-1. Transmitter and Receiver Placement
The tracing currents generate alternating circumferential fields around the conductor. These alternating fields induce two
signals into the receiver’s sensor. As the receiver is moved back and forth across the cable in a search pattern, the
pitch of the audio output from the receiver increases and decreases.
The heavy line in Figure 4-2 represents the increase and decrease in pitch of the audio signal as the receiver is moved
back and forth over a line or a cable excited by the transmitter. Moving from
A
to
D
causes the pitch to increase to a
maximum at
B
and decrease to a minimum directly over the target. At
C
the pitch again increases and then decreases
at
D
.
The MAC-51Bx can be used to trace any long conductive element such as a anode string or metalized warning tape as
well as cable and pipe.
Schonstedt Instrument Company
4-1
TRANSMITTER
RECEIVER