March 2011
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Bell System microwave relay system

This is a map of the AT&T microwave relay system as it was in 1960. It is interesting for several reasons.  First of all, before there were communications satellites, this is the way that data was transferred from one location to another.  That data would have been digitized and TDM encoded on a T-carrier, then loaded onto a microwave path.  TV networks had loops that transversed the country, distributing network video and audio to all the markets in the US.  The first transcontinental New York to San Francisco microwave route was established in 1951.  Through the fifties and sixties, the network was filled in across the US and Canada.

Radio networks had been using wired TELCO networks for program distribution for years, although they required far less bandwidth than TV.  This was during the time when network affiliation was vitally important to a station.  Radio networks provided news and other special event programming, as well as some long form shows which were an important source of information for the listeners.  Any network programming prior to 1980 or so would have been carried by this system.

It was not until the use of C and Ku band satellite services that networks could offer multiple channels of programming.  Now, entire radio formats could be programmed remotely and beamed into hundreds of stations across the country simultaneously.  That would have been far to expensive to implement over TELCO lines, as the line charges were based on mileage of the circuit.

Bell System microwave relay routes

Bell System microwave relay routes

Click for higher resolution.

This system included thousands of hardened microwave relay sites, each built to exacting specifications and fully redundant.  At the time, the long distance telephone system was an integral part of the US defense planning.  Sites were spaced 20-40 miles apart, depending on terrain.  In congested areas, like the northeast, area mountain tops are dotted with these sites today, mostly empty.  Most of these sites went off line in the late 1990’s as phone companies switched to fiber optic cables for telephone and data traffic.

American Tower, Inc. purchased most of these sites in bulk from AT&T in the year 2000.  Some sites are well positioned for Cellular Telephone, 3G and 4G wireless data services, plus other things like Media Flow and general use applications like FM broadcast and two way.  Many sites, however, do not meet any specific need and sit empty.  There was a large fire sale by American Tower in 2002 in which they unloaded about 1,900 of these sites as they were redundant.

I wrote a post titled Cold War Relic: ATT long lines site, Kingston,NY detailing one of these sites near me.  Keep in mind, there were thousands of these sites throughout the country.



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9 comments to Bell System microwave relay system

  • J. Aegerter

    Actually, 1967 sites were purchased by ATC in 1998 from AT&T. The “fire sale” in 2001 and 2002 was do to huge tax assessments and bills that carried over on the properties and became burdensome to ATC. Municipal assessors had sky high assessments on these properties, and AT&T almost never contested an assessment. It was just too much for ATC to sustain, and non-productive sites had to be disposed of. The number was probably around 300 that were sold. In 1988, AT&T had about 250,000 employees, and the goal was a cutback to 100,000. Generous 5-year severance packages were offered to supervisory personnel when the de-commissioning of the trans-con microwave network network began a year later. The fiber-optic network was being built near metro areas throughout the late ’80’s, and continues today. The huge bandwidth obtained with this technology, along with low noise and immense cost savings in maintenance personnel and other operational expenses dictated the cold war era radio relay sites to be dumped. These days, Wireless Internet entrepreneurs are busy making use of many of these sites for point-to-point transport and distribution to their customers in areas where there are poor facilities to transport high-speed Internet traffic. As long as there is wireless, there will always be a need for transmission towers. “The cord is invisible, dad”!

  • Rupert

    Is there really one called Anarchist in British Columbia?

  • Paul Thurst

    I seems there is. In my trips up north, I have found our Canadian neighbors have a sense of humor when naming their locations. One such place, where my wife’s family comes from was formerly called “Bastard Township,” since renamed Rideau Lakes township. Anyway…

  • Rupert

    Actually, doing some research – here it is!

  • Vito

    This helps explain why during my time in the USN in the late 1980’s phone calls home could range around 3 bucks a minute! The infrastructure costs for this system had to be HUGE!

  • David

    There was no T1 in 1960; it came into being in 1962. The microwave and coax networks were analog multiplexed; look up terms “FDM” “supergroup” and “jumbogroup”. The coax carried ~50 Khz->40 Mhz and coast to coast, needed 1000 db of gain. The microwave needed less active gain as the horns had insane gain at the higher frequencies.

  • Kris KE4AHR

    The above map predates TDM and digitization. Early implementations of the wireless technology started as “TD-2”, FM microwave on 4, 6, and 11GHz and moved to SSB/AM with the introduction of AR6A. AR6A was the last analog microwave system. The digital microwave systems followed after that with the DR6, DR10, and so on.

    Other names of the systems were TD-3, TH, TH-3, TJ, TM, and so on.

  • Richard Doucet

    The TD-2 sites in Canada operated from 1956 by Eastern Tel and Tel, purchased by the Provincial Telcos in 1978 and shut down in the early 1980’s. Some of the towers are still standing.

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