Category Archives: to 1912

Better detection than the coherer


You can impose waves, and waveforms, onto current in lines. I’d never thought about the frequency of an electrical signal changing, but that’s what makes voices audible in telephones. Pretty obvious.

‘Detection’ of radio signals means changing their frequency down to a range to which a pair of headphones (and your ears) can respond. You can do it with a transformer, such as the one I’ve found here, in one of those Ladybird ‘achievements’ books for children. Listening for a signal transformed to audio is a more sensitive way of detecting signals than trying to line up metal filings in a coherer, such that their collective resistance drops, and getting a bell to ring. 

Marconi is credited for devising this first, and doing it, as near as I can tell, in 1902. It became standard shipboard equipment for a decade or so, gradually being overtaken by systems that did the trick instead with galena crystals or with the vacuum tube diode, which Ambrose Fleming rolled out in 1903.

The received wisdom goes that nobody, not even Marconi, was able to say why this funny transformer setup worked. It begs the question, of why he devised it.

The system consists of a primary coil, through which RF signals run, a secondary coil into which current gets induced, some strong magnets perfusing their flux lines through the whole system, and a slowly moving (by hand or by clockwork) core of iron wire.

The reason it worked was, more or less, that the iron atoms in the moving core would line up in conformity with the magnetic field, in the absence of incoming current into the primary. (Why the core had to be moving for this, I don’t know.) When a pulse arrived, the atoms would change orientation, behaving in the manner of the core of an electromagnet. That change was detected by the secondary coil. We’re taught to say that ‘the magnetic field collapsed’ at that moment, though it’s not clear to me what this means. As soon as this collapse happened — and here my reading varies — the listener heard a tone or a click. I don’t know which. Either way, Morse code was audibly detected. 

This system was known to contemporaries as the ‘magnetic detector’, or the ‘Maggie’.  You can see a picture of one of these at John Jenkins’ SparkMuseum, here.


Photo credit:  F.G. Goodall, Robert Ayton, illustr., The Story of Radio (Wills & Hepworth, 1968), p. 31. 

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What amateur culture was in 1906

Screen Shot 2018-09-20 at 10.58.53

The best teaching case in the very beginning of amateur culture, because it’s so well documented in QST, is that of Irving Vermilya, in Mount Vernon, New York. I’ve done some posts about this fascinating kid and his circle already. Between 1903 and 1910 he was part of a rowdy and growing cell of experimenters across town, several dozen teen scroungers who communicated illegally with each other by backyard telegraph (they purloined the power from the city tram) and made life hell for commercial and military interests on the air, where they attracted the attention of the Department of the Navy. (When they were bored, the kids liked to jam the fleet in Brooklyn.) The navy, for reasons I’ve never understood, was the arm of the government generally charged with management of wireless communications at the federal level. (This endured all the way to World War 2.) A number of these Mount Vernon kids grew up and got jobs in wireless, and Irving Vermilya was one of them.

Exactly the same scrabble between tinkerers, syndicates, and a generally befuddled Uncle Sam was happening in other cities at the very same time, and exactly the same slow move to eventual citizenly resolution. In 1906 Technical World Magazine reported on a dozen high schoolers in Newport, Rhode Island, who had come under inspection by one Commander Albert Gleaves, USN, for having caused some serious problems for a nearby torpedo installation. The nucleus of the kids’ organization was a homebrew transmitter in a converted henhouse. The Commander came away blinking, telling Washington that these kids were really very ingenious, and that their example proves that anyone can get on the air, cheaply, and that the army and navy should take note of this and do it too. In the free-for-all world of 1906 it wasn’t clear whether a reprimand or a commendation was actually in order.

Two of these Newport Irving Vermilyas were Charles Fielding, a telegraph messenger, and his pal Lloyd Manuel, he of the henhouse. They were not especially interested in matriculating into commercial wireless, at least for very long. They wanted to make fortunes as wireless inventors. Their families could ill afford to spend money for whims, as Technical World politely put it, which might explain the boys’ ambition.

It probably does explain their ingenuity. They made spark gaps out of old nails. They wound their coils on jars and curtain rollers. They made detectors out of arc-light carbons and sewing needles, or, emulating Fessenden, from incandescent lamps that they filled with nitric acid.

I do find Lloyd Manuel possessed of a 500-watt station in 1924, at 169 Thames Street, Newport, a modest address, under callsign 1BOG.  He stayed on course, by the look of it, and went legitimate, even if he didn’t make a fortune.  No mention of Charles Fielding.


Says who:

“Wireless Station in Henhouse,” Technical World Magazine, September 1906, pp. 62-3.  Available at

United States Department of Commerce, Amateur Radio Stations of the United States, Edition June 30th, 1924, p. 13.


Filed under to 1912

Who was in the amateur game in 1904

young pioneers

There’s a fascinating snapshot of radio culture in 1904 in the June issue of Amateur Work, about a couple of Boston eighth-graders who built a wireless station in shop class, that had an eventual range of a good 8 miles.

This Amateur Work is probably a descendant of the serial of the same name whose publication began in 1881, a do-it-yourself manual in lathes, clocks, and violins, greenhouses, book-binding and electro-plating, glass, microscopes and fishing tackle, sun-dials, fly-tying and photography – you get the idea. These early issues are being digitized by the Smithsonian [] right now, and they’re very good reading.

By 1904 this publication was carrying articles on wireless. The art was still young. The editors felt obliged to put quotes around “wireless,” and the young inventors, Samuel Breck and Newell Thompson, called their transmitter a “disperser,” and their receiver a “responder.” The project apparently surprised the Boston school system.

Nevertheless, it got off the ground swiftly. The boys had seen a wireless exhibit in a Mechanics’ Building fair only at the start of the school year. When they came asking for help, their shop teacher and their headmaster were both quick to get involved. Visitors came to the school to watch the prototype in action. The lads’ parents helped them arrange subsequent distance tests of growing lengths across the Charles River.

The lesson is that wireless culture was developed enough in mid-1904, in the popular press, in trade and educational institutions, and in the public imagination, that even schoolboys could be mentored onto the air, and fairly readily.

Says who:

“Wireless” telegraph plant by Amateur Work readers.  Amateur Work, June, 1904, p. 223.  Available at


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Club Life in 1908: snapshot of the wireless world

WSB 1908

1908 was a big year for wireless clubs.  They formed on the backs of magazines, typically electrical trade journals, whose pages hobbyists scoured for construction information.  It was natural that editors would encourage their attention.  Periodical sections devoted to these early clubs are very detailed pictures of the amateur community.  From their pages we can tell exactly who these people were, how they organized themselves, and what they could do technically.

The famous club is that of Luxembourg immigrant and future radio luminary Hugo Gernsback, who founded Modern Electrics in April, a catalogue that, due to demand, also contained features and articles.  On this circulation list in the following January he set up a “Wireless Association of America,” which, he claimed, gathered 10,000 members in its first year.

A less famous example is Electrician and Mechanic, which had its own newish club in place by August 1908.  Membership was 114, spread fairly evenly among 27 states and Ontario and Prince Edward Island.  Massachusetts had the most members, for some reason.  It was free to join, existing merely as a roster of stations and their descriptions.  Its function was simply to encourage local chapter meetings and exchange of information.  It grew quickly.  By October, the magazine ran a special article on the proliferation, and sophistication, of the amateurs in Baltimore, reckoning their number at 30, and their age-range from under fifteen to about 45.

Why Baltimore?  There was a professional nexus.  “Certain employees of the C. & P. Telephone Company, who advanced from the filings coherer stage to the tuned circuit and detector,” encouraged local enthusiasts, person-to-person, rather like a club.  Two others were ex-professionals as well, former operators of the De Forest station in town.  It was common that professional men used the good offices of their firms for non-commercial radio generally.  Providence reader ‘W.W.B.’ wrote in to ask for contacts in his city, offering a downtown place to meet at no cost.  “I am the department manager of a large firm,” he said.  “We could meet at my office and talk over the matter of forming a local branch.”

They really did need to talk with each other.  The wireless art was elevating so quickly that even the magazines were having trouble keeping up.  Reader ‘R.H.M’ in St. Paul, Minnesota, fretted that he could not get articles fast enough, particularly on high frequency transformers.  He wished that Electrician and Mechanic would devote a big section monthly to practical construction.  ‘C.W.W., of Melrose Highlands, Massachusetts, wished for an explanatory piece on the hot-wire ammeter, having tried in vain to find out how this instrument was made and how it worked.  The closed core transformer was the nucleus of the 1908 station.  ‘M.A.’, in Campobello, Massachusetts, wanted an article on building one, for about $10, that would work on 100 volts, 60 cycles per second, which is to say, house current.  Some stations, such as that of ‘W.S.B.’ (shown), stilled used batteries.  His used nine cells, delivering a goodly “7 or 8 amperes.”

W.S.B.’s station was in Brooklyn.  He had managed to talk with the De Forest station four miles away.  He received signals from Fire Island plainly, and could detect transmissions up the Connecticut coast, as far Wilson’s Point (off Norwalk) and Bridgeport.  His receiving range was thus about 50 miles.  He thought he may have heard ships farther off than that.

1908 must have been an exciting year.


Says who:

“ The Wireless Club,” Electrician and Mechanic, September 1908, pp. 137-8.

“Wireless Telegraph Stations in Baltimore,” Electrician and Mechanic, October 1908, p. 146.

“Wireless Club,” Electrician and Mechanic, October, 1908, p. 179.


Picture source:  Electrician and Mechanic, October, 1908, p. 179, available at

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Poldhu-Newfoundland 1901: actually a shortwave achievement?


It’s well-trammelled ground, over whether Marconi really got a low-frequency signal across the Atlantic in 1901, like he’s famous for doing.  More precisely, the issue is whether he could have.  We don’t know what frequency he was using (Marconi didn’t either), and there are gaps in our knowledge about his equipment.  So we don’t know for sure that it was possible.  But David Sumner, G3PVH, in a superb piece of reconstructive detective work, has shown that the big jump may well have happened – but not at low frequency.  If it happened, it very likely occurred by spurious emission in the 30 meter shortwave band.

It was John Belrose, VE2CV, who gave us the canonical 500 kHz, or 560 meters, at which we suppose the transmission occurred, and he it was who also pointed out the difficulty of a long-distance leap at that frequency, particularly during daylight.  There sits the problem.  But Sumner’s argument goes like this.  A spark transmitter can generate secondary signals with high peak power.  The ‘jigger’ coil Marconi was using may have a self-resonance at about 10 mHz.  The transmitting antenna, from what we know of it, could have been resonant at that frequency, as could the receiving antenna (which, incidentally, was wind-borne on its kite in the right direction for great-circle propagation).  The feed-point impedance at 10 mHz would suit Marconi’s particular coherer better than one at 500 kHz.  This coherer and the earphones he used form a sensitive enough detector to receive HF broadcasting.  Normal propagation on 30 meters at the time of Marconi’s documented reception is transatlantic.  (I myself have crossed the Atlantic on 10 mHz lots of times, and at 100 watts peak, not his 10 megawatts.)

The technical details of Sumner’s sleuthing are a gripping read.  He made his own jigger, after Ambrose Fleming’s Poldhu design, and tested it with an antenna.  He sourced a Collier-Marr ‘phone at the Oxford Museum of the History of Science.  He takes us through previous work on coherer curves, too, a fascinating trip all by itself.    It’s a magnificent article, and its bibliography is full of treasures for the scholar, as you’d expect.


Says who:

John S. Belrose, ‘A radioscientist’s reaction to Marconi’s first transatlantic wireless experiment,’ Conference Digest, 2001 IEEE Antennas & Propagation Society International Symposium, July 8-13, vol. 1, 22-5.

David Sumner, ‘UK to Newfoundland, 1901 Style – the possibility of HF communication,’ RadCom, July 2018, 44-54.

Picture:  Wikimedia Commons (

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Range, in 1897

‘So, how far could they get, say, in the 1890s?’  Basic question to be able to answer.  I’m put in mind of an astronomer friend, expert in quasars and black-body radiation, who blushed when she couldn’t tell a layman how far away Mars is.

If anyone asks you, say that in 1897 the Marconi system, in the hands of the army and navy, was good for two or three miles.

That means it was no longer an induction system.  It was ground wave.  ‘Even a mountain between the transmitter and receiver does not, it is said, prevent transmission[.]’  It’s not at all clear (and Marconi couldn’t say in the trans-Atlantic tests several years later) what the wavelength was.  (We think we know, but that’s another post.)

Says who:  ‘Topics of the Times,’ New York Times, May 26, 1897, p. 6.

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Amateurs underfoot in 1907

ruhmkorffAmateurs by 1907 were numerous, and intrusive, and many of them backward technically. Electrical World took notice of a policeman’s son in Washington who jammed the Navy Yard and harassed professional operators. From New York Lee De Forest thundered that the lad typified ‘the ubiquitous amateur with his high-school Ruhmkorf coil’ (pictured), who was not only a vandal but a slovenly practitioner of outdated and disruptive arts. Roving detectives were needed, and robust legislation at the Federal level. Improper damping was causing chaos, he foamed. Communications must be limited to the sustained oscillation methods. “The day of the barbarous spark discharge is numbered,” he prophesied, “and the sooner it is classed with the filings coherer the better.”

Says who:  Lee De Forest, “Interference with Wireless Messages,” Electrical World (June 22, 1907) XLIX, 25: 1270.

Picture source, forum page, Model T Ford Club of America.  Heinrich Daniel Ruhmkorff was a German instrument maker, d. 1877, who commercialized at mid-century earlier iterations of the induction coil.  This model is probably a Ford variant.  Amateurs cannibalized these routinely for spark gap transmitters.  The resulting signal was a wideband splatter.

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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.

Image source:

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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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