US1592883A - Repeater for transmission lines - Google Patents

Description

H. A. BARTON ET AL REPEATER FOR TRANSMISSION LINES Filed Jan. 27,

All.

HIM/11w A TTORNE Y July 20 1926.

MAM AAAAAM "In" Mun glllhllh nn 'WI 1 "I principle of the Events i the latented July 20, W26.

RENEE A. BARTON, 033 NEW YORK, AND HARRY NYQUIST, OF ELMKURST, NEW YDRK,

ASSIGNGQRS TO AMERIGAN TELEPHONE AND TELEGRAPH COMPANY, A GORPORA- TION 015' NEW YORK.

BEPEATER FOR TRANSMISSION LDQ'ES.

Application filed January 2?, ma. Serial 1%. e15,s7e.

this an object of our invention to im another ob'ect is to equalize the ellect of lines of di erentlcngth on a repeater of the type which repeats hoth ways with a-single amplifyin glects of arinvention will :oecome apparent on con ation or a. limited number of specific examples of practice in accordance with the invention whi are disclosed in the fol-lowing specie or: taken with the aceompa dra: it will be understood that the escription applies to these aaamp mention and that the cope-or tnveno is pointed out in zended Etererxdcg 3: element These and other dbrawings, Figure 1 is a diagram of iission line embodying our invention. fig. .2 is a curve diagram that will referred to in ex laining the and Figs. 3. and .3 illustrate respectively different ways oi realizing the invention in connection with. over which both side and phantom circuits operated. I

Fl 1 represents a telephone transmission line intendedtor simultaneous two-way operation and compiising an interposed repeateroi the so-called fill-type. This means that the repeater operates both ways but uses only a single emplifymg element A for this purpose. The usual three-winding hynerd-transformer T 1s designed so that 1f the lines vextending each way therefrom are equal 111 all respects, then an incoming Wave.

on eitherline will go in part to the input side of the amplifier A. The amplified output will then go equally to the line both ways vfrom the transformer and none of this output will get back to the input of the amplifier A, because of the absence of any potential drop across the input terminals due to the'balanced output.

The impulses put upon the line from the p r sfit W 3 be tefl ted back is I also be increase some degree from the terminal stations E and W and if these are both far distant, any reflection is highly attenuated before it returns to the repeater. If either or both terminals are not far distant the reflected waves may have considerable magnitude and will enter the input of the amplifier A.

In the case where one station W is near and the other station E is distant it is ossible to improve the circuit bymeans W ich will ;be described.

It might appear that to lengthen the line to ,station W by interposing artificial line would do more harm than goodbecause such interposed artificial line must attenuate the transmission either way between the two stations E and W. But in accordance with the principle of our invention, as we shall show,- there may be a positive advantage gained by interposinga properly de signed artificial linebetween the repeater and the nearer station W.

The network or artificial line N is interposed, as shown in F ig. 1. Let its equivalent in' standard miles. be represented by the character L. Since a wave going out from the repeater to-the station. W and reflected back therefrom most traverse the network N twice, the attenuating ellect on that wave due to interposing the network N will be represented by 2L. But so far as transmission is'concerned from E to W Y or from W to E, the attenuating efiect of the network N is only L. v

If sufilcient gain is given bythe-amplify Eng element to overcome the attenuation of the reflected wave, singing or. sustained oscillations are set up. Theelement A will be adjusted to give a gain which is less than the singing gain by a specific margin, e. g. 5 standard miles which must be allowed between singing and operating gain in order to secure good quality. sition of the network N the attenuation of the reflected waves has been. increased by 2L so that the ain in the amplifier A can by 2L and the margin of 5 miles betweensinging and o eratin gain is still maintained. It should e note that. th fore o g s atement is t e, h fi fl By the interponumerical value this margin may have. The insertion of the net has-increased the transmission loss between E and W either way byL. However, it has made it possible to increase the gain of the repeater 2L which results in a net gain of L. I

'A. practical method for determining the propermagnitude of the network N as measured in standard miles L will now be explained in connection'with Fig. 2. By standard miles we refer to units of attenuation of any apparatus interposed between a transmitting point and a receiving point, whose number L is-given by the formula Z=21.13 log R where R- is the ratio .of received current when the apparatus is not interposed to received current when it is interposed. Various values of L are tried and the utmost repeater gain without singing is also determined for each value of L. 'These values of L are laid off as abscissae. in Fig. 2 and the correspond ing values of gain forjthe repeater A are set Fig. 2.

But. since the gain in the repeater, as indicated by the curve G, is offset to some extent by the loss L in the network N, a new curve marked G-L-is constructed by diminishing each ordinate of the curve by the corresponding value for L. This curve G-L will have a distinct maximum Ivaluc, as appears in F ig.- 2,-and the value of L at this maximum is the appropriate value to be given to the network N.- Fig. 2.is drawn for an actual example of a 19 gauge medium heavy'loaded circuit containing a 21-type repeater with 35 miles of line on one side and 10 miles on .the other side. It will be seen that there is a net improvement of 1.8 standard miles by interposing 4.5 standard miles for the value of L in the network N. I

The network N'must have the same characteristic impedance as the circuit in which it is interposed; this may be accomplished by design according to well understood principles.

Figs. 3, 4 and 5- show alternative ways in which the invention may be practiced in connection with 'lines comprising side and phantom circuits. The 21-type phantom group repeater is indicated diagrammatically by the rectangle with the legend QI'I PG'R. In Fig. 3, a'network N is provided for each pair having in each conductor the two resistances in series, each R/2. Bridged across between them is the shunt resistance 1'. R and 1' are given appropriatewalues in accordance with well nown principles of design so that the network shall have.the same characteristic impedance as the line and shall give the loss found by the methodpreviously described. Then the mid-points of the two-shunt reup as ordinates, thus giving the curve G in' a complete independent sistances, each having the value 1', are con nected by a resistance p such that Subject to this condition, the loss inserted in the phantom circuit and th characteristic impedance presentedto it will be approximately. correct.

It maybe necessary for the purpose of securing proper balance to use condensers as shown in Fig. '3 by the character C to make the characteristic impedance of the inserted network more accurately equal to that of the line. $9

where the networks N are pilt in the local circuits determined by the repeatingcoils S, which are interposed inaccordance with the principle of phantom design. In this case, network N of proper design will be interposed in the taps that goto complete the phantom circuit, as is shown in Fig. 1 5. An advantage of the arrangement in Fig. 5 is that it will give less danger of cross-talk between the side circuits and the phantom circuit.

WVe claim:

-1. In combination, a 21-type repeater, two lines of different length extending thefefrom and .a network interposed in the line of shorter length, said network having the same characteristic impedance as the lines, and an attenuation value such that the increase in the gain in the repeater made possible by the interposed network will be more than the one-way transmission loss in the 195 network. v

2. The method of increasing the gain at which a 21-type repeater between two lines of different length maybe operated, which consists in causing the unbalance waves on the side of the shorter line to traverse an interposed network twice of the same characteristic impedance as the line while the effective transmission will traverseit but once.

3. The method of determining the optimum attenuation to be introduced in the shorter side of a transmission line with an interposed 21-type repeater, which consists in plotting against said attenuation the maximum repeater gain diminished by said attenuation thus givingthe desired attenuatilon corresponding to the maximum. on the p ot. 4. In combination, a transmission system comprising two sides and a phantom with an lnterposed Pal-type phantom oup' repeater, networks in each side making it its possible to im rovetransmission on each side with these networks constituting means further to improve transmission on the phantom circuit.

5. In combination, a transmission systern comprising two sides and a phantom with m interposed 2l-typo phantom group repeater, aiid appropriate networks to make it possible "c-o improve transmission on each side and on the phantom.

' In testimony whereof, we have signod our no names to this specification this 25th day of

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