Doing research for a project, I stumbled across this look at AT&T’s defunct Long Lines system. From the 1950s through the 1990s, the telecom company used a series of relay stations across the U.S. to transmit telephone calls, military communications, and even TV shows:
The stations were connected via line-of-sight horn antennas which transmitted (or received) microwave signals. A call placed in one part of the country would be passed on to the next relay station, then passed on to the next, and so on until it reached the station nearest its destination. Then it would be sent through cables to the telephone company then to your house. Each horn antenna was positioned so it made a direct path (line-of-sight path, or “as the eagle flies” path) to the next station.
If you’ve ever passed abandoned concrete bunkers with metal towers on top, they might very well be leftover relay stations. Fascinating to remember how communications worked in an era before satellites, cell phones, and fiber optics.
—Linked by Dan Moren