Patent GB-425639-A (GB)
Title: Improvements in or relating to submarine electric cable systems
IPC: H04B3/00
Filed: 1933-12-18
Abstract: 425,639. Repeaters. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Buckley, O. E. ; 13, Fairview Terrace, Maplewood, and Jacobs, O. B. ; 20, Hamilton Road, Morristown, both in New Jersey, U.S.A.) Dec. 18, 1933, Nos. 35642 and 35643. Convention dates, July 21 and Oct. 6. [Class 40 (iv)] [See also Group XXXVI] In a submarine cable system, employing repeaters of the thermionic type, the repeaters are structurally secured to the cable and are preferably enclosed under the cable armouring so that they may be laid and brought to surface with the cable,the thermionic tubes of the repeaters being operated under low filament and anode current conditions to ensure long life and being supplied with direct current from the ends of the cable. Fig. 1 shows a cable 10 having one-way thermionic repeaters R1-Rn and a return conductor 16, the repeaters being energized with current from batteries 7, 13 which are connected across the cable core and the return conductor at each end of the cable. Regulating resistances 9, 15 in the battery circuit control the gain at the repeating points ; or a constant gain may be obtained by using as the resistances 9, 15 three electrode space discharge tubes which are operated as constant current devices. The transmitting transformer 2 associated with the cable is isolated from the battery 7 by a condenser 1 and filter 8, the receiving transformer 5 at the other end of the cable being similarly isolated by condenser 4 and filter 14. The repeaters, which are connected between adjacent cable sections, may comprise an amplifying tube 40, Fig. 3, having input and output transformers 41, 42, the filament of the tube being connected between the cores of the two cable sections in series with signal chokes 44, 49 and grid bias and anode voltage dropping resisters 45, 47. The transformers 41, 42 are isolated from the direct current flowing in the cable core by condensers 43, 51. Decoupling of the input and output circuits is effected by a condenser 50. The components of the repeater are disposed under the cable armouring 53, Fig. 4, within a steel casing 54 having tapered end portions provided with glands through which the ends of the cable sections pass. The casing 54 is covered by a lead sheath 70 which extends for a distance over the cable ends and over which a jute filling is applied to provide a gradual taper of the cable cross - section adjacent the repeater. Heat - insulating baffles may be disposed between the components of the repeater. The repeaters may be designed to compensate for unequal attenuation of the frequencies transmitted by the cable. For two-way working, separate cables may be employed for the two directions of working and these may have common or independent batteries for supplying current to the repeaters. Fig. 5 shows a terminal circuit for connecting a number of land lines, such as L1 to a multiple channel single sideband carrier wave transmission system comprising two one-way submarine cables 10, 20 having independent batteries 7, 27. The land line L1 connects with a four-wire line comprising repeatered transmitting and receiving branches 60, 61 respectively. The branch 60 is connected to the cable 10 through an automatic volume control 62, modulator 63 having carrier source 64<1>, band filter 64, amplifier 65 and sending transformer 2. The modulator 63 and band filter 64 are such that only one side band of the modulated carrier is passed to the amplifier 65. A separate branch 60 operating at a different frequency range is provided for each land line, the amplifier 65 and transformer 2 being common to all the transmitting branches. A carrier side band received from the cable 20 passes through the common receiving transformer 22 and amplifier 75 and is selectively transmitted through the appropriate filter 76 to a demodulator 72 and low pass filter 74 and thence to the receiving branch 61 of the four-wire line. One of the channels may transmit a pilot frequency over the cable to control the gain of the amplifier at the receiving end or to control the gain all along the line. In a modified system twin core cables are used and the direct current for operating the repeaters passes through the two cores in parallel, in which case the condensers for isolating terminal and repeater transformers are dispensed with. In another system, twoway operation over one cable is effected by the use of two ranges of carrier frequencies for the two directions, the two ranges being subdivided at the terminal and repeater points by filters. Fig. 10 shows a two-way repeater for use in such a system, connected between sections of a cable 10 and supplied with direct current from the cable core through chokes 44, 49. Signals from left to right pass through transformer 101, low-pass filter 95<1>, equalizer 104, band eliminator filter 105, equalizer 106, transformer 41, amplifier 100, transformer 42, low-pass filter 952, and transformer 102. Signals passing from right to left traverse successively transformer 102, high-pass filter 94<1>, equalizer 103, band eliminator filter 105, equalizer 106, transformer 41, amplifier 100, transformer 42, high pass filter 94<2> and transformer 101. The equalizers 104, 103, 106 compensate for unequal attenuation of the different frequencies transmitted, whilst the band eliminator filter 105 suppresses frequencies between those utilized for transmission in opposite directions and may sharpen the cut-off of the other filters. To provide for greater flexibility of the cable the components of the repeater may be accommodated in a number of separate housings, such as indicated at 111-117.