US1922193A - Signal transmission system - Google Patents

Description

haw/5 Aug. 15, 1933.

C. A. BODDIE SIGNAL TRANSMISSION SYSTEM Filed July 30, 1927 INVENTOR Clarence A.Boddie 2 r 7 AITTORNEY I J i 1 Patented Aug. 15, 1933 UNITED STATES PATENT OFFICE SIGNAL TRANSMISSION SYSTEM Clarence A. Boddie, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, a Corporation of Pennsylvania Application July 30, 1927. Serial No. 209,408

7 Claims.

In order to satisfactorily attain the aforementioned objects and certain others incidental thereto, I have found it best to couple the transmitting and receiving instruments to the over ead ground-i: ssociated with high- 60 ension po nes, rather than to the power- 'll'ie ground wires, preferably Wired radio, or carrier-current signal transtwoirrnumberf'are generally strung on the same mission over metallic conductors is of particular importance in connection with the remote control of power-generating stations and it is also being widely adopted for the communication of messages, either telegraphic or telephonic, between the various units of a power-generation installation and between the substations tied-in to the power-distribution network.

In order that satisfactory point-to-point communication may be maintained, it is customary to utilize, at each station, a frequency for trans- 2 mitting' signals that differs materially from the frequency on which the said station customarily receives. It is also becoming usual to so arrange the various frequencies employed that multiplex signal-transmission is possible, i. e., that a plurality of messages may be simultaneously transmitted and received over the same conductors without interference.

During the course of numerous experiments I have made with carrier-current installations arranged for multiplex transmission, I have found that the reception of signals on certain of the frequencies employed was seriously hampered by the presence of harmonics of other transmission frequencies. It was often noted that the second, third, or higher harmonics of the carrierfrequency generated at one transmitting station coincided very closely with the fundamental frequency being generated at another station, with the result that the first referred-to station could 4 not satisfactorily communicate with other stations in the network.

It is, accordingly, an object of my invention to provide, in transmission systems of the type described, instrumentalities and circuit connections whereby undesired harmonics of transmitting frequencies are prevented from interfering with the satisfactory reception of signals.

Another, and closely related, object of my invention is to provide, in remote-control systems employing carrier-currents, means whereby undesired harmonics of the frequencies utilized for the control of the relays at a certain substation are prevented from causing unpremeditated actuation of analogous relays at a different substation.

poles that carry the high-tension lines, their purpose being to relieve the lines of excessive charges that may be induced thereon during electrical storms. To this end, the ground wires are connected to earth through choke-coils and protective spark-gaps at a plurality of points along their length, the spark-gaps being adjusted to break down under excessive potentials. In order that the carrier currents shall not be diverted by the ground connections, I associate therewith additional choke-coils arranged to offer an extremely high impedance to the carrier-frequencies.

In addition, I have greatly modified the coupling devices interposed between the transmitting apparatus and the ground lines by adding thereto a circuit, or a plurality of circuits, opaque to the harmonics of the locally generated oscillations.

Among the novel features of my invention are those particularly set forth in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with further objects and advantages thereof, will best be understood from the following description of a specific embodiment, taken in connection with the accompanying drawing.

The single figure of the drawing is a schematic 9 view of a carrier-current transmitting and receiving system comprising a preferred embodiment of my invention.

In order that the drawing shall not be unduly complicated by the presence of a plurality of figures which are merely duplicates of one another, I have not shown all of the transmitting and receiving units ordinarily associated with a complete power network, but have illustrated only two of such units. It is, of course, to be understood that, in multiplex transmitting-receiving systems of the previously mentioned type, there will be a large number of transmitting andreceiving sets similar to the ones shown, each of which is designed to operate at certain predetermined frequencies.

Referring to the drawing, a plurality of powerlines 1, which may extend between any two points in a power-distribution network, are paralleled 110 by a plurality of overhead ground wires 2. As

before stated, the ground wires are for the purpose of rel mving the high-tension lines of charges accumulated thereon, and for this purpose, they are provided, at intervals, with charge-dissipating devices 3. Each of the charge-dissipating devices comprises an iron-core inductor 4 connected in shunt to the ground wires 2: and provided with a mid-tap 5 mound. A high-frequency choke coil 6 is interposed between each of the ground wires and the inductor referred to, these choke coils being each shunted by a safety spark-gap '7.

A transmitting station comprises a thermionic amplifying device 10 having a filament 11, a plate 12 and a grid 13, the filament being prefer ably provided with a ground connection 14. The amplifying device is supplied with exciting current at any desired carrier frequency from a master-oscillator 15 which is connected to the filament and grid thereof. The master-oscillator, which is shown in the drawing merely as a rectangle, may be of any desired type.

Plate potential for the amplifying device is supplied from a direct-current source 16 through an iron-core audio-frequency choke-coil 1'7, and an air-core radio-frequency choke-coil 18. The output or plate circuit of the device comprises an inductor 20 shunted by a tuning condenser 21, one end of the inductor being connected to the plate 12 through a blocking condenser 22, and the mid point thereon being connected to the filament and ground through a conductor 23.

A thermionic modulating device 25, comprising a grid 26, a filament 27 and a plate 28, is supplied with plate potential from the direct-current source 16 that supplies plate potential for the power-amplifying device 10.

The filaments of the thermionic devices 10 and 25 are connected, in parallel to a source of filament power 30, by means of conductors 31 and 32.

The secondary winding 33 of an audio-frequency transformer 34 is connected in series in the grid circuit of the modulator tube 25, the primary winding 35 of this transformer being energized by a microphone 36 in series with a source 37 of direct-current potential.

The circuit network, including the master cscillator, the power amplifier, the modulator and the microphone, is shown merely as illustrative of any system designed to impress modulated high-frequency currents upon an output circuit which may be coupled to the overhead groundwires 2. In certain cases, the network referred to may be replaced by a much more involved system designed for multiplex transmission. In other installations, the network may be replaced by a combined transmitting and receivin system equipped and arranged for break in operation. In still other installations, the network referred to would be replaced by control devices arranged to transmit a definite predetermined series of high-frequency impulses to a distant receiver in order to there control the operation of selector-switches, etc., which, in turn, actuate controlling-devices associated with generating, transforming or switching apparatus.

Irrespective of the manner in which the modulation or control of the generated high-frequency oscillations is effected, the problem of impressing them upon the overhead ground wires for transmission to a receiving device is substantially the same. According to my invention, the coupling arrangement interposed between the oscillation generator and the ground wires comprises an inductor 40, the ends of which are connected to intermediate points on the output inductor 20 through a plurality of condensers 41 and 42. The inductor 40 in turn, is connected to the overhead ground-wires 2 through a plurality of highly insulated coupling- condensers 43 and 44.

The output circuit, comprising the inductor 20 and the variable condenser 21, is tuned to the carrier frequency employed by the transmitting station. The circuit connected thereto, which 'comprises the inductor 40 and the condensers 41 and 42, is also tuned to this frequency.

Both of these circuits are preferably so made that the decrement of each is quite low. They are, accordingly, sharply resonant to the carrier frequency, and quite opaque to the harmonic frequencies thereof.

In order that the transmission of harmonic frequencies to the coupling circuit which includes the inductor 40 and the condensers 41 and 42 shall be minimized, the points on the output inductor 20 to which the said condensers are connected may be so chosen that they are substantially voltage nodes with respect to the predominant harmonic.

In addition, the points on the coupling inductor 40 to which the condensers 43 and 44 are connected may be so chosen that harmonic voltages developed there'oetween are a minimum.

Accordingly, the harmonic frequencies are progressively attenuated between the output circuit and the ground-wires 2, and are prevented from being impressed across the said wires with sufficient amplitude to influence a receivin device 50.

The number of coupling circuits interposed between the output circuit of the transmitting set and the transmission channel may, of course, be increased, a single one of such circuits being shown merely as illustrative.

The illustrated receiver 50 may either be the receiver intended to be normally influenced by the transmitting device or it may be a receiver which would be accidentally actuated by a harmonic of the transmitting frequency but normally actuated by the fundamentai carrier fre- Q quency of a different transmitting station.

My invention is, as before stated, particularly adapted to multiplex carrier-current communication systems. It is not limited thereto, however, being also useful in connection with systems wherein but a few frequencies are being employed for communication between definite stations, since, even in such systems, there exists the likelihood that more than two stations will be simultaneously communicating, and, in such event, interference caused by harmonics might introduce complications into both the reception of inteiiigence and the remote control of machinery.

Although I have illustrated and described only 3 a single embodiment of my invention, many modifications thereof will be apparent to those skilled in the art. My invention, therefore, is not to be limited to the simplified diagrammatic showing, and not otherwise except as limitations may be imposed thereon by the prior art and expressed in the appended claims.

I claim as my invention:

1. In combination, a guiding channel for carrier waves, a plurality of wave generators at different fundamental frequencies coupled thereto, receiving means associated with said guiding channel and tunable to receive at the fundamental frequency of one of said generators said receiver being capable of being influenced by harmonics of the generated wave of another of said wave generators when tuned to receive at said fundamental frequency and means for rendering said receiver free of said influences, comprising devices for preventing the impressing of harmonics of said wave upon said guiding channel.

2. In combination, a wired guiding channel for carrier waves, a plurality of means for generating carrier waves at different frequencies, a receiving device tunable to one of said carrier waves and capable of being influenced by a harmonic of others of said carrier waves, and means interposed between said generating means and the channel for preventing said harmonic from being impressed on said channel.

3. In combination, a wired guiding channel for carrier waves, a plurality of means for generating carrier waves at diiferent frequencies, a plurality of receiving devices capable of being undesirably influenced by a corresponding generating means, at least one of said receiving devices being capable of being undesirably influenced by a harmonic of the carrier wave generated by at least one of said generating means, and means between the guiding channel and said last-mentioned generating means for preventing the undesired harmonic from affecting said receiving device.

4. In combination, a wired guiding channel for carrier waves, a plurality of means for generating carrier waves at different frequencies, a plurality of receiving devices capable of being influenced by certain of said generating means, at least one of said receiving devices being capable of being undesirably influenced by a harmonic of the carrier wave generated by at least one of said generating means, and means for the suppression of said harmonic interposed between said guiding channel and the generating means giving rise to said harmonic.

5. In a signaling system, an oscillation generator having an output-circuit, a circuit resonant to the frequency of the oscillations generated, a guiding channel, means for coupling said resonant circuit and said output circuit, and connecting means between said guiding channel and a point on said resonant circuit that is substantially a voltage node with respect to a predominant harmonic of the oscillation-frequency.

6. In a signaling system, an oscillation generator having an output-circuit, a circuit resonant to the frequency of the oscillations generated, a guiding channel, means for coupling said resonant circuit to said output-circuit, and connecting means between said guiding channel and a plurality of points on said resonant circuit that are substantially voltage nodes with respect to a predominant harmonic of the oscillation-frequency.

'7. In a signaling system, an oscillation generator having an output-circuit, a circuit resonant to the frequency of the oscillations generated, a guiding channel, means for coupling said resonant circuit and said output circuit, and connecting means between said guiding channel and a point on said resonant circuit that is substantially a voltage node with respect to a predominant harmonic of the oscillation-frequency, said connecting means comprising devices for impeding the passage of direct current.

CLARENCE A. BODDIE.

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