US2370853A

US2370853A - Electrical carrier wave signaling system

Info

Publication number: US2370853A
Application number: US394457A
Authority: US
Inventors: Fairley Frank
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1940-10-24
Filing date: 1941-05-21
Publication date: 1945-03-06
Anticipated expiration: 1962-03-06
Also published as: BE472658A; GB544746A; NL72112C; FR932704A

Description

March 6, 1945. F. FAIRLEY ELECTRICAL CARRIER WAVE SIGNALING SYSTEM Filed May 21, 1941 2 Sheets-Sheet 2 AGENT Patented Mar. 6

vided comprising first and second srs'rrm Frank Fairley, London, England, asslgnor to Intel-national Standard Electric New York, N. Y.

Corporation,

Application May 21, i941. Serial No. 394,451 In Great Britain October a4, 1940 This invention relates ing systems. I

object of the: invention is to providea to carrier wave signalsinglechannel system which is intended to have a wider field of use than the known \types of single channelsystems hitherto used. According to afeature of the invention, in I a single channel carrier, wave signaling system. transmission is effected over a transmission linefrom a first terminal station to a second terminal station on one modulated sideband of a carrier'frequency and in the other direction on both modulated side-bands of the same carrier frequency, a source of carrier fre quency'waves being provided at the firstterminal station only and means being provided" thereat for selecting and demodulating only one of the received side bands.

According to another aspect of the invention 'in a carrier wave signaling system a first terminal station comprises a transmitting branch arranged to transmit one modulated side-band together with unmodulated carrier frequency waves 'and a receiving branch arranged to select and demodulate the other side-band of the same carrier frequency and a'second terminal station comprises. a single circuit which per forms the double, function of modulator-and demodulator, the carrier frequency waves for modulation and demodulation at'the second terminal station being supplied from the first terminal station. x K

According to a still further aspect of the in:- vention a carrier wave signaling system is' pro terminal sta tions connected by a' transmission line and a third terminal station connectedto a point in 4 Claims. (01. 178-44) drawings, Figs. 1 and at: which are respectively schematic lay-out diagrams of; the equipment at the two terminal'stations-df a system according to the invention whilst Fig. 3 is a layout diagram of a further system-according to the invention.

Referring to Fig. 1, the terminal equipment thereshown. consists of the basic circuit used ina known type of single channel carrier system.

, Considering the transmission on the carrier channel, speech from the switchboard is applied via the terminating set of hybrid coil TS to the modulator M, which is of the balanced type, in which the carrier is suppressed. One of the sidebands is selected by the band filter BF and applied to the transmitting amplifier TA from whence it passes via the directional filter said transmission line intermediate said first.

and second terminal stations, 'said' first and second terminal stations each being arranged to transmit one modulated side band and to the same. carrier frequency, and said third terminal station comprising. a single circuit adapted to transmit both modulated side-bands and to receive and demodulate either side-band transmitted from the' first or second terminal station, the carrier frequency waves used for modulation or demodulationat the-,third terminal. station being transmitted over..the'- line from. either one of. the first or second terminal sta- The abovefeatures of the. invention will be better understood from the following descripreceive and demodulate the other side band of tion taken in conjunction with the accompanying 55.

TDF. and highpass line filter HPL to the open wire or cable line L. In the receiving direction the'sideband passes via the receiving directional filter RDF to the demodulator DM and the reproduced speech passes via the low pass filter LP and is amplified by the receiving amplifier RA for transmission to the switchboard via the 4,-wire termination. The oscillator O supplies the carrier frequency both to the modulator and demodulator. A voice frequency circuit is provided viapthe low pass filter LPL. It may be-arranged by switching that the directional filters 'I'DF and RDF are interchanged in circuit position and that a second hand filter passing the opposite sideband of the carrier frequency is connected in place of the original band filter, thus converting what may be termed an A terminal into a .B terminal. The provision of such a switching arrangement avoids the necessity for having available two types of .terminals for any emergency connection which it may be desired to install. This system, since it uses suppressed carrier and a directional transmission of frequencies, may be readily repeatered and extended to cover any large distances.

The output of the oscillator O isconnected to the' junction of filters TDF'and RDF.' -The terminal shown in Fig. 1 will then transmit both the upper sideband of the carrier frequency and the carrier frequency itself. Such a terminal is used in. conjunction with'a'terminal of the type shown in Fig. 2 which corresponds in its broad aspects with the inert terminal of a, system as described in British specification No. 427,605, and requires no power supply for its operation. The upper sideband of the carrier frequency and carrier frequency itself applied to the inert terminal pass via the line filter HPL to the modulator-demodulator M, which ls an unbalanced type of modulator, and the reproduced speech passes via the low pass filter LP to the switchboard. For transmission in the other direction, speech from the switchboard passes via the low pass filter LP to the modulator-demodulator M, where it modulates the carrier frequency transmitted from the terminal of Fig. 1. Both sidebands pass via the high pass line filter HPL to the terminal of Fig. l, in which the lower sideband only is received via the receiving directional filter RDF. The lower sideband then is demodulated in the ordinary 'wayby the remainder of the equipment. Such a system will have the advantage of the system described in British specification No. 427,605 in that no power supply is required at the inert terminal, but will avoid the limitation of this system that the lowest overall transmission equivalent obtainable is that of the line at the carrier frequency, together with the basic losses of the two terminals. In this case. due to the use of'one sideband in one direction and to the selection of the other sideband from the two sidebands sent in the other direction, it will be possible to obtain considerable gain at the Fig. 1 terminal without danger of singing, and to make up for the attenuation of the open wire line at the carrier frequency.

According to a modified arrangement shown in Fig. 3, if two terminals are located at the two ends of a circuit, one being set to become the A terminal, i. e. to transmit the upper sideband of the carrier frequency and the other being set to become the B terminal, i. e. to transmit the lower sideban'd-of the carrier frequency and if it is arranged that either but not both of these terminals is at the same time allowed to transmit the carrier frequency itself from the oscillator O to line, it is possible to connect in shunt on this circuit at an intermediate point an inert terminal of the Fig. 2 type and to operate the system using the Fig. 2 as an intermediate station. The A" terminal will be similar to Fig. 1 whilst the B terminal will also be similar to Fig. 1 with the exception that the connection from the oscillator to the junction of the filters 'I'DF and RDF will be removed and the filter BF adjusted to pass only the lower side-band. The Fig. 2 terminal may receive the transmitted sideband from both the "A" or "3 terminal and at the same time still receive the transmitted carrier from the terminal A which is arranged to transmit this carrier and is thus able to demodulate either sideband at will. In the other direction, the Fig. 2 terminal generates both sidebands one of which is received by the A terminal and the other of which is received by the B terminal. Since it is possible to arrange that the carrier is transmitted from either of the terminals "A or "B", it is convenient to arrange that the terminal transmitting the carrier is the nearest one to the Fig. 2 rather" than that the more distant one should transmit the carrier. It will be appreciated that in order that the system may operate satisfactorily it necessary that the terminal B which is not transmitting the carrier frequency must suppress thecarrier received over the line from the distant terminal before demodulation. If there is any appreciable amount of carrier remaining at demodulation, lack of synchronism will cause the usual troubles associafed with excessive carrier leak on suppressed 1. A single channel two-way carrier wave signaling system comprising a first terminal station, a second terminal station and a two-wire signal transmission line interconnecting said first and second terminal stations, at source of carrier frequency waves at said first terminal station only, means for transmitting one modulated side band of said carrier frequency from said first terminal station to said second terminal station over said transmission line, means for transmitting unmodulated carrier waves from said source over said transmission line to said second terminal station, means for transmitting both modulated side bands of said carrier frequency from said second terminal station to said first terminal station over said transmission line, and means at said first terminal station for selecting and demodulating only one of the side bands received thereat.

2. A single channel two-way carrier wave signaling system comprising a. first terminal station, a second terminal station and a two-wire signal transmission line interconnecting said first and.

second terminal stations, said first station including a source of carrier frequency waves, a transmitting branch comprising means for transmitting one modulated side band of said carrier frequency and a receiving branch comprising means for demodulating the other side band of the same carrier frequency, and said second terminal station comprising a single circuit which performs the double function of modulator and demodulator, and means at said first terminal station for transmitting unmodulated carrier waves from said source over said transmission line to said second terminal station for eflecting modulation and demodulation thereat.

3. A two-way carrier wave signaling system comprising first and second terminal stations interconnected by a single two-wire signal transmission line, and a third terminal station connected to a point in said transmission line intermediate said firstand second terminal stations, means at said first and second terminal stations to transmit one modulated side band and to receive and demodulate the other side band of thesame carrier frequency, a single circuit at said third terminal station for transmitting both modulated side bands of the same carrier frequency and for receiving and demodulating the side bands transmitted from the first and second stations, and means at one of said first and second stations for transmitting carrier frequency waves over said transmission line to said third terminal station for effecting modulation and demodulation thereat.

4. A carrier wave signaling system according to claim 2 in which a modulator in said transmitting branch and a demodulator in said receiving branch at said first terminal ,station are supplied from said source of carrier waves, and an output of said source is also connected to said transmission line.