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PCBD-May2014

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38 The PCB Design Magazine • May 2014 Long before Facebook and Twitter, there was a more primitive type of social network. Hailing from the Old West, it allowed distant commu- nities to meet remotely to share music, spread news and to just gossip. The non-proprietary, ad hoc network was an unwitting model of democ- racy and free speech. Unfortunately however, it collapsed—overwhelmed by commercial pres- sure. The long-forgotten social revolution, and extremely basic technology, was built on barbed wire fences. Barbed wired fences appeared in the United States in the 1860s and their success, in the con- trol of cattle, swept across the North. However, the South, fearing that the product may harm their cattle, was hesitant to buy the fad at first but ultimately succumbed. Ironically, the barbed wired fence is associated with the cowboy, but unfortunately, it also sounded their end. As with all communications systems, get- ting connected, particularly in remote areas, is always a challenge. In the early 1900s, the Bell Telephone company was focusing all efforts on connecting urban areas and like the telephone companies of today, had little interest in con- necting remote communities, due to the cost of the infrastructure. However, an enterprising rancher fig- ured that the West was already sprawled with wire—barbed wire—and discovered that if you hooked two Sears or Monkey Ward telephone sets to a barbed wire fence, he could talk be- tween the telephones as easily as between two city telephones connected via an operator's switchboard. A rural telephone system that had no operators, no bills—and no long-distance charges—was born. But that lack of broader connectivity even- tually doomed the ad hoc net- work. The commercial phone system's ubiquity, and espe- cially their coveted connec- tion to distant cities, eventu- ally dominated. By the 1920s, the barbed wire telephones and the networks they helped spawn had disappeared. By comparison, today's long-distance digital commu- nications operate over vari- ous types of media including coax and twisted pair cables. And multilayer PCBs also transfer data via microstrip or stripline transmission lines. Surprisingly, all of these dif- ferent types of media can be modeled using the same equations. The Telegrapher's Equations accurately model BEYOND DESIGN column by Barry Olney in-CirCuiT Design PTy lTD Transmission Lines: From Barbed Wire to High-Speed Interconnect Figure 1: Barbed wire fence (courtesy of fenceworkshop.com).

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