US1662888A - Automatic volume control for telephone lines - Google Patents

Description

March 2o, 192gl `J. HERMAN AUTOMATIC VOLUME CONTROL FOR TELEP HONE LINES Filed Dec. 5l, 1925 1N VEA/TOR JTe/fm/an/ TTORNEY 'Patented Mar. 20, 1928.

UNITED STATES PATENT OFFICE.

JOSEPH HERMAN, OP NEW`YORE, N. Y., AssIoNoR 'To AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OE NEW YORK.-

A'UTOMATIC VOLUME CONTROL FOB, TELEPHON LINES.v

Application led December 31, 1925i Seri'aIlNo. 78,658.

. This invention relates to telephone transmission systems, and more particularly to methods of and means for effecting current volume control in such systems. e l

The invention is particularly applicable to telephone transmission systems connecting microphones to distantl radio broadcasting stations. Y

It is the object of applicants inventionto limit automatically the volume of the telephone currents transmitted over the line without changing the volume at the receiving end.y l The above lstated object is attained in general as follows: At the sending station the peaks of the telephone currents, when these currents exoeeda predetermined safe value, are automatically converted into direct current suitable for transmission over an ordinary telegraph circuit. The direct current impulses are caused to effect automatically a reduction of the telephone current volume at the sending station input to the line. Simultaneously, the direct current impulses are transmittedover a telegraph circuit to the receivingstation, where they automatically eiiect an increase of the current volume at the outputv from the line, thereby compensating for the volume reduction eftected at the sending station.

Applicants invention will be more clearly lunderstood when the following detailed description is read with reference to the accompanying drawing, which shows diagrammatically one desirable form of the circuit arrangements for volume control as applied to a telephone transmission system connecting a microphone to a distant broadcasting station.

With reference to the details of the drawing, the telephone currents from the microphone at the sending station A pass through the potentiometer P and the amplifier 1 to a gain-controlling circuit including the hyy brid coil 2. This gain-,controlling circuit has in it a liXed resistance 25. A variable gain control is obtained through the variable balance of the hybrid coil 2, which variable balance is Iobtained by'varying the plate cir- -cuit impedance of' the vacuum tube Vw, as will be..more fully discussed below. From the hybrid coil 2 the telephone currents pass through the amplier 3 over the telephone line to a gain-controlling circuit at the receiving station B. This second gain-controlling circuit includes the hybrid coil 4 and a fixed resistance v26. The variable gain control is obtained through the variable balance of the. hybrid coil 4, which variable balance in turn is Obtained by varying the plate circuit impedance of the vacuum tube V3, as. will be more fully discussed below. 'From the hybrid coil 4 the telephone currents pass through vthe amplifier 5 to the broadcasting station.

Across the telephone line ,at the points 6 and 7 in the output of amplifier 3, there is connected through the coil 8 a volume indi.

cater, including the vacuum tube V1.` The grid circuit ot' this vacuum tube includes a battery 27, this battery impressing on the grid a negative voltage ot' such value that normally little or no plate current ows.

` This-vacuum tube permits va direct current to flow in its plate circuit when an alternating wave of suiiicient amplitude is applied to the grid circuit. Applicants volume indicator differs-from the common type ymerely in that in place 'ot the usual milliammeter there is connected in the plate circuit a polar relay R1, which, as will'4 appear more clearly below, is in effect slow operating and slow releasing. This polar relay R1 has .three windings, 9, l0 and 11. 'The winding 9 serves as a biasing winding, and is operated from a local battery through'the resistance 12, in the drawing the plate battery ofthe volume indicator being utilized. for this purpose. Winding 10 is connected into the plate circuit of the vacuum tube V1 and vserves as the main operating winding of the relay. Winding 11 serves as an auxiliary holding winding and is operated from the positive and negative batteries connected to the contacts of relay R1, as indicated in the drawing. This windin 11 is connected from the armature of t e relay 4to ground' in seriesv with the resistance 13 and the capacity 14. It will hold the relay armature ltemporarily on either Contact for a period impulses suitable for transmission over an ordinary telegraph circuit.

To the armature of relay R1 there are connected the windings of two additional polar relays, R2 and R3. As Will appear more clearly below in the discussion of the operation of applicants system, the relay R2 controls the volume reduction at the sending stationby varying the plate circuit impedance of the vacuumtube V2, and relay R3y transmits-the direct current impulses over the telegraph line to the receiving station "B, where these impulses are caused to eifect a compensating volume increase by varying the plate circuit impedance of the vacuum l tube V3.

plate current of the volume in lncrease suliiciently to throw the armature ofl The -operation of the Volume control system will now be described in detail. For the purpose of illustration, the value of the resistance 25 is chosen as 15,000 ohms, and lthe Value of the impedance of the tube V2 as from 6,000 ohms to 15,000 ohms. While these values are arbitrarily chosen, they indicatethe difference in values which is suitable. Likewise, at the receiving station B, the value of the resistance 2G is chosen as 5,100 ohms, and the value of the variable impedance of the tube V3 as 6,000 ohms to 15,000 ohms, as is the case with the tube V2. When the armatures of. relays R1 and R2 are on their s acing contacts S,- the plate impedance o the tube V2 at one end of the circuit including the hybrid fcoil 2, differs widely in value from the balancing resistance 25st the other `end of the circuit. `It is well understood in the art that, given this difference, the hybrid coil 2 will offer only-a small loss to the ltelephone currents passing through" it from 'amplifier' 1 to amplifier 3. If the volume levelof the telephone currents at the inputto the telephone line ein ceeds a predetermined value, the peaks ofthese currents are automatically converted in the volume indicator into pulsating direct current inthe plate circuit. This occurs because the voice waves of. amplitude greater than the predetermined value .which are impressed uponjthe grid circuit make the grid potential so much less negative that a substantial amount of current is permitted to flow inthe plate circuit. Conse uently, the

dicator will relay R1 from its spacing contact S to its Vmarking contact M. This operation of the increasing of the amunt of negative voltage on the grid of the tube Vzincreases the plate circuit impedance of' that tube, as is well understood, and consequently, this plate eircuit impedance Will be nearer to balancmg4 the 15,000 ohm resistance 25 at the other en yof the circuit including the hybrid coil 2.-

'line has become low enough to result in the..

release of the relay R1 in the volume indicator circuit. The armature of relay Riot course is returned to its spacing contact S, and likewise the armaturev of relay R2 is returnedv to its contact S. 'The result is the gradual discharge of the condenser through the resistance 19. The level ofv the tele hone currents at the input tofthc. line will) then riseagain until relay R2 is again operated, and the above described process will be repeated. It will be evident to those skilled in the art that' the relay operations responsive to the peaks of the voice currents, as described above, will. establish .an average voltage on ,condenser 18 ot such valuethat the proper input level to the telephone line will be maintained. 4

As stated above, the operation ofI relay R, results in Vthe operation ot' relay Y When the armature of the latter relay is thrown to its marking contact M, direct current impulses arevtransmittei'l over the telegraph circuit to the relay Rl at the receiving station B. This relay acts on the circuits of the -`vacuum tube V3 just as the relay R2 at the sending station A acts on the circuits of the tube V2. When, in response to'the impulses transmitted over the telegraph line, the armature of relay R, is thrown to its markingcontact M, the negative pole of the battery 20 is connected to the grid circuit of 'the tube V3. Current from the battery 20 flows through the lowpass filter 2l and the resistance 22 and gradually establishes a negative voltage across the condenser 23. The increase ot' the amount of negative voltage on the grid of the tube V3 raises'the plate circuit impedance of the tube lfrom 6,000 ohms (arbitrarily chosen) toward 15,000 ohms. Since, as stated above, the value of the lixed resistance 26 in the receiving station gain-controllingr circuit is 5,100 ohms, `the increase of plate circuit impedance in the tube Vain response to the operation of relay R4 results' in the further unbalancing of the hybrid coil 4.. Consequently, the transmission loss through the hybrid coil is decreased, and the volume output from the line is increased.

It should be evident from the above deat the input to the line and by causing a compensating increase of the current volume at the output from the line at the receiv-v ing station. Furthermore, it should be evi dent that this operation is 'rapid and entirely automatic.

In connection With applicants arrange ment for volume cont-rol, there have been described gain-controlling circuits of a particular type. It is to be understood that such specification is merely for the purpose of illustration and that any suitable gaineontrolling means may be substituted. Also,

4it is to be understood that many other changes from the arrangement sli-own -mai-y be made Without a departure from tlie spirit and scope of applicants invention as defined in the appended claims. YVhat is claimed is: l. In a system for the transmission of telephone signals over Wires, the method. of

limiting t'lie current volume in the line,

which consists in automatically converting at the sending station the peaks'of the telephone currents, when said currents exceed a predetermined value and only at such times, into direct currents, and causing the direct current impulses automatically to eHect a reduction of the volume at thesending station input to the line and afcoinpensating increase of the volume at the receiving station output rom'tlie line.

2. In a system for the transmission of telephone signals over Wires, the method of f limiting the current volume in the line, which consists in automatically converting atthe sending station. the peaks ofthe telephone currents, when said currents exceed a-.predetermined value and only at ysuch times, into direct currents, causing the direct cur-y rent impulses automatically to effect a reduction ofl the volume at the sending'station input to the line, transmitting said impulses to the receiving stationl over-a separate path, and causing said impulses automatically to effect a compensating increase of lthe. volume at the receiving' station output from the` line.

3. In a system for the transmission of telei `phone signals, said' system including a sending station, a receivingfstation, and. a transh mission line connectingsaid stations, automatic means atthe sending stat-ion for converting the peaks of the telephone currents,

December, 1925.

when said currents exceed a predetermined phone signals, said system including a sending station, a V receiving station, and a telephone line connecting said stations, automatic meansA at the sending station for converting the peaks of the telephone currents, When said currents exceed a predetermined value and only at such times, into direct currents, automatic means at the' sending station controlled bythe direct current impulses for reducing the input volume to the telephone line, a telegraph circuit for carrying 4. In a system for the transmission of teletlic direct current impulsesto the receiving station, and automatic means at the receiving station controlledfby said impulsesfor ett'ecting a compensatingmcrease of thev volume of the telephone currentsat the output from the telephone line.

5. `Ina system for the transmission of teleing station, a receiving station, and a tele'- phone line connecting said stations, a vacuum tube volume indicator connected across the input to-the telephone line at the sending sta- `'phone signalsasaid system including a sendtion, an effectively slow operating and slow releasing relay iii `the plate circuit of said volume indicator, said relay operating when the telephone currents exceed'a predetermined value, automatic means controlled by said relay for reducing the input volume to 4the `telephone. line, a telegraph lcircuitv be` tween the-"sending station and th-e receiving station, automatic means controlled by the relay for sending impulses over said tele` graph circuit, and automatic means at-,the

'receiving station controlled bysaid impulses for effecting lat the output from the ltelephone line an increase of the Volume equal to the reduction thereof effected at the sending station.

In. testimony whereof, I have signed` my name to this speciication this 30th day of JOSEPH HERMAN.

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