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 MIL-HDBK-1013/1A
3)
Ported Coaxial Cable Sensor (PCCS). The PCCS is an external
line sensor consisting of a coaxial cable with the outer conductor (or
sheath) open along the length of the cable. A pair of such cables, one for
transmission and the other for reception, and the associated transmitter,
receiver, and processor constitute the ported coax system. The cables are
buried a few inches below the ground surface. The receiving cable lies in
the electromagnetic field surrounding the transmitting line. An intruder
entering the field increases the coupling between transmitter and receiver,
producing a detectable change of received signal level. Detectable target
velocities range from 0.07 to 23 feet/second (f/s) (0.02 to 7 m/s). The PCCS
generates an electromagnetic corridor at the boundary of the area and detects
intruders in the corridor. Disturbances of the electromagnetic field by
intrusions exceeding predetermined thresholds cause an alarm with intrusions
pinpointed to a specific zone. An alarm zone can be set from 33 to 5,250
feet (10 to 1,600 m) but is typically 330 feet (100 m). The soil in which
the cables are buried can have a large effect on system performance. The
soil conductivity will vary greatly from a clay soil (high conductivity) to a
sandy soil (low conductivity). A clay soil will not allow as much energy to
reach the surface and produces a lower sensitivity than a sandy soil.
Different installation techniques are used depending on the soil type and
conductivity. A standard 12-inch-square (0.3-m-square) trench can be used
only in soils with an average conductivity of 40 MHOS per meter or less, and
with an average dielectric constant of 35 or less. Running water resulting
from heavy rainfall and wave action on standing puddles which cover or cross
the detection zone will increase false alarm rates for the system.
4)
Microwave Fence Sensor (MFS). There are a large number of
commercially developed microwave sensors currently available. One difficulty
with microwave sensors is that the terrain must be extremely flat, roughly
3/8 inch (?9 mm) in elevation/depression over a 10-foot (?3-m) span. Blowing
snow and dust can also cause false alarms. The MFS is employed as a bistatic
microwave intrusion detector. Its detection zone consists of a narrow region
between transmitter and receiver antennas. The received signal is the vector
sum of the direct transmitted structures and objects. Moving objects (e.g.,
humans and vehicles) produce changes in the net vector sum of the received
signal. Detection occurs when the resulting received signal crosses a
predetermined threshold. The transmitted signal is tone-modulated to
eliminate mutual interference when multiple MFS sensors are operated in close
proximity to one another. The primary detection mode is the beam-break mode
where the target passes directly between the MFS transmitter and receiver
antennas. A second and equally important mode is the multipath reflection
mode in which the reflected wave from an off-axis target destructively
interferes with the direct wave at the receiver. In addition, alarms are
produced when the transmitted signal or its modulation is disturbed, when the
equipment is jammed, or when the enclosure tamper switches are actuated.
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