Marconi Rides Again!

This was a very recent and interesting re-discovery. On April 26, 1901 patent 777 was issued to Marconi's Wireless Telegraph Company. This memorably numbered British patent was ambiguously titled "Improvements in Apparatus for Wireless Telegraphy."  It's more vague that manly criminally trolled software patents today. In 1904 the U.S. grated Marconi a matching patent numbered less memorably as 763,772. See above.

The patent is a difficult read even on a scale of 19th century electrical patents. It's a mix of wrong assumptions, archaic terminology and technically pedantic. But this one uniquely contains new and only inadvertently patented technology. Yes. Marconi drew, but did not describe a unique feature within the patent. Fixated on building coil configurations upon his prior patent 586,193 he missed something big.

At Cambridge, Gehan Amaratunga and Dhiraj Sinha led a group of engineers looking into that very detail. The drawing depicts a transmitter linked to an antenna which is connected to a coil. But the coil  had one end grounded (marked "E" for Earth) and the RF signal was clearly fed to the middle of the coil. That detail inspired Amaratunga's team to develop a way to reduce the size of a GHz antenna using dielectric material to emit radio waves.  More here. Early testing with piezoelectric films at 1575.42 MHz have already proved that the technique can be used to radiate 1 watt at 60% efficiency from a tiny chip.

Bear in mind how amazing this omission was. This patent was at the center of a legal dogfight back in 1900.  The patent addressed the endemic problem of RF interference. It resolved the issue by tuning all the primary components: coils, aerials etc. That's why the patent is so specific with the number of turns of wire in each layer on each coil.  There was no other way to tune a circuit at the time. However the solution was stolen directly from an 1897 patent held by Professor Oliver Lodge. Furthermore, Tesla patent 645,576, granted in 1900 described a four-circuit system for a transmitter and receiver with all four circuits tuned to the same frequency. In 1892 William Crookes first predicted tunable transmitters would be invented. He didn't predict that  Marconi would then steal it. More here. But my main point there is that three highly competent radio engineers looked that that configuration and didn't see what Amaratunga saw.

Previously it was not understood why or how a piece of dielectric material could radiate signals when a RF signals were applied at one end. It's completely counter-intuitive. All of our understanding began with 100 year old equations developed by Maxwell. The IEEE refers to the behavior as "asymmetric coupling between the spark generator and the antenna." It allows the transformation of the RF electric signal into electromagnetic radiation.  The concept is borrowed from quantum theory and it's the first explanation of how Marconi’s transmitter emitted electromagnetic waves over a century ago. More here.

There Is No Aether Either

Science achieves progress largely through consensus. That consensus is never that we are exactly right but that our assumption is probable. We proceed with it as an accepted theory and dominant paradigm. It's something that the religious right has difficulty with— the lack of absolute certainty and static stability.  But it's been a pretty good system for the last several centuries and brought our species a great number of technological advances. But very often to step forward, we must discard an erroneous assumption. In 1887 the Michelson–Morley experiment proved that there was no aether. Hertz discovered radio waves in 1888. the timing was no coincidence. More here.

In the case of "luminiferous aether" this was a medieval, pseudo-scientific alchemists idea that had less evidence behind it than dark matter. In the 17th century they called it æther, ether, aether wind, and even an "aethereal Medium." The æther was descended from the idea of the classical elements like earth, air, water and fire. It was referred to in Plato's dialogs "there is the most translucent kind which is called by the name of aether." He considered it a sub-type of air. But that was more than 400 B.C.!

Sadly we were still in the depths of that aether idea more than two thousand years later. In the 1880s Sir Oliver Lodge and James Clerk Maxwell were waxing poetic about the damn aether.  Maxwell believed that the propagation of electric and magnetic waves required a physical medium like waves in water. He discussed his scientific basis for aether in two papers in particular. In 1856, he published the paper On Faraday's Lines of Force and in 1862 he followed it up with On Physical Lines of Force which suggested that light, electric fields and magnetic fields could be explained in a unified electromagnetic theory.  In 1864 he wrote a paper debuting that theory: A Dynamical Theory of the Electromagnetic Field. He downplayed the aether in the third one and focused on the waves movement through space.

Michelson and Morley put it to rest in 1887. If the aether was real  it was thought that it should be possible to measure it's effects or motion. But since it was assumed to move at the speed of light it was also assumed it's perturbations would be also impossible to measure. Maxwell pointed out in 1878 that it would have to be inferred from second order effects. In 1881 Albert Michelson used a half-silvered mirror to split a light beam  and recombined them in an eyepiece to examine transverse displacement. He assumed that a beam reflecting parallel to the flow of aether would take longer than a beam reflecting perpendicular to the aether. His results were negative. He took this as a confirmation of Stokes' hypothesis of complete aether dragging.  There is a lot more detail on this in the book The Ethereal Aether by Loyd Swenson.

In 1885 Michelson began working with Ed Morley at Western Reserve University to improve on the 1881 experiment. A similar experiment was constructed but with extreme efforts applied to reduce vibration. it sat on a block of sandstone in a trough of mercury (above). They rotated the interferometer trying to find the flow of the aether. There was nothing. Instead of reporting the null result Michaelson reported the observation of one-fortieth of the expected displacement. but more importantly that this was within the range of experimental error that would allow the speed to be zero. Others confirmed the null result and thus radio waves were free to travel through a vacuum when Hertz discovered them the following year. 

Oliver Lodge in the ether

It is first most important to know that Oliver Lodge was wrong. He successfully transmitted radio signals on August 14th, 1894 making him one of the very earliest to do so. But his theory of it's function was pure bunk. He wrote a book "The Ether of Space" which proposed the ether occupied all space that was otherwise apparently empty. He placed it on the mantle with the Alchemists understanding of matter: earth, water, air... ether. In all fairness... Newton believed in ether too.

Lodge performed his demonstration one year after Tesla transmitted a radio wave, but still before Marconi managed the feat. It makes him an early pioneer, and one that's often overlooked. He was the physicist that used the term "coherer" to describe the early radio detecting device. Branly called it a "radio-conductor"a term that didn't catch on.

Lodge was a believer in the aether (ether). He believed that radio waves occupied a somewhat fantastical medium called ether which only radio waves could pass through. He demonstrated this at a meeting of the British Association for the Advancement of Science at Oxford University. he was a professor of physics and mathematics at University College in Liverpool and one of the few people alive at that time who could assemble such a device.

Lodge used a Coherer based on Edouard Branly's coherer design. But he made one small improvement. That early coherer was a glass tube of metal filings. When a current was applied they clung together lowering the resistance. Lodge created what he called a "trembler" which shook them apart to return the resistance to it's initial value, restoring sensitivity. This "trembler" was literally a tiny mallet. I don't mean to deprecate the improvement; that separate concept was important. Later revisions led to what was called a decoherer, a "trembler" powered by the cohering current. Tesla's improvement to the trembler simply rotated.

Lodge was a little crazy. He was a firm believer in life after death, and was known to consult psychic mediums who helped him consult with death friends and relatives. This is probably where that ether crap originates from. Nonetheless in 1898, Lodge applied for a patent [ 609,154] for an adjustable induction coil that made it possible to tune the transmitter and receiver. Within the decade the coherer was sidelined in favor of crystal tuners, but tuning, that improvement was fundamental. As late as 1943 American courts were affirming Lodge's patent over Marconi's tuned circuits.Radio wasn't everything. He invented the spark plug, the loud speaker and was knighted in 1902. He retired in 1919 from teaching and ether in general to the family trade; a clay merchant.

The Loudspeaker Part 1

Before the fight even starts. Allow me to define "Loud Speaker"
n. A device for converting electrical energy to sound
Loudspeakers are electro mechanical devices working on the basis of electromagnetism. They convert a given electrical signal, using electromagnetism, into moving air, what we call sound.

Early radio had a problem. Things were quiet. Too quiet as they say in the war movies. Things needed to get louder, not loud enough to rattle your windows with the massive sub-woofer in the trunk, but at least loud enough to hear at all. Radio's did not have amplifiers yet. Everything was operating with an output power measured in milliwatts.

Siemens filed the first significant patent for the loudspeaker horn. It was the predecessor to all acoustic models used in phonographs players. His German patent was granted July 30, 1878 and his British patent No. 4685 was granted Feb. 1, 1878. It was not a patent for audible transmission, it never carried sound. (He tested it wish DC transients.) Alexander G. Bell nailed that with his telephone patent in 1876. What Siemens patented was "the mechanical movement of an electrical coil from electrical currents transmitted through it" A moving coil transducer! and we all know from radio production I class that if the coil moves... it's dynamic.

So in 1874 Ernst W. Siemens was the first to scientifically describe the dynamic transducer, with a circular coil of wire in a magnetic field. His model is suspended so that it can support axial motion (be springy).

But what to do with all these moving springs and no sound? Siemens applied for a second German patent, No. 2355, filed Dec. 14, 1877. This one was for a non-magnetic parchment diaphragm as the sound radiator of a moving-coil transducer. His diaphragm had a cone shape, with an exponentially flaring trumpet shape. See picture above.. Many people thought it looked like a daffodil or other flower. Strangely despite the fact that he could plainly see the coil moving, It was the two Americans, Chester W. Rice and Edward W. Kellog, that patented the moving coil principle in 1924.

But like all test models it didn't work so well. It wasn't very responsive. the axial mounting wasn't exactly perfect etc. etc. So this math nerd named Oliver Lodge starting noodling with it. He'd recently decided that math was boring and moved over to chair the physics department at Oxford. During his tine there he conducted experiments in the propagation and reception of electromagnetic waves. It was he that proved in1888 showed that radio-frequency waves could be transmitted along electric wires. It was he that fixed Édouard Branly's "coherer" so that Morse code could even be received. In his spare time he electric spark ignition for the internal combustion engine. Needless to say, he was a bright guy.

Mr. Lodge improved upon the speaker in 1898 with British patent No. 971. He added non-magnetic spacers to keep the air gap between the inner and outer poles of a moving coil transducer. He called it a "bellowing telephone" because of the cone-shape. It's off topic but like many geniuses in his spare time he was also a nutter and a bit of a sun worshipper..

Radio for Navigation (pre tomtom)

Throughout history men have gotten lost on long trips, flubbed their ability to use maps and refused to ask for directions. About 100 years ago it got harder to get lost.

I see this as developing in three major steps
1. radio wave detection
2. first attempt at a navigable beacon
3. first large scale implementation attempt.
In 1894 British physicist Sir Oliver Lodge demonstrated the possibility of signaling using radio waves. He did this with a device called a coherer [pic below], a vacuum tube filled with iron filings. He did not invent this device. In fact the Coherer had been invented 10 years earlier by Temistocle Calzecchi-Onesti. The coherer had gone through revisions in the hands of Edouard Branly and Alexander Popov. [Popov actually invented a radio communication system based on the coherer, is yet another candidate for inventor of radio]

The Coherer was a radio-wave detector and the heart of the early radiotelegraph receiver. It functioned as a rough gauge of resistance. I So now we could measure the radio wave, and thus distance from the transmitter by signal stregnth ... a fixed point. [later revisions to sensitivity allowed this to decode the first dots and dashes]
Around 1900, only 6 years later, Tesla opens the Wardenclyffe Tower facility and advertises it's services. He intended for the massive Wardenclyffe tower facility to be a radio beacon for navigation, and even time synchronization. But by 1905 Tesla had to shut it down. It was sold for $20 grand in debts.
In WWII radio navigation matures into practical use. The need to blow more people up more efficiently begets the need to pinpoint aircraft position. RDF is born. The Radio Direction Finder works by pointing a directional antenna in "various directions" and then listening for the direction in which the signal from a known station comes through most strongly. (this skips the triangulation needed to make an estimate with a coherer.) In WWII pictures of aircraft the RDF antennas are easy to spot on German World War II aircraft, as wire loops under the rear section of the fuselage. In Allied aircraft it was enclosed in a small teardrop-shaped fairing.
RDF using aircraft tuned into brodcasts of morse code letters. This technique is still used today by commercial aircraft. Most modern detectors can also tune in any commercial radio stations, which is particularly useful due to their high power and location near major cities.