Tuesday, April 02, 2024

Making The Right Choice

     Going into WW II, it was RADAR time, and everyone knew it.  Watson-Watt and his team get a lot of well-deserved credit for demonstrating the principle and dreaming up the hardware, but people had been messing around with various forms of "radio ranging" for quite some time even then.

     It was obvious early on that higher frequencies -- meaning shorter wavelengths -- gave better resolution.  It's like the "pixels" that make up a video display: for a given screen size, more and smaller ones give you a better picture than fewer larger ones.

     So with all that knowledge and experience, why on earth did Britain's Chain Home radar warning system use shortwave radio frequencies?  The antennas were immense, clusters of towers hundreds of feet tall, separate sets for transmitting and receiving, far too large to be pivoted for scanning.  The operator didn't get a nice plan position indicator display like modern weather radar, just a screen with a series of "pips."  She (and it was almost inevitably "she") had to turn a large knob to line up an indicator with a pip to get direction, then flip switches and go through the same process again to get altitude -- and even then, she wasn't done: bearing and altitude gives you "slant distance" and you need to do a little trigonometry to plot the location on a map, going from polar (bearing and distance) to Cartesian (X,Y) coordinates in the process.  Only then can anyone to begin to do something about the incoming threat.

     The hardware was mostly haywire, jack-leg, kludged.  The transmitters were based on a BBC shortwave broadcasting design, uprated for higher power and with an improvised pulse generator; the radar receivers were built from readily available, consumer-grade parts.  When the British coast was lined with radar stations, they were found to interfere with one another and the UK fixed that by using the country's power grid to synchronize the stations, each one in turn operating in its own fraction of a second.

     Chain Home was manpower-intensive (mostly womanpower): operators, calculators, runners, collators, technicians to maintain the cantankerous equipment, riggers to do the same for the antennas, and a network of filterers and map-plotters to turn the data from all the stations into a cohesive picture of incoming bombers.  It started out as a massive kluge and they just kept adding on.

     The system was, in the words of one of the men who helped design it, "third best."  What it had going for it was that it was a thing they could build then and there, mostly using what was already available.

     The very best system ("which might never arrive" according to the same expert) would have required the invention of entirely new hardware.  The Brits eventually did just that, with the cavity magnetron and scanning antennas matched to plan position indicator displays, but it was a long time coming.  Even second-best had a long development timeline.  They went with what they knew worked, with what they could manufacture without major invention.

     Once it was up and running, they applied inventive skills to making it work better.  "Fruit machine"* analog computers automated the process of calculation, correction and coordinate conversion, letting a single operator and a wall of electronics replace five or six people.  The complex process of integrating the information and directing fighters called for remarkable innovation in command and control -- innovations that the Germans never worked out; indeed, the lack of that structure in the U. S. military doomed the detection of incoming Japanese airplanes at Pearl Harbor to an historical footnote instead of a striking example of a successful early warning.

     The Brits slapped together little more than junk to build Chain Home.  It was barely good enough for the task at hand, especially early on -- but it was just good enough, and they learned as they went.

     It was the right choice.  Germany built sophisticated radars, more slowly and without developing the mapping/directing infrastructure to make good use of them: wrong choice.

     There are tradeoffs between good enough and quick enough, and knowing how much weight to give each one can make all the difference.
* That was the nickname for the thing.  It had a nice, big "go" lever like a slot machine for the operator to pull once they'd got the range and altitude information into it.  The console looks like a radar crossed with a pinball machine, installed in a telephone exchange by workers in a hurry to finish -- but it did the job.


Eck! said...

I'd add that the British developed the communications (telephone/radio)
so that command, control, and coordination of their visual, Radar observers, and in air fighters could be mapped and the aircraft
could be directed with the right priority.

They also understood automation where it was practical with their technology. I think the code breakers were the big deal and also
a long term impact we see every day.

I give them credit as they did this while under direct attack.


Joe in PNG said...

Lord Hardthrasher's yootoob channel has a good series on the Battle of Britian. He's like a more sober, upper-class version of Lazerpig, but just as amusing.
And as the sotted Scottish swine noted, Great Britian has 3 ways of fighting wars:
1)Put some upper-class twit in charge, lose badly, and proclaim victory
2)Put someone actually competent in charge
3)Kinda Wallace & Grommet your way through things through improvisation from various madmen using what's in the shed.

Rick T said...

Kludges that work are the hallmark of Gen0 (development) systems thrown in to use out of desperation. The Brits had plenty of space but no time, and probably liked the extra range they got with Shortwave frequencies instead what we use now.

Using the electrical grid as a synchronizer to time the stations was a detail I had not heard before. A brilliant solution to a hard problem.

Do I read echos of these kinds of installations in your descriptions of the Drive Rooms back in the Hidden Frontier?

Roberta X said...

Rick T: You might read multiple echoes. WW II RADAR built on, expanded and refined the methods and techniques of early electronic television. WW II codebreaking built the first electronic computers -- and both things required a level of command and control coordination that had never been done before.

The Hidden Frontier interstellar drive technology is based on that, but also based on my years in radio and TV broadcasting; there are many similarities between NASA's Mission Control and a busy TV control room (especially before automation stuffed the whole process into a few computers and servers, operated by two or three people). Both of the real-world models owe a great deal to the WW II experience using technology on a large scale in a rapidly changing real-time environment.