1086 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



through a similar low impedance connection in series with the output 

 line. A comparison of the received currents, with and without a repeater, 

 will give an indication of the insertion gain or loss. 



The principles involved in making this type of transmission measure- 

 ment are shown in Fig. 24. The voltage source and the current measuring 

 detector are assumed to have negligible impedances compared to the 

 impedances of the lines Z\ and Zi . 



In the reference condition of Fig. 24, the driving voltage Eo and the 

 current measuring device are in series with the two line impedances Zi 

 and Z2 . The resultant current will be determined by the source voltage 

 Eo divided by the vector sum of impedances Zi and Z2 : 



/o = 



Eo 



Zi + Z2 



where Zi + Z2 indicates a vector addition of the two impedances. 



In the "measure"condition of Fig. 24 the repeater, represented by the 

 network A'', is inserted into the circuit between the voltage source and 

 the measuring device, and, although the voltage Eo is assumed to re- 

 main constant, the addition of network N into the circuit will change 



REFERENCE CONDITION 



■z, 



Eo 



Eo 



qp qfp 



OSCILLATOR DETECTOR 



MEASURE CONDITION 



Z,+Z2 



■z, 



Eo 



I,' 



^MOr 



'X. 



OSCILLATOR 



I, REPRESENTS A 

 CHANGE FROM Iq DUE 

 TO INSERTION OF N 



I, 

 INSERTION TRANSMISSION = 20LOG,oy- 



^0 



Fig. 24 — Principles of insertion measurements. 



