US1590428A - Wired radio broadcasting system - Google Patents

Description

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WIRED RADIO BROADCASTING SYSTEM Filed August 25. 1925 June 29 1926,

June 29 1926.

R. D. DUNCAN, JR

wIRsD RADIO BnoADcAsTING SYSTEI June 29 1926.

' v. 1,590,428 R. D. DUNCAN. JR wma RADIO BROADCASTING sYs'ml Filed August 25. 1925 s sheets-sheet s ull'l. IIIIIIIIIIIIIII.

i "La i @RC Mmm Patented June 29, 1926.'

UNITED STATES PATENT OFFICE.

ROBERT D. DUNCAN, JR., 0F EAST ORANGE, NEW JERSEY, ASSIGNOR TO 'WIRED RADIO, IN C., OF NEW YORK, N. Y., A CORPORATION OF DELAWARE.

WIRED RADIO BROADCASTING SYSTEM.

Application led August 25, 1925.

My invention relates broadly to carrier wave broadcasting systems and more particularly to a system of wired radio broadcasting wherein the distribution of the high frequency signaling energy throughout the wired radio broadcasting system may be readily determined from the broadcasting station and the high frequency energy supplied to the line wire system accordingly.

One of the objects of my invention is to provide a wired radio system for the broadcasting of high frequency electrical energy over electric power lines in which the manner of distribution of the high frequency energy at various parts of the power line system may be observed at all times by the operator at the broadcasting station for regulating the amplitude of the high frequency currents in different parts of the system.

Another object of my invention is to provide a testing system for a wired radio broadcasting installation to inform the operator at the broadcasting station of the performance of the wired radio receivers distributed at various points over the line wire system.

Still another object of my invention is to provide a system for the broadcasting of entertainment and the likeI over electric power lines where a portion of the high frequency energy at various points in the power distribution lines is utilized for actuating measuring devices at the broadcasting station for indicatingr the energy level condition of the wired radio broadcasting system over substantially the entire area thereof.

A further object of my invention is to provide a polyphase system for transmitting high frequency carrier currents over electric power lines and measuring the i11- tensity of the high frequency energy on the various phases at different points throughont the line wire system.

A still further 'object of my invention is to provide means for determining the electrical center of high frequency carrier currents over a power distribution system in a city or other community for adjusting the intensity of the high frequency signaling current fed to the various parts of the system for securing desired signal level throughoutthe power distribution syst-em.

My invention will be more clearly understood by reference to the following specili- Serial No. 52,285.

cation and the accompanying drawings in which:

Figure 1 is a diagrammatic view of an electric power distribution system showing feeders leading out from a sub-station or power house for conducting the power and high frequency carrier currents thereover; Fig. 2 illustrates a plurality of channels leading out from a sub-station or power house over which the high frequency signaling currents are conducted through high frequency power control equipment for measuring the high frequency current per phase which is conducted over the feeders; Fig. 3 illustrates one arrangement of measuring apparatus which I may employ for determining the signa-l level at various points `-in the power distribution system; and Fig. 4 shows a two channel communication system and measuring apparatus in connection therewith for determining the signal level along the feeder.

In a wired radio broadcasting system wherein high frequency carrier currents, either single or polyphase, are superimposed upon an electric power transmission system, either single or polyphase, it has been determined from experiment that the high frequency power per feeder and consequently the high frequency power supplied to the system, which yields a uniformly satisfactory signal level at the various Wired radio receivers connected to the lines during the daylight hours may yield a much lower signal level during the dark hours or at night. Experiment further indicates that this decrease in signal level occurs almost simultaneously with the increase in normal electric lighting load taking place during the dark hours and is a minimum substantially at the same time the peak or maximum power load occurs.

This decrease in received strength with a constant high frequency power input to the system arises mainly from two causes; (1) the power absorbing effect of the many electric lights that are switched on, and which in the homes of the consumer are connected in parallel with the wired radio receiver, and (2) a change, and, under some conditions of secondary loading, a material increase in the high frequency input impedance of the various distribution transformers scattered along the lines, the function of which is to step down the relatively high primary power voltage to a lower value, usually 220 or 110. The effect of (1) is to by-pass a portion of the available high frequency current from the wired radio receivers; the effect of (2) is to decrease the total high frequency current available for the plurality of receivers connecting with the secondary of the individual transformers.

It is to be noted that, because of the high frequency characteristics of the line wire system, a wired radio transmitter operates substantially at constant potential, constant current output and not at constant potential, variable current, as is the case with low frequency electric power generating apparatus.

The decrease in high frequency power along the lines may be overcome by increasing the power supplied to the distribution system at the power house or sub-station. The practical difficulty here arises, however, of determining the exact amount of high frequency power required, as the same will vary for different feeders, and for different phases of the same feeder; the demand may also occur at different times for different feeders. By my present invention I provide a method of obtaining a direct measurement of the required increase or decrease in the high frequency power per feeder or per phase per feeder to suit the load condition of that feeder, or phase, and to place convenient to the operator in charge of the hi h frequency transmitter, visual and audible means for 'ascertaining the average signal level per feeder.

There are many special problems presented in a wired radio broadcasting system and among these the following characteristics should be noted:

(l) The feeders extending from a substation or power house may vary greatly in len th and at the same time carry equal loads. For example, a short feeder may supply an apartment house district of city where the density of loadin is high; a long feeder may supply a su urban district where the load density is much less. A wired radio receiver located at the extreme end of the short, heavily loaded feeder may yield a much lower signal level than a receiver located at the same physical distance from the sub-station but on a long feeder' with low load density.

(2) Large transformers, such as are employed where the load density is high (for example, larve apartment houses), usually have better thigh frequency characteristics than smaller units.

(3) There is a limiting ratio of signal level to line noise level which restricts the degree of amplification permissible at the receiver. Economic factors also aid in imposing this restriction.

(4) From both an economical and operating standpoint, a standard type of receiving tuner and detector is generally required. This equipment is normally so designed, and the transmitting power input so adjusted that a uniformly satisfactory signal, sa for reception with telephone receivers, is olyitainable at all points on the system. For locations electrically close to the sub-station where there is a superabundance of high frequency energy, the receiver sensitivity at the time of installation is arbitrarily lowered and adjusted to the proper value,

. For the purpose of more clearly understanding my invention a. typical alternating current. distribution system can be considered wherein electric power is distributed from a sub-station at a voltage approximating 2500, and usually at three phase, employing a three wire system. The 2500 volt lines serve as feeders and extend out from the sub-station to various distances up to several miles depending upon the density of electrical loading. The feeders contain distribution transformers connected usually to each of the phases throughout the length of the feeder, the transformers reducing the voltage to 220 or 110, as the case may be, and the latter carried over secondary leads, whose length rarely ever exceed several hundred feet, into the home of the consumer. The wired radio receiver is connected through the usual plug and socket directly to the 110 or 220 volt leads in the manner of an electric light or other household appliances.

There are normally a number of sub-stations supplying power to a given community, the sub-stations receiving their power in turn from one or more power houses. From eX- periment it has been determined that best results are obtained if there is a wired radio transmitter for each sub-station, which is preferably in the form of a vacuum tube power amplifier arrangement receiving its high frequency control energy from a master source which also supplies the transmitters at the other sub-stations. Furthermore, it has been determined that still better results are obtained if the high frequency transmitter is arranged to supply varying amounts of power to different feeders at the line or outgoing side of said feeders, with the switchboard power control, voltage and current metering apparatus serving as a choking means which prevents short circuiting and consequent absorption of high frequency energy in the transformer secondaries or in the generators which are connected to the common switchboard bus bar system, to which are also connected the feeders.

Referring more particularly to Fig. l of the drawings, reference character l indicates a sub-station or power house containing suitable transforming or generating equipment. Extending from sub-station 1, is a three phase, three wire feeder system 2, a single phase feeder 3, and a two phase four wire feeder 4. I have represented the three phase and a two phase feeder system entering the same sub-station merely for the purpose of illustration, and itwill be understood that various types of feeder systems may be employed. Each of feeders 2, 3 and 4 contains throughout its length distribution transformers 5, which step down the feeder voltage to a suitable value and supply it over secondary conductors 6, to the electric power consuming equipment not shown, of the consumer. TheV wired radio receivers, not shown, are also connected to secondary conductors 6. The power rating of transformers 5, vary greatly, for example, from 0.5 to 50 kilowatt-s, and though only a few are shown in Fig. 1, the feeders may contain a large number. On polyphase feeders it is the practice to so distribute the transformers that 1the loading per phase is approximately e ua qAt some point along the feeders, indicated at 7 8, 9, there is installed measuring equipment shown in detail in Figs. 2, 3, 4 and indicated as enclosed by dotted lines A, B, and C which are shown connected with substation 1, by s ecial conductors 10.

In Fig. 2 tiree phase feeders 2, single phase feeder 3, and two phase feeder 4 are shown connecting throughl high frequency power control equipment 11, 12, 13, and through the high frequency power feeders 14, 15, 16 to a source of high frequency energy, either single or polyphase, not here shown, and through the low frequency power connections 17, 18, 19 to the power apparatus indicated at 20. Equipment 11, 12, 13 is shown to contain high frequency ammeters 21, 22, 23, measuring only the high frequency current per phase of feeders 2 and 4 and of single phase feeder 3, and some Aform of control apparatus for varying the high frequency power introduced per phase per feeder and here indicated by the numerals 24, 25, 26 and 27. The latter power controls may vary the coupling between the high frequency feeders 14, 15, 16, and the power feeders 2, 3, 4, or vary the tuning of the latter or effect an equivalent variation, so that the introduced high frequency power per phase per feeder is variable, measurable, and directly under the control of an operator.

The apparatus contained at A on power lines 2 1n Fig. 1 is more clearly shown in Fig. 2 and consists of inductances 28, 29, 30, connected, for example, in Y, to the three phase feeder 2 throu h protective-'tuning condensers 31. Inductively coupled to inductances 28, 29, 30, are secondary inductances 32, 33, 34, which are in shunt with variable capacities 35, 36, 37. No mutual coupling is assumed to exist between the individual inductances 28, 29, 30, and between 32, 33, 34. Connected across each of the capacities 35, 36, 37, is a circuit containing leading back to the sub-station. Condensers 59 serve as a means of by-passing the highfrequency current component from primaries 41, 42, 43. Wires 10 are shown to operate into audio frequency amplifiers 48, 49, 50, the output circuits of which contain ammeters 51, and telephone jack 52. The numeral 53 represents a pair of telephone receivers attached to plug 54, and which may be plugged in at the jacks 52 for observing the condition of the line at the point A along the line.

Apparatus contained at B on a single phase feeder 3 is essentially the same as one phase of feeder 2 at A and one secondary system. A coupling circuit 70-71 is connected across the line at 8 and secondary system 72 tuned by capacity 73. A detector 74 is provided which delivers rectified energy to audio frequency transformer 55. The audio frequency transformer 55 operates into special lines 10, which in turn operate into audio frequency amplifier 56 containing in its output circuit ammeter 57 and jack 58. In the case of two phase feeder 4 at C in Fig. 1, there would be two duplicate installations as at B in Fig. 2, givin rise to four special wires 10 running bac to the sub-station 1, as shown in Fig. 1.

From a consideration of Figs. 1 and 2, it will be observed that with modulated high frequency current flowing over feeders 2, 3, 4, and with the proper circuit adjustments at A, B, C, audio frequency currents will flow back to the sub-station or power house over special wires 10. With the apparatus shown at A, B, C, properly located on the feeders the operator in charge of the transmitters, by merely plugging phones 53, at jacks 52 0r 58, or by visual observation at ammeters 51 or 57, is able to obtain a direct indication of the signal level on the feeder at locations 7, 8, 9. I have provided a standard source of signals at jack 63 conveyed direct from the studio over lines 60 and amplified at 61. A meter 62 is provided which indicates the desired strength of signals while by plugging in telephones 53 at 63 the desired quality of the reproduced signals may be observed for comparison with the signals delivered over the other circuits.

Locations at 7, 8, 9, of apparatus A, B, C,

may be determined to meet a number of conditions. If the physical length of the feeder is short, and other factors permit, apparatus A, B, or C may be located at the extreme end of the feeder. On long feeders usually it would be uneconomical to locate this apparatus at the extreme end, as the cost of running the special wires 10 would be excessive. Local line conditions generally dominate in determinin the exact location at 7, 8, 9, but practice has shown that somewhere near the center of t-he electrical length of the feeder yields the best results. Such locations may then be thou ht of as the electrical center of the fee er. That is to say the apparatus is placed at such points along the feeders as will enable the operator back at the sub-station 1 to know accurately the average conditions existing along the feeders at points substantially beyond the sub-station. By locating the rectifying apparatus at substantially the electrical center, a direct current component is obtained which is proportioned to the amplitude of the high frequency current on opposite sides of the electrical center so that the mean condition of the distribution line may be directly observed.

In Fig. 3 I have illustrated an arrangement for determining the high frequency power level of the line 2 even when no modulation is occurring. The apparatus up to condensers 59 is the same as that shown within enclosure A in Fig. 2. Inductances 64 are high frequency choking coils which prevent the passage of high frequency currents over special lines 65, corresponding to lines 10 of Figs. 1 and 2 which run back to the sub-station, to direct current ammeters 66. It will be noted that with 11nmodulated high frequency current iowng out over feeders 2, 3, 4 and with the proper adjustment of the tuning apparatus at A of Fig. 3, due to the presence of the rectiiers 38, 39, 40, direct current, proportional in value to the root mean square value of the high frequency feeder current, will ow over lines 65 to the sub-station or power house and actuate ammeters 66, which correspond to ammeters 51 and 58 of Fig. 2. In a manner similar t-o that outlined under (1) and (2) preceding, the proper indications of these meters when not modulating is obtained for the required signal level at the wired radio receivers when modulating and the high frequency power input to the ditl'erent phases or feeders governed accordingly.

The apparatus shown in Fig. 4 is for a two channel service and comprises sets of measuring circuits connected to the three phase line 2. One set of circuits is similar to the circuits which connect to the line at 7 in Fig. 3. The other set of circuits is connected at 75 to inductances 76, 77 and 78 through tuning and stopping condensers 79. Tuned secondary circuits 80, 81 and. 82 are coupled to inductances 76, 77 and 78 and convey the received signaling energy to rectifiers 83, 84 and 85 by which a direct current is developed in the circuits which extend over lines 86 to the sub-station for connection to direct current ammeters. The sets of circuits are tuned to the different frequencies which are being employed for the transmission of separate programs on different channels so that the condition of the current in the feeders at different frequencies may be observed. The number of channels may be extended indefinitely. The apparatus of Figs. 1 and 2 is shown only for single channel communication.

When the location of 7, 8, 9, of appa ratus A, B, C, has been determined, there are a number of ways in which the system of my invention may be operated, two of which are described in the following:

The apparatus at A, B, C, is adjusted to give an indication at ammeters 51 and 57 with the proper adjustment of the wired radio receivers, connecting with lines 6; situated at both a greater feeder distance from the sub-station or power house. than the electrical center of the feeder, and between the sub-station and the electrical center, to yield the desired signal level for all conditions of feeder loading, that is, for day and night operation. Since the current flowing at ammeters 51 and 57 in Fig. 2 will be fluctuating in value, being proportional at any instant to the intensity of modulation or to the received audio frequency current, either the average value will have to be adopted as a standard of reference or the deflection maintained below a certain maximum. Knowing the required indications of ammeters 51 and 57, it remains for the operator, by virtue of adjustments 24, 25, 26, 27, to feed only the required amounts of high frequency power to the different feeders or to the different phases of the different feeders and at the required times.

Another method of operation of the system is to properly locate the position of the measuring apparatus at 7, 8 and 9, along the lines and then observe the signal level at telephone 53, when plugged into jacks 52, 58, and compared with a standard of signal level as supplied from the studio over lines 60 to audio frequency amplifier 61 through ammeter 62, to jack 63.

The two methods may be combined or variations of the two devised to properly determine the distribution of the high frequency carrier current over the line system. If the physical and load conditions of the feeders remain constant from day to day, it will be noted that there will be a direct relation between the low frequency load current supplied to the feeders and observed at the normal sub-station ammeters and the required high frequency current observed at ammeters 21, 22, 23. This relation once obtained by the methods described herein will enable the operator to maintain the required control over the high frequency power supplied per-phase or per feeder.

The method shown in Fig. 2 supplies audio frequency current to the sub-tation and hence there would be no current indication at ammeters 51 and 57 2 in absence of modulation at the transmitting source. It is sometimes advantageous to know the high frequency power level on the feeder without modulation and for this reason the circuit arrangements of Fig. 3 are provided. The apparatus A, B, C, shown in Figs. 2, 3, 4, may be suitably housed and mounted on the pole which supports the transmission line or in manhole adjacent the underground conduits in which the conductors are run.

It will be understood that instead of special apparatus at A, B, C, standard distribution transformers may be employed, with a wired radio receiver connected across its secondary leads, with the audio frequency energy conveyed back to the sub-station over special wires to the meter` circuit. I prefer however to employ the special air core circuits as illustrated herein. The broadcasting equipment has been represented as located at the sub-station or power house where the high frequency electrical currents may be impressed upon the power distribution line. It will be understood however that the broadcasting apparatus may be installed atan desired point in the. system and that the location of the studio with respect to the broad-casting apparatus may be selected to meet local convenience. The voice currents may be readily conducted from various points throughout the city by line wire telephone to modulate the broadcasting apparatus which in turn impresses the si aling currents upon the power distribution system.

While I have described my invention in certain particular embodiments, I desire that it be understood that modifications may be made and that I intend no limitations upon the invention other thanthose imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A wired radio broadcasting system comprising in combination, an electric power generating station, a pluralit of polyphase transmission lines exten ing from said generating station for conveying electric power from said station for distribution over a given area, a source of polyphase high frequency current,means for impressing sald quency current, for determining a measure of the amplitude of the high frequency current at said points, said means electricall connected with current indicating means a jacent aforementioned means for controllably impressing polyphase high frequency current on said polyphase transmission lines, said combination providing means for determining and controlling the distribution of the high frequency current over said polyphase transmission lines.

2. A wired radio broadcasting system comprising in combination a plurality of electric power sub-stations, a plurality of polyphase transmission lines extending from said sub-stations for conveying electric power therefrom for distribution over given areas, a plurality of sources of polyphase high fre uency current, means for impressing said igh frequency current upon said polyphase transmission lines in controllable intensity, a plurality of electric power distribution transformers connecting at different points with the different phases of said polyphase transmission lines, a plurality of wired radio receivers connecting with the output circuits of said distribution transformers, means associated with said polyphase transmission lines at points on said lines remote from said sources of high frequency current for determining a measure of the amplitude of the high frequency current at said points, said means electrically connected with current indicating means adjacent aforementioned means for controllably impressing polyphase high frequency current on sald polyphase transmission lines, said' combination providing means for determining and controlling the distribution of high frequency current over said plurality of polyphase transmission lines.

3. A wired radio broadcasting system comprising in combination a plurality of. electric power generating stations, a plurality of transmission lines extending from said generating stations for conveying electric power therefrom for distribution over given areas, a plurality of sources of high frequency current, means for impressing said high frequency current upon said plurality of transmission lines in controllable intensity, a plurality of wired radio receivers connecting with said transmission lines,

means associated with said transmission lines at points on said lines remote from said sources of high frequency current for determining a measure of the amplitude of the high frequency current at said points, said means electrically connected with current indicating means adjacent aforementioned means for controllably impressing high frequency current on said transmission lines, said combination providing a means for determining and controlling the distribution of the high frequency current over said plurality of transmission lines.

4. In a wired radio broadcasting system, the combination of a plurality of polyphase electric power transmission lines, a source of polyphase high frequency signaling current, means for impressing said high frequency current in controllable intensity upon said transmission lines, a plurality of electric power distribution transformers connecting at different points with the different phases of said polyphase transmission lines, a plurality of wired radio receivers connecting with the output circuits of said distribution transformers, measuring apparatus comprising a plurality of rectifier circuits connected to said polyphase transmission lines at points remote from said means of impressing high frequency current on said transmission lines, a plurality of responsive devices located adjacent said means of controllably impressing high frequency current on said transmission lines, and connections between each of said rectifier circuits and said responsive devices for observin the electrical characteristics of said hig frequency signaling energy at points remote from the point of impression of said high frequency current on said transmission lines.

5. In a wired radio broadcasting system the combination of a plurality of polyphase electric power transmission lines, a plurality of sources of polyphase high frequency signaling current, means for impresslng said polyphase high frequency currents in controllable intensity upon said polyphase transmission lines, a plurality of electric power distribution transformers connecting at different points with the different phases of said polyphase transmission lines, a plurality of wired radio receivers connecting with the output circuits of said distribution transformers, means associated with said pol phase transmission lines at points on sai lines remote from said sources of high frequency current for determining a measure of the amplitude of the high frequency current at said points, said means electrically connected with current indicating means adjacent aforementioned means of controllably impressing high frequency current on said transmission lines.

6. In a wired radio broadcasting system the combination of a plurality of electric power transmission lines, a plurality of sources of high frequency signaling current, means for impressing said high frequency signaling currents 0n said transmission lines in controllable intensity, a plurality of electric power distribution transformers connecting at different points with said transmission lines, a plurality of wired radio receivers connecting with the output circuits of said distribution transformers, means associated with said transmission lines at points on said lines remote from said high requency current sources for determining a measure of the high frequency current at said points, said last mentioned means being electrically connected with current indicating means adjacent aforementioned means of controllably impressing high frequency current on said transmission lines.

7. In a wired radio broadcasting system the combination of a plurality of electric power transmission lines, a plurality of sources of high frequency signaling current, means for impressing said high frequency signaling currents on said transmission lines in controllable intensity, a plurality of electric power distribution transformers connecting at different points with said transmission lines, a plurality of wired radio receivers connecting with the output circuits of said distribution transformers, at least one wired radio receiver suitably located on each of said transmission lines electrically connected with current indicating means adjacent said aforementioned means for controllably impressing high frequency current on said transmission lines, said combination providing a means for determining and controlling the distribution of the high ifrequency current over said transmission mes.

8. A wired radio broadcasting system comprising in combination a line wire distribution circuit, means for impressing high frequency carrier current on said line wlre circuit, means for controlling the amplitude of the carrier currents at the time of impression upon said line Wire circuit and means located at the electrical center of said line wire circuit for determining the average condition of the carrier wave energy in said line wire circuit on each side of the electrical center thereof, said means being arranged to actuate measuring devices adjacent said first mentioned means for controlling the amplitude of the high frequency carrier currents at the point of impression upon said line wire circuit.

9. A wired radio broadcasting system comprising a plurality of line wire distri bution circuits, a source of high frequency electrical energy operatively associated with said line wire circuits for impressing high frequency currents on said line wire distribution circuits, and means located at the electrical center of said line wire circuits and connected with measuring devices located at a point adjacent said source, whereby the characteristics of said high frequency electrical energy on opposite sides of said electrical center may be determined.

10. A wired radio broadcasting system comprising in combination an electric power generating station, a plurality of feeders for conveying power from said power gen erating station for distribution over a given area, a source of high frequency electrical energy, means for impressing said high frequency electrical energy upon said feeders and regulating the characteristics of said high frequenc electrical energy, measuring devices locate at said power generating station, means connected at points along said feeders for determining the characteristics of the high fre uency electrical energy in said feeders, and connections between said means and said measuring devices in said power generatin station for observing the characteristics o the high frequency electrical energy at points remote from said power generating station.

11. In a wired radio broadcasting system the combination of a line wire distribution circuit, a source of high frequency electrical energy, means for impressing said electrical energy upon said llne wire distribution circuit, a measuring device located adjacent said source of high frequency electrical energy, means located at the electrical center of said line wire distribution circuit for determining the characteristics of the high frequency electrical energy therein and connections between said second mentioned means and said measuring device whereby the characteristics of the high frequency electrical energy in said line wire distribution circuit on either side of the electrical center thereof may be observed at points remote from said source.

12. In a wired radio broadcasting system the combination of a polyphase electric power distribution circuit, means for impressing polyphase high frequency signalin energy on said circuit, a plurality of wire radio receivers arranged to be connected with said power distribution circuit for actuation by said polyphase high frequency signaling energy, measurin apparatus connected with said power distri ution circuit at points adjacent the connection of said wired radio receivers therewith for determining the characteristics of the high frequency signaling ener in the several phases thereof, and connections between said measuring apparatus and a measurin device adjacent said means for observing t e characteristics of said high frequency signaling energy at points remote from said means.

13. In a wired radio broadcasting system the combination of a olyphase electric power distribution circuit, means for impressing polyphase high frequency si nalin energy on said circuit, a plurality o wire radio receivers arranged to be connected with said power distribution circuit, through the normal distribution transformers, for actuation by said pol phase high frequency signaling energy, an measuring apparatus connected with said power distribution circuit for comparing the amplitude of the high frequency signaling energy in each of the several phases at points remote from the point of impression of said polyphase si naling energy with respect to the amplitu e of said energy at the point of impression upon said circuit.

ROBERT D. DUNCAN, JR.

Lowenstein et a1 1,522,308 25o-a Clement` u i 1 Re.16,'231' Z50-6

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