This low frequency is most useful for line tracing and identification over long distances. It does not couple easily to unwanted lines. but
It is too low for induction, and it falls within the band of power frequency harmonic interference.
8 kHz
This medium frequency is the most useful general-purpose signal, high enough for induction, outside the power frequency interference band, and with limited coupling to wanted lines. but
It may not be high enough to impose a strong signal on small diameter line like telecom cables.
33 kHz
This higher frequency is easily applied by induction to most lines, so is very useful for initial search. It travels on small diameter lines. but
It couples more easily to unwanted lines and loses its strength over shorter distances than lower frequencies.
100+ kHz
This very high frequency range deals with the difficult cases – induction onto small diameter lines in dry sandy soil, and short lengths of cable. It is very easy to apply by induction but
It couples very easily to unwanted lines and does not travel far.
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