Improvements in or relating to arrangements for determining the transmission characteristics of electrical apparatus, circuits or transmission lines

摘要

352,752. Telephone and like transmission measurements. AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd., Strowger Works, Liverpool, and TURNEY, T. H., Beracah, Aughton Park, Lancashire. July 26, 1930, No. 22596. [Class 37.] An arrangement for determining the transmission characteristics of electrical apparatus, circuits, or transmission lines includes an adjustable network adapted to vary the phase without changing the impedance, so as to obtain a null indication. A source S1 is connected through high resistances R1, R2 to the primary winding of a transformer XF1 having two secondary windings a, b in which equal voltages are generated. The secondary winding a is connected through the actual line &c. under test to the primary winding of a transformer XF2, and the secondary winding b is connected through a " loss pad " LP and a phase-shifting network PH to the primary winding of a transformer XF3. The secondary winding of the transformers XF2, XF3 are connected as shown to resistances W, amplifier A, and telephone receiver R. The phase-shifting network PH comprises a lattice of inductances and capacities arranged to be simultaneously varied so as to vary the phase shift while maintaining the impedance constant. The coils should have low loss and the condensers should be shunted by resistances of such value as to make the powerfactor of the combination equal to that of the coils. The impedance of the apparatus to be tested is balanced by varying the resistances forming the "loss pad " LP and the phase-shift network PH is adjusted until no sound is heard in the receiver R. The apparatus may be modified for use with constant current instead of constant voltage.