Title:
Carrier frequency communication system
United States Patent 2378326


Abstract:
This invention relates to line wire communication systems of the carrier frequency type, and more particularly to such a system for transmitting signal or control influences by carrier frequencies on alternating current power lines. In the various applications of power supply and distribution...



Inventors:
Rees X, Frank
Howard, James Y.
Application Number:
US54451444A
Publication Date:
06/12/1945
Filing Date:
07/12/1944
Assignee:
GEN RAILWAY SIGNAL CO
Primary Class:
Other Classes:
307/140, 340/12.32, 340/13.23, 455/402
International Classes:
H04J7/02
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Description:

This invention relates to line wire communication systems of the carrier frequency type, and more particularly to such a system for transmitting signal or control influences by carrier frequencies on alternating current power lines.

In the various applications of power supply and distribution systems, it is sometimes desirable to be able to communicate certain controls or signals between points associated with the power line, as for example, for the transmission to some central point of indications showing the operation of power transfer relays and the like.

The primary object of the present invention is to provide a simplified and improved organization for the communication of controls by carrier frequency over alternating current power lines.

Generally speaking, and without attempting to define the nature and scope of the invention, it is proposed to utilize the alternating current on the power line as a synchronizing means for carrier frequency transmitters and receivers, in such a way as to afford two separate control channels for the same carrier frequency. Considered more specifically, the plate circuits of a conventional carrier frequency oscillator and a power amplifier tuned for the same frequency are energized during the same half cycle of the alternating current on the power line, so that such transmitter and receiver thus associated are effective during certain half cycles to transmit carrier frequency which may be cut on and off, or keyed in conformity with a code to communicate the desired control or signal. In a similar manner, another transmitter and receiver operating at the same carrier frequency may be governed by the alternating current on the power line so as to be effective during the other half cycles, thereby affording another separate channel of communication on the same frequency.

Various other characteristic features, attri-' butes and advantages of the invention will be in part apparent, and in part pointed out as the description progresses.

The accompanying drawing illustrates diagrammatically and conventionally one specific embodiment of the invention, the parts and circuits being shown more with the view of facilitating an explanation and understanding of the invention, than for the purpose of showing the particular construction and arrangement of parts preferably employed in practice.

In the accompanying drawing, Fig. 1 illustrates two transmitters and their associated receivers connected with a power line to provide two separate communication channels for the same carrier frequency; and Fig. 2 is a schematic explanatory diagram of the carrier frequency pulses.

For the purposes of explanation, the invention is shown in connection with the transmission of a power-off indication, or the like, from two different field locations of an alternating current power line to some central office. In a power supply system for railway signaling, for example, the switch machines, signals, relays and the like at the various locations along the railroad track are supplied from an alternating current power line, ordinarily through rectifiers, and sometimes using storage batteries as stand-by sources. Such power lines, usually operated at about 550 volts, ordinarily have their various sections supplied from a suitable source of commercial 60 cycle alternating current; and in many instances auxiliary or emergency sources of power are provided, such as another commercial source, or a generator driven from a gasoline engine or run from a local battery, with a suitable power-off relay or equivalent means for cutting in the auxiliary source of power upon failures of the main source. In a system of this type, it is desirable to transmit to some central office an indication of the power failure, ,so that the appropriate action may be taken without delay. In fact, with such an indication of power failure at a central office, it may not be necessary to provide an auxiliary power source, but rely upon the local stand-by source to carry the load until the power failure can be remedied.

Accordingly, the particular embodiment of the invention as shown for one channel of communication relates to the control of an indication lamp, or equivalent device, in a central office by a poweroff relay PO at a field location, but it should be understood that this is merely typical or representative of the type of signal or control that may be transmitted in accordance with this invention, as indicated generally by the control relay X and indicating lamp BL for the other channel of communication.

The transmitters and receivers for the two channels of communication on the same carrier frequency in accordance with this invention are alike and a description of one will serve for both. The transmitter A comprises an oscillator of the conventional type operating at a suitable carrier frequency, such as 5000 C. P. S. The specific form of oscillator shown is a self-starting type utilizing what is commonly known as the series feed Hartley circuit. Briefly considering the elements of this oscillator, the heater 5 is energized from the secondary 6 of a transformer AT having its primary 7 connected to the local power mains 8, 9 feeding the power line L through a step-down transformer 10. The tank circuit for the oscillator comprises a coil or inductance divided into two parts 12 and 13 and tuned to the desired carrier frequency by a condenser 14. The intermediate point in the inductance is connected to the cathode 15 of a typical triode. One part 12 of the inductance of the tank circuit is included in the circuit for the plate 18 which is energized by the secondary 17 of the transformer AT arranged to provide the desired plate voltage. A condenser 18 shunted around this secondary 17 by-passes the high frequency components in the plate circuit.

The circuit for the grid 22 includes the other part 13 of the inductance; and a grid condenser and grid leak 23 of the usual form serves to provide the desired grid bias with self-starting characteristics. The inductance or coil 12, 13 in the tank circuit of the oscillator is loosely coupled through a coil 24 and coupling condensers 25 to the power line L.

In the typical example shown, it is assumed that a power-off relay PO is energized through a double wave rectifier 29 from the connections for the main power source, and will act, upon failure of this main power source to open at its front contacts 32, 33 the connection from such main power source to the mains 8, 9 and the power line L, and establish through its back contacts 32, 33 a connection to the mains 8, 9 from an auxiliary source. The deenergization of the relay PO also opens at its front contact 35 the grid circuit for the oscillator, and thus stops further operation of this oscillator.

In accordance with this invention, the plate circuit of the oscillator for the transmitter is energized with a 60 cycle alternating current potential derived from the power mains 8, 9 through the secondary 17 of the transformer AT. Consequently, the tube of the oscillator will operate on the half cycles of this power current which cause the plate to be positive with respect to the cathode; and hence a train of waves at the carrier frequency will be transmitted during alternate half cycles of the power frequency, as indicated in the diagram a in Fig. 2.

The receiver A associated with this transmitter A comprises a suitable power amplifier controlling the energization of an indicating means, such as a relay AK and a lamp AL. In the particular arrangement shown, the receiver comprises one stage of a power amplifier of the pushpull type, using a composite tube having the elements at two triodes in the same envelope. The heaters 40, 41 for these push-pull triodes are energized in multiple, through a secondary 42 of a transformer ATR having its primary 43 connected to the power line L by wires 44, 45 and a transformer 46.

The primary 49 of the input transformer 50 for the amplifier is connected by blocking or coupling condensers 51 to the power line L; and the secondary 52 of the input transformer 50 which is tuned by a condenser 53 to the particular carrier frequency in question, has its terminals connected to the grids '54, 55 of the triodes, and its midpoint to the cathodes of the tube through a biasing resistance 58 and by-passing condenser 59 in accordance with the usual practice. The plate circuits of the composite tube, including the primary 60 of the output transformer 61, are energized from the secondary 62 of the transformer ATR connected to the power line, with a condenser 63 for by-passing the high frequency component in the plate circuit. This receiver A is connected to the power line L in such a way that the plate circuits of its push-pull amplifier are positive with respect to the cathodes during the same half cycle of the power current that the transmitter is effective.

As shown, the secondary 65 of the output transformer is connected by a double wave rectifier 66 of the copper-oxide or equivalent type to an indicating relay AK of the usual neutral type and slightly slow release, which in turn controls the lighting of an indicating lamp AL 1 through a circuit readily traced on the drawing from the terminals of a suitable source of alternating current designated BX and CX.

Thus, the amplifier of the receiver responds to the series of pulses at the power frequency such as 60 C. P. S., with each pulse comprising, a train of waves at the carrier frequency, such as 5000 C. P. S. This succession of pulses maintains the relay AK energized. When the relay PO is deenergized as a result of failure of the main power source, and the transmitter stops sending these pulses of carrier frequency, the relay AK is deenergized, and the lamp AL is extinguished.

Other forms of visual or audible indicators may be controlled in the same way.

c0 It can be readily understood how another transmitter B located at the same or some other field location along the power line, may be arranged to have the plate circuit of its oscillator effective during the other half cycle of the power :. current, and that another receiver B may be arranged to be effective during this other half cycle, so as to provide for communication from this other field location of a power-off indication, or such other control or indication asmay be desired, io as indicated by relay X. The symbols (+) and (-) representing an instantaneous polarity of the secondary terminals of the transformers AT, ATR, and BT, BTR supplying plate potentials indicate that the connections are such that each transmitter and its associated receiver have their plates energized positive during alternate half cycles. Also, while the receivers for the different channels of communication on the same carrier frequency are shown as located in the same place 5o in a central office, it is obvious that these receivers may be located at different points along the power line.

In this connection, it can be appreciated that the excitation of the plate circuits for a transmitter and its associated receiver should be substantially in phase, with due regard to the quantitative response of the indicating means governed by the receiver; and hence in locating the transmitters and receivers due consideration must be given to the possibility of a shift in phase along the power line due to its loading or length.

If the receivers are located at the same point as indicated, and the transmitters are relatively close together, shifting in phase along the line is not material, since such phase shifting applies to both communication channels alike. Also, for the ordinary length of power lines and the character of loading contemplated for use in connection with this invention, the shifting in phase is too small to be a factor in the practical operation of the system.

The use of an alternating potential derived from the power line for energization of the plate circuits for the transmitter and its associated receiver also eliminates the need for a battery or other power supply of direct current for these plate circuits.

From the foregoing it can be seen that there has been provided in accordance with this invention a system of carrier frequency communication for power lines, in which two separate communication channels are available for the same carrier frequency. While not specifically illustrated, it can be readily seen that the transmission of the pulses of carrier frequency at the frequency of the power supply may be keyed or coded for the communication of distinctive controls, as well as wholly cut on and off. Also, the same scheme may be duplicated for a plurality of different carrier frequencies.

The particular organization and arrangement of parts and circuits shown is merely illustrative or typical of one embodiment of the invention; and it should be understood that various additions, adaptations and modifications may be made in this particular embodiment shown and described without departing from the invention.

What we claim is: 1. A carrier frequency communication system for providing separate chanels of communication at the same carrier frequency over an alternating current power line comprising, two oscillators generating the same carrier frequency and operatively connected to said power line, two receivers responsive to the same carrier frequency and operatively connected with said power line, and means energized from said power line for rendering each of said oscillators and an associated one of said receivers effective in turn during alternate half cycles of the power current on the power line.

2. A carrier frequency communication system for transmitting control pulses over an alternating current power line comprising, an oscillator at one location along the power line operable to generate a carrier frequency and having its plate energized with an alternating current potential derived from the power line, a receiver at another location along said power line tuned to the same carrier frequency as said oscillator and having its plate circuit energized from said power line during the same half cycle, means for governing the operation of said oscillator, and indicating means, governed by said receiver.

3. In a carrier frequency communication system of the type described for alternating current power lines comprising, a plurality of self-starting oscillators operable to generate the same carrier frequency, a plurality of receivers tuned to respond to the same carrier frequency, -means for coupling said oscillators and receivers to said power line at different field locations, means responsive to the power energization of said power line for rendering each one of said oscillators and a particular associated one of said receivers effective at different time periods, signal control means for independently governing the output of said oscillators, and indicating means independently governed by said receivers.

4. A carrier frequency communication system of the character described comprising, two transmitters comprising self-starting oscillators generating the same carrier frequency and coupled to an alternating current power line, two receivers having power amplifiers tuned to the same carrier frequency and operatively coupled to said power line, and means responsive to the alternating current energization of said power line for energizing IU the plate circuits of one transmitter and its associated receiver during one-half cycle, and the plate circuit of the other transmitter and its associated receiver during the other half cycle.

5. A carrier frequency communication system for indicating failures of power sources feeding power lines comprising, a transmitter adjacent a power source of alternating current and including an oscillator having its plate circuit energized by an alternating potential from said source for applying pulses of carrier frequency to the power line during certain alternate half cycles, a receiver at a central office tuned to the same carrier frequency and including a power amplifier having its plate circuit energized with alternating potential from said power line during the same alternate half cycles, means for rendering said transmitter ineffective upon failure of said power source, and indicating means maintained energized so long as said receiver is receiving spaced pulses of carrier frequency.

6. In a system for transmitting a control between points on an alternating current power line, a self-starting oscillator at a field location having its plate circuit energized with the alternating potential on the power line and operable to apply pulses of carrier frequency during certain alternate half cycles of the power frequency, a receiver at a central office including a power amplifier tuned to the same frequency as said oscillator and having its plate circuit energized by alternating potential from said power line during the same half cycle, means for at times rendering said oscillator ineffective, .and indicating means at the central office normally energized so long as said receiver responds to pulses of carrier frequency.

7. A carrier frequency communication system for providing two separate channels of communication of carrier frequency current over an alternating current power line comprising, two oscillators generating carrier frequency current and operatively connected to said power line, two receivers one for each of said oscillators and each tuned to the frequency of its oscillator and operatively connected with said power line, and means energized from said power line for rendering each of said oscillators and an associated one of said receivers effective in turn during alternate half cycles of the power current on the power line. 60 FRANK X. REES.

JAMES Y. HOWARD.