US1932568A - Superimposed carrier telephone and carrier telegraph system - Google Patents

Description

H, A, AFI-EL 1,932,568

SUPERIMPOSD CARRIER TELEPHONE AND CARRIER TELEGBAPH SYSTEM Oct. 31, 1933'.

Filed June 20, 19251 .NNN

INVENTOR magy/ff@ ATTORNEY Patented Oct. 31, 1933 SUPERIMPOSED CARRIER TELEPHONE AND CARRIER TELEGRAPH SYSTEM Herman A. Affel, Ridgewood, N. J., assignor to American Telephone a corporation of New and Telegraph Company,

York

Application June 20, 1931. SerialNo. l545,749

2 Claims.

This invention relates to superimposed carrier telephone and carrier telegraph systems, and particularly to a method and means for preventing the carrier telephone currents from causing interference to the carrier telegraph signals when,- ever the said telephone currents exceed a predetermined value.

In a carrier signaling system in which a plurality of channels are operated over to the same transmission line, it is customary to amplify the currents of all channels by passing them through the same amplier at each repeater station along the line. No diiculty is experienced with that mode of operation as long as all channels are employed for the same purpose, that is, if all transmit telephone signals, or all telegraph signals.

It is sometimes desirable, however, to employ one or more of the channels of a multi-channel carrier telephone system for telegraph purposes, that is, to transmit over the selected channel a plurality of telegraph modulated waves. Experiments made upon such a combined system have shown that when the combined currents of the telephone and the telegraphy waves were amplied by the same repeated the telegraph operation suffered and frequent false signalsl were pro-` duced. That difliculty arose from the fact that whenever the -telephonic currents exceeded a predetermined limit, the amplifiers at the repeater stations would be overloaded and the gain of the amplifier would drop. That would cause a'corresponding drop in the amplitude of the telegraph currents and wouldproduce the false operation of the relays at the terminals. That situation could be remedied either by lowering the level of the telephone currents passing through the amplifier very substantially, that is, 15 to 20 db., or an ampliiier could be provided having much larger tubes than would be necessary for normal operation. The rst alternative is undesirable from the standpoint of plant operation, because of the 'resulting greater interference from external sources, and theflatter is uneconomical because of the greater cost of equipment and maintenance.

The object of this invention is to provide a system whereby the occasional excessive telephonic currents or voltages may be eliminated before they reach the common amplifiers at the repeater stations, thus preventing the detrimental eiect upon the telegraph channels hereinbefore described.

This invention will be apparent from the following description when read in connection with the `attached drawing showing schematically a simple form of embodiment of the invention.

In the drawing, A, B and C represent three terminal circuits by which signal modulated Waves are produced and impressed upon the line L for transmission to a distant station, which distant station would. preferably have terminal equipment similar to that shown in the drawing. Connected between sections of the line L is a re'- peater R of which only `the high frequency branch is shown in detail,` since it is with that portion that the present invention is concerned. The terminal circuits A and B are arrangedv to transmit and receive telephone signals, and the terminal circuit C is adapted for sending and receiving telegraph signals. Circuit A comprises a telephone set 1 which is connected with the line windings of the hybrid coil 2.y The trans--v mitting branch which is bridged across the line windings, includes a modulator 3, a current limit.- ing device 4, and a band lter 5 intended to transmit the range of frequencies constituting onev of the telephone channels. The device 4 includes a gas filled, or vacuum discharge device operable at a predetermined voltage, which is applied by the transformer vwhose primary *winding` is bridged across the transmitting path of circuit A. The band lter 5 is connected With the com mon transmitting branch 6 having therein an amplifier 7 and a iilter 8. The outputof that lter is connected to the line L by the branch circuit 9 which includes a high pass filter 10. The receiving branch of the terminal circuit A includes a band filter 11, and the demodulator 12, the said band filter being designed to pass the range of frequencies intended for reception by the circuit A. The receiving branch of circuit A is connected With the common receiving branch 13 which includes the filter 14 and the receiving amplifier 15. lIt will be seen that the modulated waves outgoing from circuit A pass -to vthe branch 6 where they are amplied and impressed upon the branch 9` which in turn impresses those Waves upon the line L. The incoming waves from the line L pass to the branch circuit 9 thence to the branch circuit 13, and those waves of the frequency transmittible through the filter 11 will be demodulated by 12 and will pass to the telephone receiver. i 1

The terminal circuit B, in which the parts similar to those of circuit A have been designated by the same numerals primed, has its transmitting branch connected with the common transmitting branch 6, and its receiving branch connected with the common receiving branch 13.

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Since circuit B functions in the same way as circuit A, further description is not necessary.

The terminal circuit C also comprises sending and receiving branches. The sending branch, namely the upper one shown in the drawing, comprises carrier sending apparatus 16- (which may be of any well known type) to which a plurality of telegraph sending circuits are connected. The output of the carrier sending apparatus is connected to the input of the modulator 17, the connection including the sending iilters 18. The output of the modulator 17 is connected to the branch circuit 6, the connection including the band filter 19, The receiving branch of circuit C which is bridgedacross the receiving branch 13, includes the band lter and the demodulator 21. The outputof the demodulator is connected with the carrier receiving apparatus 22, the connection including the receiving filters 23. The output of the carrier receivingv apparatus is connected with the telegraph receiving-` circuits. f The repeater R is shown as a two-way two element repeater, the upper branch comprising lters and an amplier for transmitting in one direction, and the lower branch being similarly equipped'for transmitting in the opposite direction.

' The object of the invention, and the manner in which that object is attained, will be apparent from the following description of the operation of the circuits hereinbefore described. The telephonic currents produced by the transmitter of 'sub-station 1 of circuit A will be impressed upon the modulater 3, and the modulated wave willbe transmitted through the band lter 5 to the transmittingbranch 6 wherein it will be ampli- 'ied by 7 and impressed upon the line L after passing over the branch 9 and through the high pass-"filter 10. If the transmitter of sub-station 1 is operated at the same time, the wave produced by the modulator 3 will also pass to the common branch circuit 6 and when ampliiied by 7 will be impressed upon the line L. Likewise, the

telegraph signals which are impressed upon the modulator 17 will produce a plurality' of waves that will be impressed upon the branch 6, and when amplified by 7 will also be impressed upon the line L. All of thosefcurrents will pass through the highfpass filter 24 at the repeater R, and will in' turn pass through the amplier in the upper branch` of that repeater. If, during the trans- 'mission' of those signals, the telephonie vibrations produced by one of the sub-stations exceeds a predetermined limit, the modulated current resulting therefrom will likewise exceed its limit,

'and as a result thereof the amplifier 25v may be gas filled tube, having characteristics such that ionization takes place at potentials beyond a certain applied voltage, and the impedance of the device, otherwise fairly high, is for those overloaded conditions, lowered to a gure approaching zero. Inasmuch as the potential required to initiate the operation of` those devices is ordinarily fairly high, that is of the order of 100 to 200 volts, the device, as illustrated, requires astep-up transformer in order that it will function. atthe lower voltages normally employed upon modulators used in telephone transmission circuits. It may be noted that the arrangement will also function if the current limiting device is connected in the circuit at the input to the modulator. f

It is to be understood however, that the invention is not limited to the particular type of current limiting device shown in the drawing and described herein, inasmuch asV otherdevices may beV employed to accomplish'the object of this invention, namely, to'effectively cut off those peaks of the wave corresponding to vibrations of the telephone transmitter having excessive amplitude.

It will accordingly be seen, with the use of devices for limiting the amplitude of the telephonically modulated waves, the amplifier 25 at the repeater R will not be overloaded, and the detrimental effect heretofore experienced upon the telegraph channel superimposed upon the telephone channels, is substantially' eliminated.

While this invention has been -disclosed as embodied in a particular form, it is to be understood that such showing is simply to illustrate the invention, which is capable of embodiment in other and dilerent'iorms without departing from the spirit and scope of the appended claims.

What is claimed is:

1. In a multi-channel carrier telephone system having a carrier telegraph system superimposed thereon, the combination with a transmission line having therein a repeater, of a terminal circuit having means to modulate a carrier wave by telephone vibrations and to impress the modulated wave upon thetransmission line, another terminal circuit having means -to modulate another carrier wave by telegraph signals and to impressV such modulated wave upon said transmission line, the said repeater of the transmission line being arranged to amplify both modulated waves, and means connected with the output circuit of the'modulating means of the lfirst mentioned terminal circuit to limit the amplitude of the telephonically modulated waves prior to their impression upon the transmission line.

2. In asystem in which carrier telephone and carrier telegraph signals are transmitted over the Same path and ampliiied by the same repeater, the combination with a transmission circuit of a repeater connected therewith, means 'to apply carrier telegraph signals to said transmission circuit, means to apply carrier telephone signals to said circuit, the latter means including a modulator and means connected the output` cirico izo

@uit of the said modulator to limit the amplitude of the modulated wave to a predetermined level.

HERMAN A. AFFEL.

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