GB754365A - Improvements in or relating to distortion-correcting circuits - Google Patents

Abstract

754,365. Equalizing networks. WESTERN ELECTRIC CO., Inc. July 6, 1954 [July 9, 1953], No. 19756/54. Class 40 (8). A distention-correcting circuit for correcting imperfections in the loss or delay of a signal transmission system comprises input and output delay lines 6, 7, which may be multisection low-pass wave filters, each terminated by a matching impedance 19, 22, and a series of adjustable transmission paths 26, 27, 38 between corresponding selected points in the lines. Each path may include a thermionic tube 41 or transistor to act as an isolating or amplifying device. In the operation of the circuit shown in Fig. 1, where the paths comprise variable capacitances 35, 36, 37 ganged together, the main part of the signal from the source 13 passes through path 26 substantially without delay and the amplitude and polarity of the signal is adjusted by adjusting the capacitances. A first harmonic " shape " is obtained by the portion of the signal which passes through the next path 27 which signal suffers a phase shift (# 1 +# 2 ). The polarity and amplitude of this signal are similarly adjusted. Similarly the nth harmonic " shape " is derived from the portion of the signal which suffers a phase shift n(# 1 +# 2 ). Thus any desired transmission loss or gain characteristic may be obtained. In a modification, Fig. 2, the loss and delay corrections may be independently corrected. In this circuit, each delay line comprises two halves 50, 50<SP>1</SP> and 60, 60<SP>1</SP>, the ganged capacitances of each corresponding branch being mechanically coupled to the other through either of two linkages 79, 80. When the circuit is used for loss correction the linkage 79 is used, the capacitances in the branches being so adjusted that the amplitude factor in the paths 95, 95<SP>1</SP> are changed by equal amounts in the same direction, and for delay correction the linkage 80 is used, the amplitude factor being changed in opposite directions. A mechanical device is shown in Fig. 5 (not shown), for controlling the choice of linkages 79 or 80 and for adjusting the capacitances. Alternative connecting paths which do not require the use of thermionic tubes are shown in Figs. 3 and 4 (not shown). In a further modification, Fig. 6 (not shown), the connecting paths comprise variable inductors. This circuit may be used to provide simultaneous or independent loss or delay correction depending upon whether the end or the middle inductors are adjusted to take the main signal path. The Specification contains a mathematical explanation of the circuits. U.S.A. Specification 2,348,572 is referred to.