. Bell telephone magazine . ds that are well sep-arated from each other, both can beused on the same routes without inter-ference. As common sites, towers, an-tennas, access roads, and power connec-tions can be used, TH systems may beintroduced with great economy. Evenexisting buildings can be utilized, al-though enlargements may be needed. With both types of systems being used,a route can have a total capacity at presentof 16,800 circuits. Thus far, the exist-ing TD-2 route between New York andSalt Lake City, with branches to Chi-cago and Denver, has been equipped withthe TH system as well. I
. Bell telephone magazine . ds that are well sep-arated from each other, both can beused on the same routes without inter-ference. As common sites, towers, an-tennas, access roads, and power connec-tions can be used, TH systems may beintroduced with great economy. Evenexisting buildings can be utilized, al-though enlargements may be needed. With both types of systems being used,a route can have a total capacity at presentof 16,800 circuits. Thus far, the exist-ing TD-2 route between New York andSalt Lake City, with branches to Chi-cago and Denver, has been equipped withthe TH system as well. In 1966 the Bell System expects tohave new equipment which will doublethe capacity of the TD-2 system. CodedTD-3, the new system will carry 1,200circuits on each channel, using the frequency band. By adding the 10,800circuits of the TH systems transmittedin the 6,000 band, a combined total ofalmost 23,000 telephone circuits will besecured. This is a far cry from the firstradio relay system introduced in 1947> 16 I. J/^ ■-^i^ T-1 microwave repeater at Chinks Peak,Idaho. One of first installations of this system. Short Haul Service The third block of radio frequenciesmade available for common carrier oper-ation—the 11,000 mc band—is more suit-able to short rather than long-haul trans-mission. This is because the microwavesin this band are extremely short—slight-ly over one inch—and therefore trans-mission may be impaired during heavyrain storms when energy is absorbed byrain drops. Nonetheless, the Bell Labora-tories has developed systems—called TJand TL—which can employ the micro-waves in this band for short-haul servicein parts of the country where the annualrainfall is light. The TJ system has a capacity of 600channels that can be maintained witha normal level of reliability. In areaswhere rain is heavy, it is possible totransmit up to 100 miles with about ten intermediate stations, but where it is rel-atively dry, it is possible to span some200 miles w
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