36S BELL SYSTEM TECHNICAL JOURNAL 



farads, the direction of the unbalances being indicated b>- red and 

 black scales and arbitrarily designated as ( + ) and ( — ). 



Fig. 14 shows the circuit arrangement of the bridge for measuring 

 the capacity unbalance between the phantom and "white" pair. 

 The oscillator, variable condenser and receiver are connected as 

 before, the "black" conductor and its mate however, being strai)ped 

 together at one of the remaining bridge terminals and ratio arms 

 Ri and i?2 each consisting of 2,000 ohms resistance, being connected 

 as shown to the fourth bridge terminal. For the condition of minimum 

 tone the variable condenser reading then gives a measure of the 

 capacity unbalance between the phantom and the "white" pair, that 



Black mate --V Conden 



is a — b. Tlie capacities a and h take into .ucount in this case the 

 capacities of the "white" and "white mate" conductors to ground in 

 addition to the direct capacities between wires shown in Fig. 13. 

 The unbalance between the phantom and "black" pair is obtained 

 in the same manner as shown by interchanging the "white" and 

 "black" conductor connections to the bridge. The test set reads 

 only half the capacity unbalance as defined in the above formula for 

 phantom to side unbalance. 



In practice the testing arraiigenieiit just tlescribcd is used to lest 

 unbalances of all quads in a cable in each direction. .\t any splicing 

 point where the tests are made the three unbalance measurements 

 in each direction for each ([uad are carefully recorded and the splices 

 then made by combining ( + ) and ( — ) values so as to neutralize each 

 other as mucii as possible thereby reducing the resulting capacity 

 imbalances and the crosstalk in each direction to a miniinum. Both 

 the bridge and oscillator are readily portable and designed for out- 

 door use. The bridge is equipped with keys, binding posts and leads 

 to allow connections to be quickly made to the cable conductors and 

 the various conditions of unbalance measured. 



(3) Impedance Tesls. The various bridge arrangements for capacity 

 measurements are essentially impedance measuring devices, the im- 



