Hacker News Reader

Comment by mynameisvlad | Hacker News Reader

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

View on HN

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.

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.

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.

> 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.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

Part of how these things always work:

- War effort requires a whole lot of capital investment -- factories built, equipment developed, people come up to speed, etc.

- Postwar, radar is still important, but the overall government expenditure falls.

- Much of the capital (manufacturing and expertise) searches for a peacetime use... and what's the low hanging fruit? Telecommunications.

That's a good observation, but the telecom and radar did sort of go hand-in-hand. The radar is typically close to the action, but the information needs to get back to HDQ, usually hundreds of miles away. So being able to ad-hoc get lots of telephone connections and/or tty links from a radar site back to the generals was a common need.

That is, war money was being applied to both.

Though not all radar uses pulses. Some are CW, as were the earliest experiments for detection (no ranging).

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?

Reply on news.ycombinator.com