Attenuation is typically around 7 dB /nautical mile at 100 kHz, as com- 

 pared to about 1 dB/nautical mile for SF coaxial cable. However, because 

 of the relatively short lengths of the multi-conductor E-M cable used in 

 ocean operations (1 nautical mile), high resolution TV signals can be 

 transmitted without repeaters at carrier frequencies around 100 MHz. 



The main reason for using a multi-conductor cable of this kind — 

 rather than a single small-diameter coaxial cable with all signals multi- 

 plexed on the one coaxial cable — is to insure precision of measurement 

 in deep sea experiments in which errors introduced by multiplexing can- 

 not be tolerated. Also, if conductors in the multi-conductor cable are 

 grouped into twisted pairs or quads, the effect of extraneous signals is 

 less than it would be for a coaxial line. 



An example of a multi-conductor E-M submarine cable is the 10,000- 

 foot 10-conductor signal cable used in the Oceanic Telescope Engineering 

 Program. 23 This double- armored plastic-jacketed cable is about 1.5 

 inches O.D. and was used in a long-term horizontal sensor array for 

 measuring temperature and pressure variations at 630 meters depth. Under 

 the armor a neoprene layer encloses the insulated conductors, providing 

 a double seal against seawater penetration to the conductors. Another 

 example of a multi-conductor E-M cable is the cable used for load hand- 

 ling, power, and signal transmission in the DOTIPOS system^ at NCEL. 

 This cable is double-armored of 1.116-inches O.D. made up of one coaxial 

 cable for command and data telemetry, a second coaxial cable for TV sig- 

 nals, and two twisted pairs of #12 AWG copper for transmission of 2400 V. 

 60 Hz power. The length of the cable is 8,000 feet. 



Most of the quad- type ocean cables manufactured by Simplex are of 

 the wet-core construction. -> The seawater actually penetrates the cable 

 into the primary insulation of each conductor such that the water forms 

 and electrostatic shield around each conductor. A single-quad cable, 

 for example, uses four #18 AWG copper wires, each having an insulation 

 diameter of 0.13 inch, and each wire having a DC resistance of 6.2 ohms 

 per 1,000 feet. The capacitance of a pair of conductors is 0.017 micro- 

 farad/1,000 feet, and the maximum working voltage about 600 volts. A 

 wet-core quad of 0.45-inch diameter will have the same capacitance and 

 working voltage but a resistance of 3.2 ohms per 1,000 feet. 



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