GB388477A - Improvements in or relating to the measurement of transmission levels on telecommunication circuits - Google Patents

Abstract

388,477. Telephone and like transmission measurements. LIGNES T•L•- GRAPHIQUES ET T•L•PHONIQUES, 26, Rue de la Pepiniere, Paris. Oct. 20, 1931, No. 29139. Convention date, Nov. 14, 1930. [Class 37.] For the measurement of transmission levels on telecommunication circuits, the voltage at the point to be measured, or the voltage at this point and an adjacent point, is applied simultaneously along two conducting paths to an indicating device, the phase and modulation of the voltage (reference voltage) in one path being adjusted to neutralize the effect on the indicating device of the voltage under measurement. An indicator 9, Fig. 1, is connected to the transmission line 1, 1<1> at the point 2 at which the voltage level is to be determined. The reference voltage is taken from the line at a neighbouring point 3. The points 2, 3 may be merged together. The voltage at the point 3 is amplified by a voltage amplifier 4 having a high input impedance and a fixed gain. The amplified voltage is fed through a phase-changing device 5 to a power amplifier 6 having a variable gain. A measuring instrument 7 calibrated in voltage levels and a fixed resistance 8 are connected in series across the output of the amplifier 6. By means of this amplifier the modulation of the voltage across the resistance 8 may be varied. The phase-changing device, 5 allows the phase of the voltage across the resistance 8 to be varied without changing its amplitude. One form of phase-changer is shown in Fig. 2, in which fixed condensers C<1> of equal capacity and variable resistances R are connected as shown between terminals A .. D. The voltage across the resistance 8 is applied to the indicating apparatus 9, which may be a high-impedance telephone receiver, in opposition to the voltage at the point 2 and the modulation and phase of the reference voltage are adjusted until a null indication is obtained. The voltage level is then read directly on the instrument 7. The amplifier 6 may have a fixed gain, a voltage reducer being employed.