GB527104A - Improvements in transmission systems for high frequency electric signals - Google Patents

Abstract

527,104. Transmission systems ; retardation lines. STANDARD TELEPHONES & CABLES, Ltd. March 31, 1939, No. 10117. Convention date, April 23, 1938. [Class 40 (iv)] [Also in Group XL] In a system of the kind in which the lower frequencies of a television or other broad band are transposed to a position above the original upper limit of the band, the low frequency currents are eliminated from the portion of the band that is to be transmitted without change by balancing them against identical currents of opposite phase. As shown, the original currents divide at V, Fig. 7, the lower path comprising a filter 1 which passes frequencies up to 60 kc. without attenuation or phase distortion and cuts off at 200 kc. The low-frequency currents then divide, a portion passing to a modulator 2 for transposing them to a position outside the original band and another portion to a phase-reversing valve 3 to enable them to balance out the corresponding frequencies on the upper path. This path in addition to valves 4 and 5 comprises a retardation network 6, which introduces a phase lag equal to that introduced by the filter 1 in the lower path, and a filter 12 for eliminating frequencies in the shifted range of the lower frequency sub-band. At the receiving end, Fig. 17, the signals are amplified at 13 and then divide, passing respectively to valves 14 and 15 the amplification of which is adjustable. Signals in the lower path are limited by a band-pass filter 16 to the shifted range of the lower frequencies and are amplified at 17, rectified by a double diode 18 and passed via a low-pass filter 19 to individual and common amplifiers 20, 24. Signals, in the upper path after amplification at 14, 25 traverse a filter 21 which eliminates the shifted band of the lower frequencies and a retardation line 22 for equalizing the transmission time of the two branches before passing to individual and common amplifiers 23. 24. Retardation lines. The network 6 which introduces a constant delay for all frequencies preferably includes negative shunt inductance which is provided by mutual inductance between adjacent sections and may comprise a uniform winding on a magnetic or non-magnetic core with tappings at regular intervals for the condensers. As shown in Fig. 15, the condensers may be replaced by the distributed capacity of the windings by using a partially conducting coil support. The Specification includes a discussion of the design of the network and its termination.