By Tom Anderson
In a previous article on alternate technology terminology, we looked at the technology of radar and went into some introductory detail on how it works. It is recommended that article is read before this one, which goes into two other technologies that radio communications ultimately led to, and which had great impact in our history.
The principles of radar had been implicit in James Clerk Maxwell's original equations of electromagnetism from the 1860s, and Heinrich Hertz, the man who provided proof that Maxwell's EM waves were real, had observed that they were reflected from metal objects. As early as 1904, the German inventor Christian Hülsmeyer demonstrated a device he called a 'Telemobilioscope' which directed a radio signal via a parabolic reflector to echo off any distant ships and bounce back to trigger a receiver, which rang a bell. Hülsmeyer's machine could only indicate whether ships were present (e.g. in foggy conditions), not their distance, but it was a first step on the path to using radio echoes to locate distant objects.
True radar technology would have to wait until the development of systems that could produce short pulses of radio waves. Remarkably, research into this technology was independently in pursued in more than a half-dozen nations in the leadup to World War II, but perhaps most comprehensively in the United Kingdom (where Robert Watson Watt had been working in the field since the 1910s) and in Nazi Germany. In each nation radar was a top secret topic as it was aware it could produce a war-winning weapon. Britain took a lead due to the invention (or more accurately radical improvement) of cavity magnetron technology at the University of Birmingham in 1940. Magnetrons allowed suitable radio pulses to be produced with a small and efficient piece of equipment, meaning radar sets could be carried by even small planes. Early work on radar also took place in France, Italy, the Netherlands, the United States (who eventually benefited from Britain sharing her findings) and the Soviet Union (who made some early breakthroughs and then lost interest at the worst possible time, immediately before the war).
The term 'radar' is of US Navy origin, originally being an acronym for RAdio Detection And Ranging. Interestingly, many countries whose scientists worked on their own systems lacked a single generic term for it, perhaps reflecting the top-secret nature of the projects; often there were just code names for individual pieces of equipment, such as the Soviet 'Zenit' or the German 'Freya'. Britain at one point called it 'RDF' (Range Detection Finding or Radio Detection Finding) and Italy dubbed it 'RDT' (Radio-Detector Telemetry). As the American acronym could be pronounced as a word, it's perhaps unsurprising that it was the one that caught on. Code names could also be perilous. During the war, the Luftwaffe had been using a radar guidance system for bombing that used two beams, but began developing a superior one which only used one beam. The project was called 'Wotan', as in the Germanic chief of the gods with one eye (Woden in English, Odin in Norse). A British signal intercept meant that Britain learned the code name, guessed what it meant, reverse-engineered the technology and had a countermeasure ready before the actual German project was on line! Unsurprisingly, after the war, Britain adopted the 'Rainbow Codes' system where colours and nouns would be combined randomly to produce impenetrable code names, such as the Blue Streak missile.
Radar ultimately works by bouncing radio pulses off distant objects and then receiving the 'echo'. Unlike reflected visible light, radio can bounce off the ionosphere and go beyond the horizon, making radar a war-winning early warning tool to pick up enemy bombers before they could be seen or heard. As well as the echo indicating distance and direction, analysis of the return signal can show whether the object is approaching the radar station or retreating from it, because the radio waves become more bunched up or more spread out (respectively). This is an example of the Doppler Effect, which can be observed in everyday life with sound waves: a police or ambulance siren sounds more high-pitched as the vehicle comes towards you but then more low-pitched as it travels away.
Radar has transitioned from a war-winning wonder weapon to mundane uses such as managing the bewildering swarm of passenger planes around a moderrn airport, or even helping to park a high-end car. But could it all have been different? It was undoubtedly the leadup to World War II that helped catalyse the rapid development of radar research, and things might well have proceeded differently without the war. Radar might well have a different name with only a small change in Our TimeLine (OTL). Some examples from AH fiction include "ELOR" (EchoLocation by Radio) from Tony Jones' "Cliveless World" and "Y-range" (short for Wireless Ranging) from Harry Turtledove's TL-191 books. The late Aaron Allston's Star Wars book "Starfighters of Adumar" features an Earth-like planet which refers to radar as the 'lightbounce system', reflecting the fact that radio waves are ultimately a form of light. Similarly, in "Look to the West" (where radio is 'Photel'), radar is 'Photrack'. If radio has a different name, remember that so must radar.
In 1945, American engineer Percy Spencer was working on a radar set including a British-derived magnetron while working at Raytheon. The radar set was set up to produce shorter-wavelength, higher-frequency range than usual, in the range called microwaves (about one metre to one millimetre in length). Spencer discovered to his surprise that the chocolate bar in his pocket had melted: he had accidentally invented microwave cooking. (One might argue that this was a discovery that could only have been made in America, as few other countries in 1945 had unrationed chocolate...)
The first microwave oven came only a year after Spencer's discovery and was dubbed the 'Radarange', reflecting its origins, but they would not become small and cheap enough for the regular consumer until the 1970s. Microwave ovens work because the wave sets up regions of separate positive and negative charge, and molecules with dipole moments (a positive and a negative end, e.g. water) will rotate to align with this 'dielectric'. The movement and collision of molecules produces heat (indeed, in many ways this is what heat is) and this raises the temperature of the microwaved product. Placing a metal object in a microwave will result in it acting like an antenna and complete a circuit, causing an electric arc (or spark) which in turn causes the surrounding air to be broken up into a superheated plasma. It is therefore not recommended!
Because of the nature of the wavelength, only certain spots within a microwave oven are ever heated at a given time. For this reason, microwave ovens contain rotating glass plates to ensure the hot spots are circulated throughout the food, or else one part would be burnt and another part unheated. For the same reason, it is generally recommended that food be left to stand for a minute or two after completion, giving time for the temperature of the food to fully equilibriate.
Microwave cooking has developed a bad reputation for its association with cheap ready meals, though there was a period in the mid to late twentieth century where it was more associated with the optimistic space-age physics in your home aesthetic of the age. Regardless, the technology has also transformed chemistry: microwave reactors mean that some reactions that used to take two days of conventional boiling now take just five minutes of microwave heating.
It is interesting to speculate on alternative names for the microwave oven. The OTL name for the technology is not especially logical and a little confusing: 'micro' waves are not of micrometre length. A more explicitly radar-derived name like the original Radarange brand name could have been preserved, for example. The aesthetics of the age in which microwave ovens were born also led SLP author Bob Mumby to dub them 'raycookers', a name which smacks of 1950s visions of the future.
These are not the only applications of radio technology, and we will look at some more in future articles.