US2000116A

US2000116A - Transmission regulation

Info

Publication number: US2000116A
Application number: US421454A
Authority: US
Inventors: Sumner B Wright
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1930-01-17
Filing date: 1930-01-17
Publication date: 1935-05-07
Anticipated expiration: 1952-05-07

Description

May 7, 1935. s. B. WRIGHT 2,000,116

TRANSMISSION REGULATION Filed Jan. 17, 1930 Io/y Zwam/Mmmm@ [ine 12e eater Annu". "uur" '.5 y |NvENToR ATTORNEY Patented May 7, 1935 UNITED STATES l PATIENT OFFICE y 2,000,116 TRANSMISSION REGULATION Application January 17, 1930, Serial No. 421,454

4 Claims.

This invention relates to circuits for the transmission of intelligence, and more particularly to the regulation of transmission circuits in which attenuation varies not only with the energy level but also with the frequency of the transmitted currents.

In long cable circuits, for instance, the attenuation is more marked for the currents of high energy level than it is for the currents of 1o low energy level: accordingly, there is the undesirable result of a relative increase of echoes,

noise and crosstalk over speech currents.y Furthermore, this effect of energy level variation is greaterat the higher frequencies than it is rat the lower.

The principal object, therefore, of the present invention is to produce a counter effect to that found in long cable circuits, whereby the resultant attenuation will be substantially in- 29. dependent Of both current strength and frequency. It will be understood, however, from the following description and discussion that the advantage of the invention is not limited to producing such a counter effect, but may reside 25 in introducing, for any purpose connected with the problems of transmission, anauxiliary loss varying with both energy level and frequency.

In general, the invention is embodied in an arrangement of auxiliary impedances inserted 3o in the circuit in association with the transmission line, as will be more fully described hereinafter, reference being had to the accompanying drawing, in which:

Figure 1 shows diagrammatically a simple cir- 35 cuit arrangement for producing, for instance, the compensating attenuation variation mentioned above;

Fig. 2 shows diagrammatically a modied arrangement for producing a similar result; and

Fig. 3 shows in like manner an arrangement for accomplishing a similar result in a somewhat more complicated but, in some respects, more advantageous manner.

With reference flrst to the details of Fig. l

`45 of the drawing, an artificial line is shown inserted in a long transmission line and .inductively connected therewith through transformers T1 and Ti.y This artificial line has two series resistances R1 and Rz, representative of any 50 suitable number of series resistances. These resistances have low temperature coenlcients. In shunt across the artificial line there are shown a resistance R, a capacity C and an inductance L. The resistance R is of high temperature co- 55 efficient and may take the form of a short, fine tungsten filament in an evacuated bulb. If the elements C and L were omitted from the shunt circuit the effect of resistance R would be to cause the attenuation to decrease as the en` ergy increased; thus, there would be rough compensation for the normal effect in the transmission line of energy level change. There would remain, however, the problem of variation of this effect with frequency variation. vWith the elements C and L included and tuned to a high frequency, the effect of change of current strength of the attenuation is made more pronounced at high frequencies than at low frequencies. Since the normal effect in long trans'- mission circuits mentioned above is that the l5 variation is more pronounced at the high frequencies but in the opposite direction to the difference of effect introduced by this network, the' arrangement disclosed in Fig. 1 will produce a resultant attenuation of the circuit substantially independent of bothenergy level and frequency.

Because of the reactances introduced by the artificial line, while all frequencies will be trans-r mitted equally well with respect to current strength, there will be other inequalities in the transmission of the Various frequencies. Thisv trouble may be corrected, if it assumes serious proportions, by the insertion in the transmissiony line of a transmission equalizer of any well known type, an example being disclosed in Fig. 1. In this case the equalizer comprises a resistance' R4, a capacity C2 and an inductance La connected across the line as indicated. A repeater may be `added kto restore the currents to the value which they had before passing through the artificial line and the equalizer.

For certain purposes it may be advantageous touse a different arrangement of shunted elements in the artificial line. An arrangement which in some cases wouldrequire a less complex 40 transmission equalizer than that shown in Fig. 1 is disclosed in Fig. 2 of the drawing. The artificial line is connected into the ,transmission` line through transformers T1' and T2. The series' resistances are represented by R1 and R2. The 4,5 resistance Of high temperature coefficient R corresponds to R of Fig. 1, taking the form of a short, fine tungsten filament in an evacuated bulb. In parallel with this resistance R there are connected a capacity C', an inductance L' and a re- 50 sistance R3 as shown. The equalizer and the repeater correspond to the elements shown in Fig. 1.

While the arrangements of Figs. 1 and 2 will prove satisfactory in many cases, in certain other cases it may be found that the resistance of R or R changes, as a function of temperature, too slowly to meet the certain requirements, In such cases a quicker action may be obtained with the somewhat more complicated arrangement shown in Fig. 3 of the drawing.

In Fig. 3 an artificial line is inserted in a long transmission line and inductively connected therewith through transformers T1l and T2. In this artificial line there are shown, or indicated, a resista-nce R1" and a series impedance Z. Provision is made for the variation of the impedance Z with change of current strength in the transmission line. Associated with the input of.' transformer T1 and the impedance Z, which is that looking into the transformer T4 as indicated, is an arrangement of vacuum tubes, resistances, capacities and inductances as shown.

If weak currents are being transmitted, the impedance Z will be relatively large because of the negative grid potential impressed on the vacuum tube V2 by the battery B3. Accordingly, interfering currents of low energy level are limited to small values. If, however, speech or other strong currents, which may be represented by I, are impressed upcn the input of the transformer T2, there is induced in the secondary winding of that transformer an electromotive force which causes l the flow of a current z' through the tube V1 and the resistance R3. The drop in the resistance R3 due to the current i is opposed to the electromotive force of battery B1. This current z' also flows through the filter L1"-C1-C2, which is designed to smooth out this current and to introduce any desired delay in the action of the circuit.

The electromotive force of battery B1 prevents the flow of current until the voice waves reach an amplitude which requires correction. When the current i becomes great enough, it has the effect 4oV of impressing a positive potential on the grid of tube V2, and thus current is permitted to flow from battery B2 through the plate circuit of the tube. This flow of plate current reduces the impedance Z, and, as will be readily understood, the

` result is a decrease of the loss through the corrector arrangement.

In order that correction may be made for the difference of effect of energy level change with frequency variation, the capacity C" and the inductance L" are introduced in series with the primary winding of transformer T3 to give the desired offsetting effect. It may be advantageous to include in series with these elements a resistance R2". The eifect of the high impedance input amplifier indicated in the drawing ahead of the elements C, L and R2", is to limit the amount of energy which will be required to be drawn from the transmission line for the operation of the vacuum tubes V1 and V2.

As is the case with the arrangement of Fig. 1 or the arrangement of Fig. 2, a transmission equalizer and a repeater may be added with advantage to the circuit of Fig. 3.

While the invention has been disclosed as embodied in certain definite circuit arrangements, it will be understood that the true scope of the invention is not limited by such specific disclosure, but is determined by the appended claims.

What is claimed is:

1. In a, circuit for the transmission of alternating currents, a regulating network including a resistance, a variable impedance effectively in series therewith, means responsive to changes in the intensity of the energy impressed on the input of said network for making adjustment of the magnitude of said variable impedance to introduce an auxiliary distortion tending to produce inequality between the ratio of two values at the input of the network and the ratio of the corresponding values at the output thereof, and means for varying such control in accordance with variation of the frequency of the currents impressed on the input of said network.

2. In a circuit for the transmission of alternating currents, a regulating network including a resistance, a variable impedance effectively in series therewith, means responsive to changes in the intensity of the energy impressed on the input of said network for making adjustment of the magnitude of said variable impedance tending to render the relation between the input of the network and 'the output thereof non-linear, and means for ance with variation of the frequency of the currents impressed on the input of said network.

3. In a circuit for the transmission of alternat-ing currents, a regulating network including a resistance, a variable impedance effectively in series therewith, means responsive to changes in the intensity of the energy impressed on the input of said network for making adjustment of the magnitude of said variable impedance to introduce an auxiliary distortion tending to produce inequality between the ratio of two values at the input of the network and the ratio of the corresponding values at the output thereof, means for correcting such control in accordance with variation of the frequency of the currents impressed cn the input of said network, and means for controlling the delay in the action of said network.

4. In a circuit for the transmission of alternating currents, a regulating network including a resistance, a variable impedance effectively in series therewith, means responsive to changes in the intensity of the energy impressed on the input of said network for making adjustment of the magnitude of said variable impedance tending to render the relation between the input of the network and the output thereof non-linear, means for correcting such control in accordance with variation of the frequency of the currents impressed on the input of said network, and means for controlling the delay in the action of said network.

SUMNER B. WRIGHT.

varying such control in accord- 1