US1993758A

US1993758A - Wave translation system

Info

Publication number: US1993758A
Application number: US585216A
Authority: US
Inventors: Albert L Stillwell
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1932-01-07
Filing date: 1932-01-07
Publication date: 1935-03-12
Anticipated expiration: 1952-03-12

Description

March 3 1935. A. L. STILLWELL WAVE TRANSLATION SYSTEM Filed Jan. 7, 193:;

LINE 1 2- F IG.

AMPLIFIER BRIDGE LINE 122mm: or

AMPLIFIER EOUALIZEI? LOSS I LOSS /l- "E USEFUL o kUXQQH-uk FREQUENCY IN KILOCYCLES INVENTOR ALST/LLWELL Patented Mar. 12 1935 STATES PATENT OFF ICE I 1,993,758 v, 1 1 1 WAVE TRANSLATION SYSTEM Albert L. Still welI, Westfield, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, 1L, a corporation of New York 7 Application January 1932, Serial No. 585,216 7 Claims. (Cl. 178-44) This invention relates" to amplifying systems and more particularly to arrangements for controlling the frequency variation of the gain of an amplifier.

"6 An object of the invention is toobtain a desired gain-frequency characteristic in an amplifier or repeater in a. transmission system in which the transmission of currents of a wide range of frequencies is required. For example the amplification characteristic may be such as to compensate the attenuation distortion of a telephone line throughout the range of speech or carrier frequencies.

This is accomplished in accordance with the invention by the use of a retroactive connection in the amplifier including a network in the am plifier output circuit which controls the frequency variation of the retroa'ctiveeifect; A feature of the invention is the arrangement of the feed-back controlling network whereby, in addition to providing a desired retroaction characteristic, it serves to prevent the transfer of energyjfrom the connected load to the amplifier input, without the introduction of any substantial transmission loss, and to maintain the proper impedance relationship between the amplifier and its output circuits.

The invention will be described in detail hereinafter with reference'to the accompanying drawing'inwhichz K Fig. 1 is a simplified schematic of the system ofthe invention;

Fig. 2 is a detailed schematic of the system shown diagrammatically in Fig. 1;

Figs. 3, 4 and 5 are diagrams useful in explaining the various aspects of the invention; and

Fig. 6'shows transmission characteristics obtainable with the network of the invention.

In the system shown in Fig. l an amplifier 10 is inserted between two line sections 11 and 12. A bridge equalizer network 13 is used in connecting the output circuit of the amplifier 10 with the outgoing line section 12. The connections ofthe bridge 13 aresuch that the amplifier can transmit with small attenuation into the line 12 and also through a feed-back circuit 14 to a Wheatstone bridge 15 in the amplifier input. The bridge network 13 is balanced'so that the line 12 is substantially isolated from the feed-back circuit, and bridge 15 is likewise balanced to prevent the retroaction currents entering line 11 while permittingthese currents to be transmitted to the amplifier input.

' Details of the arrangementoi Fig. 1 are shown in Fig. 2 in which the amplifier locomprises a vacuum tube 17 with associatedpow'er supply "em cuits. The incoming line 11 is connected to the' input circuit of tube 17 through the input bridge 15 and the output circuit of the tube 1'7 is'connected to the outgoing line 12 through the bridge equalizer 13. The input bridge 15 comprises four resistance arms R1, R2. R3 and R4 arranged in the usual manner, the four junction points being designated A B,C' and D. Theinput circuit of the tube 17 is connected between the terminals A and B while the line 11 is connected between Y B and D. The feed-back circuitfrom the output bridge-equalizer 13 is connected between Af I and C in conjugate relation to the line 11. The bridge equalizer 13 is also composed offour'arms R, Z11, Z21 and R0, the latter being represented by the internal impedance of the tube 17. The corners of this bridge are designated A, B, C and D. The tube impedance R0 is connected between A'and B; Z11is connected between Band C; R is between C and D; and Z21 is between D and' A".

The outgoing line 12 is connected'b'etween- B and D'and the feed-back connection is made toterminals A and 0. As shown diagrammatically in Fig.3 the line 12 and thefeed-back'circuit, which includes resistance bridge 15, form the diagonal branches of bridge 13'and may be made conjugate by balancing the bridge. Balancing of the bridge network is accomplished by making" the resistance branches equaLthat is R'=Ro,*andby con structing Zn and Z21 as inverse imp in accordance The; network of'Fig; 3 without changein' any 3 with the formula v Z11Z21=R0 edances related part presents other aspects thatmay be brought into prominence by redrawing thev diagram as shown respectively by Figs. 4 and 5. Fig. 4 em phasizes the transmission relation between the amplifier space path resistance R0, and the ime pedance of line 12.. The impedances Z11 and Z21 together with resistance R and the resistance of the feed-back circuit constitute a bridged-T network, which, when the branch impedances are so proportioned that the resistance of thefeedback circuit and the impedance of line12 are both equal to R0, becomes a constant resistancegnete work of the type'disclosed in U. S. Patent 1,606,817

issued November 16, 1926, to G. I-I..Stev enson.

.W kr

The propagati given by The loss repre the line loss.

on constant, P1 of this net In order that the loss between the amplifier and line 12 may be small it is desirable that the impedance Z11 should be large. The condition that the feed-back circuit resistance be equal to R is achieved by so proportioning the resistances of bridge 15 that in addition to conforming to the condition of balance, namely R1'Rs'=R2"R4',

they are related in accordance with the equation Fig. 5 emphasizes the transmission relation between the space path of the amplifier and the feedback circuit, which latter as above mentioned includes bridge 15. In this aspect the coupling network constituted by the impedance of line 12, resistance R, and impedances Z11 and Z21 also forms a constant resistance bridged-T network of the type shown in the above mentioned patent to Stevenson. The voltage transmitted through this circuit is impressed across terminals A and C of bridge 15 and a constant fraction of this voltage represented by the ratio is impressed upon the grid of tube 1'7. This voltage is in substantially opposite phase to the voltage impressed on the grid from line 11 and serves to diminish the amplification of the system.

The frequency variation of the voltage fed back through this circuit is determined by the propagation constant P2 of the coupling network of Fig. 5, the value of P2 being given by The loss represented by this propagation constant will be designated as the equalizer loss.

As already indicated maintenance of a low line loss requires that the impedance Z11 shall be large and that impedance Z21 be correspondingly small. This requirement corresponds to a large loss in the. circuit represented by Fig. 5 and hence to a relatively small feed-back voltage. The impedance- Z11, however, may be strongly variable with frequency, although always large enough to main.- tain a low line loss, and due to this variation the value of the feed-back voltage and hence of the effective amplification may be made to vary through a wide range for a given frequency change.

The particular form of the bridge 13 illustrated in Fig. 2 is suitable for the equalization of the loss in a transmission line at carrier current frequencies, for example line 11, which increases at a substantially uniform rate with frequency. In this case it is necessary that the amplification gain should increase with increasing frequency and, therefore, that the degenerative: retroactive effect should be strongest at the lower frequencies. This requires that the impedance Z11 should increase in value with frequency. As illustrated Z11 comprises an anti-resonant circuit in parallel with a series combination of a resistance and an inductance, the anti-resonant circuit being tuned to a frequency somewhat higher than the upper limitingfrequency of the desired operating range. The impedance Z21 is of course of inverse type to Z11.

The frequency variation of the line loss and the equalizer loss in this case is illustrated by the curves of Fig. 6.v The inverse relationship between these losses indicated by Equations 2 and 4 small.

is demonstrated by the form of these curves. It will be noted that the line loss, while negligibly small at the higher frequencies becomes considerable at very low frequencies. The extent to which it increases may be controlled by proper design of impedances Z11 and Z21, an inverse effect being produced in the low frequency value of the equalizer loss. The useful frequency range, as indicated in the diagram is from 4 to 40 kilocycles per second and in this range the line loss is quite The frequency variation of both losses may be so coordinated by the design of impedances Z11 and Z21 so that the net over-all amplification of the system accurately compensates the attenuation distortion of the associated line. The increasing value of the line loss at frequencies below the useful range may be used to advantage under certain circumstances, for example in a fourwire transmission circuit in which a number of amplifiers such as shown in Fig. 2 is included. The line loss in this case will serve to prevent low frequency singing around the fourwire loop.

What is claimed is:

l. A transmission system comprising a line having a frequency selective transmission characteristic, an amplifier in said line, input and output circuits for said amplifier, a feed-back circuit for connecting said output circuit to said input circuit and a unitary network adapted to substantially prevent transmission from said line to said feed-back circuit or vice versa and having a frequency selective transmission characteristic for currents transmitted from said output circuit to' said feed-back circuit, which simulates the transmission characteristic of the line.

2. A transmission system comprising a line having a frequency selective transmission characteristic, an amplifier in said line, said amplifier requiring for its eflicient operation the equalization of said line characteristic, input and output circuits for said amplifier, a feed-back circuit for connecting said output circuit to said input circuit and a unitary network adapted to equalize said line characteristic both by selectively attenuating currents passing from said output circuit to said feed-back circuit in a manner to simulate said line and by selectively transmitting currents from said output circuit to said line in a manner adapted to off-set the transmission characteristic of the line.

3. A transmission system comprising a. line having a frequency selective transmission characteristic, an amplifier in said line, said amplifier requiring for its efiicient operation the equalization of said line characteristic, inputand output circuits for said amplifier, a feed-back circuit for connecting said output circuit to said input circuit and a unitary network adapted to equalize said line characteristic both by selectively attenuating currents passing from said output circuit to said feed-back circuit in a manner to simulate said line and by selectively transmitting currents from said output circuit to said line in a manner adapted to off-set the transmission characteristic of the line, said network substantially preventing transmission from saidline to said feed-back circuit or vice versa.

4. A transmission system comprising a line having a frequency selective transmission characteristic, an amplifier in said line, said amplifier requiring for its eflicient operation the equalization of said line characteristic, input and output circuits for said amplifier, a feed-backcircuit for connecting said output circuit to said input circuit and a unitary network adapted to equalize said line characteristic both by selectively attenuating currents passing from said output circuit to said feed-back circuit in a manner to simulate said line and by selectively transmitting currents from said output circuit to said line in a manner adapted to off-set the transmission characteristic of the line over a range of useful frequencies, said network greatly attenuating frequencies below said range to prevent singing.

5. In a system for controlling transmission, an amplifier, a line associated therewith, a feed-back circuit connected to said amplifier and a bridge network comprising a pair of inverse impedances, a pair of resistance arms connected alternately beiwveen said inverse impedances, said line being connected across one pair of diagonally opposite corners of said bridge, said feed-back circuit being connected to said bridge in conjugate relation to said line, and said amplifier constituting one of said resistance arms.

6. In a transmission system, a section of transmitting medium having a varying efiiciency dependent upon the frequency of the wave transmitted therethrough, an amplifier for off-setting at least a portion of the transmission loss of said section, input and output circuits for said amplifier, a feed-back circuit for connecting said output circuit with said input circuit, incoming and outgoing lines for connecting said amplifier to the medium, a network comprising a resistance and two general impedances, said resistance and one of said general impedances being connected across one of said lines, said feed-back circuit being connected across the resistance and the other of said general impedances, and one of the said circuits of the amplifier being connected across the entire network, said network being designed to substantially prevent transmission between said line and feed-back circuit, to approximately simulate the varying efliciency of said section to be equalized for transmission between said amplifier and said feed-back circuit and to cause a relatively small transmission loss between said'amplifier and said line.

7. In a transmission system, a transmitting medium having a varying efliciency dependent upon the frequency of the wave transmitted therethrough, an amplifier for oif-setting at least a portion of the transmission loss of said medium, input and output circuits for said amplifier, a feed-back circuit for connecting said output circuit with said input circuit, incoming and outgoing lines for connecting said amplifier into said medium, a network comprising a resistance and two general impedances, said resistance and one of said impedances being bridged between the terminals of one of said lines, said feed-back clr-'- cuit being bridged across said resistance and the other of said general impedances, and one of said amplifier circuits being bridged across the whole while substantially preventing transmission between said line and said feed-back circuit.

ALBERT L. STILLWELL,