To detect tool passage, the external antenna (or receiver itself if
using the internal antenna) should be placed parallel with the
pipeline and on top of the pipeline location waiting for the tool
to
pass. The receiver gain should be set as high as possible without
detecting interference or noise. When the tool passes underneath
the antenna, the operator should be able to see the transmitter
signal rise in strength on the receiver. The 22Hz light and any
appropriate code lights will turn on (to match either a standard,
continuous, or coded transmitter), and the buzzer will sound. As
the transmitter continues on down the pipeline the signal strength
will decrease until the transmitter is out of range. When the signal
is at its peak is when the transmitter is directly below the antenna.
When working near noise generated by neighboring electrical
lines, large electrical apparatus, or erratic movements of the
antenna, the technician should recognize that these signals can
trigger the 22 Hz detect light and buzzer, as well as the A, B and C
code lights of the receiver. If the receiver seems to have picked
up a stray signal then simply stop and steady the receiver. Check
to see if there is the distinctive solid tone or beat of the
transmitter. If no solid tone or pulsing beat is detected then most
likely noise triggered the receiver and the operator should
continue the search.
When walking with the receiver to locate a transmitter (such as to
locate a stuck pig), the external antenna is least likely to pick up
noise when
gently
suspending the antenna by holding the cable,
allowing the antenna to point to the ground. As the technician
approaches the transmitter with the antenna in a vertical position
over the line, the signal level indicated by both the meter and
lights will increase until the antenna is directly over the
