Dec 302017
 
How to locate and eliminate noise and interference comming from power company utility poles and equipment--RFI, TVI, line noise, etc.
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How to locate and eliminate noise and interference comming from power company utility poles and equipment–RFI, TVI, line noise, etc.
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POWER LINE INTERFERENCE

by J. D. Delancy, K1ZAT/3


Radio interference can result from numerous sources.
Almost every conceivable home appliance can cause
interference. Power lines delivering power to residential
and commercial users are another major source of
interference. This article will be limited to radio
interference: the sources, and means of locating them
when caused by a power utility distribution systems.


To understand sources of power line noise, it is
necessary to know power line construction. Generally,
power line construction consists of wood poles,
conductors, insulators, transformers, guy wires, cross
arms, and other ancillary hardware. It is important to
realize the power line acts as a tuned circuit with a
very complex antenna array. The distance between poles
and number of lines, amount of transformers, taps on the
line, hardware attached, and so on make up the tuned
circuit. Because of this, the line impedance is
different at various locations. The impedance change
causes standing waves and makes it extremely difficult to
discern exactly the source of noise. To further
complicate locating the noise, generally there are many
wires on the same structure. The amount of noise on the
wires depends on coupling to the noisy line. This noise
can transfer from wire to wire. Once again, standing
waves and impedance play a critical role adding to the
complexity of locating radio interference caused by power
lines.


It has been observed that noise frequencies above 30
megahertz do not travel great distances along power
lines. Nevertheless, noise can cover several miles,
appear to be from many sources, and yet be confined to
only one originating point. It is also true that several
sources of noise can be occurring on a single section of
line.All power lines have some degree of noise. All
noise generation originates from the 60 hertz source.
The radio signal to noise ratio is an important factor as
to how much the power line will cause interference.


There are several companies manufacturing interference
locating devices. Some of this equipment is quite
expensive. No one noise locating piece of equipment is
all inclusive for all problems. With this in mind,
equipment and test procedures will be described using
available equipment. The simplest of equipment is a



portable broadcast radio with a zero to one milliamp
meter with series resistance connected across the voice
coil of the receiver. Using the receiver as a measuring
device, and driving several miles on each side of the
interfering source will indicate some highs and lows in
noise level. These highs and lows can be the result of
standing waves. It is often a monumental task to
determine which high is the actual interference source.
Generally one location will be louder than the others.
If the problem is related to loose hardware, nuts, bolts,
cross arm braces, insulator pints, etc., a slight tap on
the pole with a sledge hammer should change the loudness
and sometimes the pitch of the noise. Case must be used
not to strike the pole too severely because this can
cause hardware changes to occur several spans away.Guy
wires may be shaken to provide vibrations to disturb the
noise generating elements.


As one gains experience in tapping poles to disturb
poles, several conclusions can be made. If the noise
changes or stops immediately, you can make the assumption
that that noise is on the pole you are striking. If there
is a slight time delay between striking the pole and
hearing a change in the noise or the noise stopping, or
starting, whichever the case may be, you may assume it
may be one, two, or three spans away. In fact, if you
hit the pole two severely you can cause a disturbance
many poles away and it can become quite confusing as to
where the noise problem actually exists. To the
uninitiated, beware of guy wires. They may be in contact
with the power lines or otherwise close enough to be a
shock hazard. If the decision is made to use the guy
wires to disturb the power lines, always look, then shake
the guy wire with an insulated pole or hook. When it has
been determined that the guy wire is free, safe, and
clear of any potential hazard it can then be disturbed.
If the noise does not change after disturbing the guy
wire and detection still makes the tester believe it
might be on the pole, observe the installation practices
used by the utility. All metallic parts must either be
well bonded or at least two inches apart. Maintain two
inch separation within the wood structure. Loose washers,
nuts, bolts, etc., are great noise generators. Improper
tie wires holding conductors to the insulators can be
detrimental. Jumpers used to connect one string of
insulators to another where slight mechanical load is
evident is a source of noise which occurs between the
ball and socket of the adjacent units.


The source of noise which is very difficult to detect,
and requires cooperation of the power company, is where
two pieces of hardware are connected physically but not
electrically. A case in point is where the Zinc plating
of hardware and the sulfur dioxide in air react forming


Zinc Sulfite. Zinc Sulfite becomes extremely hard and
non-conducting. Tightening hardware may or may not bond
the metallic pieces well enough to eliminate the noise.


In conclusion, the important thing to remember is that
noise is broad band in nature, is stronger in the lower
frequency range, and diminishes very rapidly in the
VHF/UHF region. Peaks and valleys can be found as you
tune through the frequency spectrum. Some care should be
utilized as to what frequency relative readings are
taken. The spark gap which causes radio interference may
disappear during a hard rain and re-appear during dry
weather. This phenomenon is related to the spark gap
which results from the close proximity of two potentials.
During dry weather the gap will arc, wet weather will
cause the gap to be shorted out and no arc will occur. A
power leak will occur but radio interference will not
exist.

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