US1459770A - System for testing line balance - Google Patents

Description

Jame 25, E923. 1,459,770

A. L. JONES SYSTEM FOR TESTING LINE BALANCE Filed NOV. 15 1921 INVENTOR q\ 1 4L Jam ATTORNEY Patented June 26, 1923.

ALVA L. JONES, 0F ASBURY PARK, NEW JERSEY, ASSIGNOE TO AMERICAN rnnnrnonn AND TELEGRAPH COMPANY, A CORPORATION OF NEVJ YORK.

SYSTEM FOR TESTING LINE BALANCE.

Application filed November 15, 1921. 'Serial No. 515,369.

To all whom it may concern:

Be it known that I, ALVA L. Jones, residing at Asbury Park, in the county of Monmouth and State of New Jersey, have invented certain Improvements in Systems for Testing Line Balance, of which the following is a specification.

The principal object of my invention is to provide a new and improved method for testing the balance between a transmission line and its network. Another object of my invention is to provide suitable apparatus with which to practice this method. In a more specific aspect my invention relates to testing the balance between a twowire line and its network, at the transformer making connection with a four-wire line. All these and other objects of my inven 'tion will be illustrated by a specificexample of procedure thereunder which I shall now describe in some detail with the understanding that the scope of the invention is de fined in the appended claims.

An ordinary two-wire transmission line or metallic circuit is indicated by L in the accompanying drawing, and a four-wire transmission line is shown at L L In the four-wire line, one pair of wires forms a circuit for transmission in one direction and the other pair of wires forms a circuit for transmission in the opposite direction. L and L are two such pairs, making the fourwire line. Repeating element-s A and A are interposed at suitable intervals, amplifying the currents in opposite directions as indicated by the arrows. v p

A four-wire line may be especially use ful in a cable, whereas a two-wire line may be suitable foran open wire pole line. The drawing has relation to a station where voice currents pass either way between a two wire line L and a four-wire line L, L

The network N balances the line L across the three-winding transformer 7H, whose output is connected by a potentiometer P to the input of the amplifier or repeating element A from which the output current goes over the line L and becoming attenuated at a certain distance, is amplified by the repeating element A and so on.

Voice currents coming in the opposite 'direction along the line L pass to the potentiometer P then to the amplifier orrepeat ing element A whose output goes to the points of the three-winding transformerH However slight this across which the line L, and its network N are balanced.

line L and its network N.

the diagram that by shifting both switches S and S up, the output of the amplifier A becomes connected directly to the input ofv the amplifier A,. It will be inevitable that some electrical disturbance will exist somewhere in the sys tem, and therefore there will be a current put from the line L into the amplifier A may be, it will be amplified at A and again at A but if the line L and the network N were in perfect bal- It will be seen from output of the element A would get across to the input of the element A Since the balance cannot be ideally perfect some of that amplified energy will get across and be amplified again by the elements A and A in tandem. If the combined gains of the amplifiers A, and A are smaller than the losses in the other parts of the circuit, this energy will be dissipated but if the gains are greater than the losses, the energy will be increased until limited by the power capacity of the amplifiers.

The high impedance monitoring coil T is bridged across the conductors between the switches S and S and associated therewith is a receiver R. A low-pass filter F is interposed in these conductors for a purpose which will be explained presently. If the circulation of energy through the amplifiers A and A, in tandem builds up suificiently it will be perceived as singing in the receiver R. e

The two amplifiers A and A can be adjusted for gain by means of the potentiometers P and P and adjustments will be made to the point at which singing barely begins. Let the gain in standard miles in amplifier A be at, and in amplifier A9 let it be a It will now be shown that the,

.80 ance none of the amplified energy from the singing point may be expressed in standard miles by the formula This means that the net gain around the circuit of A and A is equal to the sum of the gains of the two amplifiers less seven miles, which is approximately what is lost across the three-winding transformer II. The dethe output of sign of the system is such that the energy which comes'in over the line L practically divides equally to the circuit ot'the .poten-- tiometer Pi to the output of the amplifi er A Again the energy which comes from he amplifier A, practically d1- vi des equally between the line L and its network N. Thus, the net effect of the transformer is to quarter the energy on each trip around the circuit oi the amplifiers A and A, in tandem. Reference to table of standard miles shows that quartering the energy means a loss of about 6!; standardmiles'. There is a little further inevitable loss in the transformer H so that the figure is taken at 7, instead of 61;.

; By shitting the switch S down so that its blades make contact with the studs 2 and 3 instead ot l and 2 the connection between the amplifiers A, and A is reversed or transposed, thus reversing the polarity of thei disturhance at this point. One of these conditions will be more favorable to singing will result in a lower value for the singpoint than the other. The lower value isthe true measure of the unbalance.

Usually the balance between the line L and the network M becomes poor at frequencies outside the useful telephonic range. In case the lines L and are loaded the behavior of he system will not be adversely afiected by the poor balance, for they will not transmit suchfrequencies; but when the am, 'lifiers l l andli are connected directly by the operationot the switches S and S,, the singing of the system will be determined by the poor balance at high frequency rather than by the unbalance in the useful range. To avoid this error, the low pass filter F is included in the connection. It is so designed asto prevent the transmission of frequencies beyond the useful range, so that the results of the test will depend only upon conditions which aiiect the operation of the tour-wire circuit.

The singing point will be determined initially in the manner described, and thereafter at intervals in practice, it will be redetermined in the same manner and if it is less than on the eariler occasion the attendant will know that the line L and the network N are out of balance to a degree, as compared with their earlier condition. Accordingly, steps may be taken to rectify the irregularity on the line L that has produced the unbalance, or steps may be taken to adjust the network N so as more accurately to balance the line L It will be seen that my method of test utilizes the repeater elements that are in normal service on the tour-wire line and that very little extra apparatus is employed.

Iclaim:

1. The method of measuring unbalance between a two-wire line and its network at the junction with a four-wire line having re peater elements therein, which consists in disconnecting said repeater elements on their sides away from the two-wire line and connecting them in tandem, and adjusting their gain to the singing point.

2. In a transmission system comprising a two-wire line connected. through a threewinding transformer to a tour-wire line having repeater elements therein, the method of testing unbalance between the two-wire line and its network which consists in disconnecting said repeater on the side away from the two-wire line and connecting its elements in tandem, and adjusting their gain to the singing point. I

3. In a transmission system comprising a two-wire line connected through a threewinding transformer to a tour-wire line having repeater elements therein, the method of testing unbalance between the two-wire line audits network which consists in disconnecting said repeater on the side away from the two-wire line and connecting its elements together with a low pass filter all in tandem, and adjnsting their gain to the s nging point.

il In a transmission system comprising a two-wire line connected through a three- W ndi g t an for 9 a ewi e ne having repeater elements therein, the method of t ting nbal n e b twe n t e t line and its network which consists in disn c i g sa epe er be the s de my from the two-wire line and connecting its elements in tandem, adj usting their gain to the singing point, and taking the sum of the gains in the two repeaters, less the loss at the three-winding transformer, as the gn an singi g Po ga 5. In combination, atwo-wire line, a fourwire line, a network simulating the twowire line, a three-winding transformer interposed between the two-wireline and its network and operatively connecting the twowire line and the tour-wire line, two opposlte repeating elements in the respective pairs of tllGfOLlPWiIG line, means to disconnect them on the side away from the. two-wire line, to reconnect them in tandam, and means to adjust said elements to determine the gain at'the singing point.

6. In combination, a two-wire line, a fourwire line, a network simulating the twowire line, a three-winding transiormer interposed between the two-wire line and its network and operatively connecting the twowire line and the four-wire line, two opp0- site repeating elements in the respective pairs of the four-wire line, means to disconnect them on the side away from the two-wire line, to reconnect them in tandem, means to reverse the polarity of this connection, and means to adjust said elements to determine the gain at the singing point.

7. In combination, a two-wire line, a four wire line, a network simulating the twowire line, a three-winding transformer interposed between the two-wire line and its network and operatively connecting the twowire line and the four-wire line, two opposite repeating elements in the respective pairs of the four-wire line, means to disconnect them on the side away from the two-wire line, to reconnect them in tandem, means to suppress currents of frequencies higher than the useful voice range, and means to adjust said elements to determine the gain at the singing point. f

8. In combination, a two-wire line, a fourwire line, a network simulating the twowire line, a three-winding transformer interposed between the two-wire line and its network and operatively connecting the two- Wire line and the four-wire line, two opposite repeating elements in the respective pairs of the four-wire line, means to disconnect them on the side away from the two-Wire line, to reconnect them in tandem, means to reverse the polarity of this connection, means to suppress currents of frequencies higher than the useful voice range, and means to adjust said elements to determine the gain at the singing point.

9. In combination, a two-wire line, a fourwire line, a network simulating the twowire line, a threewindiug transformer interposed between the two-wire line and its network and operatively connecting the twowire line and the four-wire line, two opposite repeating elements in the respective pairs of the four-wire line, switching means to disconnect the repeating elements on the side away from the two-wire line, to reconnect them in tandem, a high impedance receivlng set across the connection made in this way between the two repeaters, and

means to adjust the repeating elements to determinethe gain at the singing point as observed with the receiving set.

10. In combination, a two-wire line, a four-wire line, a network simulating the two-wire line, a three-winding transformer interposed between the two-wire line and its network and operatively connecting the tw0-wire line and the four-wire line, two- ALVA L. JONES.

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