How receivers with tappers worked

1899 receiving apparatus

Okay, I think I’ve figured out how the very first receivers worked.  The really clever part is how the tappers knew when to tap.  Here is a diagram from 1899.  It’s what Professor Green was using at Notre Dame, so it derives from Marconi, by way of popular magazines (Marconi himself being secretive about his current equipment).  The magazine that printed this diagram was American Electrician, hence the ‘AMER. ELEC.’ caption.

The heart of the system is the ‘coherer’, item ‘C’ in the diagram.  This is not a detector, exactly, in the sense that Fleming’s ‘diode’ (or De Forest’s ‘Audion’) is.  We Radio Shack kit veterans will remember using tiny solid-state diodes to hear AM radio.  As far as I understand it, the coherer doesn’t do that.  If you put headphones onto it, you wouldn’t hear radio.  What the device does is drop its resistance as soon as radio frequency energy, which is to say, induced current from the antenna, goes through it.  That’s all.  It’s a honey bee-sized tube of nickel filings, mostly, that cling to each other, or ‘cohere’, in response to that current.  Suddenly the coherer’s resistance falls to tens of ohms, having been a matter of megohms before.  They will stay cohered even after current from the antenna ceases.  An automatic tapper physically jars them loose again, rendering the coherer into a high-resistance device again.  It’s a cumbersome system, where the tapper taps between each Morse code dot and dash.  Got it so far?  Keep your eye on that changing-resistance thought.

Look at the diagram.  Find the loop circuit containing the coherer, a battery, and three coils.  Notice that the antenna comes into the top of the loop, and there’s a ground connection out the bottom, too.  That battery isn’t strong enough by itself to make current flow around that loop.  That’s because the coherer resists too much.  But along comes a radio signal.  It hits the antenna, inducing current.  The current enters the loop and turns left, into the coherer.  The reason it doesn’t turn right is because of the impeding effect of the two ‘choke coils’, as they’re called (‘A’ and ‘A’).  The coherer coheres, resistance drops, and now the circuit activates.  The ground connection is to offer a place for the induced current to go.  In the absence of a relative vacuum, for so I think of voltage gradients, the current wouldn’t enter the system.

See coil ‘R’?  That’s an electromagnet.  Sometimes they’re called relays, other times solenoids.  It’s a coil with an iron core.  Activate it, and you close a metallic switch.  When you do — now follow the other loop, the one with the other battery in it — you get current that activates two other electromagnets:  one is ‘S’, that makes a mark on a moving paper tape, or else rings a buzzer, or just makes telegraph office clicks; the other is ‘V’, which squeezes the armature of the tapper against the coherer.

Here’s the clever part.  That tapper armature was already resting against the tube.  It’s springy.  If you bend it hard against the tube with all that current in the system — and then the current drops, because the radio signal stops coming through the antenna — the springy armature will give a little bounce against the side of the tube as its relay stops functioning.  Plink!  The particles are now decohered, ready for the next signal.

The light bulb at the coherer is to suppress arcing between the armature and the coherer (which would interfere with cohering and decohering).  I don’t know what the other light bulb is for.  It’s probably just to smooth current feeding the printer relay.

I think this is how it works.  Pretty clever!  It wouldn’t work very well if there were lots of people on the air.  It couldn’t have been very sensitive, either.  Professor Green tried to optimize it, by substituting an ammeter coil for the clunky buzzer coil he’d been using for his tapper.  If any engineer is reading this, and I’m misunderstanding something, please tell me!

receiving apparatus complete

This circuit diagram and attendant picture come from Jerome J. Green, “The Apparatus for Wireless Telegraphy,” American Electrician, July, 1899, pp. 344-6, reproduced at

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How the Americans were doing in 1899

notre dame

How were the Americans doing in 1899?  Sad to say, they were trailing the Europeans by a long way. Professor Jerome Green machined some parts in the Notre Dame physics labs to match what he thought Marconi was using, and he was able to send messages between a pair of campus buildings.  Then he signaled from a flagpole on campus to a point two miles off campus.  Then he went portable and signaled three miles across the city of South Bend.  Mishakawa, 6 miles away, proved too far.  After that he made trials around the Polk Street rail station and the ‘Tribune’ building in Chicago.  This little jump, of three-quarters of a mile, turned out to be impossible.  He reckoned it was because there were too many wires and buildings along the signal path.  These he imagined must absorb the waves, because in subsequent trials in the city over routes clear of wires detectable signals passed freely.  Finally, he tried signaling over water, from the Chicago River lifesaving station to a moving tug.  Two miles was about the limit of what he could do, but it was better than what he could manage in the city.  Over water, Professor Green observed, Marconi was achieving his best results; Ducretet, in Paris, by contrast, was managing about five miles, much less than the over-water record.

It was primitive equipment the Americans were using, even this technically savvy American (and he said ‘primitive’ himself).  He didn’t know how waves propagated, and he had no notion (nor did Marconi) that wavelength and optimal antenna size are related.  He thought the name of the game was adjusting the receiving apparatus mechanically to register clear dots and dashes.

Says who:  Jerome J. Green, “The Apparatus for Wireless Telegraphy,” American Electrician, July, 1899, pp. 344-6.

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Jurassic radio: Mahlon Loomis

loomis library of congress

Mahlon Loomis applied for letters patent in July of 1872 for a kind of wireless telegraphy between towers on two mountaintops.  His idea was to allow a voltage gradient to build in each tower, passively, a system of static electricity drawn from the atmosphere, that could be discharged by an operator down the hill sitting at his key.  The signal itself he conceived as travelling from one tower to the other underground.  He claimed to have managed the feat, too, with kites instead of towers, between two mountains in West Virginia, 14 miles apart.  He asked Congress for research money, which was denied.  It is a truism of wireless telegraphy schemas all the way to and including Preece that signals were expected to move through ground (or water), not air.  It was for Marconi to render practical Hertzian waves.  Loomis’s is unusual among the old designs for conceiving no process of induction, between long parallel wires.  On paper this one looks the most like radio.  Maybe it was.

Who says:  The picture above, diagramming the West Virginia triumph, resides in the Library of Congress.  The narrative, in its pre-Preece context, comes from John Joseph Fahie, A History of Wireless Telegraphy, 1838-1899 (Blackwood, 1899), pp. 73-8.


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What they heard in the beginning: buzzers, not tones

poor irving

Poor Irving Vermilya.  He tried to hear Marconi’s transatlantic test signals between St. John’s, Newfoundland and Poldhu, in Cornwall, early in 1902.  All he got through his cohera (sic) was a buzz generated by the neighbors’ doorbell.  This illustrates something interesting, which historians of prehistoric radio should understand.  It wasn’t headphones through which proto-hams were listening.  They weren’t monitoring atmospherics.  (That’s surprising, given that bored railroad telegraphers had been doing that along their landlines for 20 years already.)  They were listening for mechanical activation of battery-operated buzzers, or in Marconi’s case, telegraph writers.  So conceptualize it this way, when you try to picture Victorians and Edwardians at the wireless.  They weren’t listening to radio they way we do.  A signal strong enough to galvanize the nickel particles in their coherer tube would render the tube conductive, whose tiny current would then activate the buzzer circuit, powered by its own battery.  After the signal stopped, a tiny hammer would tap the tube to separate the particles, and the buzzing would cease.  (I still have to figure out how the hammer knew when to tap.)  So what you heard was door-buzzing in Morse Code and, faintly, a lot of little plinks beneath it.  It was a common demonstration to onlookers, to activate one’s receiver with a doorbell buzzer.  One of Marconi’s own men did this for a journalist at the Needles Hotel station in 1899.  Induction coils talk to each other, he explained, by something they called ‘Hertzian waves’.  What is a door buzzer but a tiny coil, with tiny oscillations?  I still don’t know why they didn’t just screw in some headphones.  Arcing coils are noisy as the dickens, and would have been easy to hear.

Who says:   Irving Vermilya, ‘Amateur Number One,’ QST, February, 1917, pages 8-12; Cleveland Moffett, “Marconi’s Wireless Telegraph,” McClure’s Magazine, June, 1899, pp. 99-112; ‘Future of Wireless Telegraphy,’ New York Times, May 7, 1899, p. 20.

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more on amateur telegraph

young irving

I won’t say too much about this chap for now, for I’ve built a whole book chapter out of him, that I want to publish when I’ve really got it right.  But I’ll tell you that the best-documented case of amateur telegrapher at the dawn of amateur radio is Irving Vermilya, a teenager in Edwardian Mount Vernon, New York.  I’ve found tons on record about him and his connections, and I’m in touch with his family, and other people who remember him.  He was a brave, resourceful, and very likeable fellow.  His story involves a crusading Dutch Reform pastor and scientific mystic, a venture-capitalist father with gently corrupt cronies all the way to the mayor’s office, some on-air sabotaging of the Brooklyn naval fleet, lots of romance, some ships, a commercial radio scandal, the Massachusetts police, and a quite a lot of death.  (That nurse girl in the picture was there to look after Irving’s little brother, who was about to die.  More was to come.)

Master Vermilya followed Marconi in the magazines, and eventually got on the air himself.  While he was working out how, one day in April, 1903, he stretched a wire to his friend Fred Skinner’s house, at 122 Chester Street (the Vermilyas lived at number 28), stringing it across busy Westchester Avenue somehow, and he screwed in a pair of student telegraph sounders at each end of the wire.  It worked.  The boys practiced Morse code together for a few weeks.  They found the little learner sets hard to use, so, through the good offices of the boyfriend of that nurse girl, he was a professional telegraph operator, they upgraded to a proper set of mainline sounders.  These were available on the cheap from a supply shop in New York called Bunnell’s.  These worked so well that other kids wanted to join the little line too.  Irving had a lot of friends, and Morse code was no problem to learn if it meant making the teen scene.  So the line expanded, and it ran for the rest of the time that Irving lived at home.  By 1907 there were 42 people online, boys and girls, and the occasional grownup.  Improvised connections, of any kind of wire that could be scrounged, ran for 6 miles, about half of it through trees, along fences and phone poles, and, hazardously, over 500-volt trolley wires; the other half, amazingly, was underground.  Strictly speaking, this was illicit.  It was unsafe and was full of violations of property.  One particular grownup on the line, Walter Flandreau, may have been quietly responsible for keeping it all functioning.  He was the City Electrician.  He was technically responsible for every wire in town.  His house was at 466 South 6th Avenue—so his spur line had to run eleven blocks, and cross railroad tracks.  Being a professional, he made it happen.  Being also Irving’s cousin, he managed to see that the police never came knocking.  And the online chat ran 24 hours a day.  The custom was to say ‘GM’ to everyone when you woke up, and ‘GN’ when you went to bed.  Irving kept his sounder ‘cut in’ all the time, and went to sleep listening to boys and girls spooning after dates.  Friends like Milo White, the lawyer’s boy, down at 137 Chester, often didn’t say their good-nights until dawn.

More about all this — a lot more — when I publish on Edwardian radio.  You’ll see why Irving’s neighborhood was exploding with antennas by 1907, as were a lot of other neighborhoods in other cities.  I’ll introduce you to some of those other Irvings too.  Before amateur radio, as I say, there was amateur telegraph.  Was there ever.

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before amateur radio: amateur telegraph

telegraph line

It’s easy to see how ready the public was for amateur radio when it came.  There were little amateur telegraph organizations all over the country at the turn of the century.  Every state probably had several, speculated the New York Evening Post.  No statistics about these unregulated outfits appear to have existed.  Cranford, New Jersey, had two by itself in 1892, which were proposing to consolidate, which would mean 30 stations on a 3.5-mile circuit.  What were these two for?  Their executive committees set them up with fire, burglar, and general emergency codes; otherwise they were for news and business.  Would they not be useful where phone lines had not yet stretched?  The Electrical Review imagined private telegraphs ‘would go far to overcome the monotony and isolation of farm life, and to offset the drawbacks of bad roads.’

‘Amateur Telegraphers,’ Electrical Review, August 6, 1892, p. 308.

photo credit:  The Atlantic (click to follow link)


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Yet more about Marconi’s 1897 demonstration set

marconi 1897

Scientific American describes Marconi’s 1897 equipment like this.  The transmitter, really a design of Professor Righi, ‘consists mainly of a small Ruhmkorff induction coil excited by a couple of battery cells.  The secondary or high tension wires terminate each in a metallic ball.  Between the two balls is placed a cubical box containing oil.  In the opposite sides of the box are fixed two brass balls, [Vaseline-based] oiltight, so that one-half of each ball is in the oil in the box[.]  On sending a current through the induction coil, Hertzian vibrations are set up in the balls and communicated to the ether.  The oil has a peculiar effect, acting as a species of brake, the rapidity of the wave vibrations being only about one-half of that stated by Dr. Lodge.  These vibrations are then given off into space[.]’  His receiver ‘consists of a tube about ¼ of an inch in diameter and 3 inches long, in which are two silver plugs terminating in wires, the ends of which are soldered to the silver plugs.  The wires are fused into the glass.  The tube is exhausted to a near approach to absolute vacuum.  The faces of the two silver plugs are very close to each other, and the space between is filled up with an impalpable metallic dust.  … [T]here are in it three constituents, one of which is nickel.  Under ordinary conditions this powder will not conduct electricity, save feebly.  … If a Hertzian ray falls on the little tube, the dust is polarized like the filings in a Hughes test tube, and the powder becomes a conductor.  … [W]e have here a make and break which can be acted on from a distance, and [then] an ordinary Morse sounder does the rest.  … [A] tiny hammer is so arranged that, the moment a [dot or dash] passes through the tube, the hammer taps the side of the tube and depolarizes the powder ready for the next signal.’

Scientific American, June 19, 1897, p. 386.

Marconi’s 1897 equipment he patented singly as 19 improvements to existing arrangements.  (Patent no. 12,039, applied for June 2, 1896, was granted July 2 the following year, in time for Toynbee Hall demonstration with Preece.)  Abstracted, the important improvements in receiving were an automatic ‘trembler or tapper’ for the sensitive tube, adjustments to the content of the metal filings and refinements to the construction of the tube (no vacuum was actually necessary, save that which results from having heated the tube while sealing it), and using a copper parabolic reflector pointed at the transmitting station.  He also calms kickback at the activation of the tapper relay with condensors or else ‘water resistances.  And he introduces little ‘choking coils’ to ‘prevent the … oscillations … across the … receiver … from running round the local bettery wires.’  Improvements in transmitting involved adjustments to the geometry of the spark gap and the introduction of oil into the chamber that separates the charged spheres, also causing one of the contacts of the vibrating brake to spin, by a little electric motor and pulley, so as to keep the platinum contacts of the interrupter clean and non-sticking.  Notice, he still couldn’t tune this.

Who says:  The Electrician, September 17, 1897, pp. 683-86.


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What Marconi actually used in 1897

marconi 1897 What is that apparatus before the great man, exactly?  Here is an abstract from the New York Times, that describes it closely, the very equipment you see before you.

The new transmitter consists of an accumulator battery, an ordinary telegraph key, [and] an induction coil sending an eight-inch spark […]  The induction coil is wound, half with thick wire, the two ends of which are connected with the key and battery, and half with thin wire, whose ends are soldered to separate metal rods, each with a large brass sphere at its extremity.  … [C]urrent passes from the accumulators … through the thick wire of the coil, and induces a current in the thin one wound over it.  The induced current rushes to the brass spheres, and in the form of bluish-tinted sparks leaps the space that intervenes.  In this space is hung an ebonite vessel filled with oil and having a brass sphere in each side, opposite to and in a direct line with the two spheres previously mentioned.  … [I]t is not unlike a big drum, with a ball stuck half through each parchment side.  From this point the electrical waves are sent out … and actuate an instrument that is in electrical harmony with the transmitter.

The receiver is like a wire hoop broken at one point[.]  At each side of the break a copper strip stands out, and these form arms for collecting the electrical waves[.]  A local battery and a sounder are intervened in the wore hoop, but its current is not strong enough to leap the gap.  The waves sent by the transmitter arrive at the copper arms, flow down them, and … pass from one broken end to the other.  Each time the waves jump the gap the electrical circuit of the hoop is completed, and the battery current is enabled to cross the break and work the sounder.

Who says:

“Topics of the Times,” New York Times, May 26, 1897, p. 6.

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What Victorians expected of countrywide communications


Here’s something interesting about the prehistory of radio.  Commercial telegraphy in the generation before Marconi grew in sophistication very fast, and its infrastructure was put to use for a lot of things besides telegraphy.  Time regulation was one of them.  We were ambitious and demanding about electric communications countrywide, and this explains our readiness to receive radio when it came.

We lacked time zones across North America until the 1880’s.  But a uniform time standard across the country was under development by the 1870’s; this had been done in England already.  It was necessary because if time was a local affair, having to do with the position of the sun overhead, then long-distance scheduling of trains of higher and higher speed was bound to be impractical.  Altoona time was ten minutes fast of Pittsburgh.  Columbus was thirteen minutes slow.  The longer the distance, the worse the problem.  Observatories did the regulating.  An early example is the Allegheny Observatory, in the Ohio River Valley, in concert with the Penn Central RR in 1869.  Jewelers in Pittsburgh had already been using Allegheny time in their stores, for setting timepieces.  By 1873 the Allegheny regulated all time between Philadelphia, Lake Erie, and Chicago.  It was probably one of the biggest systems of its kind in the world.  Besides the jewelers’ and railroad lines, they managed a third ‘city loop’ for ad hoc messages, such as answering requests for sidereal time — a measure of the precision they expected.  ‘Sidereal’ is time reckoned against stars, instead of the sun.  The Allegheny kept pushing, and so did other observatories, in collaboration with other railroads.  The general idea was to decrease the number of local times east of the Mississippi, and then work on the west, in preparation for one nationwide standard of time.  The city loop was to be developed into the regulator of city clocks, which would themselves regulate local police stations.  It was all mechanized.  Clock wheel teeth activated cascades of relays, which made an online beat, heard in offices as a small bell, with regular interruptions for denoting minutes and hours.  It was exactly like the atomic clock beat we hams used to listen to on shortwave in the ’70’s.  The observatory clocks were battery-powered.  Sidereal corrections were made with a transit every fair night of the year except on Sunday.  Measurements for barometric and temperature corrections also took place, twice daily.

Who says:  S.P. Langley, “On the Allegheny system of electric time signals,” Journal of the Society of Telegraph Engineers, 1873, pp. 433-441.

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How the ether stood in 1897

marconi 1897

Here’s a photo of Marconi in 1897.  He wasn’t sure how Hertzian waves travel, or the waves he generated with this apparatus either, which he suspected were different from those manufactured by Hertz.  Nobody really understood them, not even with the benefit of Maxwell’s equations.  There was this ether business, a cypher, that people didn’t necessarily believe in but which explained things about invisible propagation that they could observe; ether was rather like dark matter now, vis-à-vis our galaxy’s not flying apart as it should do.

What was known about the ether, as of 1897?  Quite a lot.  First, it was understood to have a density expressible on the order of  10 to the minus 27th, calculated somehow ‘from the energy with which the light from the sun strikes the earth.’  It is a substance so fine that atoms sit like marinated cherries within it.  It perfuses all matter in the universe, so that all physical things are in continuity with all other physical things.  Yet things are not continuous with the ether.  Vibrate the ether, and the vibration will pass through distant objects – but the objects themselves will not vibrate.  The earth does not push through the ether, like a boat; the ether allows the earth to pass, as water allows a moving sieve to pass.  Rays, of light or electricity or Röntgen beams, move as vibrations of the ether.  For reasons not yet understood, the ether will conduct every kind of ray through every kind of substance.  Nor does it conduct rays at the same speed through every substance.  The ether in glass carries light at about 120,000 miles per second; through the air, closer to 192,000.  Glass alone, with no ether inside it, allows light to pass at a pokey 3 miles per second.

Who says:  H.J.W. Dam, “Telegraphing without Wires. A Possibility of Electrical Science,” McClure’s Magazine, March, 1897, pp. 383-92.

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