748 BELL SYSTEM TECHNICAL JOURNAL 



transmission over the line and restored to original condition at main terminal 

 points. At intermediate points appropriate groups of channels may be 

 removed, inserted, bridged, or relocated in the frequency spectrum of the 

 line. 



Experimental Studies of a Remodulating Repealer} W. M. Goodall. 

 This paper describes tests made on an experimental broad-band microwave 

 f.m. repeater. A superheterodyne receiving unit is used with a microwave 

 reflex-oscillator transmitting unit to form a repeater. An experimental 

 setup for testing this repeater in a circulating-pulse system is described. 

 Oscillograms showing the performance of the repeater on a multilink basis 

 are discussed. 



An Electronic Regenerative Repeater for Teletypewriter Signals. ^ R. B. 

 Hearn. The important factor in teletypewriter signal transmission over 

 circuits is the relative position on a time scale of the code pulses. If this 

 timing is preserved, wide amplitude variations can be experienced without 

 errors resulting. Correctly timed signal pulses at the transmitting end 

 of a circuit are not necessarily properly timed at the receiving end, as the 

 transmission path may shift the timing of some transitions with respect to 

 others. However, if the signals are not too badly changed or distorted, it is 

 possible to retime them at an intermediate point and send them on in their 

 original form. 



Many arrangements have been devised for automatically retiming and 

 retransmitting teletypewriter signals. These arrangements are known as 

 regenerative repeaters. A few of these have been designed to make use of 

 electronic timing arrangements and the purpose of this paper is to describe 

 such an electronic regenerative repeater, known as repeater TG-2P, designed 

 originally for use by the Armed Forces. 



Submarine Detection by Sonar. ^ A. C. Keller. Sonar, the only effective 

 method of detecting completely submerged submarines was a major factor 

 in the defeat of the f/-boat and the winning of the Battle of the Atlantic. 

 A majority of the 996 enemy submarines sunk during World War II was 

 detected and located by sonar. The word sonar is formed from the phrase 

 SOund Navigation And Ranging and apphes broadly to under water sound 

 devices for listening, echo ranging, and locating obstacles. 



The QJA sonar system, one of those which got into active service during 

 World War II, is described here. This equipment was designed by Bell 

 Telephone Laboratories and manufactured by the Western Electric Com- 

 pany. 



* Proc. L R. E., May 1948 (pp. 580-583). 



6 Trans. A. L E. E., vol. 66, 1947 (pp. 904-911). 



• Trans. A. L E. E., vol. 66, 1947 (pp. 1217-1230). 



