
Section I
General
Introduction
The all purpose MAC-51Bx Magnetic and Dual-Frequency Pipe and Cable Locator is the only underground locator that
combines magnetic locating (for iron and steel objects) with dual-frequency cable/line tracing into one compact system.
The system consists of two major units: a dual-frequency (LF and HF) transmitter and a three-mode receiver (MAG, LO
and HI). The transmitter operates up to 60 hours on eight alkaline C-cell batteries; the receiver up to 120 hours on two
9-volt lithium batteries.
Figure 1-1. MAC-51Bx Magnetic and Dual-Frequency Pipe and Cable Locator
Magnetic (MAG) Locating Mode
The receiver is the only unit for operation in the Magnetic mode. Set the Mode switch to MAG, adjust the Gain control,
and you have the best magnetic locator available. Operation in the Magnetic mode is explained in Sections II and III.
Switching between LO, HI and MAG modes while tracing a cable, is a unique method for unscrambling ground clutter.
Gas and water pipes in the immediate vicinity of the target with a HF trace signal being applied may emit parasitic
signals that can distort the cable locating null. In the magnetic mode, cast-iron water pipes and gas lines can be identi-
fied quickly and even classified as to their type by the conventional spacing of joints, which provide the strongest
signals.
Cable/Line Tracing (HI/LO) Locating Modes
The MAC-51Bx transmitter simultaneously transmits 571 Hz (LF) and 82.5 kHz (HF) signals. When applied to any
continuous metal conductor, the HF trace signal jumps gaskets between pipe sections and small breaks in the line. The
LF trace signal does not bleed onto adjacent or crossing lines, and will stop at a complete break in the conductor. With
the receiver you can select and compare received audio signals from both frequencies without having to return to the
transmitter.
Setting the receiver’s Mode switch to LO allows you to trace the cable, locate a complete break (where the signal disap-
pears), and then continue tracing beyond the fault by switching to the HI mode. The approximate depth of an
underground cable can be determined using the 45° null-point triangulation method. Operation of the MAC-51Bx in the
LO and HI modes is explained in Sections IV and V.
Standard Accessories
Basic accessories supplied with the MAC-51Bx include a headphone jack, spare batteries holders and a conductive
cable assembly with ground stake. An inductive signal clamp, mini transmitter and headphones are available as options.
Schonstedt Instrument Company
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