High frequencies can energize the parts of the utility system
that typically are not energized by lower frequencies and
would otherwise be unlocatable: stubs, dead-ends, and poorly
grounded laterals. This frequency range can also help you
locate through high resistant rubber insulating pipe joints
or broken tracer wire because it can penetrate the gap and
still impose signal on the further side of the conductor.
They also induce well.
The drawback to this currency range is this range bleeds
heavily into the ground surrounding the conductor, which significantly
reduces it's range. Higher frequency signals also couple more
readily onto nearby conductors. As a general rule using higher
frequencies in congested areas increases signal distortion
causing greater confusion. This of course could result in
incorrectly marking the target utility. Care should always
be taken to minimize distortion.
Very High (262 kHz)
Frequencies in this range are most often used as a last resort
on highly resistive circuits that can't be located with a
lower frequency. These frequencies penetrate the soil easily,
energizing all nearby conductors. They are very good inductively
but because they energize almosr everything they can make
the locating envirinment confusing. Very high frequencies
also bleed heavily to ground, which significantly limits the
distance they can travel.