GB783456A - Improvements in or relating to arrangements for determining network insertion loss - Google Patents

Abstract

783,456. Insertion loss measurement; voltage measurement. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Dec. 19, 1955 [April 20, 1955], No. 11355/55. Class 37. Insertion loss of a network is measured by energizing the network and a calibrated adjustable attenuator from a variable frequency oscillator, and connecting a calibrated adjustable phase-shifting means to combine the attenuator output in antiphase with the network output at a null indicator; balance being achieved when the attenuator and the network outputs are equal and opposite in phase. A variable-frequency oscillator excites test network N1 and attenuator N2 over series input impedances R1, R3 to energize respectively load impedance R2 and the centre-point of the primary of a hybrid transformer, whose remaining terminals are grounded over variable impedances R4 and R5; a variable capacitance C1 being connectible by switch S across either half primary. The secondary is connected in series with the network output across impedance R2 to the input of an amplifier feeding a null indicator; it being shown that by adjustment of R4, R5 and C1 the phase angle of the attenuator signal is adjustable to antiphase with the network signal, and by adjustment of the attenuator the signals are made equal in magnitude for a zero indication; the network insertion loss being then equivalent to the attenuator setting plus the insertion loss of the hybrid network determinable from the settings of R4, R5 and Cl.