NEGATIVK IMFKDANOK TKLKI'IION" K l< KPKATIORS 1089 



of the repeater, is inserted into tho ^•acant E2 repeater position for 

 picking up the connections to the incoming and outgoing hnos. A jack 

 ended cord, connected to the test phig is patched into the test set for 

 applying the line connections to the repeaters under test. 



The first position of the rotary function switch arranges the test set 

 for the reference condition. The incoming and outgoing E2 repeater 

 lines provide the terminations, as shown in Fig. 26(a). The low impedance 

 voltage source is obtained by means of an oscillator working through 

 a step-down transformer having an impedance ratio of 000:2 ohms. The 

 low impedance side consists of two equal well balanced windings, one 

 winding being inserted into each side of tho line, to form a balanced-to- 

 ground voltage source. The received current is measured by means of a 

 detector working through an identical transformer having one of the 

 2-ohm windings connected into each side of the line for maintaining 

 the balanced-to-ground circuit. 



Switch position 2 connects the El or E2 repeater into the test cir- 

 cuit between the sending and receiving impedances as shown in Fig. 

 26(b). The change in detector reading will indicate the insertion gain 

 or loss of the connected repeater. 



The third and fourth switch positions change the arrangements of 

 El, E2 and E3 repeaters for the insertion measurements of the various 

 repeater combinations, as shown in Figs. 26(c) and (d). Fig. 26(e) in- 

 dicates the connections for testing the E3 repeater alone on switch posi- 

 tion 5. 



IMPEDANCE MEASUREMENTS 



The second section of the type-E repeater test set has been arranged 

 to measure the impedance of two-terminal networks and the return 

 loss between any two impedances or between an unknown impedance 

 and a specified network. The impedance measuring circuit consists of a 

 hybrid coil arranged in the form of a balanced bridge for measuring 

 return loss. The driving voltage and detecting device are connected 

 across conjugate arms of the bridge and the unknown impedance and a 

 resistance standard are applied across the opposite conjugate arms of 

 the bridge circuit. 



Simple transmission measurements made across the hybrid coil, 

 between the oscillator and detector sides of the bridge, are the only 

 determinations required to find the return loss between any two im- 

 pedances or the magnitude and phase angle of an unknown impedance. 

 Such a device has several advantages over other types of impedance 

 bridges in that no critical balances are required, no cahbrations are 



