Microwave radio systems were first introduced by the AT&T Long Lines Department for the telecommunications industry in the 1950's.  As long distance traffic and network reliability grew microwave towers were seen sprouting up on remote mountain tops, open fields and central city districts.  Short towers were used on sites were topography had the advantage such as a mountain ridge or hill line.  The taller towers, some reaching 300 feet into the sky were usually located on flat terrain such as the desert valleys or endless plains of the Midwest states.  Trapezoidal "horns" were initially used and later higher capacity "cornucopia" horns supplemented the trapezoids. 

California had a strong "backbone" of this microwave system which connected the state to neighboring cities and the rest of the nation.  The microwaves would carry both telephone, television and limited data traffic streams.  The microwave network also played a vital role during the "Cold War" for both secure and unsecured military communications.

There were basically two types of microwave sites, junction (switched) and repeater (relay).  

Junction/switched sites were larger, sometimes manned, which provided switching of microwave signals from one path to another.  Signals could be rerouted to various paths or underground cables depending on traffic load, bandwidth and location.  End points to these microwave paths were usually located at a toll office or tandem central office in the major cities

Repeater sites were in a sense relays that provided a point to allow amplification of the signal and a "jump" to the next tower or site.  These sites were usually placed to redirect (not reroute) signals around obstructions (hills, mountains) or on long routes.

With the invention and installation of higher capacity fiber optic lines in the 1970s microwave use slowly dwindled to serving as a back up system, or serving telecommunications in remote areas where fiber optic installation was cost prohibitive.  By the mid 1990's though, microwave transmission had all but been retired permanently.  The towers that stood the test of time were tuned down for good, their site being sold to wireless telecommunication companies or even private parties.  Horns and equipment have sadly been removed from numerous sites.  The towers now stand bare but provide the height and location now to serve the modern technological revolution of cellular, paging and wireless.



AT&T SOCAL MAP 1987.jpg (131468 bytes)AT&T Socal Map 1987  AT&T NORCAL MAP 1987.jpg (131006 bytes)AT&T North Cal. Map 1987


Also Please visit NORTHERN CALIFORNIA MW 1978  A wonderful collection of vintage sites from old slides

Note: Sorry for the crudeness of the maps. They were taken with a digital camera off the master.   The maps should give a basic idea of routes and locations in the California region.  Symbols are: round dot is a microwave repeater site and Triangular shapes are junction or switching points. The fuzzy lines are cable or FO routes.

Thanks to Wayne Hayes for the use of these maps.


Back to Telephone Central Offices