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Патент USA US2132044

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‘Oct. 4, 1938.‘
_ 2,132,044
Filed April 13, 1935
2 Sheets-Sheet l
Oct. 4, 1938.
Filed April 15, 1955
2 Sheets-Sheet 2
()1 O
,0 g a
Patented Oct. 4, 1938
Horace E. Overacker, Palo Alto, Calif., assignor
of one-half to Harry N. Kalb, San Francisco,
Application April 13, 1935, Serial No. 16,180
8 Claims. (Cl. 178-44)
My invention relates to the elimination of power
line noise in radio broadcast receivers, and more
particularly, to a means and method which can
be applied to open wire lines to attenuate a de?
5 nite range of frequencies traveling thereon.
Among the objects of my invention are: To
isolate selected portions of open wire line service
areas in order to prevent radio interference from
reaching those portions; ‘to provide an attenua
10 tion system for open wire lines to prevent travel
'of radio interference thereon; to provide a means
and method for increasing the attenuation of
undesirable frequencies on open wire lines carry
ing relatively low frequencies; and to provide a
15 means and method for reducing power line inter
ference in radio reception.
My invention possesses numerous other objects
and features of advantage, some of which, to
gether with the foregoing, will be set forth in the
20 following description of speci?c apparatus em
bodying and utilizing my novel method. It is
therefore to be understood that my method is
applicable to other apparatus, and that I do not
limit myself, in any way, to the apparatus of the
25 present application, as I may adopt various
other apparatus embodiments, utilizing the
method, within the scope of the appended claims.
Referring to the drawings:
Figure 1 is a diagrammatic view of a three
30 wire power line having a branch service area sup
plied thereby, the branch line being provided with
attenuation devices.
Figure 2 is a similar diagram showing how a
certain section of a power line may be isolated
from the effect of traveling radio frequencies by
the use of attenuation coils.
Figure 3 is a view in elevation showing one
means of attaching attenuation coils to a power
Figure 4 is a perspective view of attenuation
coils inserted in a three-wire transmission line.
Figure 5 is‘ a diagram showing the per cent
e?iciency of two attenuation stages on noise elimi
nation within the broadcast band.
Figure 6 is a sectional view showing how a
capacity member may be attached to the coil to
increase distributed capacity and capacity to core.
Noise heard in radio receivers comes from vari
ous sources, the most important of which, is the
power line.
Power line noise has been a source
of receiving set interference since the beginning
of radio broadcasting. In many cases, interfer
ence originating in and being radiated from power
lines is so strong that radio receivers cannot be
55 used at all and other power lines have su?icient
local noise to prevent distant reception though
local reception may be good due to the high power
of nearby broadcasting stations. This interfer
ence problem is one of the most troublesome the
power companies have to contend with because 5
people living in localities with strong interference
very justly believe they have a right to average
radio reception.
As yet, however, satisfactory
ways of preventing such power noise have not
been available.
The usual procedure is for power line inspectors
to follow up individual complaints and then
remedy a speci?c nearby noise source. As the
remedy is individualistic, other complaints follow.
The service thus becomes endless and expensive,
and oftentimes the only solution offered is to
recommend changes in the installation of the re
The‘only satisfactory solution of the problem is
one which will apply towards the removal of all
interference from the power lines so that the
remedy can be applied directly to the power trans
mission lines in such a manner that all of the
receiving sets adjacent thereto will be protected
from such interference. All power companies 2,
now fully recognize the problem as above out
lined and many do all they can to prevent radio
noises on their lines. The technique, however, is
largely empirical and not consistently reliable.
Up to ten years ago, power transmission lines
were built with no regard for possible radio noise
or interference. As progress has been made in
the understanding of the various causes of noise,
many of the old lines have been altered with par
tial success. Even the new lines, however, still 3
present several sources of radio interference which
the power companies have been unable to elimi
nate. In the meantime, however, much can be
done to the transmission lines to prevent these
noises, even though generated, from reaching
groups of radio set users and it is with this phase
of the problem that the present invention is con
Noises heard in radio receivers are caused by
electrical disturbances and sparking originating 4,
in insulators, transformers, and hardware asso
ciated with power lines, and from corona on con
ductors and around insulators. Both the corona
and the spark discharges which take place in the
various portions of the power system have the _,
negative resistance characteristic of all electrical
arcs and set up radio frequency oscillations which
cause high frequency currents to flow along the
power line. Fortunately, these currents do not
@1156 radiation to any great distance, or power 55
inserted in each conductor of the line on the same
of interference than it is.
In Figure 1, service area I is supplied directly’
The radio frequency currents and voltages set
up inductive and electrical ?elds which affect re
from the line, whereas, in Figure 2, service area 2
ceiving antennas located within a few hundred
feet of the power lines. ‘While the interferences ’
has the main transmission line 3 passing directly U!
therethrough and having attenuated sections on
thus extend .only a relatively short distance at
right angles to the lines, the noise travels along
thelines with little attenuation, a single source
of noise sometimes causing interference for twen
ty miles or more adjacent the conductor.
either side. In either case, noise originating
anywhere along line 3_is blocked off from the
service area, by the attenuation sections.
Furthermore, the modern distribution system
introduces high voltage lines into the heart of
thickly settled portions of metropolitan areas,
15 thus bringing the power noise originating at al
most any point along the main line directly into
inductive relationship with large numbers of re
ceiving antennas. If, therefore, the’ problem of
actually preventing the noise at all sources is de
20 ferred, at least, the noise can be prevented from
Figure 3 shows one preferred embodiment of 10
an inductance ‘suspension adapted for high volt
age transmission lines; and I prefer to utilize
.what is ‘known in the art as a deadend pole 5 for
the application of the attenuation coils A; and in
this instance, I prefer to utilize two separate coils
differing in their inherent capacity and tuned by
their distributed capacity and by the capacity to
the core to different frequencies. In Figure 3
only one conductor is shown and it is to. be un
derstood that a similar coil assembly is, to be ap
entering service areas.
plied to the remaining conductors supported by
Thus, insulators,’ transformers and other noise
producing components ofv a power line may be
the pole whether there be two, three or moreyas
the invention is applicable to systems of any
phase and. having any number of conductors,
On the dead end pole 5 is fastened a cross arm 25
6‘ having attached thereto on opposite sides an
insulator 9. The main line conductor H3 is dead
treated within the service areas, but this will not
25 stop interference. unless the insulators oriother
noisy components are treated along the'entire
line. It is, therefore, very desirable from an
economic standpoint to have ameans for prevent‘
ing noise on untreated parts of the line from
30 coming into the treated parts within ' de?nite
service areas.
’ended on each side of the arm in the hook ll of
the respective insulators 9-~9. I prefer to utilize
separate’eye-bolts 'l—-'! for holding the insulators 30
to eliminate shunt capacity.
Telephone,,telegraph,. and all other open. wire
lines designed to carry relatively low frequency
'I'wo'tuned attenuation coils are usedyand each
comprises an iron core l2 within the insulating
currents have the same di?iculti‘es, and my in
frame l3, the. ends of the core being within the
coil winding, the insulated frame being supported 35
by an inverted U strap l4 and having a heavy
35 vention, while described as applied; to power lines,
which are-the greatest offenders, is obviously ap
plicable to any open wire, line or other line where
on such interference exists.
Broadly, the present invention comprisesiplac
ing inductance coils in‘ series with allline wires
at regular intervals. along a short section of the
lines. If- these coils areplaced substantially less
than about one-fourth wavelength apart, they
have the eifectof reducing‘ the attenuationof the
45 line,.as in telephone practice. If; however, as in
the present invention, the coils- are located at a
distance onthe order of an odd number of one
quarter wavelength of the lowest frequency to be
attenuated, the. line attenuation for, that, and
50 higher frequencies, is greatly increased. By
properly. spacing the coils a very great increase
in attenuation is obtained over placing the same
three coils or a single large coil, atone point in
noise would be a much more widely spread source
- -
My invention also comprises the use‘ of two
tuned coils in series with each wire of a line, all‘
coils being placed. at the‘ same. pole. In this ‘case’
the two coils in series are tuned‘ to different fre
coil l5 preferably of the’same gauge wire as the
line wound around the core and spaced there‘
from'.‘ The strap I4, is ?rmly attached to the
main line conductor I 0 by clamps I‘! and one end
of the coil i5 is attached to the strap by a con
nection IS, the other end of the coil being con
nected to the similar end of the opposite coil by
a jumper 20 passing under the cross arm.
this case, the coil is left uncovered and exposed 45
to the elements.
I‘prefer to tune the coilsto a different band in
such a manner that thefrequency bands attenu
ated overlap, thus broadening, by the use of two
such’ coils the total band attenuated by the coils. 50
The tuning isv preferably accomplished by adjust
ing the inherent capacity of the coil to where it .
is resonant within the band. In order to accom
pli'sh this,.wire l5 for example, may be insulated
and bankwound, or crossed upon itself, but I ?nd 55
that a more convenient way to increase distrib
uted capacity and capacity to core, is to place
upon the core l2 an insulated metal piece 29'
quencies within’ the‘ frequency band itisdesired
passing through the coil and attach this piece to
to attenuate, thus securing a. wider band of at
tenuationv than can be‘secured by a slngle'tuned
clamp I9, as shown in Figure 6. In this way, 60
standard coils may be used either tuned or un~
tuned, simply by virtue of whether or not the
metal piece is connected to or disconnected from
My invention also comprises the isolation of
service areas as by blockingrthe main line wires
65 oneach‘ side of. the service areas’ with spaced in
ductances. to attenuate frequencies coming in
from either direction.
By attenuating a short'section of open wire line
with coils‘ spaced on the order of one-fourth
70 wavelength apart for the lowest frequency it is
desired to stop, a high attenuation. of noise can
be secured and Figures 1 and 2 show de?nite
, service'areas l and 2 isolated from a main trans
mission line 3 by attenuation coils 4 spaced more
75 than one-fourth wavelength‘ apart and preferably
the line.
In certain other installations it may be desira 65
bleto utilize a single coil per conductor per loca
tion either mounted as shown in Figure 3, or
mounted on top of the cross arm as shown in
another embodiment illustrated in Figurerll.
Here, the coil’is wound on the core as before and 70
covered with a weatherproof cover 2|, the coil
and core not being shown‘. The assembly, as
before, is supported on. the U bar 22 which is
mounted on a standard insulator and pin 24; for
example, by an appropriate clamp 25; The U 75‘
bar insulated from the core and connected at one
end to line H), preferably through the outlet of
the coil. The other end of the U bar has an insu
lating leg 26 upon which is mounted a surge gap
comprising gap arms 21 and 28, the lower'gap
arm being connected'to the‘ U bar and the upper
arm 21 being connected to the opposite emerging
lead 29 of the inductance coil, which lead then
drops to connect with the main conductor [0 on
10 the other side of- the pole. The gap between the
arms 21 and 28 is adjusted so that surges which
.-might cause trouble within the coil may pass
around the coil without damage thereto.
r In both of the installations, as above outlined,
15 or in others which will be readily apparent to
the inductance per mile of two wires, for example,
in the power line is about 4 m. h.
Hence, one sec
tion is equivalent to lengthening the power line
only half a mile, a very small percentage of the
length of most lines.
From the above data, it is evident that section
al attenuation can be successfully used to stop in
terference travel on high voltage power lines by
using one, two or more sections of attenuation as
required by the severity of the noise. However, 10
it should rarely be necessary to use more than
two sections, i. e., coils at more than three con
secutive positions. In this case, I prefer to make
the middle coils substantially twice the induct
those skilled in the art, the coils are preferably
ance of either end coils. Isolating a section of 15
power line from radio noise produced on other
placed on or close to the same cross arm. or pole
parts of the system by this method is exception
and inserted as connecting links in discontinu
ities of the conductors carried by the cross arm
ally inexpensive as the number of turns of wire
is small per coil and no high voltage condensers
are involved.
The effect of attenuating the line has been
computed, assuming the resistance of the coils to
be negligible, which is the case for air core coils.
It has been found that theattenuation of the line
25 with pure inductance does not continue to in
crease as the frequency is raised above the value
at which the coils become one-fourth wavelength
apart. Rather, the attenuation increases to a
maximum and then decreases at approximately
30 half a wavelength spacing to form a pass band.
The attenuation thus alternately increases and
1. In combination with a power line. having a
break therein, a loading coil comprising an iron
core, an inductance wound on said core and in
decreases and a series of pass bands occurs which
pass bands are very undesirable from the stand
sulated therefrom, a conductive hanger mechan
ically attached to said core but electrically in
sulated therefrom, and means for supporting
point of stopping interference.
said core and inductance in de?ned relation to
In order to eliminate the pass bands for the
purpose of stopping noise, the radio frequency
resistance of the coils is made high. A high
resistance to radio frequencies and a very low 60
cycle resistance is obtained in the same coil by
40 using an iron core.
This result is obtained be
cause the iron losses, principally eddy current
losses, increase very rapidly as the frequency is
increased. Experiments showed that a coil could
be made with a 60 cycle resistance of .1 ohm, and
yet have a resistance of over 1000 ohms at 1000
k. c. The term ‘.‘attenuation coil” as used here
in means, therefore, a coil having a relatively
low low frequency resistance and a relatively high
said break and by said hanger, said inductance 35
being electrically bridged across said break.
2. In combination with a power line having a
break therein, a loading coil comprising an iron
core, an inductance wound on said core and in
sulated therefrom, a conductive U-shaped hanger 40
the legs of which are mechanically connected to
opposite ends of said core and insulated there
from, and means for clamping said hanger to a
conductor of said line at one side of said break,
one end of said inductance being connected to
said hanger and the other end crossing the break
to close the break.
3. In combination with a power line having a
high frequency resistance.
break therein, a loading coil comprising an iron
Figure 5 was computed from actual ?eld
strength measurements made onpole No. 15 of a
3-wire, 60 cycle power line supplying an isolated
area. Two stages of attenuation were used, the
coils being applied to poles No. 6, 8 and 10, the
noise originating at pole No. 1. The per cent
ef?ciency of the attenuation coils over the broad
core, an inductance wound on said core and in
cast band was even greater than that shown by
the curve, as there was a small amount of noise
originating within the isolated area itself. The
00 coils were spaced two poles apart, in this case
approximately approaching one-quarter wave
length of. 600 meters, the lowest frequency it was
desired to attenuate.
It is possible in most cases to choose poles
65 closely approaching the proper spacing.
ever, it is to be understood that when pole spac
ings are not such that proper attenuation can be
had, the conductors may be opened between poles
by a strain insulator, and a coil such as shown in
70 Figure 3, for example, mounted on the conductor
in series therewith and bridging the discontinuity.
The attenuation coils do not materially affect
the transmission of 60 cycle power because the
total inductance of one section is less than 2 m. h.,
76 a section comprising two sets of spaced coils, and
The above described method of stopping noise
along a power line by means of attenuating coils
is superior to the actual application of band stop
?lters, for example, because of the fact that
shunt condensers are exceptionally expensive and
in themselves liable to create trouble in the line
I claim:
sulated therefrom, a metal piece disposed about
and insulated from said core within said induct
ance, a conductive hanger mechanically attached
to said core but electrically insulated there
from, means for supporting said core and induct 55
ance in de?ned relation to said break from said
power line by said hanger, said inductance being
electrically bridged across said break, and means
for electrically connecting said metal piece to said
4. In combination with a power line having a
break therein and a loading coil comprising an
iron core having an inductance insulated from
and Wound thereabout, said inductance being
electrically bridged across said break, a conduc 65
tive hanger mechanically attached to but elec
trically insulated from said core, said hanger be
ing positioned to support said coil from said pow
er line in de?ned relation to said break, a metal
piece positioned between and insulated from said
core and said coil, and means for connecting said
metal piece electrically to said hanger.
5. In combination with a multi-conductor pow
er line carrying commercial frequencies, means
for attenuating radio frequencies on said line 75
7 2,132,044
xhigherdthan aipredetermined minimum compris
'7.‘ Means for ' attenuating radio "frequencies on
ing an attenuation coil in series-with each con
ductor-at av'certain location?said coil-having are~
an open wire line,~comprising arplurality of iron
core attenuation coils .spaced:along said clineat
csistance in the order of 10.1 ohm‘and' an induct
ance in the order of 0.24'vmil1ihenry at 1000
‘a :distance of ‘the order of an -_odd number of
cycles; and a-resistance in'the orderof 1000‘ohms
and-van inductance in-the order'of>0.18 millihen
ry at ‘1000 kilocycles, and a similar attenuation
beattenuated, each of said coils havingavresist
coil'in series with: each conductor separated from .
said ?rst coil by a distance greater than-an odd
:number- of quarter wavelengths of the lowest:fre
vquency to be attenuated. ' '
'6. In combination with a multi-conductor pow
er line carrying commercial frequencies, :means
'for attenuating radio frequencies on said line
higher than a predetermined minimum ‘com
o prising iron core attenuation'coils in-series with
:each conductor atone; geographical location, and
:additional iron-core ‘attenuation coils in series
.20 with each conductor at another geographical‘lo
cation spaced fromthe ?rst by a distance'of'the
.orderof an odd number of quarter-wavelengths
of the lowestfrequency to be attenuatedreaoh of
said coils having a resistance'in the order'of 0.~1
.25 ohm andv an inductancein the order’ of 0.24 milli
henry at 1000 cycles, and a resistance in the
' order of 1000 ohms and an inductance :in _.the
order .of 0.18 millihenry vat-1000 kilocycles.
quarter-Wavelengths of the'lowest'frequency'to 3
'ance in the order of 0.1 ohm and an inductance in
the order of ‘30.24 millihenry at 1000cyc1es, andla
resistanceyin the order of 1000-ohms and anin
ductance in-the order of 0.18 v'millihenry‘at 1000 v10
8. Means forattenuatingradioirekquencies on
an open wire'line, comprising-a group of three
iron core attenuation coils spaced along ‘Said,
line at a distance of the order of an- oddnumber
of quarter-wavelengths of the lowest :frequency
to be attenuated, the central-coil of said group
having-twice'theinduotance of either of-the end
coilsin said'group, and each of said end coils
having a resistance of the order of 0.1 ohm-landagor
an inductance of the~order'of-0.24 millihenry at
1 kilocycle, and resistanceon ‘the order ‘of 1000
ohms andinductance onthe order of'0il'8 ‘milli
~henry at 1000Akilocycles.
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