Monday, 26 September 2011
Since no-one buys my books, and I had rather they were read free (or ‘for free’ as it seems one now says) than not at all, I set up this blog with the intention of scanning the print versions and putting them, page by page, here. Unfortunately the technical limitations of this site — one might reasonably have expected better from Google — are making this very difficult: pdfs nearly always come out garbled, especially if more than a page long, and even word documents lose their formatting. As for foot- and marginal notes, they get put arbitrarily in the midst of, or even superimposed over, the main text.
However I shall persevere. Here is (I hope) the cover of my one book-length collection of my own poetry:
Hmm. Didn't work quite as I asked it to, but it will do for now. Next time, you lucky people, you will get the back cover. Then perhaps some of the actual contents.
Friday, 9 September 2011
Below, I have tried to copy in my new book. In spite or because of using pdf, the formatting has been garbled, the marginal notes and all the illustrations left out. Nevertheless I hope it might pique the odd interest. Anyone interested in seeing the thing in its entirety should e-mail me directly - rather than 'posting a comment' - and I will send it to them as a pdf attachment.
Important Note made in August 2014: This version of 'Anatomy of Wireless' has not appeared here as originally laid out and is missing its illustrations. If you wish to see it properly, please send me an e-mail email@example.com and I will send you a pdf; it's just under 40 pages long.
Anatomy of Wireless1
1 Why ‘Anatomy’? pages 311-12 of Northrop Frye’s ‘Anatomy of Criticism’ (Princeton University Press 1957) explain. There is of course also an element of homage to Robert Burton’s wonderful ‘The Anatomy of Melancholy’.
Simon Darragh 1
I wrote this book entirely off the top of my head. A curious expression: I mean I wrote it entirely out of the contents of my mind.1I didn’t check any dates or facts,2 I gaily ignored some things that might cause a reader to say ‘hold on a minute’, and I spent time nit-picking where the reader might say ‘Oh, do get on with it.’ Even so, I don’t think there’s anything so wildly wrong that it will seriously mislead. Besides, the readers I’m after are ones I hope to entertain at least as much as edify or inform and the wrong is notoriously more fun than the right.
1 Even if we subscribe to the quaint notion that the mind and the brain are one and the sameα, the top of my head would hardly be the place: it would be somewhere inside the brain; the frontal lobes, I suppose.
α the Mind-Brain Identity Theory turned up in the mid twentieth century, the product of a group of philosophers. (They were Australian, which some might think a mitigating circumstance.) It looks easy to refute: the brain is a physical object inside the skull, white, (it seems it’s not grey), having a certain weight and volume and gloopy consistency. The mind is none of these things. To be fair, the theory has ways round these obvious objections, but why bother?
2 But then of course if they’re facts they don’t need checking do they? A fact is a fact is a fact, as Gertrude Stein didn’t say. What need checking are statements, to see whether or not they are (in fact) statements of fact.
3 Persuading Microsoft Word that one can have footnotes to footnotes wasted a lot of my time, as the essays of the excellent David Foster Wallace suggest it must have wasted a lot of his.
Voices don’t carry far. Beyond bellowing from hill-top to hill-top, all human communication is the conversion of the voice into and from some more transmissible thing. This is a book about one such conversion, but rather in the sense that Moby-Dick is a book about fishing or Between the Acts one about a village fête. You will find in the main text what is I hope a straightforward account, all the way from Faraday’s experiments with magnets and coils in the mid nineteenth century to the arrival of transistors in the mid twentieth, of the development of wireless communication. Any readers who are interested only in that, and have no interest in, to name just a few things, metaphysics, vintage motorcycle clubs, music, Sod’s Law, Proust, and Greek etymology should ignore the footnotes and especially the footnotes to the footnotes.3The curious and perverse who have little interest in wireless but picked the book up anyway might like to skim the main text and concentrate on the footnotes. 2
Apologia Pro Illustrationibus Mea1.
1 I have probably got the Latin wrong. I think ‘pro’ takes the Dative or Ablative, and I think Dative and Ablative plurals are usually –ibus.
2 Well its second of course: appearances to the contrary I didn’t write the thing using a planchette board.
This book’s first2reader, my friend Howard Gamble, suggested it would be much improved by the addition of illustrations. ‘But I can’t draw’ (as the reader will see). ‘That doesn’t matter.’ Having seen some of Faraday’s own illustrations in his notebooks – wonderfully, they have to this day never been out of the old Royal Institution building in London where he lived and worked – I agree, so have used some of my own illustrations. Wherever possible however I have used other sources. Many were taken from ‘Newne’s Wireless Constructor’s Encyclopaedia’ by F.J. Camm, my grandfather’s copy of which, now passed down to me, used so to fascinate me in my early teens. This lovely book has no publication date, but I would guess the late 1920s or early 1930s. I have been unable to find any present copyright holder, but hope the shades of Mr Camm and his anonymous illustrator – perhaps they are one and the same – will be pleased rather than annoyed by my use of the book’s excellent diagrams. Don’t be frightened by the example below; I won’t be using more than a few of its items. 3
In 2010 the British Museum held an exhibition called ‘A History of the World in 100 Objects.’ A huge and beautiful book was published, which could theoretically help you to find and understand these objects, but it was far too heavy to carry about like a catalogue. BBC radio ran a series: having discovered long before that people who didn’t have to do it were thrilled to be on the radio, so didn’t need paying, they invited readers to write in telling them about their own special object.
I thought of writing in to tell them about mine. Then I thought of the way, and the desolate place, in which I’d found it, and how this epitomized the brutal selectivity – no, not even that, the arbitrary obviousness – of which past cultural objects our society reveres, charges admission to see, and which it ignores, and decided not to bother. When I die, my object will go into the skip with the rest of the rubble it so clearly is. ‘What did he want to keep that for? A doorstop? A paperweight? No, chuck it. Chuck out the papers under it too.’ 4
Chapter I: From Faraday to Crippen
That he1 should need paperweights says something about a person, though now that so many people have computers and printers perhaps not as much as it did once. What he uses as a paperweight says more. No-one actually buys a paperweight as such. They use a Venetian or Lalique glass ornament; the worn-out piston from the old BSA Bantam; a pink stone from the beach; one of those water-filled globes that make a snowstorm.
1 Or she of course – can we take that as read hereafter? The ways round the problem – and certainly it is a problem – remain clumsy, and that I won’t use them does not indicate that I’m a sexist pig, still less make me one. Being careful to use gender-neutral pronouns merely paints over sexism.
2 Here I have ignored an obvious problem: how did Faraday detect electric currents? In this experiment he couldn’t have used a compass-needle because the magnet-waving would have made it go haywire. Most current-detecting instruments rely on later developments of Faraday’s work. As I say, I have ignored this problem. Sorry, but see ‘Cautionary Preface.’
Transformers – not the huge humming grey ones you’re not supposed to go near and that supply electricity to whole rows of houses, but the smaller ones you find in some kinds of old domestic electric equipment – make good paperweights, though that wasn’t what Michael Faraday had in mind when he invented them.
Here we first meet Michael Faraday.
In the course of his electrical experiments Faraday noticed that a nearby compass needle would often flicker. It seemed to happen only when he made or broke the electric circuit; a steady current had no effect. Now a compass is a tiny magnet – could he get a converse effect? Placing a magnet near a wire didn’t do anything, but if he waved the magnet about an electric current was induced in the wire2, and if he wound the wire into a coil and waved the magnet up and down in the space inside the coil the effect was greatly increased.
Conversely again, a coil of wire with a current flowing through it is one kind of magnet. Clearly, magnetism and electricity were closely related. But not very clearly. Putting a coil with a current flowing through it – an electromagnet – near another coil didn’t induce a current in the second coil. There was, however, a momentary burst of electric current in the second coil every time he connected or disconnected the supply to the first coil. Arranging for very rapid connection and disconnection – a kind of alternating current, like that in most present-day house wiring – could induce usable amounts of electricity (had there been any ‘uses’ for the stuff) in the second. And winding the two coils round opposite ends of a diameter of an iron ring made the thing work really well. 5
Faraday explains to a large audience
Faraday had invented the transformer, and incidentally refuted the adage that necessity is the mother of invention. Much later transformers became very useful indeed: electricity supplies all over the world are now almost always ‘Alternating current’ – in effect, being connected and disconnected a hundred times a second1 – because en route the electricity has been converted into magnetism, then back into electricity, in transformers. That’s why those big grey transformers hum, (The note is somewhere around A flat, 2½ octaves below Middle C) and the iron ring is why even the little one I use as a paperweight is heavy.
1 120 in America, which always likes to be one, or even twenty, up. 6
Faraday’s work was looked on with suspicion by the more conservative natural philosophers. There seemed to be no connection, physical, electrical, or anything else, between the magnets and the coils. Resort to notions of a connecting ‘ether’ were beginning to look like a cop-out by this time, and anyway wouldn’t help, because the experiments would have worked in a vacuum, though I don’t think it was tried.1 Given a big enough current and a sensitive enough compass, you could get an effect right across the room. Even the transformers would sort of work, a little bit, with no iron ring and the coils well separated. What was happening had always been forbidden by those who took natural laws as prescriptive rather than descriptive. It looked like, indeed was, action at a distance.2
1 But they would. Definitely.
2 But aren’t seeing the stars, or even the cat, getting sunburnt, the planets staying in orbit round the sun and not whizzing off tangentially into outer darkness, the apple falling on Newton’s head and resulting in not only the law of gravity but perhaps also his mental breakdown years later, are they not all cases, known long before Faraday, of action at a distance? Well, yes and no. The history of science – particularly the theory and philosophy of science, and particularly particularly when those who prefer to get the phenomena to conform to the laws, rather than getting the laws from the phenomena, are concerned – is not linear but has recursive loops, and old ideas and prejudices can return long after new ideas seem to have refuted them. Where, for instance, a causal mechanism can be ‘established’ – which means ‘posited’, i.e. made up, at least as often as it means ‘discovered’ – the distance is neglected. Or perhaps rather redeemed or forgiven. The space in between is somehow filled up with causal stuff, and that we haven’t been able to find out what this causal stuff is or any of its properties, is due to our limitations rather than its non-existence. Ours is not to reason why.
How great a distance? Faraday probably didn’t bother to try more than a few inches; he was more interested in the close-up effects. The more distant effects of what came to be called electromagnetic radiation were investigated later, and from another direction. Or rather, along what seemed to be a mere curious by-road. Our very ability to use roads at more than horse or bicycle speeds is a branch off this by-road, and it is now time for this metaphor, tired 7
before I picked it up, to have a rest. Back to transformers, but first a short detour (oh sorry) via Signor Volta.
Volta invented the Volta pile. Put a copper coin on the table, and a disc of cloth or paper soaked in a mild acid, or just salty water, on top of it, then a silver coin on top of that. Fix wires to top and bottom, and run them to the muscle of the nearest frog’s leg. (His friend signor Galvani always had some.)1 The frog’s leg twitches, because it has received an electric shock. An electric shock of a pressure of, as it happens, about one volt.2 Volta stacked more of these units – copper, soggy cloth, silver – into the eponymous pile, getting of course one more volt per unit. Beyond about forty it will make a human leg twitch, even a dead one – this is the frightening area investigated by Signor Galvani, and anyone with a taste for films based on the Frankenstein story will know that high-voltage electricity – which always looks good on film – is important. Domestic electricity supplies are about 220 volts, and will do more than make your leg twitch.3At these sorts of voltages you can get sparks4by holding the wires from each side of the supply – from top and bottom of the volta pile, or from live and neutral of the mains socket5 – close enough together. The electric pressure is great enough to break down the air between the wires and jump across. Actually it doesn’t just make one jump: too much electricity crosses with the excitement, and some jumps back. It bounces back and forth thousands of times in a fraction of a second before settling down.6
How to make sparks.
Signor Volta and his piles.
1 Were they friends? Or even contemporaries? Do Italians eat frog’s legs?
2 Yes of course, he measured it with a voltmeter. I did say the history of science has recursive loops.
3 In the interests of Homeland Security, America prefers 110 volts.
4 The ‘sparks’ you get at lower voltages are technically not sparks but arcs.
5 Do not try this at home. Or indeed in anyone else’s home.
6 This jumping back and forth is an unimaginably rapid reproduction of Faraday’s alternate connection and disconnection, and has similar effects. More about that later.
7 ‘It turns out’ indeed. Explanations should be as simple as possible, but not more simple. But please, let it pass for now.
Back, remembering volts, to Faraday’s transformer. It turns out7 that the voltage you get from the secondary coil of a transformer is very simply related to the voltage you put across the primary. Assuming a perfectly efficient transformer – and by the early twentieth century they had efficiencies well into the 90s per cent – and the same number of turns of wire in each coil, then the volts you get out are the volts you put in. Suppose, then, – yes, you’ve got it – I put twice as many turns on the secondary as on the primary? Yes, I double the volts. 8
Surely yet another basic law, and a rather more robust one than that nonsense about ‘Action at a distance’, has been broken here? Have I not got something for nothing; am I not well on the way to inventing some kind of perpetual motion machine?1 No. Volts are the equivalent of pressure, but there’s something else: Ampères, after Monsieur Ampère. Increase the volts and you decrease the amps a corresponding amount. More about amps later. (I think I said that before. I seem to be giving what are I think called hostages to fortune. But all shall be redeemed in time, as T.S. Eliot didn’t say.)
1 Patent offices will no longer even bother to look at specifications for perpetual motion machinesα. We laugh now at the dogmas of those in the past with a prescriptive rather than descriptive view of scientific laws, but that one – the law of conservation of energy – has, unlike most, become stronger with time. If someone were to invent a perpetual motion machine now, he would have to smuggle it through the patent office under some less inflammatory description.
α One patent office did shut up shop completely – some time in the 1920s I think it was – on the grounds that everything had been already invented. But that was in America.
2 Which I just made up of course; don’t be silly.
Qualms about basic laws temporarily calmed, what happens if I put, well, millions of turns of wire on the secondary coil? Yes, I can get some pretty impressive sparks. A transformer of this kind is called an induction coil, and delighted the upper-class audiences at such places as the Royal Institution, and continues to do so, I hope, in schools where science is still taught and the budget runs to apparatus for demonstrations. (I mean scientific demonstrations, not ones about cuts to the education budget.) But like much of the stuff invented by Faraday or developed from his ideas, it didn’t seem to be much use, if ‘Use’ excludes delighting and amusing.
Then came the internal combustion engine. This relies on repeated explosions of a petrol/air mixture, tightly squeezed inside a cylinder. How to set the explosion off? One could hardly apply a match: the explosion had to happen inside the cylinder, and even in the slow early engines it does so several times a second. Furthermore such engines were often used to drive vehicles, and the necessity to light a match several times a second would probably, even in those traffic-free days, have led to accidents. So someone thought of ‘Hot tube’ ignition: a metal tube, closed at its outer end and giving on to the cylinder at its inner, was kept red-hot by an external flame, and a mechanically operated flap over the inner end opened at just the right moment to expose the hot tube to the mixture, making it explode. While a great improvement on the match idea,2hot tube ignition wasn’t very satisfactory.
The petrol engine.
Next came the magneto. This was so good that it remained in use right up to the 1960s, especially on racing motorcycles. The magneto ingeniously
The magneto. 9
makes use of all the Michael Faraday ideas I’ve described, and it’s sad that he never lived to see one in operation.1An induction coil – which, remember, is a transformer with thousands of times more turns on its secondary coil than on its primary – is rotated, by direct mechanical gearing to the engine itself, inside a cylindrical magnet. This rotation of a coil inside a magnet generates electricity, and the many-turned secondary winding ensures that this electricity is of a very high, spark-inducing voltage. On the non-driven end of the rotating assembly is a sort of rotary switch, known as the contact-breaker, which turns on and off to ensure that the really high spark-inducing voltage occurs at just the right moment in the engine’s cycle.2 A fat well-insulated cable, able to withstand the high voltage,3takes the electricity to the spark plug – that simple device still used on all petrol engines – so that the spark occurs right inside the cylinder.
1 I think. I mean, yes, of course it’s sad if he didn’t, but I suppose it’s just possible he did. See cautionary preface.
2 Oddly enough – well, not at all oddly really, but the full explanation is complicated and ‘need not detain us’ – that really high voltage occurs at the moment the contact-breaker breaks, rather than makes, the electrical connection.
3 A jolly trick at meetings of vintage motorcycle enthusiasts is to get some naïve newcomer to put his finger into a magneto high-tension socket while the owner rotates the drive gear. It hurts, but it isn’t really dangerous, because although the voltage is in the thousandsα, the amps are negligible.
α it takes about 30,000 volts to jump a gap of one centimetre. Thus a lightning strike to the ground from a cloud at a height of, say, one kilometre has a voltage of around three hundred million. Big numbers, like the millennium, don’t really mean much, they’re just an artefact of the way we choose to measure things. Still<
People who remember AM radio – that’s the Long, Medium, and Short Waves – and the old 405 line black and white television will probably also remember the irritating crackles or jagged lines on the television screen that often happened when motor vehicles passed nearby. It happened because the sparks in petrol engines are, like any electric sparks, causers of the ‘Action at a distance’ that so disturbed the more dogmatic scientists witnessing Faraday’s experiments with coils and compasses. Some mysterious influence must, it seemed, be radiating from Faraday’s coils. It didn’t travel far; just to the nearby compass or second coil. It might not be immediately obvious that the mysterious influence radiated by sparks is of the same type, but the fact that you use an induction coil to make sparks is a clue.
A proleptic mention of radio.
What is this influence? To say that it’s a wave, though true, seems little more explanatory than saying that birds fly south in the winter because they 10
are under the influence of a migratory instinct.1 The ontological status of waves is insecure. If you tie a long rope to a tree in the garden, then pick up the other end, hold the rope reasonably taut and give it an upward or downward jerk, a kink in the rope travels from your hand to the tree, where, with any luck, it is reflected back to your hand. But what has actually travelled? No part of the rope moved, except briefly up or down as the kink, or wave, passed. Ripples in a pond, when you lob a stone in, are much the same: one clearly sees something radiate outward from where the stone sank. But what actually moves outward? Nothing at all, that is to say, no thing. If you take the trouble to scatter corks about the pond before throwing the stone in, they don’t move along with the wave: they simply bob up and down as the wave passes.
1 The case of homing pigeons is interesting: apparently there are something like compasses in pigeons’ brains: small pieces of an iron compound that, being magnetic, are influenced by the earth’s magnetic fieldα and somehow prompt the bird in its efforts to get home.
α The earth is an enormous, but, fortunately or unfortunately, not very powerful magnet. Iron ships don’t get dragged to the North or South poles, but perhaps, if the earth were a really powerful magnet, suitable steering gear might have been developed to enable ships to travel free, without engine or sails, on even, as it were, diagonal courses. Direct East or West travel would remain a problem. When the ancients first discovered Lodestones – lumps of the very same iron compound found in pigeon’s brains – they were rather worried about the possible existence of a whole island of the stuff, which might pull all the nails out of passing ships so that they fell to pieces.
2 It is indeed a mythological system, but not ‘just another’ one. Without mythological systems we would all collapse from existential angst. Science, with its internal consistency and ability to predict events, may be the best mythological system man has ever had, but it is hubris to claim that it is, unlike all other systems, a description of ‘How the world really is’.
3 Metaphysics is divided into Epistemology (Theory of knowledge) and Ontology (Theory of existence). It is only called Metaphysics because in the collected works of Aristotle the book about these things comes after (‘Meta’ in Greek) the book about Physics.
So really there’s no such ‘thing’ as a wave. So in saying that what ‘comes out of’ coils with rapidly changing currents in them, or what ‘Is radiated by’ sparks is a wave, we are not committing ourselves to positing an extra but invisible and untouchable ‘thing’ in the universe: we are not ‘really’ breaking what has been a rule of philosophy, including natural philosophy as science used to be called, since at least the times of Duns Scotus and William of Occam. The whole idea of waves, at least the ones we can’t see (though what is it we see?) is rather dodgy, and a handy weak point for attacks by people who think science is just another mythological system.2
The ontological status of waves
Enough metaphysics3 for now. Back to sparks, whose radiated electromagnetic waves have a much greater range than those of Faraday’s 11
alternating current coils; more even than those from the huge grey transformers that supply power to whole streets.1
1 In the late twentieth century there were claims, dismissed as loony by most scientists, especially those employed by electricity companies, that the radiation from power supply transformers, and even overhead transmission lines, was significant and harmful. As I write, the jury is still out, or would be were the thing to come to court and the power companies required to show that what they do is not harmful. Absence, or paucity, of evidence that something is harmful is not the same as evidence that it is not harmful, as scientists, including those working for power companies, know full well.
2 English speakers mangle all foreign words on principle.
3 He also connected the ends of large loops of wire – in effect, single-turn ‘coils’ – across the spark gaps at both ‘transmitting’ and ‘receiving’ parts of the apparatus, but to explain what these were for would entail both recursion and prolepsis.
4 As far as I know no-one has ever been able to reproduce this experiment. I once watched two of my school physics teachers spend an entire fruitless afternoon – thereby ruining the innocent activities of the school wireless club in the next room – trying to do so. Reproducibility, obliging the experimenter to describe his experiment in scrupulous detail, so that others can try it, and only if they get the same results does it count, is a basic requirement in science, and the inability of others to reproduce an experiment usually leads to ridicule and ostracism not of those who failed, but of the one who claimed to have succeeded. Nevertheless in this case we take Herz’s word for it because what came later seemed to show that it must have happened.
5 You can make an induction coil out of an old car ignition coil, but I won’t say how as it’s rather dangerous.
The German scientist Herz (pronounced ‘Hairts’ or, by most English speakers, ‘Hurts’2), suspecting the existence of these electromagnetic waves, or perhaps having rudimentary evidence of them, (see Cautionary Preface), connected large metal plates to each side of the spark gap on an induction coil. At the far side of the room he took a similar pair of plates and arranged a tiny gap between them.3 He claimed that whenever he set the induction coil in action he could see a tiny spark between the plates across the room.4
the first wireless message.
With hindsight, and stretching a few points: Herz had sent the first wireless message.
Instructions for making a simple wireless transmitter and receiver
Not all that simple, unless you’re well off: you’ll need an induction coil – two, if the recipient of messages is to reply – which would be expensive and difficult to find.5 So what follows is more a description of how a wireless transmitter and receiver might be made rather than instructions for making. 12
It is a development of Herr Herz’s experimental apparatus. In place of the metal plates either side of the induction coil’s spark gap, one takes a wire from one side to earth. Literally earth, or the Earth: attach the end of the wire to a metal rod, or indeed a metal plate, buried in the ground.1 A wire from the other side of the spark gap is taken up high and suspended across the garden to, say, a convenient tree, to which it is attached via an intervening insulator, such as a piece of glass or porcelain.2 This is the aerial,3 from which the electromagnetic waves – wireless waves, later called radio waves – radiate.
1 The earth itself can be used in many cases, certainly this one, as a huge electrical conductor. This is very handy: electric circuits, as their name implies, are (topologically if not in appearance) circular, so the departing electricity needs a way back to its source after it’s done its work. The earth itself can be so used, hence the electricians’ Cranmer-like expression ‘Earth return’. If the ground is damp, so much the better. Domestic electricity installations also use an earth. Very often the water pipes, if they’re metal, are used for this, as at some point they disappear into the ground. In Greece this is for some reason not allowed, so a metal rod is used, and I have seen electricians, as a final touch to a new installation, er – urinating on the earth rod. Greece being Greece, this may also have some superstitious or religious significance.
2 All things electric, including the electromagnetic waves we are about to make, have a strong desire to get to the ground, and all electrical work can be considered as ways to make electricity do something on its way there. Obviously, like everyone else, it prefers not to work, and will take any available short-cut to earth. Hence the need for insulators.
3 The adjective ‘aerial’, originally pronounced with four syllables, long predates the three-syllable noun. I can’t read Shelley’s poem about the church in Lechlade without thinking of both wireless and signor Volta – he calls it an ‘Aerial pile’.
4 ‘Is there anybody there? Knock once for yes, twice for no.’ Presumably two knocks would really be ‘Yes, yes’; we need a better system.
A similar arrangement is needed at the receiving end. One plate is replaced by a wire leading to an aerial, the other by a wire leading to earth.
The Aerial, the Earth,
The spark gap in between is replaced by some more sensitive detector of electrical disturbance in the ‘ether’ – a pair of headphones is ideal.
All being well, every time the induction coil is turned on and made to spark, a hissing, crackling noise will be heard in the earphones at the receiving end. Depending how high the aerials are, and in the absence of large objects such as buildings between transmitter and receiver, the absence also of other sources of interference such as passing motor vehicles with electric ignition – i.e. almost any motor vehicle built after 1910 – such an arrangement could have a range of several miles. Given that list of absences, wireless transmission should work very well across large bodies of water; the sea itself makes a fine ‘earth’. More of that in a moment.
And the Sea.
But the occasional hiss in a pair of earphones hardly constitutes communication, except at the level of first contact in a spiritualist séance.4 A 13
huge improvement is to turn the supply to the primary winding of the induction coil on and off rapidly and easily1 by means of a spring-loaded switch – a telegraphist’s key in fact. One can then use Morse code2; sparks of long and short duration would cause long and short hisses or crackles in the earphones at the receiving end.
1 Yes I know it’s already going on and off many times a second because that’s the way an induction coil works. What I mean now is turning the external supply (the battery or whatever) on and off easily, but not that rapidly, so as to interrupt and restore the whole spark-making process. I hope that’s clear.
2 Samuel Morse’s code is a system of dots and dashes – or longer and shorter bursts of sound, durations of sparks, whatever – to represent letters of the alphabet. Thus ‘A’ is •– (Dot dash) and, for example, ‘V’ (for ‘Victory’) is, famously, •••–, as used by Beethoven for the first subject in the first movement of his fifth symphonyα.
α I suppose it’s just possible Morse invented his code – used also in earlier forms of telegraphy, long before wireless – before Beethoven wrote his symphony. Slightly more probable, but not much, is that Morse knew the work and deliberately chose the motif for ‘V’. Almost surreally improbable is that Beethoven’s theme was inspired by the Morse code ‘V’. (There is a fine joke about Beethoven’s non-existent wife and the ‘Dit-dit-dit-daa’ theme, but we must get on.)(And there’s an even better one about the telegraphist’s daughter, but as I say<)
3 The common Greek word for a ship’s wireless operator is still ‘Marconistis’.
4 A great shame: he so nearly got away with it, and so richly deserved to. I once lived in a squalid squat in Hilldrop Crescent, Camden Town – it might well have been the house Crippen had lived in. Some of the older residents could just remember him and his wife, and the little secretary Ethel le Neve with whom he ran off. They all said he was a nice, inoffensive man, and that Belle, his wife, was quite horrible.
Arrangements little more sophisticated than these, and made by the Marconi company, were installed in many ships early in the twentieth century.3 More people would have died in the Titanic disaster but for the Marconi apparatus, and Crippen had the dubious distinction of being the first murderer in whose catching ship-to-shore wireless telegraphy played a part.4
The first mention of Guglielmo Marconi. 14
Chapter II: From Marconi to Elvis Presley.
The first telephone proved to be useless until the invention of the second. Spike Milligan.
What happens when you have three or more telephones? You could connect them all together, but one might wish to talk to just one of one’s fellow telephone-owners and not all the others. No problem: it is just a matter of wires; one invents the telephone exchange, manned, or rather womanned,1 by someone with sets of plugs and sockets enabling connection between any two telephones. At first one picked up the receiver and told the person at the exchange who one wanted to talk to;2 later numbers were assigned to each telephone, and later still came the dial, enabling the telephone company to throw the uppity woman out of a job by replacing her with a bank of ingenious automatic rotary switches.
The Telephone Exchange.
1 Telephone exchange people have traditionally been women. A good new opportunity for women’s independence, and the rise of the telephone coincides with the rise of limited emancipation for women. Typewriting is similar: ‘Typewriter’ originally meant the person – again, nearly always a woman – who operated the machine. There is something underhand about this linguistic shift. Consider the word ‘Manufacturer’. Etymologically, and I suppose originally, it meant someone who makes something with his hands. But now, if someone tells you he is a manufacturer, the one thing you can be sure of is that he never gets his hands dirty.
2 I mean of course ‘To whom one wanted to talk.’
But wireless communication is just that: wireless. How can the signal, radiating outwards in all directions, be distinguished from the many others that might be floating about? Of course, even in the early days, the wireless operator would precede his Morse-encoded ‘I say, chaps, we seem to be sinking’ with ‘R.M.S. Titanic here,’ but this was of only limited help: the listener would be presented with so many dots and dashes in his earphones, this group from that transmitter, that group from another, that they would merge into a general noise: communication would break down as soon as there were more than about three people transmitting at the same time. The human mind, using that combination of fine instruments the ear and the brain, can pick out one voice, and what its owner is saying, from the general buzz of conversation in a crowded room, but at this stage in wireless communication we are dealing with undifferentiable hisses and crackles in earphones.
But now everybody knows that you ‘tune’ a radio. Increasingly, the job is done automatically: you press a button and the digital display winds up or
down to the next station.1 Some will remember the magnificent wooden-cased valve radios, with their typically semi-circular glass dials, warmly lit from behind and marked with romantic names like ‘Hilversum’, ‘Reykjavik’, ‘Schenectady’2. A needle, moved by a hand-operated knob, swept slowly round, and between the bloops and bleeps and whistles, in came the distant voices or music.
1 Yet another case of control being taken out of the hands of the operator, who doesn’t have to bother to think about it: the job is done for him. Anyone, such as myself, who has desperately tried to get a word-processing application on a computer to set out a document the way he wants it, rather than the way Bill Gates thinks he ought to want it, will know how frustrating this assumption of stupidity and incompetence can be. And anybody who has not yet done so might like to read that passionate work ‘The Case for Doing Things with your Hands’ by Matthew Crawford.
2 I understand Schenectady is not actually a frightfully romantic place. But the name still looks good on the dial of an old radio.
3 Tie the middle of a piece of string round the handle of an ordinary dinner fork, wind the ends of the string round a finger of each hand, put your fingers in your ears, let the fork dangle and swing it against, say, the edge of a table. The fork will vibrate at its natural frequency, and you will be surprised by the strength and musicality of the note you hear.
This tuning of a radio is not just analogous to but very much the same thing as tuning, say, a guitar by tightening or loosening its strings, or a wind instrument by sliding part of its tubing in or out. So it is time for a big digression away from radio waves and into sound waves.
Nice warm radios in wooden boxes
All physical objects except the softest and floppiest have a ‘natural frequency’: the speed, in numbers of wobbles per second, at which they will vibrate when struck. For many physical objects this speed lies within the range – from about 20 cycles per second, or ‘Herz’ as they’re now called in belated recognition of the great German pioneer of radio, to around 5,000 Herz – that, when transmitted to the ear, humans recognize as sound. One often notices, when hitting a rigid object such as a bar of metal, that it rings.3 Very large objects have very low natural, or resonant, frequencies. The resonant frequency of a good solid bridge is likely to be around only two or three Herz. It can be set in vibration by giving it regular thumps, even quite small ones, at this frequency. This can set up an alarming, even dangerous movement, and is why soldiers are ordered to ‘Break step’ when crossing a bridge. It’s just possible that their silly Sousa-march-like military ‘tramp-tramp’ will have the same frequency as that of the bridge, which could then shake itself to pieces,
Armies and organists wrecking things. 16
and serve the army right.1 Similarly church organists are warned not to play a particular note – a very low one, but different for each church – too often or too long. The right, or rather wrong, note can shatter the stained-glass windows. In Germany after the war the occupying forces often needed to demolish bomb-damaged buildings, many of which were too unstable to be approached with heavy cranes and such-like. Instead they tiptoed in with a large loudspeaker, connected to a powerful audio oscillator2 at a safe distance. Trying various frequencies they could often find one that made the building shake itself to pieces, at the expense of the unfortunate loudspeaker. On a smaller scale, one hears tales of opera singers shattering wine glasses by singing the same note as the glass’s resonant frequency, though frankly I suspect such stories are, as they say, apocryphal.3
1 You may have seen the surreal (though real) film of a big suspension bridge in America shaking itself to pieces. This was caused not by an army tramping across it (so much for ‘Homeland Security’) but by regular puffs of wind – themselves another phenomenon of natural frequency – coming down the valley. Since then, civil engineers have taken care to consider local conditions when designing bridges. The case of the Millennium footbridge over the Thames in London was similar: there, the vibrations of foot passengers caused swaying. Though unlikely ever to be dangerous, many people found this disturbing. God forbid that anyone should ever be disturbed in our bland society, so engineers went to great lengths to spoil the elegant design by adding shock-absorbers to damp the vibrations.
2 I shall discuss loudspeakers and oscillators later, if I ever get that far.
3 Now that we know how intimately bound up are pitch and frequency, we tend to regard this not so much as a correspondence as an identity. Thus, while some say that the note Middle C ‘has’ or ‘corresponds to’ a frequency of 256 Herz, others just say Middle C is 256 Herz.
What is happening here are cases of ‘Resonance’ or ‘Sympathetic vibration’. Those lucky enough to own two guitars will be familiar with this. Provided one’s two guitars are made carefully in tune with each other, then after playing, say, the open bottom ‘E’ of one guitar and immediately damping it, the player is likely to hear the same note mysteriously still sounding from his other guitar, leaning innocently against the wall on the other side of the room.
Long coil springs can provide a convincing demonstration of the phenomenon, at frequencies well below the limit of human hearing. If you can get hold of two such springs, suspend them from, say, two light fittings in
You can hang it from the ceiling. 17
different parts of the room,1 and hang small weights from them, adjusting them so that the two springs bounce up and down at the same rate. If you now wait for one spring to stop bouncing, and set the other going, you will find that, after a little while, the other spring starts going up and down in sympathy.
1 Better find some other suspension point unless you’re a competent electrician and a dab hand with the polyfilla. Do it when there’s no-one else in the house. It’s possible that a returning male member of the household will be amused and intrigued and might help with the experiment. A returning woman is more likely to call it ‘silliness’ and complain about the mess. I don’t say this is how things ought to be, merely that, unfortunately for both men and women, it’s usually how it is. This is part, but only part, of the reason there have been so few women scientists, though those few there have been have often been very distinguished indeed, perhaps because of the need to combat stereotypes.
2 These coils are a development of the simple large loops used in Herz’s apparatus. By the way, I use ‘Transmitter’ and ‘Receiver’ for both the operators and the apparatuses. (‘Apparati’?)
3 Yes, I know: you’re not supposed to start a sentence, let alone a whole new paragraph, with ‘But’. Similarly a preposition is the wrong thing to end a sentence with. But what is good enough for Shakespeare, Donne, and Doctor Johnson is good enough for me, and I shall leave it in.
Back to Wireless
Something similar to the spring experiment can be applied to wireless communication. A coil of wire has, as well as its physical, bouncy, material frequency of oscillation, a much higher – thousands or millions of times higher – natural electromagnetic frequency. Including a coil of wire in the cable leading to the aerial of our primitive spark-transmitter will filter out many of the chaotic many-frequencied waves, and emphasize those whose frequency coincides with that of the coil. A similar coil at the receiving end enables one to pick out just that one transmitter.2 A set of coils of various sizes would let the receiver choose one among many transmitters to listen to. This system of interchangeable coils was, with refinements, in use for certain kinds of radio transmission and reception right up to the 1960s.
But3 this arrangement of sparks and coils was still pretty rough. A powerful or nearby transmitter using one size coil could easily swamp transmissions from one using a different size, no matter how carefully coil sizes were chosen. A more refined, sharper way of filtering out the specious frequencies and emphasising the chosen one – of ‘tuning’, by close analogy 18
with the tuning of a musical instrument – was needed. This came in the form of the condenser.1
1 During the second half of the twentieth century the term ‘condenser’ became unfashionable: one is now supposed to call it a ‘capacitor’. Incidentally the unit of electrical capacity is the ‘Farad’, in again belated recognition of the chap we started with. Farads being huge, for most wireless purposes the Microfarad and even the Picofarad are used. Even more incidentally, the unit of inductance – the electrical value of a coil – is called, delightfully, the ‘Henry’, and again there are Microhenrys.
A ‘fixed’ condenser.
It is hard to think of a really good equivalent, in the field of physical vibration and resonance, of the condenser. Perhaps the weight on the bottom of the spring in the ceiling-dangling experiment above. A simple condenser consists of two metal plates placed close together but not touching. Better still is two sets of semi-circular plates, one fixed, the other mounted on a rotatable spindle allowing it to interleave, without touching, the fixed set. This is called, rather obviously, a ‘variable condenser’, and when connected across the coils in both transmitter and receiver it gave really sharp tuning. The device is only now, in the twenty-first century, being superseded.
And that was in about 1933.
The messy, noisy spark was still a problem. With the invention of the thermionic valve – those glowing things in old radios – new ways of making much cleaner, more accurately tuneable electromagnetic waves were 19
developed. I shall explain valves1 later; suffice it for now to say that the electromagnetic waves generated by this new arrangement of valve, coil and condenser – called a ‘Radio Frequency Oscillator’2 were so clean and neat that, paradoxically, they carried with them so little ragged noise that very little but clicks at the beginnings and ends of the dots and dashes3 could be heard in the receiver’s headphones. New ways had to be found of adding, either at transmitter or receiver, a ‘noise’ – actually the rather more tuneful ‘bleep-bleep’ familiar to listeners to the Short Wave – to the radio frequency ‘carrier’ wave.
1 Called ‘Tubes’, pronounced ‘Toobs’, in America.
2 An oscillator is something that oscillates; that is to say it ‘vibrates’ in an electromagnetic rather than physical way. An osculator is something that kisses.
3 Skilled telegraphists could nonetheless mentally reconstruct the full dots and dashes from these clicks. Similarly, skilled users of more old-fashioned wire-borne telegraph messages learnt to do the same when the paper or ink in the device that printed the messages ran out.
Why confine the added noise to the bleeps of Morse code, interesting only to radio amateurs and, until recently, ships’ wireless operators? One could instead add, at the transmitting end, Elvis Presley, Beethoven’s C# minor quartet, Melanie singing that work of genius about roller skates, or, God help us, the wit and wisdom of Jeffrey Archer.
You got a brand new key.
And that’s it, really: sound waves, even when converted into electrical form, don’t carry very far. Electromagnetic waves of much higher frequency can carry round the world and further. Add the two together at one end, subtract the radio frequency ‘carrier’ at the other, and hey presto, wireless. Sorry, radio.
Simple really, isn’t it?
The exciting possibilities of wireless 20
Chapter III: Extras.
In the first chapter I described in some (but not much) detail the development of wireless communication from Faraday’s investigations of electromagnetic induction up to the actual practical use of wireless, or radio. The second chapter was a mere sketch of its development up to the point where even the non-specialist at home could listen to speech, or music, or even the silence of a John Cage composition, on his ‘wireless’1. There is a lot I’ve left out. What follows might, I hope, fill in a few gaps, especially the glaring ones of chapter II.
1 The term ‘Wireless’, tout court, now thought a touch quaint, is indeed odd: the first motorised vehicles were called ‘Horseless Carriages,’ and this was abbreviated to ‘Cars’. I don’t think anyone ever said ‘I’m just popping out for a spin in the horseless’.
2 Shame they didn’t call it the ‘Bellophone’.
3 Small children can often hear higher frequencies. It is interesting that the upper frequency limit of hearing decreases with age, much as the child’s voice deepens in pitch (lowers in frequency as he or to a lesser extent she grows.) One often hears the expression ‘A gin-soaked voice’; drinkers often have lower-pitched voices; presumably the alcohol slackens the tension of the vocal cords, much as slackening a guitar string lowers its pitch. On the rare occasions that I sing I have a bass voice.
4 But not, unlike electromagnetic waves or indeed wireless, through no medium at all, i.e. a vacuum. Suspending an electric bell inside a glass jar and then pumping the air out, so that the bell can be seen to be vibrating but cannot be heard, is one of the more satisfying school physics demonstrations.
Microphones and Loudspeakers.
At the end of chapter II I mentioned too casually the conversion of sound waves into electrical form. How does one do that? A pioneer of this was Alexander Graham Bell, generally credited with inventing the telephone.2The microphone I shall describe is a non-existent simplification – though identical in principle – of Bell’s design.
Sound is caused by – one might say simply is – physical vibrations of frequencies between about 20 Herz and about 5,000 Herz, or vibrations per second.3These vibrations can travel through air or another medium4and then, impinging on some other object such as a human ear-drum, cause that to vibrate correspondingly.
A thin metal plate, clamped at one edge, will therefore vibrate when one speaks to it. Suppose, remembering Faraday’s experiments, we attach a bar 21
magnet, end-on, to the opposite, free edge of the metal plate, and surround the magnet with a coil of wire?
I did say I couldn’t draw.
As the plate vibrates, the magnet moves up and down, generating an alternating current in the coil which, electrically, more or less matches the sound impinging on the plate. We have invented the microphone.
Now suppose we make two of these things, place them far apart, even in different rooms, and connect the coils together with a long pair of wires? Speaking into one of these devices will generate the electric current whose fluctuations more or less match one’s voice. The current runs along the wires and passes through the coil on the other device, causing the magnet at that end to move up and down, so that the plate at that end vibrates in a way more or less matching the voice speaking at the other end. We have now invented the loudspeaker, and incidentally the telephone: since the two devices are identical, the person at the ‘hearing’ end could reply to the speaker, who would hear him at his own microphone/loudspeaker. 22
Modern microphones and loudspeakers tend to use the ‘moving coil’ design, in which (duh) the coil is attached to the plate, or diaphragm, and the magnet held stationary. The principle is the same; movement is always relative1 to something or other. The difference in physical appearance between modern microphones and loudspeakers is to do with efficiency in sound-gathering and sound-radiating respectively, and belies a total identity in their way of working.
1 The old story of Einstein sticking his head out of the train window at Reading and calling ‘Excuse me, what time does Paddington pass this train?’ is of course apocryphal. Whatever else Einstein was he was not a smartarse, and anyway Paddington is a terminal station.
The Thermionic Valve.
Sounds very impressive, doesn’t it? So much so that Microsoft Word’s dictionary doesn’t recognize ‘Thermionic’. But then Microsoft Word knows fewer words than many an eight-year-old.
An electric current passing through a wire will, if the current is strong enough and the wire thin enough, generate heat, caused quite literally by the 23
friction of the electricity passing through.1 The wire can get red hot, but early attempts to use this as a source of light were frustrated by the wire’s melting before it got hot enough to radiate much light. Wires of high melting-point metal such as tungsten were tried, but these would not so much melt as oxidize, that is to say burn. Oxygen is necessary for burning, so enclosing the wire in an evacuated glass bulb solved the problem. Most electric light continues in the early twenty-first century to be made this way.2
1 It was early realized that electricity – ‘static’ electricity is another matter – is not so much a ‘thing’ as a movement, though quite what it is and how fastα and in which direction it moves was not yet known. Nonetheless it passed from one side, or pole, of the battery or generator, through a conductor, and back in at the other side. The two poles were arbitrarily labelled positive – where the electricity comes out – and negative – where it goes back in. They had of course a 50% chance of getting it right. In accordance with Sod’s Lawβ they got it wrong. In fact, it is electrons that flow, from negative to positive. However the convention that ‘electric current’ (as opposed to electrons) travels from positive to negative survives.
αthere is an apocryphal story that the speed and direction were once tested by getting a circle of monks (why monks?) to join hands, the circle being completed by the connection of an electric shock machine to the free hands of the two monks at each end of the ring. When the handle of the machine was turned all the monks jumped in the air simultaneously; a sight worth seeing.
βSod’s Law is the well-known one about the dropped piece of toast landing butter-side down. That is actually − by analogy with Einstein’s Special (the one you can understand) and General (the one no-one understands) Laws of Relativity − Sod’s Special Law, from which is derived Sod’s General Law. Sod’s General Law states that if something can go wrong, it will.
2 I think it was a chap called Swan – not Proust’s Swann, but another, one-‘n’, Swan – who invented the vacuum-‘filled’ electric light bulb. Unfortunately the entrepreneurial Edison dined, like Chaucer’s Monk, (Monks again) on Swan, as he did on so many other inventors, and got most of the credit (and of course the money) himself. I do however remember a make of light bulb called ‘Ediswan’; a name that doubtless resulted from some absurd legal compromise. This practice of the boss getting the credit for the inventions and discoveries of his minions survives in all too many research departments.
3 I shall describe the electroscope later. It’s very simple.
4 Americans still call it the ‘plate’.
Some of the electrons whizzing through the white-hot wire get so hot they ‘boil off’ the filament and collect in an invisible cloud around it, much like the steam over a pan of boiling water. Someone, and I’m afraid I forget who it was, had the bright idea of introducing into the glass bulb an extra piece of metal, not connected to the filament but supported on a piece of wire passing through the glass envelope. He was able to show, using a sensitive device called an electroscope,3 that enough of the ‘boiled off’ electrons gathered on this extra piece of metal to give it a definite (negative, because they were electrons) electric charge.
Swan’s Electric Light Bulb.
He next connected the positive pole of a battery to the plate, or ‘anode’ as it came to be called,4 connecting the negative pole back down to one end of
The Devious Edison. 24
the filament, or ‘cathode’ as it now was. The anode, being now positively charged, attracted the free boiled-off electrons very strongly – just as with magnets and their north and south poles, opposite charges attract each other – and electrons flowed out of the anode, through the battery, and back down to the cathode. However, if he reversed the connections of the battery, wiring its negative pole to the anode and its positive to the cathode, no electrons flowed, because the piece of metal, now having a negative charge, strongly repelled the cloud of electrons, which remained around the filament.
He had invented the thermionic valve, called a valve because it allows the flow of electricity in one direction only.
The simplest possible thermionic diode circuit
In the diagram above1, I have used the conventional circuit-drawer’s symbol for batteries. A battery is a development of the Volta Pile. A single-cell battery2 – corresponding to just one pair of metal discs separated by acid-soaked cloth in Volta’s original pile – is represented in the diagram below:
1 Frankly this circuit is quite useless and merely wears out its two batteries; I’m just trying to explain the principle, you see. The diode, like the first telephone, becomes useful later.
2 Which is therefore not strictly a ‘battery’, but believe it or not I don’t want to confuse you. 25
The long stroke is the positive pole, the short the negative. Of course, just as in the Volta Pile, these cells can be stacked together, to make batteries of higher voltage. Anything more than about three cells is usually represented using a dotted line between the two end cells.
A single-cell ‘battery’ typically has a voltage of between one and three volts; enough to keep the filament hot. To drag the electrons across the vacuum, the other battery needed to be of higher voltage. Jumping forward, early valve-operated radios typically used a ‘Low Tension’ two volt lead/acid battery or ‘accumulator’, like one cell of a car battery, to keep the filaments hot, and a ‘High Tension’ battery of around 100 volts to drag electrons across vacua.1
1 Understand that there is no really necessary electrical connection between the low tension battery, heating the filament, and the high tension battery, dragging the electrons across the valve. They are only connected together because the filament is both the heating device – for convenience, heated electrically – and at the same time the cathode, or source of electrons. These could be separate, and indeed were in later valves, where the cathode was made of a substance specially good at ‘boiling off’ electrons and wrapped tightly around, without actually touching, the filament or ‘heater’.
2 Oddly. ‘Diode’ is etymologically derived from Greek, and ‘ought’ to mean ‘Two roads’. But the whole point is that there’s only one road, and a one-way one to boot.
The diode, as this vacuum device came to be known,2 had and continues to have a variety of uses, not least in wireless communication.
The diode was used mostly in the early stages – both chronologically and in the sense of the stages the signal received at the aerial must go through before it emerges at headphones or loudspeaker – of (the) radio (set). Next came the triode, which, as the name might suggest, introduced a third item, or ‘electrode’, into the glass bulb. This was a grid, known as the Grid, (duh), placed between the cathode, where the electrons are boiled off, and the anode, where they are collected. If the grid was made electrically negative, it inhibited the electron-cloud around the cathode from zapping across to the
The Triode. 26
anode. If made electrically positive it attracted the electrons but, as it was a grid, most of them shot through it to arrive faster than ever at the anode.
Conventional diagrams of diode and triode
The great thing about the triode was that quite small changes in grid voltage caused quite large changes in the current flowing out of the anode. Suppose we were to connect a microphone to the grid, and put a loudspeaker in the anode circuit? Speech or music at the microphone would generate an electric voltage fluctuating between positive and negative. This would affect the flow of electrons through the valve, and the fluctuations, greatly magnified, would be reproduced in the current flowing out of the anode. These would then be converted back to sound as they passed through the coil of the loudspeaker; the speech or music at the microphone would come out of the loudspeaker much louder. We have invented the amplifier. Here is a circuit diagram, leaving out certain inessential1 details:
1 Or at least, too complex to describe.
Simplified Amplifier Circuit 27
In the diagram I have used two new circuit-drawer’s symbols: A fairly obvious one for the loudspeaker, between the valve’s anode and the positive pole of the HT battery, and a less obvious one for the microphone, between cathode and grid.1There is a small battery across the filament to ‘boil off’ the electrons, and a much larger one to drag them through the circuit.
1 The other side of the microphone is connected to the cathode because the electrical variations at the grid need to be relative to the voltage at the cathode. It is usual, in valve circuits, to regard the cathode as the zero or basic reference point. In general, the negative poles of the batteries, and the ‘neutral’ sides of such things as microphones, are all connected together, often via the metal chassis of the apparatus. If this is not done, stray electric charges could build up at various points, interfering with operation. This is analogous to, but not quite the same thing as, the well-known ‘Earthing’ of household electrical apparatus and entire installations.
2 Nowadays this lid would probably be made of plastic, but at first it would probably have been made of porcelain, or perhaps vulcanite, a heat-hardened rubber named after that fiery mythical chap Vulcan.
I think the triode was invented by a chap called de Forrest, and was at first known as the de Forrest ‘Audion’. It has been immensely useful – for instance, instead of the microphone, we could feed into the grid a weak wireless signal to amplify it – and is only now, in the early twenty-first century, falling out of use, because of the invention in 1949 of the transistor by the ghastly William Shockley. For various reasons – partly distaste, mainly ignorance – I shall not have much to say about transistors, but I shall try. First, let us go back to a much earlier invention.
I mentioned the electroscope in connection with the invention of the thermionic diode. It is a delightfully simple though very sensitive device for detecting, though not really measuring, electric charges, an electric charge being a surplus, or a poverty, of electrons over or under the normal, neutral, balanced state. It consists of a glass jar with a non-conducting lid,2through the centre of which passes a metal rod. The top, external end of the rod terminates in a metal ball, and at the bottom end, inside the jar, is attached a pair of pieces of gold leaf, fixed at the top edge and so looking like a Greek capital lambda. (Λ). Gold leaf is chosen because it conducts electricity but is also very light.
To use it, one first touches the knob at the top to ‘earth’ it. Provided one is not wearing rubber-soled shoes, any stray electric charge in the electroscope will leak away through one’s body, and the two legs of the lambda will flop together for a reason that will I hope become clear in a moment.
One then picks up the electroscope by the jar – or one could make the connection with a piece of insulated wire, bared at the ends – and connects 28
the knob to whatever it is one suspects of being electrically charged. The electric charge will communicate itself to all the metal parts of the electroscope, because electric charges spread themselves all over conducting surfaces,1and the two pieces of gold leaf will splay apart, because they have similar electric charges and so repel each other.
1 Though the spread is not even: it tends to concentrate at sharp edges and points. This is why lightning conductors have sharp points at the top: the charge, being concentrated, leaks away more easily from a point, diverting possible damage from vulnerable parts of, say, a church tower.α
αThis seems to suggest the false, or more accurately meaningless, notion that lightning travels from ground to cloud rather than vice-versa. I have heard smartarses insist that this is in fact the case; usually the same smartarses who insist that bath-plug vortices are clockwise in the Northern hemisphere and anti-clockwise in the Southern, and get quite cross when one shows them an anti-clockwise example in the Northern hemisphere. Plausible as it might seem from the case of lightning conductors, the idea that lightning ‘travels’ from ground to cloud, or indeed vice-versa, actually makes no sense. This is one of the many interesting areas where Physics merges with Metaphysics.
2 It wasn’t until I was well into my fifties that, while struggling to finish an excellent but too-large dish in a Greek restaurant I suddenly thought ‘I don’t have to do this,’ pushed the plate aside and lit a cigarette. The sudden feeling of liberation was almost worth fifty years of enforced over-eating.
3 Note the correct use of the subjunctive here.
The Electroscope, uncharged (left) and charged (right)
This section is not for the faint hearted. It is a complex subject so, unless you’re feeling brave or were brought up to eat everything on your plate,2you might like to skip it.
At the end of Chapter II I spoke, as if it were3 the easiest thing in the world – it isn’t – of ‘adding’ music and speech to the radio-frequency carrier 29
wave. This process is called ‘Modulation’ and what I shall briefly and incompletely describe is Amplitude Modulation or AM; the sort used for the long-established but now obsolescent Long, Medium, and Short Wave radio. The Frequency Modulation (FM) that came in in the 1950s is mind-boggling, and I suspect that the new DAB system of adding a digital sound signal to the carrier wave is actually rather easier to understand, especially for those familiar with the workings of computers and CD players.
If one just ‘adds’ an audio signal (sound waves converted into electrical form) to a radio frequency signal the result is a mess. One has to impose the audio signal in such a way that both it and the RF carrier signal remain intact and can be separated at the receiver. If a sound signal is represented graphically, with time for the horizontal or x-axis and voltage for the vertical or y-axis, it looks something like this:
Audio frequency signal
A radio wave, whose frequency is thousands of times higher than that of a sound wave, would on the same system of representation look something like this:
Radio frequency signal
except of course that the wave’s ups-and-downs would be, using the same scale, much much closer together than I can draw them.
A weak radio-frequency wave, one of low ‘amplitude’, i.e. strength, or height and depth in our representation, might look like this: 30
Amplitude Modulation works by using the audio signal to vary the amplitude, or strength, of the radio frequency signal. Let us suppose the sound we want to transmit, by imposing it on our carrier wave, is the musical note middle C, though it could of course be anything including the many very un-musical noises broadcast by the BBC and others. Now middle C has a frequency of 256 Hz. As I said this is much, much lower than the frequency, which might be thousands or millions of Hz, of our carrier wave. Middle C might look on our graph, as I said before, something like this:
Using it to vary or ‘modulate’ our carrier wave, we finish up with something like this:
Amplitude modulated radio frequency signal 31
This contains both the RF carrier wave, represented by the close-together waves, and the audio signal, represented here by the general outline, or ‘envelope’, (I have marked it in) of the combination.
Now suppose, after picking this up at the receiver, we pass it through our loudspeaker? The RF component of the total wave-form will not be a problem: nothing as massive as a loudspeaker cone could possibly vibrate that fast; it will just ignore it. One might think the loudspeaker would instead simply follow the general outline, i.e. our original middle C. Unfortunately not: looking again at the diagram of the modulated wave, we see that the general outline at the top, representing a fluctuating voltage – always positive, but going up and down 256 times a second – is exactly mirrored by the same thing at the bottom – a fluctuating negative voltage. They will simply cancel each other out and nothing will be heard.
This is where the diode comes in: as we said, a diode is a valve, allowing electricity to pass in one direction only. So if we pass our total signal through a diode, it will allow through only the stuff above the horizontal time-axis of our graph, and block the stuff below. The wave we get on the other side of the diode will look like this:
Rectified or ‘detected’ Amplitude modulated radio frequency signal.
and this set of electrical fluctuations – again, the loudspeaker won’t even try to follow the very rapid RF half-waves, but just the general outline, the line on top – will indeed give us back our original middle C or other sounds.
I have left out a lot in this brief outline of amplitude modulation. Although I have outlined the way the sound signal is extracted from the carrier wave at the receiver, I have glaringly omitted any account of just how it was imposed on the carrier wave to begin with, at the transmitter; it’s just too complicated so I have described only the principle. Anyone who has understood everything so far and now wants jam on it is probably ready to read the proper technical books on the subject.1
1 It’s just possible you might still be able to find the relevant books at your public library, as I did as a teenager. But seeing the general dumbing down and even closures of our public libraries, the wholesale destruction of ‘old’ books that rivals the activities of the Nazis shortly before the Second World War, I doubt it. 32
The diode described under ‘The Thermionic Valve’ and whose use in wireless receivers I have just mentioned under ‘Modulation’ might be called an artificial semi-conductor: ‘Artificial’ because the product of artifice, ‘Semi-conductor’ because conducting electricity in one direction only. There are also natural semi-conductors. As long ago as the mid nineteenth century our first man Faraday, investigating silver sulphide, found it behaved oddly when he tried to pass electricity through it. While silver sulphide is not quite a semi-conductor in the modern sense, it did seem to be not quite an insulator – something through which electricity just will not pass – nor a proper conductor like, notably, metals.
The first really useful semi-conductor was the crystalline element Germanium, used in crystal sets, those wonderful devices that enabled one to listen – albeit at very low volume – to radio broadcasts without the use of valves; without, in fact, any source of electrical power other than that of the picked-up wireless signal itself.
In practice a small crystal of germanium, often no larger than a match-head, was fixed in a metal cup, which provided one of its two connections. The other connection was made by the ‘Cat’s whisker’; a tiny metal probe which was moved over the exposed surface of the germanium crystal until a ‘sensitive spot’ – an area of particular purity – was found and the radio signal, or rather the sound that it carried, was heard. Some arrangement, such as a slightly stiff universal joint, was necessary to keep the cat’s whisker temporarily in place.
A crystal detector
This type of ‘detector’ was very ticklish to operate: an accidental nudge or even the heavy tread of someone coming in with a cup of tea could knock the 33
cat’s whisker off its painstakingly found spot and interrupt reception. Later, ways were found to purify the germanium, attach the cat’s whisker permanently, and encapsulate the whole thing in a blob of glass. These germanium diodes continued to have uses in wireless and even television sets right up until the 1960s.
Here is a circuit diagram of the simple radio receiver known as a ‘Crystal Set’:
A simple crystal circuit
At the top left is the aerial, receiving the wireless signal. The tuning circuit, consisting of the coil (this example uses a ‘tapped’ coil, with a choice of aerial connections) and the variable condenser, (the latter represented by the two lines crossed diagonally by an arrow) filters out, more or less, the unwanted wireless signals, which pass to the earth connection at the bottom, (like lightning and indeed all forms of electric energy, radio waves have a strong ‘desire’ to get to earth by the easiest possible route), while the wanted signal has to pass through the diode – represented by the large arrowhead touching a line – before it can get, via the earphones at the right, to earth.
You can, even now, make and use a crystal set, if you can find the necessary components. There is something quite magic about being able to hear a wireless broadcast – you’ll probably only be able to get the nearest strong AM station – with something so simple and needing no power supply.1
Hot music and the ultimate portable radio.
1 There have been cases of people hearing radio broadcasts coming out of their old-fashioned electric fires. Anyone who has experienced this, and is perhaps reading this book in the confines of the psychiatric ward where their concerned relatives have taken them as suffering from hallucinatory paranoid delusions might be relieved to hear that this can really happen: the spiral element of the fire is of course a coil, and a speck of rustα can make the connection at one end or the other a diode. Show this to the shrink in charge of your case, if you’re lucky or unlucky enough to meet him in today’s N.H.S. I even once heard of a lady who got Radio 2 on her dental fillings: the case was authenticated by her friends, who danced to the music. Now if only it could have been Radio 3<
α Early amateur wireless constructors sometimes got good results using a rusty pair of pliers as a detector. 34
In the 1940s the ghastly William Shockley had the one good idea of his life when he added a third electrode to the semi-conducting diode. This was the equivalent of the grid in the thermionic triode valve, and controlled the current through the device, which became known as the transistor.
Transistors can do everything the thermionic valve can do, are compact and cheap and use very little power. In the following years the thermionic valve became almost obsolete, though it was some time before transistors could manage really powerful amplification, for which valves were still useful. Germanium, one of the Earth’s rarest elements, was soon replaced by silicon, one of its most common. The now ubiquitous silicon chip contains in effect, by a process of microscopic etching, hundreds of transistors in something the size of a fingernail.
Shockley and Awe: the Transistor.
But something of Shockley’s bad vibes – he was as notorious for his racist ‘theories’ as he was famous for the transistor – must have clung to his invention. When I experimented with transistors in the 1950s the only thing I made that actually worked was a little audio oscillator which, connected to a telegraphist’s key, helped me practice Morse Code. I remember I powered the tiny single transistor with what was in effect a single-cell Volta Pile – two small dissimilar pieces of metal poked up from the chassis, and you spat on them to set the thing bleeping. But I never really got on with transistors: their advent marked the end – except for this book; a final exorcism – of my obsession with wireless and I moved on to other things: Jazz, Motorcycles, Beethoven, and the Metaphysical Poets.
The Return of Signor Volta.
– •••• • • –• –•• 35
Some time in the 1990s I went on holiday to Cornwall with my friend Kate. We went in her car and spent a lot of time just driving round aimlessly. In some quite empty place I saw a signpost, ‘Poldhu’, pointing down a narrow road toward the sea. ‘Oh, we have to go there!’ ‘Why?’ ‘Tell you later. Come on.’
There was a small beach at the end of the road. High bluffs, broken to cliffs where they met the sea, on either side. No buildings at sea-level; the beach was quite desolate and so very beautiful. But high up on the right-hand bluff, as we faced the sea, was a building. A narrow path led up from the beach.
The building turned out to be a lifeboat station. A lifeboat station at the top of a cliff? But there was a tiny and dangerous-looking funicular1railway down to the actual boathouse at the bottom. Fortunately for Kate the operating system was firmly locked. We put a few coins in the R.N.L.I. box.
1 I had always thought this splendid and rather silly-sounding word was not the Latinate technical term it looks like, but a jolly Tyrolean invention, witness the jolly Tyrolean song ‘Funiculi, funicula’. Turns out though that it is: from the Latin ‘Funiculus’, a thin rope. Not too thin, one must hope. There is, and has been since I think Edwardian times a fine funicular railway on the Leas at Folkestone. In my childhood the journey cost an old penny and was advertised as ‘The Quickest Way to the Sea Front.’ ‘Yes; cut the cable!’ we used to snigger. The operator has since told me that the cable is routinely replaced, by law, every seven years. Under the two cars are huge wedge-shaped water-tanks, and the railway works by pumping water into the tank of the car at the top until it’s heavier than the one at the bottom, when the brake is cautiously slackened. At the bottom the water is pumped out and sent to the other car, now at the top. There is a similar railway on Lykavvitos Hill in Athens, but I don’t recommend it. Using it always reminds me of Patrick Leigh-Fermor’s story: as he was hauled up the side of a precipice in Northern Greece to the monastery at the top, he asked the monk who shared the net with him how often the rope was replaced: ‘Oh, every time it breaks.’
‘Now can we look up on the other side, that big white building on the cliff-top?’ ‘Oh, all right, if we have to.’ We did.
That other very large square building had once, I knew, been an hotel. A sign at the beach end of the long upward-sloping drive said it was now an old people’s home; Kate was all for leaving now. ‘No, we have to go and look.’ ‘Oh, Simon.’ At my insistence we walked straight past the old people’s home and out to the cliff edge behind it. A hundred yards ahead of us was a granite obelisk with a globe on its tip. Close up, we found a brass plaque: ‘From a spot near here<’ 36
Which spot, exactly? I looked about, remembering old photographs I’d seen. ‘It must have been – hmm – somewhere there,’ pointing to the middle of a featureless field. ‘But there’s nothing there, Simon!’ ‘Just a minute, please.’
I climbed over the fence and set off over the field, hoping the cows in it really were cows. (It would have been rude, and perhaps risky, to get close enough to examine their rear appendages.) In the middle of the field I tripped on some crumbling concrete: the remains of three or four shallow steps. From the top of the steps I saw spread out before me what had once been a tiled floor, the tiles now mostly broken, those remaining faded from their original black and red to grey and ochre. There was nothing else. After a little thought I took out my Swiss Army knife1and started to dig round one complete tile, but it wouldn’t come loose, though all around it were free incomplete fragments.
1 Never be without a Swiss Army knife.
2 Yes of course cows talk to me. They are selective in whom they will talk to, but will probably talk to you if you will only listen.
3 The usual miseries said that the attempt would fail because Wireless waves travel in straight lines and the Earth is round. They did have a point: Einstein had not yet shown that light waves, and therefore also radio waves, are curved by passing close to massive objects such as the Earth, but this curvature is so slight as not to help much. Marconi used a kite to partially overcome the problem, but to overcome it completely his kite string, or rather wire, would have needed to be a touch long. There are three ways of working out just how long: Trigonometry, Cartesian co-ordinate geometry, and scale drawing. I have not worked it out; suffice it to say that the length would have needed to be equal to about half the distance across the Atlantic. Nonetheless signals got through: what happens is that a substantial part of the transmitted radio wave travels not parallel (or rather tangentially) to the Earth’s surface, but upwards, and is reflected back down again by the ionosphere: a radio-reflective layer in the upper atmosphere provided proleptically by God at the Creation to overcome this problem.
Meanwhile the cows kept coming closer; close enough to nudge me with their wet muzzles: ‘Ooh, what are you doo-ing, Simon?’2Cows are intelligent creatures, but their easily-aroused curiosity can sometimes lead them, quite without malice, to trample you to death. I had to keep stopping and waving at them, when they would stagger back a few paces.
Final Fragments of Guglielmo Marconi.
Eventually I settled for a fragment of about a square foot: most of one red tile and parts of the adjacent black ones. Kate called me a vandal, but by now that floor will be unrecognizable; it may well have been broken up and carted away to the tip by the farmer, and no-one else seems to care. So I am glad I preserved my little piece: part of the floor of the hut from which the first transatlantic wireless signal3 was sent, to be received at the top of Signal Hill in Newfoundland by Guglielmo Marconi. 37