Triplett Mitigator Loop Coil – 3232 - Manual (Page 8)

Some noise mitigating craftspersons may opt to use the CMSG (C-MESSAGE) [PMSG] (PSOPHOMETER)
filter instead of either the 20/F [1/F] or FLAT [NONE] filters when making a Loop Coil measurement. This
is understandable when one considers the effect of the CMSG [PMSG] filter. Essentially, the CMSG
[PMSG] filter is more sensitive to frequencies that can be easily heard by the customer (subscriber).
Consequently, when measurements are made with a CMSG [PMSG] filter, the measurement favors the
frequency components that are most audible to the customer. Since the customer complaint usually is
about noise on the line, this approach makes some sense.
However, because the CMSG [PMSG] filter sensitivity is dissimilar to the 20/F [1/F] filter sensitivity, the
test results may be difficult to interpret. What is meant by this statement? Well, it means that the true
strength of the magnetic field is not accurately measured when using the FLAT [NONE] or CMSG [PMSG]
filters. Only the 20/F [1/F] filter produces a true representation of the magnetic field strength. When the
FLAT [NONE] or CMSG [PMSG] filters are used, the user must understand that the measurements will
be “skewed” by the effects of the filters. Even so, viewing the Loop Coil’s output signal with various
filters engaged is meaningful to the experienced craftsperson.
SECTION 8: LOOP COIL TEST METHODS
A Loop Coil test is usually performed when harmonic noise has been found in the Circuit Noise and
Power Influence on a pair or group of pairs (cable). Since this type of noise is usually caused by a power
exposure, it is necessary to identify the location of this power exposure. The offending exposure may
parallel the entire length of the telephone cable or it may only parallel it for a few spans.
As explained in the MITIGATOR Application Notes, high Circuit Noise and Power Influence that contains
harmonic noise is most often the result of magnetic fields radiating from power lines that parallel phone
lines. Since a Loop Coil measures magnetic fields, it is appropriate to use such a coil to search for the
source of the noise.
The process typically starts at the customer site where spectral Circuit Noise and Power Influence tests
are performed on a pair. The measurements are typically CMSG (C-Message) [PMSG] (Psophometer)
weighted (filtered) so the harmonics most annoying to the customer are viewed on the MITIGATOR
screen. The ANALYSIS mode of the MITIGATOR can be used to make suggestions to the user as to the
possible causes of the harmonics. If the customer is experiencing problems related to excessive levels
of 60Hz [50Hz], a FLAT [NONE] spectral test will reveal the amount of 60Hz [50Hz] present. A HAR-
MONIC TABLE test will display the 60Hz [50Hz] level in volts.
After identifying the offending harmonics, the Loop Coil can be used to track down the exposure where
the harmonics are being induced onto the telephone cable, and further, to help identify the actual cause
of the fields radiating from the power line.
A common misconception by first time users of Loop Coils is that the coil will lead the user to the source
of the harmonics by simply finding the strongest magnetic field with the coil. Although this is a possibil-
ity, it is very unlikely that a harmonic source will actually be found by this method. To understand the
proper method of tracking a harmonic with a Loop Coil, it is first necessary to understand how harmon-
ics are created and propagated (sent) through the power system.
SECTION 9: HARMONIC SOURCES AND LOADS
There are numerous scenarios that will result in harmonic currents flowing in a power lead. Of these,
there are several which occur more frequently than others.
9.1: CUSTOMER LOADS AND MAGNETIC FIELDS
The MITIGATOR Applications Manual points out that harmonic currents in a power line can be the result
of various customer loads that pull current in surges, and that this type of equipment usually contains
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