The Limitation of the Gain of Two- Way Telephone 

 Repeaters by Impedance Irregularities 



By GEORGE CRISSON 

 InTRODU TION 



BHCAl SI-', of the fact that it is a (liftiriill anil exfK-nsive matti-r 

 to l)iiil(l and maintain tin- lii^li K^aili' circiiils that are ro(|uiri-cl 

 for motlcrn lonn distanre li-lophonc transmission with repeaters, 

 nKin\- workers in this held ha\e attempted to devise some form of 

 two-way repe.iter which would he ahle to ii'ivv as large a gain as 

 desiretl without singing or poor <iiiality due to irregidaritics existing 

 in the lines. The>' have thought that if such a rei>eater could he 

 constructed it would permit the use of lines less carefully built and. 

 therefore, cheaper than are at present retjuired, and that fewer 

 repeaters would he re(|uired ln-caiisi' larger gains could be obtained 

 at each repc-ater. 



As a matter of fact the irregularities in ihe lines have a very im- 

 portant effect and control, to a great extent, the repeater gains which 

 can lie used whene\er a telephone circuit is arranged so as to be 

 capable of transmitting in both directions over a single pair of wires 

 with constant efficiency. 



It is the object of this paper to explain, in a \er>- simjile wa\', 

 why this is true. To do this the phenomenon of electrical reflection 

 is first made clear. Then a two-way repeater system is introduced 

 and the effects of reflection upon this system are explained. After 

 mentioning several of the types of repeaters which have been used 

 successfully, the paper concludes with an explanation of the fallacies 

 underlying a numlx-r of schctiies which ha\e been jiroposed from time 

 to time by various in\entors. 



Ri:i-I.IiCTI().N IN TllIKlMloM-: i.I.NKS 



Whenever discontinuities or irregularities exist in telephone cir- 

 cuits, reflection of a certain part of the speech wave takes place 

 at each irregularity. In order to appreciate why it is that irregularities 

 in two-wire telephone circuits affect ver>' greatly the amount of 

 repeater gain which can be secured whenc\-er two-way operation is 

 desired, it is first necessary- to obtain a clear picture of why it is that 

 reflections take place at irregularities. 



Fig. 1 represents an infinite ideal telephone line without repealers. 

 If such a line is non-loaded or continuously loaded each part of it 



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