5 ms·

Microwave radar brought direct phone calls to millions

78 points by Stratoscope 4y ago

tyingq 4y ago
It seems to imply that the work on radar long predated using microwaves for telecom, which doesn't sound right. There was a telecom microwave link across the English channel from Dover to Calais in 1931. I suppose the use in radar might have brought some technical improvements or lower costs that made it more practical.
- mynameisvlad 4y ago
  The Wikipedia article is pretty clear on this: > Although an experimental 40-mile (64 km) microwave telecommunication link across the English Channel was demonstrated in 1931, the development of radar in World War II provided the technology for practical exploitation of microwave communication. > During the war, the British Army introduced the Wireless Set No. 10, which used microwave relays to multiplex eight telephone channels over long distances. A link across the English Channel allowed General Bernard Montgomery to remain in continual contact with his group headquarters in London. https://en.m.wikipedia.org/wiki/Microwave_transmission https://en.m.wikipedia.org/wiki/Microwave_transmission
  - tyingq 4y ago
    I did see that, but it doesn't explain it terribly well. Radar is a different use case of higher powered pulses versus sustained tx/rx, multiplexing vs not, and so on. So there's overlap, but they aren't exactly the same. Some deeper explanation that showed what, exactly, radar did to make regular telecom practical would have been more satisfying. "Cheaper klystron amplifiers" or "higher selectivity receivers", etc.
    - mynameisvlad 4y ago
      Further in the same Wikipedia article: > The development of radar during World War II provided much of the microwave technology which made practical microwave communication links possible, particularly the klystron oscillator and techniques of designing parabolic antennas. The fact that pre-war the links were a few dozen miles, vs transcontinental links post-war shows that it really wasn’t a viable technology before radar. And that’s generally true for most technology; war and the military tent to speed up the pace of technology development greatly.
      - tyingq 4y ago
        Helpful, though if you consider the "Wireless No 10 Set" as an example of a practical microwave radio...it didn't use a Klystron, and some of the enabling technologies like pulse code modulation and time division multiplexing didn't come from radar. The premise seems overstated to me...there's certainly some crossover, but both radar and microwave telephony were progressing in parallel. >transcontinental links post-war That would have to be relays. Even with tropo-scatter, microwave radios are only good for a few hundred miles. The "few dozen miles" limitation would just be the normal earth-curvature limitation that line-of-sight brings.
        itishappy 4y ago
        > there's certainly some crossover, but both radar and microwave telephony were progressing in parallel Looks like it, see what I've been reading: > Work on klystrons became very intensive during WWII. Radar was independently invented in Germany and Britain before the war, and was initially implemented at UHF frequencies using triodes as sources. The invention of the klystron in the US encouraged the British in a search for a higher power microwave source, one which would make possible both better target discrimination and more compact transmitters. The 1941 invention of the magnetron by Randall and Boot in Britain16 provided such a source for radar transmitters. The same year, (and before Pearl Harbor) a visit by British scientists to America launched an extraordinary collaboration between Britain and the US, which resulted in magnetrons and klystrons being manufactured for the war effort in Western Electric, Sperry, and other American factories. The reflex version of the klystron, perfected at Sperry and in British laboratories, served as the local oscillator in superheterodyne radar receivers. Magnetrons powered the transmitters. Together, the magnetron and the klystron made possible airborne S-band radar, a major factor in securing air superiority for the RAF. https://web.archive.org/web/20150924102609/http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-7731.pdf https://web.archive.org/web/20150924102609/http://www.slac.s... > The klystron was the first significantly powerful source of radio waves in the microwave range; before its invention the only sources were the Barkhausen–Kurz tube and split-anode magnetron, which were limited to very low power. It was invented by the brothers Russell and Sigurd Varian at Stanford University. Their prototype was completed and demonstrated successfully on August 30, 1937.[5] Upon publication in 1939,[3] news of the klystron immediately influenced the work of US and UK researchers working on radar equipment. https://en.wikipedia.org/wiki/Klystron https://en.wikipedia.org/wiki/Klystron
    - madengr 4y ago
      Though not all radar uses pulses. Some are CW, as were the earliest experiments for detection (no ranging).
  - jhgb 4y ago
    Wouldn't it be much more accurate to say that both Wireless Set Number 10 and the nascent radar technology in the early 1940s independently took advantage of the recent (<1 year?) invention of the cavity magnetron?
- jcrawfordor 4y ago
  While there was important early work, fixed microwave telecommunications really didn't emerge as a significant component of the telephone system until after World War II. The high cost, short range, and demanding maintenance requirements of microwave systems made them impractical as a toll carrier except in rather narrow circumstances. Through WWII the Bell System, for example, was relying on buried cables (which they used with analog multiplexing, achieving fairly substantial capacity but at a high installed cost). The first major landmark in civilian microwave telecommunications is 1951, when the Bell System completed the first transcontinental microwave route. This too was primitive by the standards of even five years later, and the large transmitters, inefficient waveguides, and basic antenna designs required that most of the equipment be installed in a hut at the top of the tower... and the range was only about 30 miles. The construction cost of these sites was very high but they already showed great promise to be more cost-effective than cable carrier. Basically all of the advancements that enabled this microwave link came out of the military. Improvements in radio transmitters (such as the klystron) were significant, but likely more significant was the rapid evolution of antenna, waveguide, and feedline design. Improved antenna gains allowed for longer ranges (moreso even than increased transmit power) and lower-cost, higher-efficiency waveguide made it possible to locate most equipment at ground level... this type of design was pioneered by radar where steering of the antenna made it impractical to mount the transmitter directly to the antenna. It tremendously reduced construction and maintenance costs. Early microwave telecom systems (through the '70s for the large part) were analog FDM, not digital, and based mostly on established FDM techniques for open-wire and cable but benefiting from the large bandwidth that microwave offered (AT&T would apply similar techniques to both buried coaxial cable and buried microwave waveguide, although the latter is sort of a famous failure). But, the AT&T lineage of digital telecommunications is also a product of WWII, with Bell Labs having developed a practical PCM method for cryptographic use. Innovations from radar design were instrumental in the development of digital radio systems later on, as radar drove a need for increasingly complex modulation techniques and equipment that supported them. This is of course a very US-centric explanation, but the GPO in Great Britain followed a broadly similar timeline to AT&T. Important radio innovations were made there was well during WWII, and imported English equipment (e.g. from General Electric, the London one) was common in US radio telecom equipment through the mid-century.
- walrus01 4y ago
  Actual widespread use of rudimentary analog microwave PTP links is a post-WW2 thing. The earliest widespread sites used square delay lens antennas in the 2 GHz band, later 4 GHz. See black and white photo here: https://long-lines.net/places-routes/Yellow_Springs/index.html https://long-lines.net/places-routes/Yellow_Springs/index.ht... Some of the oldest AT&T Long Lines sites with this type of equipment were built in the general corridor from Boston-NYC-WA DC
xattt 4y ago
There was a contemporary article in a National Geographic issue in the late 1940s-1950s that talked about the Long Lines network. It was a fascinating read, but I could never find the article again online.
- jes 4y ago
  I remember seeing such an article as well. Might it be one of these? [1] https://www.long-lines.net/history.html https://www.long-lines.net/history.html [2] https://www.bellsystemmemorial.com/longlines_book1.html https://www.bellsystemmemorial.com/longlines_book1.html
FridayoLeary 4y ago
Ot but i heard that recently it has become significantly more expensive to make international calls to/from certain countries. Can anyone confirm and explain what's going on? Are we going backwards in this way?
- ftth_finland 4y ago
  The bandwidth for phone calls is next to free. However, price does not nearly always follow costs. International phone call prices are mainly set by monopolies and regulators. If you want free, make a VoIP call.
- isthisthingon99 4y ago
  People have mostly switched to VoIP/whatsapp/signal. In order to maintain the infrastructure, they have to charge fewer people enough money.
Aroga 4y ago
deleted 4y ago
[deleted]
Gordonjcp 4y ago
I was just thinking how bare the towers at Bruxie Hill were looking when I drove past yesterday. End of an era, all those squat square masts getting stripped of the huge dishes that shot microwave links all up and down the country.
Nomentatus 4y ago
What seems to be missing from this article is the note that microwaves can only be produced by cavity magnetrons; and those were a WWII invention. Perhaps the most important invention of the war - certainly in the top 3.
PaulHoule 4y ago
https://99percentinvisible.org/article/vintage-skynet-atts-abandoned-long-lines-microwave-tower-network/ https://99percentinvisible.org/article/vintage-skynet-atts-a... In the United States there are abandoned Microwave towers left over from this kind of system. People have investigated them out in New Mexico, they run roughly parallel to I-81 between Syracuse and Binghamton and many cities have microwave antennas built into or on top of old central office buildings in cities like Manchester, NH. American Tower has bought up many of them and could potentially lease the properties for cell phones, broadcast radio and TV, emergency communications, amateur radio, etc. but these are frequently sited in locations not favorable at all for these uses.
- walrus01 4y ago
  There's public KML/KMZ files of most of the AT&T Long Lines sites if you search enough. Probably 5-10% have been demolished entirely for various real estate/land re-use reasons. One note that much of the same technology was used by the other assorted non-ATT legacy phone system operators like GTE. It all looks the same to an observer on the ground looking at old horn antennas but not everything that looks like an ATT Long Lines site was actually Ma Bell.
- teeray 4y ago
  They’re very robust sites, since they were all nuclear hardened. I remember one near me which was fed with underground coax that ran through my town to an underground facility about 10-20 mikes away. It was always a point of curiosity since the underground lines were prominently marked with grave warnings for anyone approaching it with a backhoe. I imagine it probably carried AUTOVON traffic.
jalk 4y ago
> Because each channel had an effective base bandwidth of 10 MHz and a TV program used 4 MHz, it was possible to house a TV program and a small number of telephone lines on the same channel simultaneously Only a few telephone lines on 6MHz!!! How large guard bands do you need on a 3Khz telephone line? Edit: layout

78 points by Stratoscope 4y ago

It seems to imply that the work on radar long predated using microwaves for telecom, which doesn't sound right. There was a telecom microwave link across the English channel from Dover to Calais in 1931. I suppose the use in radar might have brought some technical improvements or lower costs that made it more practical.

mynameisvlad 4y ago
The Wikipedia article is pretty clear on this: > Although an experimental 40-mile (64 km) microwave telecommunication link across the English Channel was demonstrated in 1931, the development of radar in World War II provided the technology for practical exploitation of microwave communication. > During the war, the British Army introduced the Wireless Set No. 10, which used microwave relays to multiplex eight telephone channels over long distances. A link across the English Channel allowed General Bernard Montgomery to remain in continual contact with his group headquarters in London. https://en.m.wikipedia.org/wiki/Microwave_transmission https://en.m.wikipedia.org/wiki/Microwave_transmission
- tyingq 4y ago
  I did see that, but it doesn't explain it terribly well. Radar is a different use case of higher powered pulses versus sustained tx/rx, multiplexing vs not, and so on. So there's overlap, but they aren't exactly the same. Some deeper explanation that showed what, exactly, radar did to make regular telecom practical would have been more satisfying. "Cheaper klystron amplifiers" or "higher selectivity receivers", etc.
  - mynameisvlad 4y ago
    Further in the same Wikipedia article: > The development of radar during World War II provided much of the microwave technology which made practical microwave communication links possible, particularly the klystron oscillator and techniques of designing parabolic antennas. The fact that pre-war the links were a few dozen miles, vs transcontinental links post-war shows that it really wasn’t a viable technology before radar. And that’s generally true for most technology; war and the military tent to speed up the pace of technology development greatly.
    - tyingq 4y ago
      Helpful, though if you consider the "Wireless No 10 Set" as an example of a practical microwave radio...it didn't use a Klystron, and some of the enabling technologies like pulse code modulation and time division multiplexing didn't come from radar. The premise seems overstated to me...there's certainly some crossover, but both radar and microwave telephony were progressing in parallel. >transcontinental links post-war That would have to be relays. Even with tropo-scatter, microwave radios are only good for a few hundred miles. The "few dozen miles" limitation would just be the normal earth-curvature limitation that line-of-sight brings.
      - itishappy 4y ago
        > there's certainly some crossover, but both radar and microwave telephony were progressing in parallel Looks like it, see what I've been reading: > Work on klystrons became very intensive during WWII. Radar was independently invented in Germany and Britain before the war, and was initially implemented at UHF frequencies using triodes as sources. The invention of the klystron in the US encouraged the British in a search for a higher power microwave source, one which would make possible both better target discrimination and more compact transmitters. The 1941 invention of the magnetron by Randall and Boot in Britain16 provided such a source for radar transmitters. The same year, (and before Pearl Harbor) a visit by British scientists to America launched an extraordinary collaboration between Britain and the US, which resulted in magnetrons and klystrons being manufactured for the war effort in Western Electric, Sperry, and other American factories. The reflex version of the klystron, perfected at Sperry and in British laboratories, served as the local oscillator in superheterodyne radar receivers. Magnetrons powered the transmitters. Together, the magnetron and the klystron made possible airborne S-band radar, a major factor in securing air superiority for the RAF. https://web.archive.org/web/20150924102609/http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-7731.pdf https://web.archive.org/web/20150924102609/http://www.slac.s... > The klystron was the first significantly powerful source of radio waves in the microwave range; before its invention the only sources were the Barkhausen–Kurz tube and split-anode magnetron, which were limited to very low power. It was invented by the brothers Russell and Sigurd Varian at Stanford University. Their prototype was completed and demonstrated successfully on August 30, 1937.[5] Upon publication in 1939,[3] news of the klystron immediately influenced the work of US and UK researchers working on radar equipment. https://en.wikipedia.org/wiki/Klystron https://en.wikipedia.org/wiki/Klystron
  - madengr 4y ago
    Though not all radar uses pulses. Some are CW, as were the earliest experiments for detection (no ranging).
- jhgb 4y ago
  Wouldn't it be much more accurate to say that both Wireless Set Number 10 and the nascent radar technology in the early 1940s independently took advantage of the recent (<1 year?) invention of the cavity magnetron?
jcrawfordor 4y ago
While there was important early work, fixed microwave telecommunications really didn't emerge as a significant component of the telephone system until after World War II. The high cost, short range, and demanding maintenance requirements of microwave systems made them impractical as a toll carrier except in rather narrow circumstances. Through WWII the Bell System, for example, was relying on buried cables (which they used with analog multiplexing, achieving fairly substantial capacity but at a high installed cost). The first major landmark in civilian microwave telecommunications is 1951, when the Bell System completed the first transcontinental microwave route. This too was primitive by the standards of even five years later, and the large transmitters, inefficient waveguides, and basic antenna designs required that most of the equipment be installed in a hut at the top of the tower... and the range was only about 30 miles. The construction cost of these sites was very high but they already showed great promise to be more cost-effective than cable carrier. Basically all of the advancements that enabled this microwave link came out of the military. Improvements in radio transmitters (such as the klystron) were significant, but likely more significant was the rapid evolution of antenna, waveguide, and feedline design. Improved antenna gains allowed for longer ranges (moreso even than increased transmit power) and lower-cost, higher-efficiency waveguide made it possible to locate most equipment at ground level... this type of design was pioneered by radar where steering of the antenna made it impractical to mount the transmitter directly to the antenna. It tremendously reduced construction and maintenance costs. Early microwave telecom systems (through the '70s for the large part) were analog FDM, not digital, and based mostly on established FDM techniques for open-wire and cable but benefiting from the large bandwidth that microwave offered (AT&T would apply similar techniques to both buried coaxial cable and buried microwave waveguide, although the latter is sort of a famous failure). But, the AT&T lineage of digital telecommunications is also a product of WWII, with Bell Labs having developed a practical PCM method for cryptographic use. Innovations from radar design were instrumental in the development of digital radio systems later on, as radar drove a need for increasingly complex modulation techniques and equipment that supported them. This is of course a very US-centric explanation, but the GPO in Great Britain followed a broadly similar timeline to AT&T. Important radio innovations were made there was well during WWII, and imported English equipment (e.g. from General Electric, the London one) was common in US radio telecom equipment through the mid-century.
walrus01 4y ago
Actual widespread use of rudimentary analog microwave PTP links is a post-WW2 thing. The earliest widespread sites used square delay lens antennas in the 2 GHz band, later 4 GHz. See black and white photo here: https://long-lines.net/places-routes/Yellow_Springs/index.html https://long-lines.net/places-routes/Yellow_Springs/index.ht... Some of the oldest AT&T Long Lines sites with this type of equipment were built in the general corridor from Boston-NYC-WA DC

xattt 4y ago

There was a contemporary article in a National Geographic issue in the late 1940s-1950s that talked about the Long Lines network. It was a fascinating read, but I could never find the article again online.

jes 4y ago
I remember seeing such an article as well. Might it be one of these? [1] https://www.long-lines.net/history.html https://www.long-lines.net/history.html [2] https://www.bellsystemmemorial.com/longlines_book1.html https://www.bellsystemmemorial.com/longlines_book1.html

FridayoLeary 4y ago

Ot but i heard that recently it has become significantly more expensive to make international calls to/from certain countries. Can anyone confirm and explain what's going on? Are we going backwards in this way?

ftth_finland 4y ago
The bandwidth for phone calls is next to free. However, price does not nearly always follow costs. International phone call prices are mainly set by monopolies and regulators. If you want free, make a VoIP call.
isthisthingon99 4y ago
People have mostly switched to VoIP/whatsapp/signal. In order to maintain the infrastructure, they have to charge fewer people enough money.

Aroga 4y ago

deleted 4y ago

[deleted]

Gordonjcp 4y ago

I was just thinking how bare the towers at Bruxie Hill were looking when I drove past yesterday. End of an era, all those squat square masts getting stripped of the huge dishes that shot microwave links all up and down the country.

Nomentatus 4y ago

What seems to be missing from this article is the note that microwaves can only be produced by cavity magnetrons; and those were a WWII invention. Perhaps the most important invention of the war - certainly in the top 3.

PaulHoule 4y ago

https://99percentinvisible.org/article/vintage-skynet-atts-abandoned-long-lines-microwave-tower-network/ https://99percentinvisible.org/article/vintage-skynet-atts-a... In the United States there are abandoned Microwave towers left over from this kind of system. People have investigated them out in New Mexico, they run roughly parallel to I-81 between Syracuse and Binghamton and many cities have microwave antennas built into or on top of old central office buildings in cities like Manchester, NH. American Tower has bought up many of them and could potentially lease the properties for cell phones, broadcast radio and TV, emergency communications, amateur radio, etc. but these are frequently sited in locations not favorable at all for these uses.

walrus01 4y ago
There's public KML/KMZ files of most of the AT&T Long Lines sites if you search enough. Probably 5-10% have been demolished entirely for various real estate/land re-use reasons. One note that much of the same technology was used by the other assorted non-ATT legacy phone system operators like GTE. It all looks the same to an observer on the ground looking at old horn antennas but not everything that looks like an ATT Long Lines site was actually Ma Bell.
teeray 4y ago
They’re very robust sites, since they were all nuclear hardened. I remember one near me which was fed with underground coax that ran through my town to an underground facility about 10-20 mikes away. It was always a point of curiosity since the underground lines were prominently marked with grave warnings for anyone approaching it with a backhoe. I imagine it probably carried AUTOVON traffic.

jalk 4y ago

> Because each channel had an effective base bandwidth of 10 MHz and a TV program used 4 MHz, it was possible to house a TV program and a small number of telephone lines on the same channel simultaneously Only a few telephone lines on 6MHz!!! How large guard bands do you need on a 3Khz telephone line? Edit: layout