A similar thing happened in the US military. There used to be a system where voice, radar info, and data were relayed back from the front lines of a conflict via a system of portable microwave stations.
Some of them short (<~50 miles) links with horn antennas like you see in this article. Longer links with parabolic dishes and tropospheric scatter. All "portable" equipment on camouflaged trucks and trailers that could be unloaded and assembled anywhere.
All of that started being replaced in the mid-90's with a combination of dedicated military satellite equipment and more use of commodity stuff like small commercial microwave network bridges, cellular phones, satellite phones, and so on. They closed out the "microwave tech" jobs and folded them in with "satcom" or other specialties.
I'm not saying you're incorrect that the military had similar tech to what AT&T had, but I'll split the hair that they actually worked together hand-in-hand.
They actually populated AT&T Long Lines towers with AUTOVON equipment which was the old military phone system in the US. Also used the same switching network to support Air Force One with the Echo Fox Presidential Aircraft network. Some of the locations were hardened for nuclear attack.
That may be true for some equipment in the miltary. The ones I'm talking about were standalone and portable, for use in a war zone. The only connections they would make to non-military equipment was after the voice/data was de-muxed into channels. That could be connected to phone lines, etc. Typically, though, pretty far downstream after passing through different equipment.
There's a bit of both going on, the military did make use of some portable equipment developed by Bell System family companies including WECo. But for the most part, military transportable equipment into the cold war was made by RCA. RCA was more of a "manufacture for sale" type operation than AT&T and had more expertise in portable equipment.
Of course, AT&T was one of the founders of RCA, but by the time microwave and troposcatter were coming into use AT&T had sold their shares. Nonetheless there was plenty of technical interchange between AT&T and RCA during that period, and some of the RCA equipment for the military was based on Bell Laboratories and WECo work.
The military often made practical decisions of whether it was better to field themselves or contract - and so military connectivity was sometimes contracted to AT&T even in surprising situations like overseas. But field-deployable portable systems have always been impractical to contract out and so the military tends to keep its own assets.
Other parts of the government took this other directions. The State Department nearly exclusively contracted to AT&T including for foreign installations. The FAA did so surprisingly infrequently, maintaining its own expansive microwave network until just recently.
In response to a post about the AT&T Long Lines network, saying something "similar" happened in the military seems disingenuous because they were absolutely partnered on the same project. To imply something is "similar" typically implies that it is separate to some degree - that's not the case with AT&T and the US military in regards to the Long Lines Network.
Sorry, that just makes no sense to me. I'm talking about mobile military equipment that talked microwave only to other mobile military equipment. Equipment that would be deployed in a war zone, where AT&T probably wasn't present. Like a connection between a forward air control post and a rear echelon camp. Both being (typically) a bunch of tents and vehicles in the middle of nowhere. Downstream from that was voice/data channels that wouldn't care what AT&T or anyone else was doing.
You seem to be talking about military use of FIXED (not portable/tactical) microwave, which is a different space.
> You seem to be talking about military use of FIXED (not portable/tactical) microwave, which is a different space.
Which is what the original post/article was about - the fixed terrestrial microwave network that AT&T ran... which was a major joint effort with the US military.
Sorry I got caught up on "similar" being confusing when the military was 100% involved with what the original post was discussing (specifically the AT&T Long Lines network) - I regret my comments.
Folkhack,
You’re simply wrong. Stop arguing when you don’t possess firsthand knowledge.
(I see you’ve added a new culpa, no worries! We all learn new stuff)
Wanna go down a rabbit hole? Remember that spectrum sale in the 2010s? What if I told you the FBI had their own microwave network that they divested of around that time?
Specifically - what am I wrong about? As-per HN guidelines specify exactly what I have said that is factually incorrect? Please quote it directly if you can, and in good faith provide sources so I can better inform myself.
I simply disagree that I'm wrong about anything that I've stated here - I have specifically visited a Long Lines AUTOVON switching site; 100% the US military was partnered with AT&T for this. I actually possess first-hand knowledge on this - I've met with site owners.
> I see you’ve added a new culpa, no worries! We all learn new stuff
OK? Honestly I was just trying to be polite and it was less of an apology and more taking the passive road out when we were obviously talking about two separate things. I don't disagree with anything that tyingq was saying - I was just trying to make a nuanced point regarding the partnership between AT&T and the US Military which is directly related to the article that was originally posted. Somewhere wires got crossed and I just decided to bow out as politely as I could.
Sometimes socializing on this site really weirds me out. Please, in good faith: what have I factually said that is incorrect here?
No prob!
Specifically this:
“To imply something is "similar" typically implies that it is separate to some degree”
So the US military has many microwave comm projects. ATT was only one of them that was left unused. Many had no ATT involvement whatsoever.
So yeah, military had contracts with ATT, but those were a tiny subset of microwave efforts.
I'm being misunderstood, I'm going try to to explain better.
I literally opened my original response to tyingq with "I'm not saying you're incorrect" as I did not want to invalidate anything they had written. I was not trying to argue a single point. I just found the grammar/set theory of "A similar thing happened in the US military" odd when that specific thing (the Long Lines microwave network) happened in the US military in a big way.
On your newly introduced point: "military had contracts with AT&T, but those were a tiny subset of microwave efforts". I do not describe the backbone of AUTOVON as a "tiny subset" of anything... The AT&T Long Lines was an engineering marvel. The achievement to reliably transmit coast to coast audio, video, and data through hundreds of redundant radio/switching sites was huge - that simply did not exist before. AT&T Long Lines is very significant to the history of microwave communications in the military specifically through AUTOVON.
I'm absolutely not arguing against the existence of military microwave tech independent of AT&T - I feel like this is obvious, but I also feel I have to state it outright after reading your comment.
Army 25P (microwave systems MOS) is still around iirc (at least in the Reserves), and speaking from personal experience, 25Q10EAC was still getting dedicated 10 week training on tropo and DGM enclosures in 2012 at AIT.
That EAC rider was certainly rare, but we were told tropo was still in play in South Korea, and as late as 2015, another company in my reserve ESB had a few tropo systems they were still maintaining and training on.
But yes, by and large, most microwave-based signal MOS were rolled into either point-to-point "multichannel transmissions" (25Q) by which a good part of your qualifications include deployment of satellite transportable trailers (STT), SMART/T systems (shared with the Marines),and the Phoenix system; and the dedicated SATCOM MOS (25S).
Love seeing these get brought up. It's a really fascinating system from an era when communications infrastructure was a bit more visible. It's one of those things where, once you learn it exists, you'll start seeing them (the towers/horns) popping up all over the place.
The gist of it seems to be that these are secure, physically guarded, literal underground bunkers built into the tops of mountains along the East Coast, housing troposcatter antennas and satellite dishes. Super cool. As far as I can tell, nobody ever truly figured out exactly what they're for, and most are still operational today. I tried driving up to one once, out of curiosity, and there are some pretty intimidating "stay out of here" signs and cameras, even at the very base of the mountain.
Chances are they were simply just meant for the military AUTOVON network, mentioned near the top of this thread. But I suppose that doesn't explain why they're still operational nowadays.
Yeah they're crazy. Super obscure bits of infrastructure and Cold War history.
It's interesting to me how all the signs in that Flickr album say "People" instead of "Personnel" (Delivery People, Authorized People Only). Was this an AT&T thing?
>It's one of those things where, once you learn it exists, you'll start seeing them (the towers/horns) popping up all over the place.
Personally, I feel the same way about cell sites today. There's a surprisingly enthusiastic community online for keeping tabs on them and tracking site design changes/upgrades. Cellmapper.net is the homebase these days and their subreddit has tons of posts asking the community to identify sites based on pictures of the equipment.
For sure. Raven Rock is badass. As a kid my family used to go skiing in the area (Liberty mtn) so it blew my mind when I found out (via the Internet) that there was an "underground Pentagon" nearby.
Fun fact if you're curious about this stuff: Site R is pretty well-known, but slightly more obscure is the "Site C"[1] radio outpost atop Quirauk Mountain a few miles away. It's kind of funny since High Rock is a crowded day-trip destination, being right on the Appalachian Trail and all, but then just a few yards away at the edge of the parking lot, there's some stern-looking security dudes guarding the Site C access road. Also, Site R supposedly links into the "Presidential Emergency Facilities"[2] network, a bunch of weird grain-silo-looking structures historically used for communications and relocation https://coldwar-c4i.net/PEF/
The DMV area is dotted with all sorts of fun "spooky" stuff. I've always wanted to make some kind of website or map summarizing it all. coldwar-c4i.net is awesome and contains crazy amounts of information, but is admittedly pretty cluttered.
I think this fits the mood. The old telephone system was entirely analogue. It remained so well into the 1980s, even when they were carrying tens of thousands of conversations in parallel on a single wire or antenna.
When I was a kid, you could hear the white noise stack successively louder on a long-distance call, as it went through each additional link. And sometimes you could hear the hum of it all, just below the threshold of intelligibility. In hindsight it's amazing how well it all worked.
Maybe a filter was slightly out of tune on that day. Recorded mid-1970s New York. The electronic beeps are in-band call establishment tones. (Yes, the same ones phone phreaks exploited. The recording was in fact made by one of those phreaks who has gone back and narrated some of his old recordings http://www.evan-doorbell.com/ )
Those are in-band signals to the switching equipment. The equipment would “hear” those tones and translate them into “machine instructions”. That’s why phreakers could exploit the system by generating those tones themselves and playing them into the phone microphone.
And even with those things being in-band, we now have authentication for BGP and the IGPs to try and constrain the ability to send control signals. SS5/CCITT5 would probably have played out a lot differently had they hand the ability to do that sort of thing like we do now.
I learned just a little about these after making the decision that my drives through Nevada would never again be boring. Once I started asking questions about what I was seeing, the "ice cream cones" or horn antennas really did stand out in a fascinating way. And $25K to buy one does seem like it could be a terrific deal in the right situation.
Another thing I asked about: When I stopped to get gas or groceries, I realized there were tall visibility flags on the back of so many Nevadan trucks, even what looked like personal vehicles. I had overlooked them for years. An interesting dive into an industry and its culture started there.
BTW, speaking of old towers that went up for sale and are possibly interesting to ham radio operators: Here's one near me (NorCal Bay Area) that was purchased by a local bay leaf grower and then opened for ham radio use--in exchange for a refurbishment effort.
Growing up in the mountains, I remember seeing a curious kind of antenna up on a mountain nearby. It didn't look like the others; from one angle it looked like a three-petal flower and across town, it looked like a giant robot with two antennae. Wondered what it was for years since it looked so unusual. Only a few years ago I learned it was a long-decommissioned AT&T Long Lines tower: an urban explorer had filmed it.
BT built a system of underground copper pipes/waveguides for microwave transmission in the 1970's - it never got beyond a testing platform in Suffolk (Martlesham Heath to Wickham Market) due to fibre optics becoming the clear winner.
There's some cool but not very ready tech called surface wave transmission lines that use horn like "launchers" to establish surface waves on single conductors like power lines. They have very low RF losses up to the tens of GHz as long as stuff stays a few wavelengths away from the lines.
In way, if you try hard enough, most powerlines could act like inside out waveguides for high data rate RF backhaul.
There is a story that the "Radio Tower" at BT Labs was built as a waveguide - this is on the A1214. Given that the office accomodation in it is so weirdly laid out I can believe that this might be so.
If you spend any time in the mountains you will see "blank" billboards up in the hills. These are "passive repeaters"[1] for microwave networks and I am surprised they weren't mentioned in the article ...
For the most part these are almost obsolete, the typical data link that many of them carried was one DS3, or at most, three DS3... The path loss is extreme. Usual setup was to go from a small town central office (CO), 3-5 km up to a nearby mountain, then bounce it off there, and 25-30 km to another nearby mountain. With big old power hungry PTP microwave gear that occupied a full 42U rack, took 1200W of power, and carried a whole lot of DS0.
Nowadays a modern PTP microwave radio that can carry 1400Mbps full duplex in the 6 or 11 GHz bands is as little as 35W of power, so many hilltop tower sites either have built electrical grid connections, off grid solar, or whatever.
Building some of those passive repeater billboards in places with no road access was very costly. Big helicopter bills and very labor intensive.
You can still see a number of them on hillsides in eastern Oregon.
Passive repeaters were certainly not common, possibly not used at all in the AT&T Long Lines network. I am not aware of any examples at least. In general AT&T did not like them, it's more common for telephone passive repeaters to have been installed by CLECs or telephone cooperatives, and later on I know MCI used some in this area. These were all later installations than most Long Lines.
I'm not sure exactly why AT&T eschewed them besides the speculation that AT&T built much of their microwave network relatively early and so the attenuation may not have been acceptable given the already short range on their links. AT&T's first generation of microwave sites had to put the RF amplifier in a hut on top of the tower because the waveguide loss was unacceptable, for example.
A very common place to find passive repeaters in the desert west is at dams, where they were almost invariably installed to provide the telephone connections to the power house.
A later interesting example of passive reflectors is the "periscope antenna," mostly used by Western Union when they operated a microwave network for a time. The actual microwave antennas were mounted on the roof of the shack pointed up, and at the top of the tower passive reflectors at a 45 degree angle "bent" it to horizontal. It put the more maintenance intensive parts on the ground at the cost of some power loss.
My dad used to work on these towers in the midwest. Back in the day, he told me that they still had plenty of capacity, but AT&T had to switch to fiber after Sprint "dropped the pin".
Fun fact: the USSR used exactly the same technology and that is why enabled the US to monitor all phone calls using the Rhyolite/Aquacade surveillance satellite: microwaves are line-of-sight and due to the curvature of the Earth (take that flat-Earthers!), the inter-station signals continue into space and are receivable by a big enough antenna.
> Built in the early 1950s... It conveyed phone conversations and television signals from the era of the Kennedy assassination through the resignation of Nixon
Even from the other side of the globe I can tell that it seems strangely short-lived. Built for a decade, then used for a decade?
Wikipedia notes tersely:
> The launch of communication satellites in the 1970s provided a cheaper alternative.
In the 1920s, 3 and 12 channel frequency multiplexing on twisted pair was introduced. It made most single-channel long links obsolete within about a decade.
In the early 1930s, both time and frequency multiplexing were introduced on coaxial cable, carrying up to 600 channels per conductor, it rendered the above twisted pair multiplexed lines obsolete within about a decade.
c. 1950 microwave relay is introduced (the AT&T long lines in question here) and undergoes explosive growth, with the cross-continental system linking most major cities built by 1960, and reaching essentially every part of the country by 1970. Such links could carry hundreds of megabit/s worth of data (or multiple 6 MHz TV analogue channels). Much cheaper than coaxial, it largely halted new coax installations. It would remain dominant into the 1980s, so more like 20 years.
Fibre optic communication was introduced in the mid-1970s. Immune to atmospheric problems, less path loss, potentially capable of carrying far more data than microwave. It made most of the microwave systems obsolete by the 1990s.
> Like their predecessor satellites, the Telstar 3 satellites operate at 6/4 GHz (C band). Simultaneous long distance telephone call capacity is 21,600. The satellites furnish voice, video, and high speed data services.
Perhaps I was overly categorical. Certainly satellites could be used for telephone calls, but my impression is that this was never a dominant use, except maybe for overseas calling (given the expense of undersea telephone cables).
e.g. I found this government report report from 1983 stating that "microwave is the chief means of transmitting long-distance telephone calls..." in the U.S., this is well after the advent of satellites: https://www.google.com/books/edition/A_Five_year_plan/NbGS1A...
Less of a joke than one might think. The GSM / 2G / 3G / 4G / 5G transition took less than 30 years, each step involved scrapping some of the old incapable hardware.
Also worth mentioning that MCI, an AT&T competitor and thorn in their side, also had a microwave relay network. The M in MCI is for microwave. There's some great info on MCI here:
For those not familiar MCI was a real innovator and an important part of internet history. Vincent Cerf, an internet giant, worked for MCI[1]. Sadly MCI was relegated to the dustbin of history as a result of the WorldCom scandal[2]. They are sadly just a part of Verizon Business today.
I had just moved to Toronto in about 2002, and was waiting for an interview. I saw one of those microwave horns on a building in the distance. Puzzling over what it was.
Interview started, talking about something glanced over the background and muttered verbally "Microwave" as it hit me that it was a microwave waveguide of some sort.
The entire lower white donut ring around the bottom of the CN tower is a radome, inside are ptp microwave dishes. It was a lot more relevant in the era before singlemode fiber went everywhere.
I lived directly across the street from one of the "Long Lines" towers on Queen Anne Hill in Seattle, WA. [1]
It was actively maintained, with various antenna arrays being attached or removed frequently. The building below was packed full of gear and service vans were coming and going all the time.
I was sorely tempted to try and climb it over the various years I lived in Seattle, but decided it wasn't worth either the arrest or death by electrocution or ground impact!
the queen anne site is a wireline CO for that region, and has cellular stuff on it. The 6 GHz microwave has been out of service for many years. It used to be a primary link across the sound, to things in Kitsap, and similar.
fairly typical USWest/Qwest central office otherwise.
The AT&T Long Lines network predates the use of digital radio for telecommunications. It used analog FDM to carry multiple calls. These towers have lasted because they, and the radio equipment, were designed to survive a nuclear war. (Another reason the fiber transition happened quickly was that fiber was more survivable.)
There are many new microwave links being deployed now using modulation techniques for digital data.
Cell carriers often use microwave backhaul as well, particularly when fiber infrastructure is unavailable. These are usually smaller dishes mounted on cell towers, rather than big horn antennas.
Where I used to live in East Texas there was one of these, well, at least a few decades ago. Never knew exactly what it was for. But it is a mirror image of the pictures. The things you learn later in life because of the internet.
The Telus CO downtown at Robson and Seymour used to have a large tower on the roof with 6GHz horns, linked to that site, and towards the site on Bowen Island which still has horns. Bowen Island was a link to the sunshine coast, across to Nanaimo, and many other places.
There is also a big site out in the fraser valley on a hilltop that was part of the long lines network with shots going east towards Hope (trans canada microwave) and down into Whatco County.
Interesting! Thank you for the information. Does the trans Canada microwave go along the coquilhalla highway? I notice that there are point to point links along the side of the highway.
Were the microwave links to Nanaimo and the Sunshine Coast replaced by fiber?
There's submarine fiber to Vancouver island now, in a diverse ring, so yes.
Still is some microwave operational on sunshine coast but not as a primary thing.
Big parts of trans Canada microwave have now been dismantled. There was a mountain top site slightly NE of Hope that could only be reached by its own cable car. And lots of other mountain top sites east of it going all the way to Lethbridge.
I used to live next to one of these! It was a useful landmark: turn right at the tower. There was also an underground bunker next to it that someone bought in recent years and attempted to make into living quarters.
The original title of the article, actually make sense in the subject of "Long Lines". But the submitted title make it sounds like AT&T totally abandoned Microwave Network. I dont know about AT&T but Microwave Network is still actively being used today and refined even in the latest 5G 3GPP Spec Rel 16, 17 and 18.
Other than that it is a nice piece and history of the system.
PTP microwave is very much in use by many carriers, it's absolutely essential for a lot of modern cellular network builds. But the actual microwave horn antennas in the 6 GHz band, that typified the inter-city AT&T long lines network, are 98% decommed in place these days. You would be very hard pressed to find a site that still has the waveguide, waveguide pressurization system, and a live FCC part 101 licensed 6 GHz radio running on a horn-to-horn path.
Of course, many countries have had a similar network. I like the towers of the Netherlands, which have similar designs to each other, even though each is unique. A few have a radio mast on top. Click the links at the bottom of https://cellnextelecom.nl/over-cellnex/locaties/ to get an impression. Currently they are mostly used as data centres, but I think they still provide some microwave links as well.
I used to live in an area served by what was then GTE and they had antennas like this. I have not seen anything listing GTE’s equivalent infrastructure. Does anything exist for that?
So some of the towers are still in AT&T's ownership but a ton of them got sold off to American Tower for resale and leasing space.
People do everything from run cellular on them, run datacenters in the nuclear hardened bunker sites, etc. Even though they're old as heck and look like something out of a sci-fi many structures are still solid and some of the sites have things like diversified utilities.
Then finally, there's the EPA... these towers can be a nightmare for EPA - specifically the ones with backup generator fuel tanks that were buried. I'm guessing AT&T didn't want to deal with the complex logistics of digging those up, horn removal, etc. and just sold many of the properties off.
The ones that are still in AT&T's ownership also have fiber co-sited at them, usually on former coax routes, like this former main station between Colorado springs and Amarillo.
There is still active microwave, but its usually in the ownership of the RBOC/IOC not a long distance carrier, and is used to link the end office to the rest of the PSTN. Microwave is also used extensively to link cell sites to other cell sites, so you need to install less fiber.
Huh - looked at that location on street view and it is so weird seeing a modern AT&T logo on a Long Lines site building!
Microwave backhaul fascinates me... I think the most interesting example of it that blows my mind is the private backhauls that are going up between major financial hubs in the US like Chicago <-> New York. Since latency is a huge deal for a lot of these HFT traders some intense stuff gets engineered:
> The researchers then used the FCC and other records to deduce that, at the time of their 2013 study, there were 15 (!) networks licensed to operate microwave links between the two cities.
Most of the non-microwave only sites were converted to fiber, so they're out there quietly humming in the night, soldiering on, just passing traffic, their facilities which were designed to be manned 24/7, might see an engineer once a week, or even once a month.
I've often dreamed about building a private national microwave network to sell capacity on. They're not expensive to build or operate with modern hardware, which doesnt need much power or servicing.
Buried waveguide! a path not taken, as fast as microwave, with more controlled path characteristics. Had fiber not worked out to be practical, this would have been the replacement for the L-5 Coax network, as fiber proved to be.
Wow - and they actually had a field test that worked...! I have such a huge respect for the engineers that worked on these systems - it feels like some wild west sorta stuff.
Cost.
Several of them are hosting cell and radio services so that "pays the rent" on the location.
Dismantling and scrapping such a tower would be enormously expensive and bring no value to AT&T shareholders.
If they're in total disrepair, I'm sure a case can be made for safety in an urban area. The two towers closest to me are in rural areas with several other radio service tenants where maintenance is a covered cost.
Legacy AT&T owns almost none of them anymore, what's left are owned by the RBOC (often the other AT&T) and as you note, have a prohibitive removal cost and are in urban centers.
Microwave back haul in telecom networks is still very prevalent the difference between what this article describes and modern day is how it is used. Now days the microwave part of the network is usually regional to connect groups of towers in a local area to a central location that has fiber or satellite access into the main network. This older system was doing the job of what fiber does today serving as the main cross country network.
AT&T sold most of them off in the early 2000s. American Tower owns a lot of them. Some others went to individual private owners. There's a company in western MT that owns about five of the mountain top sites for instance. Very few of the rural/suburban sites are still owned by AT&T. The sites where AT&T still happens to be the ILEC in an area may have horns on a central office roof just because they're very expensive and a huge hassle to decommission.
Many of these towers are also used for other equipment as well, and not abandoned.
It's also worth mentioning that big equipment like this isn't designed to be removed from towers, and not only would be expensive to remove, but extremely dangerous. It's a lot safer and cheaper to just leave it there, and mount additional equipment (cellular equipment, etc) elsewhere on the tower.
There's usually other antennas on the tower for cellular or VHF/UHF, so the tower itself is maintained. And the microwave horns and waveguide are typically aluminum and/or copper.
THey don't actually own many (most?) of them anymore. Most have been sold and are owned by a handful of "tower operating" companies who will lease space on the tower. The ones in areas with no other market for radio towers have been/are being scrapped.
We've got networks like this all over rural America. Only instead of giant towers they're little consumer fixed wireless nodes, getting 1-25Mbps (or more!) via 2.4GHz. 5GHz if you're lucky.
Some of them short (<~50 miles) links with horn antennas like you see in this article. Longer links with parabolic dishes and tropospheric scatter. All "portable" equipment on camouflaged trucks and trailers that could be unloaded and assembled anywhere.
All of that started being replaced in the mid-90's with a combination of dedicated military satellite equipment and more use of commodity stuff like small commercial microwave network bridges, cellular phones, satellite phones, and so on. They closed out the "microwave tech" jobs and folded them in with "satcom" or other specialties.
Some of the equipment:
https://en.wikipedia.org/wiki/AN/TRC-97
https://www.marines.mil/Photos/igphoto/2001740716/ (apparently still used by the Marine Corps)