dmt@PacBell.COM (Dave Turner) (09/15/90)
In article <4019@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: > While the first undersea repeaters for TAT-1 in 1956 used vacuum >tubes, isn't it interesting that *seven* years later Western Electric >*still* considered vacuum tubes more reliable than transistors for >submarine cable repeater use? In a couple of related Radio-Electronics items: November, 1965: Coaxial Cable Handles 32,400 Channels A new coaxial cable system, with nearly twice the capacity of any broadband system now in use, has been announced at Bell Telephone Laboratories. The new system, the L-4, covers a broader band than even microwave radio. The cable contains 28 coaxial conductors and operates at frequencies twice as high as those used in its predecessor, the L-3. The L-4 marks the first use of transistor repeaters in a coaxial cable system. They are spaced every 2 miles. In addition, there are regulating networks about every 14 miles, equalizing networks every 50 miles and additional equalizing networks at main repeater stations as much 160 [sic] miles apart. Thus repeater gain is kept constant, though changes in temperature and other factors vary the cable losses. Voice channels can thus be maintained over routes of several thousand miles. September, 1966: New Undersea Cable System First to use Transistors Bell Telephone Laboratories' new undersea telephone cable system can carry nearly six times as many two-way conversations as any present US undersea cable. The new SF system, as it is called, provides for 720 two-way channels, compared to 128 two-way circuits in the previous SD system. Transistor amplifiers, used for the first time, help broaden the bandwidth and therefore increase the number of voice channels. The transistors are expected to have an even longer life than the estimated 25 years of tubes previously used in such amplifiers. The amplifiers will be spaced 10 nautical miles apart, and each will provide a gain of about 40 dB. The first cable used in the new system is expected to be a 1,250-mile stretch between Jacksonville, Fla., and St. Thomas, Virgin Islands. Quoted without permissions. -- Dave Turner 415/823-2001 {att,bellcore,sun,ames,decwrl}!pacbell!dmt