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not only to test the new E2 and E3 repeaters but also the older type of 

 El repeater, which has been in use for several years. All test connections 

 which are required to measure individual repeaters or combinations of 

 El o; E2 and E3 repeaters are made by the operation of a single rotary 

 control function switch. Such a sj'stem will avoid the unintentional 

 errors and time consuming operations which attend the setting-up of 

 complicated patch cord connections. 



The first five positions of the function switch are arranged to make 

 transmission measurements of an individual repeater or any combina- 

 tion of El or E2 and E3 repeaters. Insertion gain and loss measurements 

 are performed with the repeaters working between their normally con- 

 nected line impedances. 



In making transmission and stability measurements, it is sometimes 

 necessary to set up trial connections of the repeater networks during 

 the initial test period or for unusual line conditions. If the actual re- 

 peater networks were used, it would require a large number of soldered 

 connections to be made for each condition of the tests. Equivalent jack- 

 ended E2 and E3 networks have been included in the test set, so that 

 with small patch cords, a rapid interconnection of the network compo- 

 nents can be made. 



As gain and stability of the E-type repeaters are both directly de- 

 pendent upon impedance variations of the lines, it is sometimes neces- 

 sary to measure line impedance to determine the causes for low return 

 loss and instability. The last four positions of the function switch are 

 arranged to make positive impedance measurements of lines, negative 

 impedance measurements of the repeaters and return loss measurements 

 between any two lines or impedances. A decade resistance standard has 

 been built into the test set to furnish a direct indication of the magni- 

 tude of the unknowai impedance. The phase angle of the impedance is 

 determined by a return loss measurement and the angular degrees are 

 read from a chart supplied with the equipment. 



Although this test set was designed primarily for tests on E type 

 repeaters, it is possible to connect other types of four-terminal networks 

 into the test set and measure impedances, return loss against known 

 impedances, and insertion gains or losses. 



THEORY OF TRANSMISSION MEASUREMENTS 



One method of measuring the insertion gain of a negative imi)edance 

 repeater, without affecting the transmission or stability of the circuit, 

 is to introduce the test voltage, through a low impedance source, in 

 series with the input line and measure the resultant current picked off 



