Blind Search
The Blind Search locating technique is used if the operator is not aware if a buried utility exists. Two people are
needed for this technique. The Transmitter and Receiver are held 25 feet away from each other. Each opera-
tor walks at the same speed keeping a distance of 25 feet from each other. When the receiver gives an audio
response, a buried utility is present between the Receiver and Transmitter.
5
Selecting Trace Signal
The choice of 512 Hz, 8 kHz, 33kHz or 82 kHz Frequency is dependent on conditions of the locate.
It is recommended to begin by using the 512 Hz signal, and continue as long as you are confident in the results.
If the signal is very weak adjust the connection or grounding. If there is no improvement in signal, try 8 kHz.
Repeat adjustments of ground and connection point before switching to 33 kHz and then 82 kHz.
512 Hz
(lower frequency) signal is usually preferred to 8 kHz (mid-range frequency) and 82 kHz (high fre
-
quency) signal, because it is less susceptible to locating errors caused by nearby cables or pipes. The 512 Hz
locating range is also longer than the 82 kHz signal. The 512 Hz signal will not travel well through disconnected
shield bonds or insulated pipe bushing.
8 kHz and 33kHz
take the best of high and low frequency. This mid range frequency is not very susceptible to
bleed off or coupling, but it can jump impedance on the utility better than the 512 Hz. It is still best to use 512
Hz, but 8 kHz is one of the most common frequencies used to locate coaxial cable and telecom pairs.
82 kHz
(higher frequency) is sometimes better than 512 Hz (lower frequency) for locating sharp corners in
cables or pipes. The 82 kHz signal is also better for “jumping” disconnected shield bonds or grounds, or trac-
ing signal may indicate one of these characteristics. The locating range is quite short for the 82 kHz signal so
Transmitter must be repositioned more often during tracing operation. Also useful for applying a signal to the
Jameson Duct Hunter
™
.
