Sunday, May 8, 2011

Running Away to the Air, 4: Deep Radio


In his appreciation in the 1946 special "Radio and Radiolocation" issue of the Journal of the Institution of Electrical Engineers, Robert Watson-Watt claims that 1% of the population of the United Kingdom worked with radio for war purposes, half that on radar. And the country shone like a dark star; peak output of Chain Home alone was 100kW of meter-length radiation. (I gather that this is the total power draw; by 1943 there were megawatt-range radar emitters installed at places such as Scapa Flow, but this would be pulses of a few micro-seconds duration.)

It's --look, here's the thing. The argument about whether wars are good for economies is on again. (AKA "does WWII prove that quantitative easing is a good idea?") So this might be a good time for a historian of technology to chime in and ask if we really understand exactly how WWII affected the economy.

On the one hand, Hayek suggesting that a draft gets you to full employment, a war economy sustains demand. In this light, we see now evidence that the American economy was going like gangbusters in 1941, and that the war, insofar as we can distinguish "miltary" effects from civilian, was a check on growth. Whatever, I'm not an economist, and you'll note that I'm not even linking to the article in question. As a historian of technology, I could cite any number of lines of research cut off at the outbreak of war in 1939, and only resumed, if at all, in 1945. If this is a story about the effects of stimulatory spending on an economy (as I think it is, because here, here, and here), then there's something better and broader about the pre-war expansion of the British electrical engineering industry, perhaps because it's less dirigiste. Point --Hayek? (I suppose with some sort of cautionary about how it will all end in tears.)

But, another point. The biggest single story of WWII radar was probably the magnetron, which permitted practical centimetric radar. And it really does look as thought it came about when the Navy asked the University of Birmingham for a radar that worked on ships that are low to the water. The working group at said, "eh, you can do that with magnetrons," and lent the Admiralty one that they'd been using since the electric kettle blew up. (J. E. Houldin, B. Eng. “The Magnetron:” J. Inst. Elec. Eng. 84 (1939): 145-6.)
 It's not a completely crazy version of events, even if in practice the Birmingham group about six months. Given the limitations of the magnetron, it's reasonable enough that everyone was trying to amp up a klystron instead, and the Japanese, per their utopian usual, actually had one at sea.

My point? Magnetron: Killer ap or low hanging fruit? It's both! (For those who can enjoy it. NBC: death spiral much?)  The magnetron story, and Watson-Watt's numbers, suggest, to my way of thinking, another way of looking it. You can't draft a population and put it to work without consequences. Obviously that's another way of making a point I've made here before, but I'm not quite done with it.

How does a plane fly at night? The First World War established that planes could use the "call and ask" method, and the radio direction finder followed. The US Post Office, however, found this impractical. Onboard radio direction finders were inaccurate and difficult to operate. Lighthouses demonstrate another method that is about as accurate as the beam of light is precise. Hence radio beacons, and "flying on the beam." For a short period in the middle of the 1930s this became an example of advanced American technology, because only the Americans were doing it. Since, in fact, it doesn't really work at ranges of more than 25 to 75 miles with the range of uncertainty being down to variable night effects, this is perhaps not the case. Radio direction finding works better --and that's before the proliferation of air defence radar networks in the late 1930s. Fortunately for inventors, most people quickly concluded that what you really needed was a short-ranged blind landing system. This wasn't something that radar could do, so the prospects for an able inventor was large. If it worked, one might even be able to slave an autopilot to the ground system and produce an aircraft that could fly itself! There was an American technology, a British proposal, and, of course, a German technology.

None of them worked, of course. The basic idea had two components. The first was an antenna array at an airport would broadcast a "beam" (actually intersecting lobes) that would guide an aircraft into a gradually-narrowing approach vector. Apart from arguments about the best kind of antenna array and wavelength, this worked well enough. The Lorenz system, developed by Dutch firm Carl Lorenz AG, could tell an aircraft where it was within a mile, one hundred miles from the airfield, and possibly out to 300 miles. (Except that you couldn't use it at that range below 25,000 feet, where commercial airliners were not yet flying.)

The second part to a blind landing, though, is the one that gets you to the ground. This is the "glide path," and what's supposed to happen is that the aircraft picks up a series of radio "gates" as it approaches the field. At each one, the pilot checks the altimeter, projects future course, and determines angle of descent until, finally, tyres touch ground. In practice, altimeter errors apart, pilots found it very difficult to pick up gates while following the beam. By 1939, Lufthansa was well along with experimenting with cockpit display devices that would listen automatically and light a series of directional signals. With aircraft designers still working out details of cockpit illumination, it was genuinely technically challenging. And the air force had another question. What if the "gates" signalled a bombing target, rather than an airfield to land on?

It wasn't entirely impossible, although an accuracy of +/-1% at a maximum range of a little over 100 miles suggested that it wasn't going to be coupled with an Amerika Bomber any time soon. Successor systems, using beacons deployed throughout coastal Europe could  (barely) possible be used on Coventry.
The story here gets a little confused, in part because of heavy dependence on  R. V. Jones, a source in whom I put little faith. (My receiver is perhaps a little sensitive on the score, but I detect signs of narcissistic personality disorder in his autobiography). British engineers were singularly impressed by the quality of the onboard display equipment and filters recovered from German bombers, but this is the sort of thing that it suited the men who failed to jam the guide beams for the devastating Coventry attack to argue.

So there's plenty of things to argue about. And where heat is being generated, may light be shed? In a postwar roundup of developments published in yet another of the JIEE retrospective articles, R. V. Whelpton and P. G. Redgment, summarise “The Development of C.W. Radio Navigatin Aids, with Particular Reference to Long Range Operation,” Jour. Inst. Elec. Eng. 94, IIIA Radio Communications (1947): 244–53. Useful radio beacon systems need to reach out to 1500 miles to provide worldwide deep ocean coverage. These will necessarily be low frequency systems, so at least you don't have to worry about designing antenna and all of the automatic gizmos that adjust their loading. On the other hand, this means that the beam will bounce off the stratosphere. You can't really distinguish between   ground and sky wave amplitudes at a distance greater than 1000 miles, but you can work around this with multiple beacons and a lot of math. The RAF famously used some early German beacons in the 400kHz range, such as Elektra, Decca, and Erika, giving accuracy of up to +/- ½○. Decca led to Loran, for which I'll point you to Wikipedia in the earnest conviction that this will prove that it is complicated, and that aircraft installations not the naked technology, were the big deal.

These devices were accurate enough for navigation; not bombing. For that, you need high frequency.  Caradoc Williams has a nice survey. ( “A Survey of Continuous Short-Distance Navigation and Landing Aids for Aircraft, Jour. Inst. Elec. Eng. 94, IIIA Radio Communications (1947): 255–66.) The basic problem was that every new system required more equipment in the cockpit. Williams was working on an “omnidirectional” beacon system  relying on aircraft-borne standard communications equipment and providing unmediated data, but, again, I'm going to point to the problem of making this work.

The article that brought it home for me was R. J. Dippy, “Gee: A Radio Navigational Aid,” Jour. Inst. Elec. Eng. 94, IIIA Radio Communications (1947): 468–80. Gee was a hyperbolic system relying on three ground stations separated by as many as 80 miles, in which stations are separated into the master and two slave stations, the latter of which rebroadcast the signal of the master station, in both cases modified obviously to avoid interference. The signals are entrained, which I intuitively suspect is a lot more engineering than Dippy's blithe summary may be taken to imply. But that's on the ground. At the aircraft, these generate a family of hyperbolas whose locus is the location of the aircraft. Dippy, and presumably everyone else, thought that  automatic reduction of the data to location was desirable. But it was not yet achieved. 

So to receive Gee, you need a loaded 4ft whip antenna  feeding into a "rather complex receiver" with 6 amplifier stages feeding a cathode ray oscilloscope tracer loaded with rectifiers &etc to turn the signal into the kind of nicely square steps needed to do the math.

And that's just GEE. By 1945, it was not unknown for a bomber to fly with a low-powered radar attached to the tail turret, a radar warning receiver in the cockpit, infrared beacons fore and aft, and a higher-powered ground scanning centimetric radar. By this time, bombsights were tied into a three-axis electronic automatic pilot (I have some lovely wartime Honeywell ads about their "automatic brain" that I really must scan up some time.) All magnetron-based radars have to be installed individually because of frequency variation, so the surface search installations on Coastal Command aircraft, but not Bomber Command H2S, had to have their antenna run punched through the wing structure and then calibrated by a team of electricians.

And I haven't even talked about the Royal Navy yet! Apparently, there were on average 40 working CRTs on every major RN naval combatant. What it comes down to is that even if Watson-Watt is aiming for the stars with his 1% figure, it remains the case that the world war saw electronic devices of unprecedented complexity deployed into the hands of something like every person, mostly male, but often female, who might be qualified to maintain them. 

Could a technology penetrate and transform a society so quickly in peacetime? Maybe some smart economist will compare the wartime social penetration and saturation of electronics technology with the computer era, and tell me. The other question is how important to this final outcome was the British national grid project. Did it prepare the way for this wartime expansion? Or, on the other hand, was this something that the British economy would have done just on the basis of its particular bias towards emergent technologies? Or, on the other hand again, am I overplaying my "anti-declinist" hand, and was Britain actually retrograde, as, say, Corelli Barnett would argue. 

So many questions. I remain, of course, available to accept very large research grants if anyone is interested in my answers.        


  1. This works with my family history - practically everyone seems to have done something with electronics, radio, or telecommunications in mid-century (and ha-what did I end up doing?). Whether that was Siemens & Halske (UK), making telephone exchanges, what became BT but was then Post Office Telephones, RN radio and radar (including commissioning the installation aboard Howe, which as a HACS IV-GB/ABU ship that commissioned post-PoW/Repulse must have been quite the Star Trek cockpit), REME radio workshops, Marconi-Elliott Automation-GEC-BAE-Selex flight control systems, MetroVickers aircraft instrumentation. I don't think anyone actually worked at Bletchley Park or TRE Malvern, but then they wouldn't tell you would they?

    The only person who didn't spent the war giving Rolls-Royce Merlins their ration of tender loving care, and also acting as a temporary riot cop in Bangalore.

  2. Fortunately, it's still all one big military-industrial complex!

    Although what about the poor jute farmers?'rourke&pg=PA41#v=onepage&q&f=false