Early radio

What exactly is radio?
Was it discovered or invented?
What are its origins?

The answers to these questions can be understood partly by studying the earliest reports on experiments with "Electric Waves" and putting them into the context of what we now know. First one can read about experiments which revealed step by step how trial and error played its part in the development of radio communication and second, having been able to establish and receive radio waves, how practical use of the phenomenon was achieved. The period of time from the date radio waves were predicted to the time the first practical equipments were being used spanned about 40 years and a further 10 years elapsed before practical voice transmissions were made and another 10 before the public began to listen to organised transmissions. It was therefore over 60 years before broadcasting materialised from the first theoretical equations.. so radio didn't just happen overnight, it was a long drawn-out process with physicists sometimes marking time until engineers came up with the new components necessary for the next step in the development.

The Early Experimenters

A number of scientists, physicists and engineers in Victorian times, although not necessarily calling them by the modern name, were familiar with radio waves and numerous experiments had been performed which demonstrated their existence. In particular it had been agreed that the "Ether" was the medium through which these new fangled waves were transmitted. It followed, that in just the same way as sound waves needed air, so the new electric waves needed something akin to this, so the word "Ether" was coined. It all began in 1864 when a chap called Maxwell wrestled with mathematical equations and knew of the theoretical possibility of electro-magnetic waves but he was unable to invent a suitable laboratory equipment which would prove his theories. In the last decade of Victoria and in early Edwardian times radio or "Wireless", as it was universally known, was still in an embryonic state. True, communication had spanned the Atlantic, but it was still waiting for new devices which had yet to be invented before it would become really useful. Even terminology in the early days was not accepted by all, and one famous chap by the name Hibbert insisted on calling it, not Wireless, but "Etheric Telegraphy". As late as 1909 he was still not aware of "Etheric Telephony", as he may have called it, because this was still in its infancy, but as early as the end of 1906, a chap called Fessenden in the USA had managed to transmit speech and music over a couple of hundred miles although all he'd done was to stick a carbon microphone in his transmitter aerial lead. The resistance of the carbon granules change with the pressure of the diaphragm moving from changes of air pressure from sounds impinging on it. Presumably the result was amplitude modulation.

Hertz's Experiments

Stepping back in time, if one could do so, and if one could magically spirit a suitable radio set into one of the old laboratories, perhaps that of Hertz, and carry out a spot of listening, the earliest radio waves created by man would be found to have been in the VHF or even the UHF region. This was fundamentally to do with the physical size of the equipment, as having established an experiment, the investigator's next step was to study and maximise the observed effects. Of course as everyone now knows, to hear a radio station best, one must first tune it in, and as the earliest spark transmitters used relatively small "tuned circuits" or aerials, so did the receivers. The size of the laboratory bench dictated the convenient size for the tuning rods (tuning coils as such not having been invented yet), and it must be said that these bear a striking resemblance to dipole aerials and a little later perhaps, when the rods grew paddle shaped ends, more akin to wideband VHF or UHF aerials. For example, if Hertz's equipment, based on what was essentially a half-wave dipole, had an overall length of about 12 inches, the wavelength generated would have been of the order of 24 inches. This represents a frequency of 500MHz. It is said that during his experimentation, Hertz's radiator ranged from several feet down to just a few inches, therefore emitting radio waves having a frequency of 100MHz to 2GHz . Neatly covering the Aircraft band, Band III, IV, V and S-Band and spanning no less than three amateur radio bands and the major mobile telephone bands.

The Hunt for a Practical Detector

In the earliest days there was no such thing as a detector and certainly no concept of modulation as such. If you needed a detector to make sense of modulation, and if you didn't know what modulation was, then clearly you would have no need for a detector. However such a device may have proved useful, if not for detecting modulation, then to detect the radio wave itself. To make a suitable detector at this time would have been no mean feat, because, at the frequencies with which the old chaps were originally working, they would have needed a pretty good detector even by modern standards! In fact it may be that this is one of the reasons why Maxwell himself got no further than his jottings. What was the first detector? Well after the spark gap, experimenters turned to other devices and of course many of those early experimenters turned to the ubiquitous Frog's Leg, first used for the detection of electicity in 1678 by Swammerdam in Italy. Nearly a century later Galvani re-discovered the technique, and once this had become common knowledge, a variety of parts from other creatures were also tested. A chap by the name of Zanotti even found that a newly killed grasshopper would emit a chirp when a current was passed through it. Such was the importance of these findings, and in the absence of other techniques, that a certain Jules Alix once proposed a system of telegraphy based on frog's legs!

Radio Transmitters

Turning now to radio transmitters, or as they were regarded "sources of Electric Waves". These evolved from induction coils. Once Faraday had established his laws concerning electric and magnetic fields, and once electric motors and high voltage induction coils were becoming familiar to the scientists of the day, some turned to experimenting with them. Before some of these early dabblers were familiar with the theory behind radio waves as such, they carried out laboratory experiments by merely observing and noting physical effects. One day when experimenting with an induction coil, one such chap called Henry (later to have inductance units named after him) noticed that he could see a small spark jumping across a narrow gap in a nearby apparatus. He must have thought he was imagining it because no wires were involved. When he caused a spark to bridge a gap in one piece of equipment, like magic, a spark appeared further down the bench in another. So interesting was this that others, hearing of the effect, switched their experimentation to observing and characterising this effect. The most famous of these was Hertz (later to have the term "cycles per second" re-named after him) who worked over quite a long period, it is said starting in about 1877, about which time he had discovered that he had, in fact, been able to generate Maxwell's hypothesised "extra long light waves". Soon the Hertz "transmitter" had grown an appendage, which was an embryonic aerial, and the "receiver" much to his surprise worked best when it had been fitted with a circular, loop "aerial" having a particular size which was related to the transmitter aerial. With this equipment he also discovered the basics behind "radio direction finding" as by turning the loop one way then the other he discovered it worked best when the its plane was at right angles to the transmitting aerial and hardly at all when end on. This then was the first radio "system" and soon, as had happened with the telephone, the two parts of this system had been physically separated and located in rooms remote from each other. This took place at Karlsruhe University, and not only were experiments made from room to room, but even to the outside world across the college grounds.

Development of the Laboratory Equipment

One of the fundamental aspects of radio, that is "tuning" of the receiver and transmitter to the same frequency, was made around this time. Terms such as "resonance" and "sympathetic vibrations" were coined and were usually compared with the mechanical interaction of two adjacent pendulums. Around this time intelligence could have been relayed from one place to another, and I suppose essentially it must have been, but alas that would have to wait a few years as the physicists involved were really only concerned with their experiments, and not being engineers as such, did not think of the wider implications of what they were observing. By simply interposing a moving paper strip between the receiver spark gap electrodes no doubt Morse code could have been printed and the dawn of wireless communications would have been born. However at this early stage in the development of radio no such extension of the strange effect was, to the best of my knowledge, ever attempted and the fact that one could "signal" across empty space, although observed, just wasn't recognised as being particularly useful. During Hertz's experimentation, around 1887, he discovered that his radio waves (which by my reckoning must have been around 83MHz.. so was this the first transmission in Band II ?) could be reflected from metal sheets and focussed by a lens made from glass, sulphur, stone or pitch and this finally convinced him, and others, that what was being observed was really an extension of light waves. Initially one could one hear a buzzing noise as the spark was regenerated at the receiver, but after a major leap forward in an experiment one day, one chap discovered that a detector, called a coherer, could be employed instead of a mini-spark gap. In England, in fact at the new Liverpool University in 1894, Sir Oliver Lodge, whose experiments with the effects of lightning, brought him to much the same conclusions, as to the nature of electric waves, as Hertz, using a coherer receiver, transmitted and detected morse code over a few hundred yards. Also active were Fitzgerald, known for his measurements of the speed of light, Trouton, Righi, Tesla and others. By then, proper coils were being used and frequencies had dropped to levels where simple detectors would actually work. Once the coherer was used in a receiver, the system performance improved by a staggering degree. No longer did one have to squint at a tiny gap between two spheres to look for a miniscule spark, one could actually see on a meter the results of generating a spark at the transmitter. The receiver spark gap was no longer required and if the early experimenters, pursuing experiments with their new found detector, had thought a little "laterally" about what they had in front of them, they could have beaten Marconi in bridging the gap between an interesting laboratory experiment and a communications system. However the system so far developed was nothing more than an interesting scientific toy… no-one had the foresight to imagine a use for it! In fact if one dwells for a moment and considers why it was Marconi, rather than the erudite Professors, that took the lead, it is obvious. People like Hertz and Lodge were gainfully employed to teach their students. They had full time jobs in Universities and much of their work on radio was extra-curricular, maybe confined to weekend dabbling. Other people at that time were actively pursuing their experiments full time, and despite the lack of convenient communication between the experimenters, each was well aware of progress of the others, and no doubt each little improvement by one individual was seized upon by others in the field. As had been demonstrated in telephony by Bell, the first past the post was he who had filed the first meaningful patent, and of course this was to be Marconi.

The Coherer, the first proper Detector

Back to practical aspects... what was the coherer? It was a glass tube containing iron filings. Such are the characteristics of iron filings, that the path through them was of high resistance, but like magic, when a tiny radio signal was applied across the tube, together with a small battery, the iron filings conducted measurably more current. So with the presence of a signal a circuit capable of detecting it was possible. Here then we have the first diode. Unfortunately once the filings had been activated they remained conductive so after the beginning of the first spark transmission had been detected something extra was needed to sense the next. The answer was a tiny hammer which whacked the side of the tube and restored the filings to their original non-conducting state. This was ingeniously brought about when, after the received signal had activated the coherer, it then operated an electro-mechanical device which tapped the side of its tube. This was nothing new as the principle was already used in thousands of homes in the electric bell. The discoverer of this first coherer detector is often loosely attributed to Marconi but, in fact, he had only introduced improvements to a device already well established. How long had the coherer been around? Well in 1890 a Professor Branly (sometimes referred to as "Bradley") of Paris is said to have discovered the coherer, but contemporary reports have it that the true inventor was a Professor Hughes who used a metallic coherer as early as 1871. It was said that his work pre-dated much of that of Hertz, but that his colleague, Professor Stokes, had put the damper on any further research on the grounds that the observed effects were merely associated with ordinary magnetic fields rather than anything new and "get back to teaching your students"... I have also seen it in a treatise by Sylvanus P Thompson that the coherer was "Lodge's device".

Towards Practical Radio

Sylvanus P.Thompson also states that it was Oliver Lodge that discovered "resonance". This latter fact was certainly true but it was a discovery that had been overlooked by experimenters such as Marconi until many years later when he came to realise its importance during development of his operational long distance radio system. Why all the confusion I wonder? Well one reason is that many of the early writers on science and physics published their books, on the new found phenomenon of wireless, when the work was still in progress and they did not have the hindsight of later authors, neither did they have instant global communications. Parallel experiments were going on in many countries throughout the world and it is quite likely that more than one scientist stumbled upon the same improvements to their apparatus and carried out the same tests as others at much the same time. For example Lodge discovered that electric waves would pass through brick walls at probably the same time as Hertz was carrying his equipment around the grounds of Karlsruhe University. I suppose one could rely on published papers to determine who was first, but then how long after the experiment did the author get round to writing up his work? If one could read contemporary diaries or laboratory notes I suppose one might get a clearer picture. In 1896, after a year of experimenting, Henry Jackson managed to transmit signals between two British naval vessels. In 1897 Slaby, a German scientist, was successfully operating spark equipment whilst his countryman Karl Ferdinand Braun after three or four years of experimenting managed to transmit over a path of 40 miles. In 1896, Marconi popped over from his native Italy where he had begun experimentating in 1894, and joined the fray and found the magical "Ether" could carry signals not only across the laboratory but across Bournemouth Bay and even, before the end of 1901, the Atlantic Ocean! What was the advance that enabled him to do this? Well, in 1896 Marconi had increased the size of the Hertz "aerial rod" to around 400 feet in length! Clearly he had moved the thing from his laboratory bench and the restrictions imposed by its physical size! With an overall length of 400 feet he generated radio waves of 240 meters, well and truly into the Medium Waveband! As luck would have it, although no-one yet could know why, these sorts of wavelengths can be received over quite large distances unlike Hertz's VHF variety which are normally restricted to "line-of-sight".

Making Use of Radio

Marconi was the most noteable contributor to the development of radio, probably because he had the right mix of engineering and business acumen. But what were his actual contributions? As an engineer, rather than a physicist, he had the necessary practical leaning and promptly introduced numerous improvements to existing laboratory hardware. First he had tackled the coherer and found that nickel silver filings were better than iron filings, and then, by fitting a couple of radio frequency chokes between the coherer and the driven circuit to which it was connected, he found that all the aerial signal, not just a fraction, was available for activating the filings. This dramatically improved the sensitivity of his receiver. Next he sorted out the RF side. Once he had found that Hertz's apparatus would work much better at propagating radio waves with much longer elements, he soon found that a "proper" aerial (as we know it) was far superior to bits of wire and paddles close to the ground. He also discovered the advantage of a good earth connection. Essentially, in increasing the physical size of the equipment, Marconi had moved from UHF transmitters to MF and HF transmitters, which as we all now know, are infinitely superior for long distance ground-to-ground communication. In the process of trying out various aerials he stumbled across "Syntonic Etheric Telegraphy" as Mr.Hibbert called it. What this meant in practice was that he embodied (rather than invented) aerial tuning and the ability to place different transmissions on different frequencies, a pretty essential thing, as up to that point it had been imagined that the only way of sharing the ether would be by using directional antennas. Another of Marconi's improvements was the magnetic detector. This was developed immediately before the thermionic valve and pre-dates its re-introduction years later in the magnetic recorder. The magnetic detector employed an iron wire continuously moving through a former carrying a pair of coils. One coil was connected to the receiving aerial and wrote a tiny magnetic signal onto the iron wire. A second coil read the recorded signal and converted it into an audible signal. Presumably this was only successful if the incoming aerial signals were substantial as at this date the valve amplifier was yet to become reality. Dwelling a moment on the magnetic detector it is interesting to note a parallel development, the "magnetic amplifier". If a small signal is applied to the coil of a suitably sensitive relay then the relay contacts could be made to close. These contacts in series with a battery, could operate a larger relay and so on. Thus a tiny electrical signal could be amplified into a signal having virtually any power. It has been said, and I tend to agree with the statement, that this invention gave rise to the moving coil loudspeaker, many years before it was first introduced, because one of the first magnetic amplifiers did indeed connect to a membrane for converting the output into acoustical energy.

An Interesting Dead-End

Now another early episode of the story of radio. In order to develop the high voltages necessary to generate a decent sized spark gap at the transmitter a dynamo, rather than an interrupted DC supply from a battery, was employed and of course the speed of the dynamo dictated the frequency of the current it generated. Up to then a battery had been used in conjunction with a magnetically operated interrupter. Alternating current could be used just as well as interrupted direct current for establishing a spark and its chief advantage to the experimenter was that you could more easily generate higher powers. You could also hear a nice buzzing noise, variable by changing the speed of rotation of the dynamo, coming from the spark. Commercial and maritime transmissions were now getting to be commonplace and a radio operator of the day would not so much tune his receiver to a specific frequency but listen on his broadband equipment for a particular tone. Different transmitters were now able to be set to different tones so they could be readily identified amongst the carcophony of buzzings. Not only could sparks be generated at low audio frequencies but at the actual radio transmission frequency. Nicola Tesla was one of the first to construct a high frequency dynamo; typically one with 400 poles would produce an alternating current of 20KHz and could be used to excite an induction coil to generate low frequency radio waves and, by suitably interrupting the spark, one could produce morse code. An interesting observation of Tesla's was that if he connected the output from an induction coil to rods at opposite sides of a room then lamps without any wiring could be illuminated anywhere in the space between them. This was in 1892.

Another Dead-End

Not all the experimenters' work was focussed on producing radio waves as such. Some went off at a tangent. A Professor Elihu Thompson performed the following experiment in 1892:- "I constructed a coil with 15 turns of very stout wire as the primary and 500 turns of fine wire in a single layer about 20 inches long as secondary. This "high frequency" transformer I then immersed in a barrel of oil and carried the terminals carefully through tubes filled with oil. I then connected an AC dynamo via a transformer supplying 12,000 volts to a battery of 16 one gallon Leyden jars which I arranged to discharge through a quarter inch spark gap and the primary of the HF transformer in the barrel of oil. A blast of air was arranged to impinge on the spark gap thus considerably raising its breakdown voltage and the result was a powerful discharge, 31 inches long between the terminals connected to the HF transformer secondary". Those who are of that turn of mind may like to calculate the frequency of the tuned circuit given the details above. Assume the HF transformer coil was say 4 inches in diameter. What was the likely power output in watts? I suppose, bearing in mind the "gallon" Leyden jars this could be the first "home brew" transmitter!

Propagation and the improvements necessary for Broadcasting

As yet propagation was a mystery. It had been observed that different effects were obtained during the hours of daylight than at night. Marconi thought it was something to do with sunlight falling on the aerial and changing its wire-to-ether characteristics. Professor J J Thomson thought it was connected with sunlight producing lots of negative electrons, only discovered a few years earlier, and that these would partly absorb the radio waves. Mr.Hibbert thought that it was connected with lightning discharges. Even by 1909 the ionosphere had not been recognised. What remained then after the earliest successes? The experimenters had yet to build a system for a specific radio frequency. In 1902 a German, or a Danish chap, contemporary writers were not quite sure, called Poulsen, managed to produce undamped electric oscillations as distinct from the heavily damped variety from spark transmitters. The latter were not too efficient because they are not able to be sharply tuned and the output of not many transmitters could fill the available wavebands. Signals were noisy, fuzzy things occupying loads of bandwidth. Huge powers were needed because of their wide bandwidth so when continuous waves were introduced, with their narrow bandwidths, efficiencies improved dramatically. The first transmitters using modulated CW used the carbon arc and this, if you wished, could be driven directly from the public mains supply as its chief requirement was high current not a high voltage. Amongst things remaining to be discovered was the cat's whisker. During the wireless telegraphy era and before wireless telephony had begun the crystal detector superseded the coherer. A contemporary circuit from late Edwardian days before WWI is shown above. The discovery of the crystal detector has its own history which in the earliest days is to some extent a little vague. Experimenting with electric circuits was not uncommon and it was whilst carrying out one such experiment that Karl Ferdinand Braun had discovered that when current was passed through two dissimilar materials in intimate contact they showed a resistance which was higher in one direction than the other. There were many such materials and of course, as time passed, the effect was applied to the detection of radio signals. Some materials were no use but others worked well, in particular a chap by the name of Dunwoody discovered that carborundum crystals were ideal for detecting radio waves. That was in 1906, and when the news broke, feverish activity by the radio fraternity resulted in many other materials being found that would work equally well, paving the way for the crystal set.   Yet to be discovered also were the laws of propagation and the whole idea of a radio frequency spectrum that today we visualise so easily. As late as 1899, after 20 years of dabbling, someone had yet to think for what purpose the new found phenomenon of radio could be used. After all wasn't the electric telegraph well established and together with Bell's telephone, didn't this meet all the requirements of the day? No, because clearly it wasn't a simple matter to connect a telegraph or a telephone wire to a ship on the high seas. Hence the reason for the choice of ships by many experimenters, such as Jackson and Marconi, for their early radio experiments. Amplification of the tiny radio signals required the thermionic triode valve which had been invented alongside Marconi's early radio experiments but which still waited in the wings, together with its cousin the thermionic diode, to be called up for detector service.

The Missing Link

What about the valve? This was discovered by accident rather than by design. The first electric lamps used carbon filaments, and although initially rather bright and efficient, became duller during use due to deposition of carbon onto the inside of the glass bulb. This was one of the reasons why Fleming had been hired by Britain's leading electric lamp Company. He was investigating the effect and had noticed that the glass remained clear where it was in the shadow of any internal fittings inside the lamp. Why was this he wondered? In the cause of figuring out the reason he inserted an extra wire into a lamp and connected this to a meter. When the lamp was lit the extra wire seemed to be a source for electrical current and, low and behold, several experiments later he had discovered that when an external battery was used to apply a suitable voltage bias, he had discovered the thermionic diode! He had found that by connecting the extra wire to the positive terminal of a battery, current could be measured flowing from the wire to the filament circuit, to which the battery negative terminal was connected. Once an inkling of this effect had leaked out others experimented with the same sort of thing. Who were the people involved and who actually took the credit? Fleming is high on the list as it was he who first patented the device on November 16th 1904. The term "valve" was Fleming's word, and over the few years following its unveiling, was variously called "The Fleming Valve" and "The Thermionic Valve". Fleming himself was keen to keep the former name and was much against the newer title "diode" as the word no longer carried any recognition of himself.   Who was Lee de Forest? Fleming has it that the American merely shadowed his own researches and in 1897 had added another electrode making the first "triode valve". Odd that the diode should be patented after the triode had been around for 7 years! Triode development however was slow and it wasn't until 1906 that the audion triode became a usable device. By 1905 carbon filament Fleming valves were being widely used in wireless telegraphy. A few years later and we find the triode being put into service but as late as 1912 it was proving to be difficult to use at more than 65 or so volts. Was Fleming the first to discover the thermionic effect? No, it is said that this discovery belongs to Edison, for it was he who had been experimenting to improve electric lamps and who had stumbled upon the effect. In fact the effect was originally called "The Edison Effect". What triggered the lamp experiments? Well it was the invention of the dynamo in 1870 that created the option to instigate a public electric mains supply. What could one use the mains for? Predominantly lighting. At that time "lighting" and "carbon arc lamps" were synonymous but the latter consumed more power and emitted more light than the average home could use. So it was then in the 1870s that Joseph Swan in England and Thomas Alva Edison in the USA turned their minds, independently to making an electric lamp for the masses. Swan may have been first to glimpse the solution in 1878 when he came up with the idea of a vacuum lamp. Edison may have been two years later in arriving at that conclusion in 1880 but by then both men were well on the way to making a practical lamp. At the end of 1881 we have the practical electric lamp and Mr.Fleming was appointed Scientific Advisor to "The Edison Electric Light Company" of London. It was here then, in an attempt to reduce the effect of the inside surface of the electric lamp from becoming blackened, that the first experiments with extra electrodes were made and the odd effect obtained when a battery was connected to the extra electrode. W.H.Preece (the telephone expert who was later to become Engineer in Chief and Electrician for the GPO) and Fleming were given a box of modified lamps and the task of investigating the Edison Effect. Over the next five years, between 1885 and 1890, the two pursued their experiments, not without some "theoretical" difficulty, as it was still another eight years after they had finished before the electron would be discovered!

The players

M.Faraday (1791-1867); J.Henry (1797-1878); J.C.Maxwell (1814-1878); J.Swan (1818-? ); G.G.Stokes (1819-1903); T.A.Edison (1847-1931); O.Heaviside (1850-1925); G.Fitzgerald (1851-1901); O.J.Lodge (1851-1940); J.J.Thomson (1856-1940); H.R.Hertz (1857-1894); Fessenden; Marconi; Branly; H.Jackson; Slaby; K.F.Braun; Poulsen; Fleming; L.de-Forest (1873-?); E.Thomson; N.Tesla; Trouton; Righi; W.H.Preece; Armstrong.

To read about radio development in the 1920s see the next page....

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