Horns Across America: The AT&T Long Lines Network

A bewildering amount of engineering was thrown at the various challenges presented to the United States by the end of World War II and the beginning of the Cold War. From the Interstate Highway System to the population shift from cities to suburbs, infrastructure of all types was being constructed at a rapid pace, fueled by reasonable assessments of extant and future threats seasoned with a dash of paranoia, and funded by bulging federal coffers due to post-war prosperity and booming populations. No project seemed too big, and each pushed the bleeding edge of technology at the time.

Some of these critical infrastructure projects have gone the way of the dodo, supplanted by newer technologies that rendered them obsolete. Relics of these projects still dot the American landscape today, and are easy to find if you know where to look. One that always fascinated me was the network of microwave radio relay stations that once stitched the country together. From mountaintop to mountaintop, they stood silent and largely unattended, but they once buzzed with the business of a nation. Here’s how they came to be, and how they eventually made themselves relics.

Long Lines

Post-war America had a connection problem — huge populations on the coasts and around the Great Lakes, with scattered and smaller cities between. Stitching these population centers together with telephone cables had already largely been completed as part of the American Telephone and Telegraph Long Lines network. But the twisted pair and coax cables of the early voice network were ill-suited for the higher bandwidth needs that AT&T’s engineers knew were on the horizon.

Without being able to force more bandwidth down the installed cables, and with existing shortwave radio links suffering from similar bandwidth limits plus the vagaries of ionospheric propagation, AT&T engineers went up the spectrum — way up. Leveraging work from a 1944 trial system AT&T built to link Boston and New York, AT&T started to plan a coast-to-coast network of microwave relay stations in the C-band from 4 to 8 GHZ that would not only carry hundreds of simultaneous telephone calls, but would yield enough bandwidth to carry the newness of the day — television signals.

The Long Lines coast-to-coast microwave system was inaugurated in 1951 with a televised address by President Truman. The system continued to be built out over the 1950s and saw increasing use by the television networks as the profits from advertising on a national level started rolling in. The Long Lines network played a huge role in shaping the post-war American culture, which by and large was televised live and coast-to-coast.

Is That a Bunker in Your Basement?

Horn antenna for the AT&T microwave system.

Image by Vladimir Menkov CC-BY-SA 3.0

A typical microwave relay station in the Long Lines system was located either on a mountaintop or on top of a tall building. On or adjacent to the equipment building was an extremely sturdy tower that held the most obvious calling card of the system — enormous “horn of plenty” style microwave antennas designed to provide plenty of gain and pinpoint directionality. Each station had a line-of-sight view of the next station in the network; they had sufficient range and were sited such that it only took 34 hops to cover the 840 miles route from New York to Chicago.

Planned and built during some of the chilliest days of the Cold War, these facilities were seen as vital parts of the national infrastructure, and were treated as such. Depending on the location, some of the structures were designed to withstand a 20-megaton nuclear blast 2.5 miles away. All of the sites had enormous backup generators with huge fuel tanks in case mains power was lost, which was a daily possibility due to the remoteness of many of the sites. Many of the facilities had large basements under the equipment room that were set up as bomb shelters, complete with Civil Defense supplies. That network engineers were expected to be at their post when World War III kicked off was never in question; AT&T even went so far as to post plaques in their facility with mission-centric messages like “Communications is the foundation of democracy,” presumably to inspire the staff as they rose from the ashes to rebuild civilization.

Done in by a Pin

In the end, AT&T Long Lines was a victim of its own success. With fat profits from telephone and television, a government-backed monopoly, and huge expensive installed base of equipment, AT&T  was too busy sitting on its laurels to notice looming threats in the 1970s. The political winds shifted and led to a different attitude toward the Bell System and a forced breakup of the giant. But it was research conducted by Bell Labs itself that led to the Long Lines network’s demise: fiber optics. Companies like Sprint seized the opportunity presented by the breakup to launch their “You can hear a pin drop” fiber networks, and coupled by improved satellite relays and the rise of digital communication modes, the end of the old analog microwave network was at hand.

Some towers at sites overlooking population centers have been stripped of their horns and now live a second life as cell phone sites, while some are so remote that they’re available for a song. But many of the sites remain largely intact on the outside, silent horns pointing off into the distance, serving now only as mountaintop monuments to a worthy national effort to stitch a continent together.

74 thoughts on “Horns Across America: The AT&T Long Lines Network

    1. The diesel generators were typically turbines; as I understand they were flexible as to what type of fuel they could use.

      If you look at the pictures in the above link pay attention to the fact that all of the equipment is mounted on springs. I believe the original implementations had all of the telecommunications equipment in racks that were hung from the ceiling with springs as well.

      1. When I was part of group of a facility that had microwave-equipment another in group was excited to see the backup generator. The man giving the tour wasn’t in hurry to get to that point, but when he did it was an I 671 two stroke Detroit Diesel. I figured that was the case, bur pretty anticlimactic for the other person. Not that I’m saying there weren’t multi fuel back up power plants. but I’d be curious to what other fuels that would be used that would be available is diesel wasn’t available.

          1. Yes, especially older less complicated (i.e. without modern high pressure injection) diesel engines can do it with more or less modifications. Some people converted their car to veg.oil. Mostly they need a fuel pre-heater, depending on climate and sometimes they start with normal Diesel fuel until the engine has warmed up.

          2. yes, there are plenty of systems out there for this. they include a separate tank for the vegetable oil and require to start up and shut down the vehicle on diesel. The oil needs to be pre-heated to be at a viscosity that can be handled by the injectors, so the start up is done to put heat into the vegetable oil and the shut down is to flush the fuel system for startup. Most modern systems do this automatically.

          3. Actually, Vegetable oil, “Bio Diesel” needs to be heated due to the vapor pressure being higher.
            The two tank solution is a cludge at best. The older diesel engines just do not run well on 100% bio diesel, but the newest ones are certified for “Up to” a 20% mix of regular diesel and bio fuel. (Federal Mandate)
            As most of you engineers know, liquids do not burn, vapors do. You can actually put out a lit “Road Flare” by sticking it in a bucket of diesel.
            Don’t try this inside the house.
            The early days found housewives following buses using bio diesel made from french fry oil. Sad really.
            And for you hippies, Willie Nelson makes his own bio diesel, mostly out of stems and seeds.

    1. The MCI microwave system was somehow better than ATT’s microwave system? MCI didn’t set any precedents. Residential customers discovered what higher long distance rates where subsidizing. The dismantling of the government regulated monopoly ended up with others companies getting a share of the long distance cream without providing basic POTS. The deregulation was all about commercial interests battling it out who’ get the money and how much. The babble about how much cheaper it will be to talk to granny was a smoke screen, no no one would notice MCI et. al. wasn’t weren’t to reduce the cost of POTS. All we got was a government regulation of a trust of government regulated utility corporation, regulation that’s pretty dam light on regulation that actual serves the general public.

    1. My Father worked at the labs from the 1950’s to the early 1970’s. I later started a precision ceramic machining corp. that provided AT&T with light sensors for their fiber optic networks. They bought tons of them. This was back in the early 1990’s. I used to be a member of the American Ceramic Society in the Lambertville chapter. Those were the days.

  1. I went to college in Northeastern Indiana. My friends and I stumbled across one of the towers while exploring back roads. It was quite surprising to see a ~200ft tall tower sprouting out of the woods. We suspected sinister purposes as the property was fenced and gated with No Trespassing signs posted on the gate. After a little research when we got home it was revealed to be a Long Line tower. Pretty cool.

  2. I remember our trip to New York in ’59, radio city and all. A brand new UN. They explained the current wonders, like the two inch wide tape for TV. The microwave towers were shown on a big map. On our way back to Indiana somewhere in Pennsylvania we saw two of the towers, the required 50 to 60 miles apart.
    I was in awe standing in front of a screen much taller than me with cartoons on when I realized that it was not a movie but TV in color and not on a picture tube! A wave hit me as I then knew that we would have TV like that in the future.

    1. Here in Australia Telecom had a similar microwave setup to connect places that were otherwise not able to be connected. It too eventually got replaced by long haul fiber links.

        1. they are used to cross sahara as well, all along the long desert roads there were small microwave towers, in some of the mountain passes you can often see both the sender and receiver as they are bouncing them through the canyons around corners.

  3. When visiting my paternal grandmother in north-central Wisconsin in the 1970s I would always gawk and stare at one of these red and white towers just outside Antigo WI. The last time I drove past in 2003 I think it was still there standing high above some of the flattest land in Wisconsin.

  4. When I was in tech school in Iowa many years ago our class got a tour of the nearest AT&T site. The technology was inspiring. I believe these sites were one of the first “webs” where signals could be instantly rerouted around failure points. Thanks for the article.

  5. Interesting write-up. Ever wonder about the effect of WWII on infrastructures? In the US we had phone, power, bridges, roads, and ports dating back to the turn of the last century (still do). In Europe and Japan, in many places this had to all be rebuilt, or newly built out, and with current technologies. England did not have the destroyed infrastructure, but a destroyed economy. The US helped some countries more than others with the Marshall Plan and other programs. Parts of China were also devastated and did not get help. The internal strife made large scale support impossible. Russia looted the north of China of resources of all sorts, including the steel rails in the railway beds. What effect did this have country by country? In other words, over time, how did having shiny new infrastructure figure in the standard of living?

    1. TBH the cold war seems to have had a bigger impact on communications, nuke proof communications in various forms got a hell of a lot of cash thrown at it for decades.

      1. The irony is that with modern day hacking, infrastructure like power distribution, communications and traffic control are even more vulnerable than the cold war era and these systems get next to no protection now. Seriously! some of these systems are even within reach of some of your more advanced script kiddies.

  6. There are places where some of these are still in use. The USA is a third world now in regards to connectivity and I know of one northern michigan town that relies on one of these that still functions for telephone service.

    1. I don’t know about 3rd World connectivity, but it is sure way too expensive. And setting up cell towers and wifi must be a lot cheaper to deploy and maintain and upgrade than a wire/fiber system. Two months on my basic phone/TV/Internet service over cable, is $350. And that is not cell service. I need an alternative.

          1. I would have to pay extra if I used that feature. This is just Comcast/Xfinity land line phone, internet (average about 15 down and 3.5 up), and basic cable TV. About $12o a month. Then Verizon for cell phone adds enough that if invested every month would make a good retirement.

  7. I used to see a lot of these towers in Michigan but most have been stripped of the horns and dishes and are either empty tower or cell tower now. I think a tower somewhere between Port Huron and Imlay just south of I-69 still has horns (as of 2015) and are probably abandoned.

  8. Sprint was originally SPRINT. Southern Pacific Railroad Internal Network Telephony. SPR laid fiber optic lines in their rights of way along their tracks for signal control and train communication. With the railroad services using only a tiny fraction of the optical bandwidth, SPR wanted to rent capacity to telcos, but that would require connecting SPRINT to the Public Switched Telephone Network or PSTN.

    AT&T, Ma Bell and the other big telcos said No way. SPR sued and won, and formed their own long distance telco. SPRINT became Sprint and was eventually spun off as a separate company.

    Had the big players just gone along with the offer to pay the railroad to use their excess capacity, the history of telecommunications and internet access in the USA would be much different.

    1. Sorry In my observations many people need lesser expectations. My internet connection is WiMax, because I have a rural residence and too far way to have DSL. The townies get less expensive service with fiber connection. In the end it’s better than what I thought I would have to do to get something better than dial up. & mile away there is a small town served by a rural telephone coop. My plan was to purchase service in that town put up a tower to link back to my place tirelessly. and provided that wide spot in the road what passes for broadband in the sticks. My WISP costs me $40 moth fit 1.5 down and .75 up unlimited data. POTS averages S45 per month. I’m on my sister’s mobile phone family plan, and that’s another $40. I don’t have CATV or Sat. TV. Before the Switch to digital I received CBS & PBS damn near perfectly, ABC FOX, and NBC poorly but good enough for me. No with digital it’s going to take and extra ordinary effort to receive OTA TV, because it’s damn near perfect or nothing. Oh well when I was kid all we had was CBS, NBC when and conditions allowed it intemperance free.

      1. Doug, with respect, I don’t think asking people to lower their standards or expectations is reasonable. In today’s world like a cell phone having internet at a usable fast speed is not unrealistic, in fact like it or not it’s becoming a necessity. My kids school manages class to parent interactions online the local government announces issues such as closures and safety issues via text message and social media. The same school also frequently uses internet in the classroom so having access for the kids education is likewise needed for homework etc.

        I have used many systems to try to get signals to various places I have needed over the decades. I can say that nothing is “great”, it’s not about lowering expectations. It’s about affordability.

        In the end as a single user of a network resource miles away your expectation can be that you can take the cheap crap systems because you simply won’t pay enough to have a quality link, or invest in a better link. I lived in an area with one telco subscriber per square mile (rural far north California). That’s not a lot of return on investment for anyone. I had a business need and found that I could have a 1meg leased line for $1200/month per site or I could put $10,000-$30,000 into a fiber network I would own and only pay $120 annually for the poles and have 10,000mbps per site x10+ sites! In the end it was about finding the capital to own the network rather than paying someone else more for a inferior product and have nothing to show for the money.

        Broken down the fiber was $300 per month per site for a year to pay for the system vs the telco $1200/m and own nothing. Speed likewise was 10,000 vs 1 mbps. So no matter how you crunch the numbers it was cheaper expect initial purchase.

        In your case a white space radio might be viable @ 20mbps over 10-15 miles is not unrealistic. Cost might be as high at $5000 but in the end less $ per mbps then you have now and you can lower the cost if you find others in your coverage area.

        Your 1.5mbps (@$26.5 per mbps) isn’t much speed for a high cost these days. I am now in Alaska and I have 1gig from the cable company, I am at the end of the road 20miles outside of a small town, so it’s not unrealistic for you to expect better. Just plan to pay for it, my link is $175+/month with a 1TB limit. ($0.175 per mbps). For comparison @ your rates it would cost me $17,000 a month. I actually feed my link into some 900 mhz radios and push it another 5 miles at 10mbps. The Mikrotik 900mhz gear costs me less the $300 for the pair for radios + antennas.

      2. Wow! I am paying $60/month for internet and getting 70 mbps speeds. I pay $10/month for my cell phone. (No internet) I don’t even own a TV so I only use the cable for internet. I do not have a land line.

  9. These aren’t dead but they certainly are not as common now. I know of at least 2 microwave links that are still in operation close to where I live.

    A microwave tower (pair) still fits into the very same economic principles. That is, they are still the most economic solution if ruining optical fiber is expensive due to distance or terrain and the bandwidth demand is low enough that microwave will suffice for a significant period.

  10. Microwave in telecom is in the midst of a renaissance. I won’t claim to be a SME in my own industry but it is known as Fixed Wireless. It uses much, much smaller microwave dishes on licensed frequencies to deliver telecom services from a provider Point-Of-Presence to a single office location. Available bandwidth I’ve seen in production settings currently around 1 Gbps though 100 Mbps and under much more common. Customers prefer it for redundancy and/or time to install intervals compared to digging new fiber in the ground. It can even be used for temporary events or emergencies. Providers prefer the same reduced intervals and avoiding the expense of last mile construction costs that often go to in market competitors.

    It will never see the density of physical connectivity. And it has its own limitations even for businesses. But it some applications it makes what is old, new again and very effective.

    1. Here in San Diego one of the engineers told me that they still use microwave as a backup between plants in case the fiber gets cut. The dishes are much smaller, and much shorter range, but they’re still around!

    2. I design microwave backhaul networks for large telecom operators. Microwave is fast becoming obsolete – there aren’t enough frequencies for the bandwidth required, and the bandwidth per channel (frequency) is far too low to meet even 4G requirements.
      Most all telecoms are going to fiber – exclusively.

  11. Microwaves are faster! The velocity factor of glass fibre is a lot less than the velocity factor of air (which is close to that of vacuum).
    Air-core fibre may improve matters, but I understand they are more at the research rather than deployment phase.

    1. This is just a factor of 1,5. Mostly that doesn’t matter. I can imagine that an air core fiber has less attenuation which could be the real reason to do research on it.

      1. High frequency trading is one place where the delay does matter. You can buy low latency Ethernet switches, low latency NICs, hardware offload (in FPGAs on the NIC) for the trading algorithm, low latency optics modules that work without needing FEC, etc.

  12. We have one of these nearby in Finksburg, MD.(between Baltimore and Westminster on Route 140 – https://www.google.com/maps/@39.5185854,-76.9113656,261m/data=!3m1!1e3?hl=en) My father, a truck driver at the time, says he delivered part of a computer(one of the old room-filling computers) to the facility when it was being constructed. He said his delivery was under the eyes of civil defense personnel, including one riding with him from where he picked up the load in Elkridge to the delivery at the construction site.

    As far as I know, the facility has been decommissioned as a primary link for years… perhaps resigned to backup status. I don’t know what it’s being used for presently, although it does appear to be maintained and occupied – it received a new aircraft anticollision paint job not too long ago. It’s in close proximity to a major local roadway, commercial property, and a residential area. I can’t imagine it being a “secure site” as it was originally intended.

    1. If you have a tower higher than 200 ft, FAA and FCC say you have to paint it, light it, and inspect it. Or take it down.

      Renting tower space can pay for all of that. And it’s a rare location that won’t be a candidate location for at least one cell base station. Towers aren’t cheap to own, but the guy next door to me has leased some of his land to one, and I think he gets $1500/mo from each tenant. The tower itself is owned, I believe, by a tower company, and they take care of all the maintenance. Best part? We get excellent cell coverage at home :-) And the red-tailed hawk likes to perch at the top while looking for lunch.

  13. I don’t have the links anymore, but there’s a lot of Bell system technical documents on the web that describe these systems in extreme detail. It’s amazing how many different standards were used on various parts of the system. Most worked well for voice, but caused big trouble when they tried to roll out wideband services like picturephone over more than a select few routes.

    1. Ah. BSP’s (bell system practices) There literally was a BSP on how to sweep the floor at a remote site. I worked for Long Lines as atechnician for a very short time right out of high school. I had worked there part time through the schools Distributed Education program. They sent me to basic electronics shool, got me a second class FCC license and generally were great to work for.

      I worked in a “main” office that was 10 miles out in the country from a small town. A couple things stick in my memory. One was setting up a video link for ABC to broadcast a college football game. The radios carried voice channels 600 per actual radio transmitter/receiver. As I recall we took down 1200 voice channels to facilitate that one TV broadcast. The other was the installation of an ESS1. That is a “computerized” electronic switching system that replaced the old mechanical rotary switches. This was for the military’s comm system that was seperate and apart from the cvilian side. Another was the installation of EF1 – but I can’t talk about that.

  14. The FAA’s tower registration search allows you to look for towers by construction data, and there weren’t many other towers going up in the 50’s and 60’s. A search there followed by a lookup on google maps helps find these quickly. Looks like many near me are owned by tower companies, and have some active antennas on them. The only bummer is that you can’t find anything shorter than the height required for registration.

    http://wireless2.fcc.gov/UlsApp/AsrSearch/asrAdvancedSearch.jsp?fromRefine=Y

  15. Crazy – I live 10 miles from one. Neighbor has taken me on a tour there (last employee there). The toilets are mounted with rubber sleeves, lights are on coil springs and there are operations manuals for the blast doors. VERY cool place, sadly VERY empty now….

  16. Apparently the Milwaukee,WI Long Line (truss tower, not the big concrete monoliths) at 26th and State was torn down between 2015 and 2016. It’s still visible from the 2015 streetview images.

    After some checking, someone make a map, but I know it’s not complete. There’s one still active in Parish, WI apparently that’s not marked.

    https://www.google.com/maps/d/viewer?mid=1E8Md0ohJ7D2h-5i1485YGrP8RCk&hl=en_US&ll=41.66710212731559%2C-89.48393045985591&z=4

  17. There was a Western Electric building in a nearby city to where I grew up.
    I havn’t thought about that (ominous looking) rooftop cluster of horns, for a long time.
    As I recall, the building sat empty for a while and then was converted into a jail.
    I used to wonder what comments the Western Elec workers might have had about that.

  18. Where I grew up, the towers were about 30 miles apart (within sight of a major highway), the terrain is hills, not mountains. So, maybe they were sited at half the maximum distance to allow the signals to bypass a “down” tower.

  19. So that’s what “pin drop” was all about. Just think, now a days we carry phones in our pockets with the audio clarity of old hand-cranked, wall-mounted phones connecting long-distance. In the future we’ll probably forgo voice altogether and revert to Morse… I mean text. Yay technology!

  20. There is a portion of the long lines system in Colorado that doesn’t appear on any map of the system and, shockingly, is STILL IN USE. Starts at the AT&T building at Zuni and 52nd Street, goes up over Berthud Pass, then over by Vail and ends in downtown Grand Junction. Serves a lot of the town in the area. I found it when I was in Dillon and noticed one of the classic horn antenna’s on top of a building. I was able to find it on the FCC site and then follow the skips. It is now run by Qwest/Centurylink.

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