US1483179A - Means for controlling electrical transmission - Google Patents

Description

I Feb: y J. S. JAMMER MEANS FOR CONTROLLING ELECTRICAL TRANSMISSION Filed June 17 2 flwew/orf Jaco J. Jam 6/ y moon s. June, or new our, a. v., assrenon r wrsrnan nancrnrc com,

mcoaroaarnn, or new YORK, n. r, a conrorron or new YORK.

MEANS FOR CONTROLLING ELECTRICAL TRANSMISSION.

Application filed June 17, 1922. Serial 1E0. 568,9l0.

I. To all whom it may concern: potentiometer setting cannot entirely com- 1t known that l, JACOB S. JAMMER, a pensate for these changes, inasmuch as citizen of the Umted States, residing at New changes in the setting of the usual type of York, in thecounty of New York, State of simple potentiometer cause repeater gain cycles.

New York, have invented certain new .and .changes which are equal at all frequencies. useful Improvements in Means for Control- The most complete compensation can only 1111 Electrical Transmission, ofwhich the be obtained by means for producing transfollowing is a full, clear, concise, and exact mission'gains or losses varying with ire-- description. quency.

The invention relates to means for 6011- The present invention provides an attenutrollin'g'the transmission gain or loss in a ating device adjustable to give changes in line transmitting currents of different freits transmission gain or loss which vary with quencies, for instance a telephone line transfrequency, and further, to provide such a deinitting different frequencies in the voice vice wherein movement of a single element frequency range, or a carrier line transinay cause the adjustment necessary to efiect mitting frequencies, for example, as high as ;=the var ing changesof gain or loss. 30,000 cycles per second and as low as 6,000 Anot e1- object is to provide a repeater comprising such a device, the device embody-- It is customary, in long lines of such char-' ing resistance, inductance and capacity. so acter, to insert repeaters giving transmisproportioned and arranged that adjustment sion gains tending to counteract the attenuy-of the -device may be made to so change ating effect of the line upon the currents the gainof the repeater by. different-amounts transmitted. Ordinarily a potentiometer is for difiierent frequencies as to compensate associated with the repeater, in order thatzfor changes in attenuation, due to weather when the line attenuation increases or dechanges forfinstance, in the line in whic creases the potentiometer setting may be 'corthe repea er is 6011116095861 respondingly adjusted to cause the repeater Ahother object is to provide an attenuat gain to be increased or decreased by an ing device of the type referredtodn the amount approximately the line attenuation form of a v ge changing potent ometer change as nearly as possible. However, the possessing inherent transmission equalizing usual changes of line attenuation are greater properties. v co for the currents of the higher frequencies In the embodiment disclosed, thepotentibeing transmitted over the line than for the ometer device comprises a resistance and an currents of the lower frequencies passing anti-resonant loop for serial connection beover the line. This is true both as regards tween the inputleadsto the device, and means cases where currents'of the voice frequency for varying the amount of the series resist-- range are being transmitted and as regards ance in circuit and, 1n efiect, simultaneously cases where currents of higher frequencies, adjusting the output leads from the device to for instance 6,000 cycles and 30,000 cycles connect them across the loop and the proper are being transmitted. In the former cases. proportion of the series resistance in cirthe predominating influence in causing cuit to cause the device to discriminate to the aochange of line attenuation usually is change desired degree against the transmission of in the temperature of the line and in the relatively high frequenmesfrom the input latter cases the predominating influence genleads to the output leads in favor of the erally is change of specific inductive catransmission of relatively lower frequencies pacity of the medium surrounding the from the input side to the output side of line, due to change of dampness. Since the the device. As is explalned herelnafter, the changesct line attenuation vary with frepurpose of this frequency d1SOI1m1 Ila.tl0n is quency, it is clear that merely shifting the to cause a-disthrtion of the transm tted currents complementary to that due to the unequal line attenuation of the different frequencies, in order to neutralizethe d1stor tion due to such inequality of line attenuation.

. I Fig. 1 shows a repeater circuit embodyeter consisting of resistances 11 and 12 and adjustable .contacts13 and 14 which may be so connected mechanically by suitable means (not shown) as to move toward or from each other simultaneously. A transmission equalizing shunt is provided,

consisting of inductance 20, capacity 21,

resistances 22 and 23, and adjustable contacts 24 and 25, electrically and mechanically connected to contacts 13 and 14, respectively. The inductance and capacity are tuned to a frequency lower than, or substantially equal to, the lowest frequency to be repeated; In a typical case where frequencies covering a range of from 6,000 to 30,000Qcyles are to be repeated, the inductance has a value of approximately 150 mil henries, the capacity is of such value as to resonate with the inductance at about 6,000 cycles, the resistances 22 and 23each have a; maximum value of about 15,000 ohms, and the resistance 11- and 12 each have a maximum value of about 48,000 ohms.

When the contacts 24 and 25 are set to cut all or nearly all of the resistance 22, 23 out of circuit, the impedance of the part of the equalizing shunt that is included between the contacts 24 and'25 is of course, very low for the frequency of 6,000 cycles to which-the inductance and the capacity are tuned, and increases With frequency so that the impedance of this part of the shunt is materially higher for 30,000 cycles than for 6,000 cycles. In other words, a curve plotted bet-ween impedance of this part of the shunt as ordinates and frequency as abscissae, sloped downward, or gradually falls, from the 30,000 cycles point to the 6,000, cycle point; If the setting of contact-s 24 and 25 be changed to include all or a large portlhn of the resistances 22 and 23 in circuit, the impedance frequency curve for the part of ,the equalizing shunt that is then included in the circuit will fall more gradually from the 30,000 cycle po1nt to the 6,000 cycle point, for the im- 1 pedance at 6,000 cycles will be increased this frequency is high compared to the inpedance of the resistance 22 and 23 and is practically at right angles to the resistance component of the impedance. Thus, as the contacts 24 and 25 are moved toward each other, the effect of the equalizing shunt is to tend to reduce the repeater gain more for the lower frequencies of the frequency range between 6,000 and 30,000 cy; cles than for the higher frequencies of this range. Therefore, when line attenuation decreases and the contacts l3 and 14 of the potentiometer '10 are moved toward each other to reduce the repeater gain sufhciently to approximately counteract the decrease of line attenuation for 30,000cycles, that is, sufiiciently to maintain the difference between the transmission level at the transmitting end and that at the receiving end of the line section the transmission loss of which the repeater is intended to control, approximately constant for 30,000 cycle current, the simultaneous movement of the contacts' 24 and 25 toward each other causes the equalizing shunt to tend to increase the repeater gain for 6,000 cycle current without tending to materially increase it for 30,000 cycle current; and the difference between the amount of repeater gain that a given change in adjustment of the/ shunt by the change of setting of contacts 24 and 25 tends to effect for low frequencies and thev amount that it tends to effect for high frequencies should, of course, be made approximately equal to the arithemetical dif ference between the decrease ofline attenuation for the high frequencies and thedecreases of line attenuation for the low frequencies. A battery 26 maintains grids 27 and 28 of the second stage of the repeater at potentials such that these grids draw substantially no current. It is, of course; to be understood that the expression low frequencies here refers to quencies of the frequency range transmitted, and not to the frequencies below the reso- "nance frequency of the equalizing shunt. It

course, that in stating that the changes of distortion prois also to be understood, of

duced by the potentiometer and equalizing shunt should be equal and opposite to those due to the line attenuation, the line referred to is the section of line the transmission loss of which the repeater is intended to control. a two stage, push-pull electron discharge repeater is shown for repeating from a line section 3, which extends West to a line section 5 which extends east. The first stage of the repeater feeds the second stage .through a gain adjusting pothe lower fre- 31, 32, and 33, a resistor composed of sections 34, 35, and 36, tap connections 37 38,

:39, 40, 41 42, 43, and 44 leading from the ends of. the resistor sections, contacts 45 and 46"adjustable for connection to the free ends of the tap connections, and a loop circuit comprising capacity 47 and inductance 48 connected between the resistor sections 33 and 34. The loop circuit is tuned to a frequency higher than, or approximately equal to, the highest frequency that is to be repeated. The tap connection comprises little or no resistance. The tap connections 37, 38, and 39 are resistance tap connections, the resistance comprised in tap connection 39 being great in comparison to the resistance of the resistor section 33, the resistance of tap connection 38 bei larger than that of ta connection 39 an being great 7 in comparison to that of resistor sections 32 and 33 in series, and the resistance of tap connection 37 being larger than that of tap connection 38 and being great in com-' parison to that of resistor sections 31, 32, and 33 in series. The part of the potentiometer shown below the tuned loop circuit is symmetrical with the part above the loop, and contacts 45 and 46 are preferably connected mechanically by means (not shown) whei'eby these contacts may be moved simultaneously toward or away from each other. A battery 26 maintains the grids 27 and 28 of the second stage of the repeater at potentials' such that these grids draw substantially no current.

As the contact 45 is movedfrom a tap connection of one resistance value to the next tap connection of higher resistance the amount of resistance in series circuit be-' tween the contact 45 and the tuned loop increases by the sum of the resistance of the resistor section between the two tap connections plus the difference between the resistances of the two tap connections; and the potential of the grid 27" is aifected as thoughv the connection of the grid were simultaneously shiftedfrom the right-hand end of the tap connection of lower resistance 'to the right-hand end of the other, or higher resistance tap connection. The operation of the part of the potentiometer that is shown .below the tuned loop will, of course, be the same as the operation of the part shown above the loop.

Supposing that frequencies covering a.

range from 6,000 cycles to 30,000 cycles, for example, are to be repeated, and that the capacity 47 and inductance 48 are tuned to 30,000 cycles, then when the cbntacts 45 and 46 are set on low resistance tap connections 40 and 44, the voltage drop across the tuned across the grids 27 and 28 (half of which latter voltage is applied to the circuit of one of the grids, the other half being applied to the other grid), is, of course, relatively high for the resonant frequency of 30,000 cycles, and decreases with frequency to a comparatively low valuefor a frequency of 6,000 cycles. In other words, a curve plotted between impedances across the loop as ordinates and frequencies as abscis- -sae slopes downward, or gradually falls from the 30,000 cycle point to the 6,000 cycle point. Whenline'attenuation decreases, contacts 45 and 46 are moved'away from each other to increase the ratio of the impedance of the part of the potentiometer in circuit therebetween to the impedance of the part of the potentiometer, the-voltage drop across which is the alternating voltage across grids 27 and 28. The effect df increasing the amount of the resistance of tap connections 37 to 44 that is included in circuit, is to tend'to reduce the repeater ain sufficiently to more than counteract the ecrease of line attenuation at all frequencies. However, the simultaneous effective shifting, of the connections of the grids 27 and 28 to the potentiometer to include between the effective points of connection an increment of impedance that is relatively greater at 6,000 cycles than at 30,000 .cycles, tends to increase the repeater gain for 6,000 cycle current more than .for 30,000 cycle current. The difference .between the gain decrease that the changeof setting of the potentiometer produces for high frequencies and the gain decrease that it produces for currents of low frequencies in the frequency range to be transmitted, should be made approximately equal to the difference between .the decrease of lineattenuation for the high frequencies and that for the low frequencies.

Y Preferably, i determining the proper values forthe resistances of section 31 to 36 and tap connections 37 to 44, these resistances are first calculated approximately, in the manner indicated below, andthe actual values to be used are then ascertained by trial. i

Fig. 3 is designed to facilitate explanation of the method of calculating the resistance values approximately. In this figure E represents the volta generated in the tubes of the first ampli er stage of Fig. 2, Z represents the plate filament impedance. of the tubes of the first stage, Z represents the impedance presented across grids 27 and 28 and is assumed to be large in comparison with impedances Z Z Z Z Z repre sents the impedance of the part of resistance sections 31 to 36 which lies between the two tap connections to which the potentiometer input leads are connected at any given time, Z representsthe impedance of the tap connection on which the input leads terminate at that time, Z represents the impedance of the tuned lop 47-48, and E represents the voltage across grids 27 and 28.

The current flowing through the input leads into the potentiometer is ML "Z,+Z,+Z,+Z, and E will equal I (Z +Z which equals The attenuation produced by the potentiometer equalizer is f and this ratio may be converted to loss in 800 cycles miles of standard 19 gauge cable by multiplying the log of the reciprocal of the ratio by 21.13, in accordance with the commonl used formula, miles loss=21.13 0/ e) Let it beassumed that the known value of Z 4 is 12,000 ohms, and that the total gain produced in the amplifying elements of the repeater is miles, (regardless of frequency), and that the line loss under the most unfavorable weather conditions can be taken t0 be 18 miles more for 30 kilocycle current than for 6 kilo-cycle current. Then it will be necessary for the potentiometerequalizer (when at its highest gain setting) to produce for the 6 kilo-cycle current a loss 18 miles greater than the loss produced for 30 kilo-cycle current; or in other words, the potentiometer-equalizer loss for 6 kilocycle current must be somewhatin excess 30 kilo-cyc preciable.

of 18 miles since even its minimum loss for,

le current will, of course, be ap The impedance Z should be made high enough for 30 kilo-cycle current, to prevent this minimum loss from bein excessive, but must be made low enough or 6 kilo-cycle current to have the potentiometerequalizer'loss for the 6-kilo-cycle current in excess of 13 miles when the potentiometerequalizer is at its lowest gain setting Assame a value of say 50,000 ohms for Z at 30 kilo-cycles. Then for this frequency the potentiometer-equalizer loss with the potentiometer-equalizer at its highest gain setting will be p o Then, since the potentiometer-e ualizer at 21.13 log =2 miles. v I (I its highest gain setting is to pro uce a loss for 6 kilo-cycle current 18 miles greater than its loss for 30 kilo-cycle current, its loss for 6 kilo-cycle current must be 18-1-2 miles, or

20 miles, at this setting. Having determined this loss, the value of Z for 6 k110- cycle current can be obtained as follows:

whence Z +l500 ohms.

e may now proceed to calculate the values that Z and Z should have for some other setting of the potentiometer, say for the lowest gain setting-that is, the setting in which contacts 45 and 46 are on tap connections 40 and 44, respectively. Let it be assumed that the maximum gain change to be produced for 30 kilo-cycle current by changing the setting of the potentiometerequalizer is 13.5 miles, or, in other words, that the minimum gain of the repeater for 30 kilo-cycle current is to be (30 -2) 13.5:

2813.5:14.5 miles, or, inunther words, that the maximum loss to be produced by the potentiometer-equalizer for 30 kilo-cycle current is to be 15.5 miles, or, in other words, that for the lowest repeater gain setting of the potention1eter-equalizer the loss produced by that device for 30 kilo-cycle current is to be 15.5 miles=21.13 log Z,+50,000 1 Z,+Z,+50,000+12,000

and let it be further assumed that the line characteristics are such that the maximum gain change to be produced for 6 kilo-cycle current by changing the setting of the potentiometer-equalizer is 5 miles, or, in other words, that the minmum gain of the repeater for 6 kilo-cycle current is to be (3020)5 :105:5 miles, or, in other words, that the maximum loss to be produced b the potentiometer-equalizer for 6 kilo-cycfe current is to be 25 miles, or, in other Words, that for the lowest repeater gain setting-of the potentiometer-equalizer the loss produced by that device is 25 miles =21.13 log% =21.13 log We may now substitute numerical trial a contacts 45 and 46 on tap connections l0 and 41, respectively will be 10 miles for 6 kilocycle current and 28 miles for 30 kilo-cycle current; and when the contacts 45 and 46 are moved to tap connections 37 and *1 the gain will be ieduced to 5 miles for 6 kilocycle current and to 14.5 miles for 30 kilocycle current. Thus, the change of setting will reduce the gain for 30 kilo-cycle current by 13.5 miles and will reduce the gain for 6 kilo-cycle current by only 5 miles.

The proper values of resistances 38, 39, i2, -13, 31, 3:2, 33, 3- 35, and 36, in Fig. 2, necessary to give the repeater gains requisite to compensate for changes of line attenuation varying with frequency may be deterlnined in the fashion in which the impedances Z, and Z have been determined above, numerical trial values being substituted in equations (1) and (:2) until such values have been obtained for all of the potentiometerequalizer resistances as will give, for the various settings of the potentiometer equalizer and for the various frequencies to be transmitted, repeater gains approximately the theoretically correct ones as closely as practicable. y

In the above calculations the impedances Z Z Z and Z,, have been used without regard to the vector relation of their components, because only approximate results were desired, and experience has shown that suflicient accuracy is obtained with this method.

While balanced potentiometer-s have been disclosed, appropriate for the balanced amhfiers shown, it is clear that the invention is also applicable to repeaters and potentiometers not of the balanced type. The specific values of frequencies mentioned herein to facilitate the explanation of the principle of the invention, are, of course, merely illustrativevalues, and the invention is not re stricted to use in connection with frequencies of such values.

The invention claimed is:

1. An attenuating device and an input and an output lead therefor, said device comprising a resonant circuit, a resistance, means for connecting an adjustable amount of said resistance between said circuit and said input lead, and means for so connecting said output lead to said resistance that during normal operation of saiddevice said output lead is at a potential between the potentials of the pointsof connection of said input lead and said circuit to said resistance.

2. A repeater for connection in a transmision hne, said repeater comprising an.

electron discharge tube having an anode, an electron discharge tube having a control elecresonant loop, a resistance, means connecting said resistance to said control electrode, and meansmovable relatively to said resistance for connecting an adjustable amount of said resistance in series between said anode and said loop, and for thereby causing said control electrode to be connected to said resistance at a point which during repeating is at a potential between the potentials of the points of connection of said anode and said loop to'said resistance.

3. A potentiometer and an output lead therefor, said potentiometer comprising a resistance element, a tuned loop circuit connected to one end thereof, tap connections of different resistances leading from ints on said element, and a contact adjusta le to engage the free ends of said tap connections, and said output lead being connected to a point on said potentiometer electrically remote from said tuned loop circuit.

4. A wave transmission system comprising apotentiometer and a source for supplying thereto currents of a relatively low frequency and a relatively high frequency, said potentiometer comprising a resistance element, an output lead connected to one end of said element, a loop circuit connected to the other end of said element and tuned to a frequency substantially as high as said relatively high frequency, tap connections of different resistances leading from different points on said element, and a contact adjustable to en gage the free ends of said connections, the resistances of and between said tap connections, the resistance, inductance, and capacity of said tuned loop circuit and the impedance of said source being so proportioned that movement of said adjustable contact from a tap connection of one resistance to a tap connection of a higher resistance causes a ter decrease in transmission at said relatively high frequency than at said relatively low frequency.

5. In a transmission line, a combined-potentiometer and attenuation equahzer comrising fixed reactive impedance and variable resistance in shunt to the line and variable resistance and substantially no 'reactance in series with the line, and means for simultaneously so varying .said shunt and seriesresistances as to compensate for unequal va-" riations in line attenuation at different frequencies.

In witness whereof, I hereunto subscribe my name this 16th day of June, A. D., 1922.

JACOB S. JR.

Images