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Signal Interference
Before drilling (preferably before bidding on a project) the interference potential at your site(s) should be
evaluated. Interference can reduce the transmitter’s range or cause variable readings and possibly result
in job slowdowns. Interference comes from two different types of sources: active and passive.
Active interference is also known as electrical interference or noise and can have varying effects upon
the DigiTrak locating equipment. Most electrical devices emit signals. Because DCI receivers have two
types of antennas in them (depth and roll/pitch), it is possible to have interference that affects one or both
signals. Some examples of active interference are traffic signal loops, buried dog fences, cathodic pro-
tection, radio communications, microwave towers, cable TV, fiber-trace lines, utility data transmissions,
security systems, power lines, and phone lines.
Passive interference sources (listed below) can reduce the amount of signal received or reradiate the
transmitter’s signal. This can cause erroneous depth readings or, in extreme cases, no signal, i.e., “1999”
in the bottom window. In addition, the FNLP and RNLP (discussed in the Locating Section) may be
affected. Some examples of passive interference are:
¾ Metal (pipes, rebar, trench plate, chain-link fence, engine blocks, etc.) – Metal acts as an antenna
and can therefore draw the receiver to erroneous locations.
¾ Saltwater – Saltwater affects conductivity and can contribute to signal degradation. Before drilling in
saltwater or brackish water, conduct a range test in the salt or brackish water to determine the
amount of signal loss (see “Transmitter Salt Water Range Test” in the Operational Tests Section).
Depth error will be increased and roll/pitch range will be reduced. A 2-point calibration can help
reduce the error (see “2-Point Calibration Procedure” in the Receiver Section).
¾ Conductive earth – Drilling through formations with high metal ore content can degrade the trans-
mitter’s signal and cause depth errors and reduced roll/pitch range. Again, a 2-point calibration can
be used to reduce the depth error (see “2-Point Calibration Procedure” in the Receiver Section).
To install your product accurately and safely, the location of every below-ground structure proximal to the
intended borepath should be confirmed by potholing. This task is the first step in familiarizing yourself
with the interference potentials near the intended borepath. The next step is to conduct an electrical
interference/background noise check, as described below.
Electrical Interference/Background Noise Check
An electrical interference check will familiarize you with your site conditions and help determine potential
locations along the borepath where the transmitter’s signal may encounter interference. Things that can
cause interference include the following: traffic signal loops, cable TV, saltwater, microwave towers, utility
data transmissions, power lines, fiber-trace lines, security systems, invisible (buried) dog fences, large
metal objects, rebar, and cathodic protection.
DigiTrak
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Mark III Operator’s Manual 35