Old Telecommunications Technology

AT&T Microwave Radio Relay Station - Watertown, South Dakota - 1970

This relay station was a small part of the nationwide Bell System/AT&T Long Lines telephone network.

Station Details

  • Vacuum tube/analog technology - Western Electric 4 GHz TD-2 microwave radio, L-carrier frequency division multiplex
  • Six separate 8-hour backup battery strings for plate and filament voltages, w/associated rectifiers
  • 40-ton airconditioning system - 4 10-ton Carrier staged units
  • 275 kW AC backup power generator - Detroit Diesel V-12, 2-stroke
  • Ultimate capacity: 15000 voice-frequency LD telephone circuits (data throughput equivalent: ≈ 1 Gb/s)


The 1970s saw a massive upgrade to solid-state equipment along with increases in circuit capacity and a roll-over to digital technology. By the 1990s microwave radio as a means of providing long-haul telephone communications had been supplanted by fiber optic cable. Microwave radio (digital) is still used extensivly for short-haul communications such as backhaul links for cellular base stations, telemetry/SCADA for pipelines and electric power transmission, power system protection and the like. Most of these old towers still exist, stripped of their original equipment, leased nowadays for cell phone, broadcasting and mobile radio communications.

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