Here is my partial specification for the conducted signals side of a
sweep. It will only be on interest to the more technically hard core
of the TSCM profession,.
I know that it is painfully detailed, but it provides a detailed
measure of what is actually being done on a sweep instead of a
seat-of-the-pants type of approach.
-jma
Conducted Signals Analysis
The TSCM survey will include a detailed written inventory of all
conductive elements present in, entering, leaving, or passing through
the area being inspected. This inventory will include, but not be
limited to all telephone wiring, all data or network wiring, all
power or lighting circuits, all environmental controls (heating, air
conditioning, etc), all security or alarm circuits, all duct work and
structural elements, and any other path capable of electrically
conducting an audio, data, or RF signal out of the areas being evaluated.
All conductors or conductive paths will be evaluated for the presence
of hostile of suspect signals from 300 Hz to at least 200 MHz by
directly coupling test instruments to the conductors under test
through the use of an impedance matching circuit and filter. The
instrument(s) being used to examine these circuits shall have a
dynamic range of at least 85 dB, and shall include a preamplifier to
overcome all noise present in the instrument or signal attenuation
caused by the coupling or filtering process. Examination of
frequencies above 200 MHz will be at the discretion of the TSCM specialist.
All conductors or conductive paths will be evaluated for any audio
signals either masked or unmasked. Evaluation of conductors shall
include the application of a biasing voltage to activate microphones
or related devices.
Bias voltage shall start as low as practical, and shall be slowly
increased to a level not to exceed that which could harm the
equipment connected to the line, or suspected to be connected to the
line. Equipment being inspected shall then be removed from the line
and the line itself inspected, but with signal levels below the
threshold of insulation breakdown. Biasing voltages and signals shall
start at one tenth or less the level expected to bias an active or
dormant device.
Insulation breakdown tests shall be performed at levels which start
one tenth the rating of the line, and which are then slowly increased
to a level that ensures a measurable breakdown of insulation without
causing actual damage to the line. The line under test shall be
discharged into a resistive load after the completion of the
insulation breakdown test.
Evaluation of signals will also include, but not be limited to
amplification of the audio band from 300 Hz to 3 kHz by at least 120
dB after the removal of any masking signals or elements.
All conductors shall be documented with a time versus capacitance
instrument such as a time domain reflectometer (TDR) or oscilloscope.
Basic measurement shall involve the introduction on a stimulus pulse
via an impedance matching network into the line under test.
Cable segments of less than 200 linear feet of line a test or
stimulus pulse shall be used with a pulse rise time not to exceed 500
picoseconds. Lines under test which exceed 200 linear feet may use a
pulse width suitable to allow impedance changes along the cable
length to be measured, evaluated, and documented. When at all
possible the cable under test should be disconnected and examined in
segments that do not exceed 150 linear feet of cable. The cable under
test shall be tested from both ends, both in a wet line, and dry line
environments.
Frequency domain reflectometery with a swept carrier shall be used at
the discretion of the TSCM specialist, and shall only be used in
addition to time domain reflectometry and not as a replacement of TDR
analysis. FDR of power lines shall include frequency coverage of at
least 200 MHz, of telephone lines to at least 600 MHz, and of premise
distribution cable to at least 1 GHz. All other FDR measurement on
other conductors shall be to at least 100 MHz.
A comb generator shall be used to insert a series of carriers into
the line under test, and harmonics of these carriers shall be
monitored along the entire length of the cable under test.
Transmitted carriers shall not exceed 100 mW at any frequency, and a
swept signal may be used to modulate the signals at the discretion of
the TSCM specialist. During the illumination of the line during this
test a broadband antenna or probe shall be passed along the entire
length of the line to check for harmonics radiating from the line
which could indicate a non-linear device or component. Every effort
shall be made to place the antenna into physical contact with the
line under test at least every 48 inches in the horizontal plane and
3 inches on the vertical plane, or along the entire length of the
cable if suitable access can be safely obtained.
Each conductor shall be separately inventoried and evaluated as a
standalone element, but also evaluated and inventoried against all
other conductors in the same cable, and all other conductors,
conductive, or quasi conductive elements reasonably located in the
same or nearby areas.
For the purpose of this specification Earth, Station, Signal, and
electrical grounds (Red and Black) shall all be considered separate
conductors and signals paths, and shall be evaluated on an individual
basis. In cases where the ground can not be disconnected for safety
reasons the conductor shall be monitored and evaluated through the
use of multiple clamp-on inductive probes at each splice or junction
points, or where the conductor enters, leaves, or passes through the
area being inspected.
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James M. Atkinson Phone: (978) 546-3803
Granite Island Group Fax: (978) 546-9467
127 Eastern Avenue #291 Web:
http://www.tscm.com/
Gloucester, MA 01931-8008 E-mail: mailto:jm..._at_tscm.com
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Received on Sat Mar 02 2024 - 00:57:17 CST