US2139232A

US2139232A - Transmission system

Info

Publication number: US2139232A
Application number: US82883A
Authority: US
Inventors: John L Hysko
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1936-06-01
Filing date: 1936-06-01
Publication date: 1938-12-06
Anticipated expiration: 1955-12-06

Description

. 6,y 14938'. J. L. HYsKo TRANSMISSION SYSTEM Filed June l, 1936 F /LTER gil /NVENTOR JL. Hrs/(o wlM AAA

A TTORNEV Patented Dec. 6;.1938

UNITED STATES PATENT OFFICE vTelephone Laboratories Incorporated, New

York, N. Y.,.a corporation of New York Application June 1, 1936, Serial No. 82,883

4 v Claims.

This inventionrelates to transmission systems and more particularly to carrier telegraph transmission systems.

Incarrier telegraph systems the signals are 5 usually sent by impressing the carrieron a transmission line in accordance with a code. During transmission the periods when the carrier is not impressed on the line are of as much importance as those periods when the carrier is impressed on the line. Arrangements'are known in which the impedance of a shunt across. the line is varied to change from the condition of transmitting the carrier to the condition of not transmitting, that is, from marking to spacing or vice versa.

l5 Heretofore such arrangements have commonly involved contacts in the carrier circuit which are opened and closed. Due to the lo'w power of the carrier at the point of control small particles of dust or other foreign matter on the contacts greatly increase the impedance presented .to the carrier with resultant false signals.

This invention has asa general object the improvement of carrier telegraph systems. Another object is the elimination of false signals from such systems.

A further object is the elimination of contacts from the carrier source in carrier telegraph systems. g

The term carrier telegraph system as used lherein includes radio as well as wire systems or a combination of them.

The objects noted are achieved according to this invention bythe use cia direct current to change the impedance to the carrier of impedance devices inserted in the carrier path.

'The invention, its objects and various features will be better understood from the following de- `scription in connection with theattached drawing, .in which: 40 Y Fig. 1 illustrates one form which the invention may take involving shunt and series impedances; Fig. 2 illustrates a modication of Fig. l in which thedirect current Apaths are individually controlled to afford a better balance; and Fig. 3 illustrates another arrangement of impedances according to the invention. Referring now to Fig. l there is illustrated an oscillator i which forms the carrier current source. In series with this source is a resistance '2 to control the output level of .the source. Also in series are transformer windings 3 and 4 of

transformers

35 and 36 respectively. The other windings of these transformers are shown at 5 and '6. In shuntto the source are transformer windings (ci. 17a-s6) 1 and 8 of transformers 31 ands33, respectively, having corresponding windings 9 and lg.

Sources of direct current Il and l2 are associated with the subscribersloop SL in which there is a key 39 and resistances R1, R2 and R3: g whose functions will appear hereinafter.

Inserted in one of the leads to windings 5 and 6 are surface type rectiers or one-way devices I I while in one of the leads to windings 9 and I0 are similar devices l5.- Y 10 Block IB represents a iilter to eliminate harmonies and other undesirable currents from the line which extends beyond the filter.

Windings 5 and Gar'e so connected that current passes through winding 5 in the opposite directionA 1li to that of the .current in winding 6. The currents induced in windings 3 and' 4 when current is impressed on or removed from windings 5 and 6 are therefore opposed and hence no current iiows to the line due to the change of current in windings 20 5 and 6, that is, no direct current kicks are impressed on the line.-

This condition exists also in transformers 31 and 38 and no direct current kicks from these transformers reach the line. 25 I The cores of the transformers are of such material and the value of direct current impressed upon them from the subscribers loop circuit is such that the cores become saturated from such current. When the cores are saturated, alternat- 30` ing current impressed on windings 3 and 4 or 'l and 8 meets only the direct current resistance of the windings since there is substantially no inductive reactance.

Signals are sent by impressing oscillating cur- 35 rent from source ion to the line beyond lter iiiv in accordance with a code. The embodiment f the v"invention illustrated in Fig. l makes use 01j' key 39 to form the code.

When key 33 is open as illustrated no currentVA 4o iiows from direct current source il. Current from battery l2 ilows throughparallel circuits, one including its own ground, ground 40, resist-` A ances R3 and R2 to the negative terminal of the battery. The other circuit includes the battery; 45

ground, lground Ml, resistance Rs, conductor M,

.conductor 42, windings 9 and i0, one-way devices l5, conductor A3, resistance R1 to the negative terminal of battery i2. No current can Iiow in windings 5 and E since one-way devices M' ar'elio poled to oppose it.

Since no direct current flows in windings 5 and 5, the inductive reactanceto alternatingcur-V rent impressed on windings 3 and 4 willbe large. At the same time since direct current iiows inl-,Q5

windings 3 and I0, the cores of transformers 31 and 38 are saturated and the inductive reactance of windings 1 and 8 to alternating current is very small. Under these circumstances windings 1 and 6 constitute a low impedance shunt and hence any current from oscillator I which may pass windings 3 and 4is' shunted. away from the iilter I6 and the line beyond, by windings 1 and 3.

Y When key 33 is closed batteries II and I2 are effectively connected in series. The potential at the point where conductor 43 is connected to the loop is positive with respect to the potential at the point where ,conductor 4I is connected to the loop between resistances Rz and R3, and therefore current flows from the positive terminal of battery I I through key 33, conductor 43, one-way devices I4 windings 6 and 5, conductor 4I, resistance R3, ground 43, and negative terminal of battery I I. Some current also flows through key 33, resistance R1, battery I2 to ground and negative terminal of battery II. There is also local current from ground 48, resistance Ra, resistance Rz, battery I2 to ground. The voltage drops in resistances R1, R2 and Ra due to the currents in these last-mentioned circuits will determine the potentials in the loop circuit which cause current to iiow through the transformer windings as described.

Direct current in windings 5 and 6 saturates the cores of

transformers

35 and 36 and windings 3 and 4 present only a small direct current resistance to thecurrent from oscillator I. At the same time since no current ows in windings 3 and I due to one-way devices I5, windings 1 and 8 present a high inductive' reactance to the current from oscillator I and .this branch becomes essentially an open circuit. Hence, current from oscillator I is impressed on filter I6 and the line beyond anda marking signal is sent.

It will be noted that no relay contacts are pres- 'ent in either the loop circuit or the signaling circuit. Since the only contacts that are present in the entire arrangement are those at key 33, false signalsdue to dirty contacts are practically eliminated.

Fig. 2 illustrates a slight modiiication of the arrangement of Fig. I to insure better balance of the direct current through windings and 6, and

9 and I6. Like parts are given the same indices inthisgureasinFig. 1.

The improved balance is obtained by inserting between windings 5 and 6 a resistance I8 and between windings 8 and I0 a. resistance I3. Sliding contacts 20 and 2l for windings 5 and 6 and sliding

contacts

22 and 23 for windings 3 and I0 may be-so adjusted that equal direct currents now through the opposing windings. Due to slight inaccuracies in winding during manufacture of the transformers the windings may have unequal ldirect current resistances and hence unequal voltage drops resulting in incomplete opposition or neutralizationA oi the induced voltages caused by the change in direct current. Upon making or breaking of the direct current circuits this unbalance'is evidenced in the transmission line 'by pulses which may cause false signals. The operation of the arrangement of this figure is thesame as that of Fig. 1. 'l

Fig. 3 illustrates a modification of the invention 'in whichv two three-winding

transformers

24 and 25 are used. Transformer 24 is composed of Input winding 26, direct current winding 21 and output winding 23 all mounted on a. common core. Transformer 25 is composed of input winding 23, direct current winding 36 and output winding 3| mounted on a common core. Direct current windings 21 and 30 are connected in opposing relation to avoid direct current kicks as described above. y

As in Figs. 1 and 2 the carrier current is generated in oscillation generator I the output level of which is controlled by resistance 2.

Windings

26 and 29 in series complete the local carrier circuit.

Windings

28 and 3| are connected in series and inductively to

windings

26 and 29 respectively. -The filter I6 associated with output windings 28 and 3I performs the same function as with the arrangements of Figs. 1 and 2.

One-way devices 32 are included in the circuit of windings 21 and 30 as is also the armature I3 of the sending relay. Direct current sources II and I2 are associated with armature I3. In this case. however, direct current source II is associated with the marking contact M while source I2 is associated with spacing contact S. Also associated with spacing contact Sand armature I3 is a resistance 33 in series with a. condenser 34 to insure spacing and marking signals of equal length as will be described later.

The cores of

transformers

24 and 25 andthe value of the current from source I2 is such that when the direct current flows through .

windings

21 and 33 the cores are overloaded and no induction occurs as between

windings

26 and 28 and between

windings

23 and 3|.

Signals are transmitted by causing sending ref, lay armature I3 to move in accordance with a code. When armature I3 is on spacing contact S, direct current flows fromground I1 through windings 21 and 30 in series, one-way devices 32, l armature I3, contact S, source I2 to ground.

' Under this condition the transformer cores are saturated and

windings

26 and 29 induce no currents in windings 23 and l3 I. Hence no current is impressed on the transmission line.

When armature I3 ison marking contact M no current ilows through

windings

21 and 33 because one-way devices 32 are poled against passage of current from the positive terminal of source II. Therefore, the currents from generatqr I will iiow through

windings

26 and 23 and corresponding currents will be induced in

windings

28 and 3| and after passing through lter I6 will be impressed upon the transmission line.

The function of resistance 33 and condenser 34 may be best explained by assuming armature .I3 on the spacing contact S and current flowing from ground I1 through the circuit previouslyl traced through armature I3, contact S to source I2. When armature I3 leaves contact S this current will continue to flow through resistance 33 until condenser 34 is charged. The value of l resistance 33 and the capacity of condenser34 are such that the time to charge the condenser is-greater than the time for armature I3 to move from contact S to contact M. When armature I3 contacts with contact-M the positive potential of sourcel II is impressed on 4the armature and current iiow through the windings ceases.

Very little, .if any, current will ow through

windings

21 and 3|).while armature I3 is on contact M and none will flow during the armature travel from M to S. Current will flow only when armature I3 contacts with contact S and upon leaving S until it contacts with contact M. It will, therefore, be seen that if the armature travel time from S to M is the same as from M to S the marking signals will 4be the same length.

u the spacing signals.

frs

It is understood that many modincations may be made in the circuits described which will be within the scope oi this invention. The invention, however, is to be limited only by the appended claims.

What is claimed is:

l. In combination, a source of alternating current, a circuit therefor, multiwinding impedance devices in series with said alternating current source, multiwinding impedance devices in shunt to said alternating current source,ga'direct current source, circuits separately connecting certain of the windings of said series and certain of the windings of said shunt multiwinding devices to said direct current source through respectively oppositely poled one-way devices, means to vary the polarity of the direct current impressed on said circuits whereby direct current of one polar,- ity is impressed on certain oi the windings of said series devices and direct current of the opposite polarity is impressed-on certain of thewindings of said shunt devices. b

2. A combination in accordance with claim 1, characterized in this that relatively opposing magnetic elds are set up by said direct lcurrent when it is impressed on certain of the windings of said multiwinding devices.

3. In atelegraph transmission system", an alterhating-current carrier source, a transmission device, a circuit connecting the carrier source and the transmission device, an inductive impedance in the alternating-current circuit in series with the carrier source, an inductive impedance in the alternating-current circuit in shunt of the carrier source, a direct-current source, a circuit including unidirectional devices. for connecting the direct-current source to the impedances, and a switch in the direct-current circuit, the switch when in a spacing position causing direct current of one polarity to ow in the shunt impedance and when in almarking position causing direct current oi' an opposite polarity to'flow in the series impedance so that the carrier source is effectively blocked from the transmission device when the switch is in the spacing position and is applied to .the transmission device when the switch is in the marking position.

4'. 'In a telegraph transmission system, an alterhating-current carrier source, a transmission device, a circuit connecting the carrier source and the transmission device,` multiwinding inductive impedances connected in the alternating-current circuit, a direct-current source, a. circuit including unidirectional devices for connecting the direct-current source to certain windings of the inductive impedances, and a switch in the directcurrent circuit, the switch when in a spacing position causing direct current to iiow in said certain windings of the impedances and when in a marking position eectively blocking the direct current from said certain windings of the impedances so that the carrier source is eiectively'blocked Vfrom the transmission device when the switch is Y in the spacing position and is applied to the transmission Adevice when the switch is in the marking position. Y

JOHN L. HYSKO;