US1709554A - Voice-frequency calling system - Google Patents

Description

April 16, 1929. H, 5, BLACK 1,709,554

VOICE FREQUENCY CALLING SYSTEM I Filed Jilly 20, 1927 /Z A5 v n l M5 1 /7 T 5% i i g; w

A A A AvA I '35 3 23 I F/G Z b i Loc/u Cmcwn 70 Tau L/NE //vv/v TOR HAROLD J. 5AA CK Patented Apr. 1 6.1929.

I UNITED STATES mnom) s. annex, or monrcram, NEW JERSEY, nssreivoa r BELL. TELEPHONE LABORATORIES, mconeonArEn, 01 NEW YORK, 1v. v n CORPORATION or NEW YORK.

VOICE-FREQUEN CY CALLING SYSTEM.

. Application. filed July 20.1927. Serial No. 207,067.

r This invention relates to circuits for differentiating between waves of ditferent durations, and particularlyv to voice frequency calling or ringing circuits for telephone systerns.

An object of theinvention is to diiferentiate between waves of different durations.

In systems, such as carrier telephone systems and those employing voice frequency toll lines and using the lowerfr equency range for telegraph transmission, it is often desirable to employ voice frequency waves for calling or signaling; It is therefore necessary that the calling-apparatus should differentiate between the calling waves and voice waves of the same frequency. In a specific preferred embodiment ofv this invention a relay is operated by voice .fre-.

quency waves in. a telephone line to open a direct connection between the battery and the winding of a second relay. However, there is provided in parallel with the direct connection a path comprising a condenser anda resistance in series so that the second relay is maintained in its operated position-- by the current through the condenser during the charging period, the length of WhlCh'lS determined by the relative values of the capacity and resistance of the circuit. This period is made of such length. that if the operating waves are voice waves the first relay will release before the condenser becomes charged and the direct connection to the winding of the second relay will berestored, while if the operating waves ere callmgwaves, which are maintained for a time relatively long compared to the time of a given frequency voice wave, the condenser will become charged and the second relay will release before the first is released. Thus the see-- I 0nd relay will respond to the action of calling waves on the first relay, but not to the action of voice waves.

With the arrangement of this invention the condenser is caused to discharge through 9. gr

resistance of very low ,value so that even when the waves impressed on the first relay are interrupted for a'very short interval the condenser will completely discharge with the result that when the relay is again operated the operator presses her ringing key, both a main and an auxiliary transmitting relay are provlded and a condenser is connected in series with the winding of the auxiliary relay. The action of the operator closes acir- I! PATENT: OFFICE.

cuit. of the main relay which impresses the calling wave on the line and closes-the circuit of the auxiliary relay which makes a parallel operating connectionto the circuit of the main relay. This arrangement assures that the main relay will beoperated for at least as long as the charging period ofthe condenser. The invention is illustrated "in the ccompanying drawing in which:

Fig. 1 shows diagrammatically one ein bodiment thereof in the receiving apparatus for a voice frequency calling circuit;

Fig. 2 shows diagrammatically an embodiment in a complete transmitting and receiving arrangement for a voicefrequency calling circuit; and

Fig. 3 shows -dia'graminatically tion of the circuit of Fig.2. h

Referring .to Fig. 1 there is shown a line 10 adapted to be connected to a signaling a modificasystem such as a telephone system over which are transmitted calling currents ofv the same frequency range as. the signalingor-voice cu rents. This line is connected to the windin of an alternating current relay -11 through a filter comprising an anti-resonant circuit 12 in the series arm and a condenser 13 in the shunt arm. This'fiIter acts to at-- tenuate waves of frequencies other than those employed as calling currents. 7, When the relay is operated a connection is made from relay 15,battery 16 to ground. .The relay 15 is provided-with two armatures 17 and 18. The armature 18' is arranged ound through its armature. winding of.

in circuit with I the winding of a third relay 19 so that whenever the relay 15 operated for at least'a definite time interval relay 19 will release.

Ordinarily relay 19 is maintained operated through the circuit from ground through winding of relay 19, resistance 20, arm 21 and contact 22of relay 15, battery 23 to ground.

When relay is operated the armature is brought up, breaking the contact between arm 21 and contact 22 and making a contact be tween the arm 21 and the armature 18 so that I is controlled by the capacity of thecondenser,

and the resistance of the circuit (primarily the resistance of the element 20) When the relay 15 releases the condenser 24 discharges through the resistance element 25 which may 7 be designed to have a very low resistance as it need onlybe high enough to prevent the relay contacts from burning while the condenser discharges. If the relay 15 remains operated for a time longer thanthe charging period of the condenser 24 the relay 19 will release making a connection from ground through'batter 26, armature 17, armature of relay 19 and winding of relay 27, causing the.

operation of the relay 27 and making a connection to the circuit 28 to give an indication that calling signals are being impressed on the line 10.

Thus when waves of short duration such as voice waves are impressed on the relay 11 "from line 10, the relay 15 will be operated,

but will release before the relay 19 releases. However, when calling currents which persist for a definite period of time longer than the charging time of the condenser 24, are impressed upon the relay 11, the relay 15 will remain operated for a suflicient length of time to cause the release of the relay 19, thus ment 25 is made very low so that the con' denser 24 will completely discharge even operating relay 27 and giving an indication in'the circuit 28. The resistance of the elewhen the operation of relay 15 is interrupted for a very short interval, thus preventing the action of a rapid succession of waves of short duration-"from building up the condenser charge to such a release.

Referring to Fig. 2, there is shown a line 30 connecting a local circuit to a toll line.

point that the relay 19 will Ordinarily low frequency ringing currents impressedupon the local circuit by the operatorkactuate the relay 31 through thearmature of 'rela 32 and condenser 33. The operation of 'r'e ay 31 makes. a connection from- 31 a holding connection from ground through battery 39, armature of relay 37, winding of relay 61 to ground, so that the relay 33 will be held in the operated position as long as the relay 37 is operated, which in turn will re main operated for the charging period of the condenser 35. Therefore, voice frequency callingcurrent will be impressed on the toll line'for a period at least as long as the charging period of the condenser 35. When the relays are released condenser 35 discharges through the resistance 40.

- he voice frequency calling current from the source 34 is of a comparatively low level and therefore will produce no undesirable disturbance in the local circuit.-

Voice frequency. calling signals from the toll line e. g. of 500 cycles are transmitted through the right-hand armatures of relay 61 (when in the released position) and filter network 41 to the winding of relay 42, which is so arranged as tonormally complete a circuit from ground through armature of relay 42, winding of relay 43, battery 44 to ground. Relay 43 in turn is arran ed so that it is thus normally operated, making a connection from theground through its armature and right-hand contact, winding of relay 45, resistance 46, battery 47 to ground. However, when the relay 42 is operated by the voice frequencycalling currents relay 43 releases opening this circuit through the winding of relay 45. However, the circuit from the ground through battery 47, resistance 46, winding of relay 45,. condenser 48, i

and resistance 49 to ground is not broken, so

that the relay 45 will remain operated for the charging period of the condenser 48 in a similar manner as in the clrcuit arrangement of Fig.1. However, if the currents whichoperate the relay 42 persist for a longertime than the charging period of the condenser 48, relay 45 will release, closing a connection from ground through armature and left hand contact of relay 43, armature of relay 45, winding of relay 32, battery 50 to ground, causing the operation of relay 32 and making a connection from the source of low fre quency ringing current 51 through the annatures of relay 32 to the local circuit.

r Fig. 3 shows a modification of the boxed in portion of the circuit of Fig. 2, the corresponding connections to the remainder of the relay 54 is normally maintained operated similarly the receiving circuits may be actuby the connection from ground throu h the armature of relay 42, connection 52, wlnding of relay 54, battery 55 to ground. However, when therelay 42 is operated this connection is brokenand the relay 54 releases, closing a connection from battery 56 through re- .sistance 57, left-hand contact and armature of relay 54, winding of relay 58, and resistance 59. However, since the winding of relay 58 and ;resistance 59 are shunted by condenser 60 relay 58 will not operate immediately. This parallel circuit has practically the same time constant as would a circuit of infinite inductance in that at first the current practically all passes through the condenser through the armature of relay 58, connection 53, winding of relay 32 and battery 50 to ground. This interval is so determined, by proportioning the impedances of the elements of the circuit, that the relay 58 will not be operated by ordinary signaling currents but only by the voice frequency calling currents which persist for a definite period.

The invention may advantageously be used on telephone toll lines or carrier and radio systems, a feature being that ringing currents of low strength or amplitude may beused, comparable to'the strength of the tele hone currents themselves. These low strengt currents are readily transmitted by the vacuum tube repeaters of a toll line and by the repeaters and terminal circuits of a carrier or radio channel. It is to be understood that the sending circuits illustrated in the drawings may be connected either to voice frequency lines or to carrier or radio channel apparatus for modulating carrier waves, and

ated directly by waves from a telephone transmission line or by waves resulting from detection of modulated waves sent over a carrier or radio channel. The claims are intended to apply both to transmission at the signaling frequency level and to transmission by means of a carrier] wave as in carrier systems.

Whatis claimed is:

1. In combination, a. line adapted for, trans mitting waves of short duration andwaves of rado orrelatively long duration both of the same fre-' quency range, a relay connected thereto and responsive towaves of said frequency range,

a source of energy, a second relayconnected to said source and controlled by said first relay, and a condenser in circuit with said second relay to prevent actuation of said secque-ncy range, a relay responsive to waves of saidfrequency range, a second relay controlled by said first relay, and means for preventlng the actuation of said second relay except by waves which persist uninterrupted for at least a definite period, said means comprising a condenser connected 1n circuit with the winding of said second relay by the operation of said first relay and a path of low re-- sist'ance through which said condenser dischargesupon the interruption of the operation of said first relay.

3. In combination, a line adapted to transmit waves of short duration and waves of relatively long duration both of the same frequency range, a relay responsive to waves of said frequency range, a second relay to be operated only by said waves of long duration, a source of current, a normally closed contact connecting said source to the winding of said second relay and opened by the action of said first relay, connections including a series condenser for supplying current to the winding of said second relay whereby on the opening of said contact said second relay will remain operated for the charging period of said condenser.

4. In combination, a telephone line, means for transmitting voice frequency calling signals thereover, a relay responsive to said sig; nals, an armature and associated contact for said relay, a second relayhaving a winding, an armature and an associate contact, connections for normally supplying operating current'to the winding of said second relay whereby after the response of said first re lay to waves in said line, the second relay is held operated for the charging time of said condenser, to prevent said second relay from being responsive to waves of short duration.

5. In combination, a line, a source of waves, a main relay for connecting said source to the line, means for operating said relay, an auxiliary relay for maintaining the operation of said main relay, a winding for said auxiliary at least as long as the charging period of the condenser. a I

6. In combination, a line adapted for trans mitting'waves of short duration andwaves of relatively long duration both of the same frequency range, a relay connected thereto and responsive to waves of said frequency range, a source of energy, a second relay com nected to said source, a condensergconnected in circuit with said second relay, and means relay dependent upon substantially complete charging of said condenser and prevent actuation of said second relay during the transmission of said waves of short duration.

In witness WhereofI hereunto subscribe my name this 18th day of July, A. D., 1927.

HAROLD s. BLACK.

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