This section describes the discovery of electromagnetic radiation and the first developments towards radio transmitters and receivers.
James Clark Maxwell
Heinrich Hertz
Pioniere der Funktechnik
Down of wireless Communication
Ferdinand Braun
Telefunken
World Radiocommunication Conference
Spark or Radio

Discovery of the electromagnetic radiation

Electromagnetic waves

To understand Electromagnetic Radiation, let’s look again at physics and the state of electrical engineering in the second half of the 19th century. Galvanism had been further developed and it was understood how electricity was generated and how it flowed through cables. It was also understood that electricity generated magnetic fields and that forces were created as a result. Eventually, it was discovered that currents could be generated by changing magnetic fields. So the following disciplines where explored:

• Magnetism
• Electrostatics
• Electrodynamics
• Induction

All these phenomena could be described in mathematical formulas. Some are simple, such as the connection between voltage and current, others, which describe the fields and their dynamics, are more complex and outside of normal school knowledge.

James Clark Maxwell

A physicist who was particularly concerned with the formulas of electricity was a Scot, James Clerk Maxwell. He managed to write down all electrical phenomena in first 20 and then in only four equations and to put them in relation to each other. This led to a so-called differential equation that described temporal and spatial changes in electric and magnetic fields. Maxwell published these equations in 1864.

This equation was a wave equation.

So it looked similar to the wave equation that describes the propagation of sound in air. If Maxwell wasn’t mistaken there should be electromagnetic waves and electromagnetic radiation!

Maxwell made the claim that electromagnetic radiation should exist. This was outrageous at the time.

At this point we should pause. There should be waves and radiation that were previously completely unknown?

To explain this situation, let’s do a thought experiment. Let’s imagine not being able to hear (and consequently not being able to speak either). Let’s assume we could still communicate well and do science. At some point some physicist would have studied the properties of air. He would have established that there is such a thing as air pressure and that air pressure disturbances propagate. He would sooner or later conclude that these disturbances propagate like waves, similar to the ripples we see on the water’s surface when we throw a stone into it. Such is the situation that Maxwell created for us. Electromagnetic waves were always there, but we had never noticed them because we had no „senses“ for them.

But the surprise went even further. Maxwell could guess that the speed of this hypothetical radiation must be very high. In fact, his estimate was close to the speed of light. The speed of light had just been successfully measured in the 1850’s. This encouraged Maxwell to make an outrageous postulate.

Light is nothing more than an electromagnetic radiation!

At the time, that was unheard of. A widely researched physical discipline, optics, was nothing more than a (further) phenomenon of electricity? „Electromagnetic radiation“? If all of this is true, how can electromagnetic radiation (like light) travel through a vacuum? Inconceivably. Especially the latter, the propagation in a vacuum, was unimaginable even for Maxwell. The same was true of almost all leading scientists of the time. Maxwell therefore postulated that the electromagnetic waves travel in an undetected medium. He called this medium „ether“.

Heinrich Hertz

Electromagnetic waves or radiation were „the subject“ of science after Maxwell published his postulate. The Berlin Academy of Sciences offered a prize for the detection of electromagnetic waves.

A young scientist, for example, was already researching this topic as a student. When he was a professor at the Technical University of Karlsruhe in 1886, he intensified his research.

But how do you generate electromagnetic radiation and how do you prove it. Going back to our comparison of the deaf scientist and the sound wave. He might notice that every time he fired a cannon, ripples would appear on a nearby water glass. So you needed a kind of cannon to generate electromagnetic waves. For Heinrich Hertz, that was a lightning or its little brother, the spark.

Heinrich Hertz recognized that electromagnetic waves could be generated with sparks.

Hertz worked with such sparks. He used an instrument that came from a Berlin physicist named Riess. It practically consisted of two needles, whose peaks could be brought very close to each other with a micrometer screw. If you applied voltage to the needles and slowly brought the needles closer together, finally a spark will appear. The distance of the needles was proportional to the voltage and so this was an instrument for measuring high voltages.

Now there was an “Oerstedt moment”. Hertz made experiments discharging Leidner’s bottles. He noticed that as he discharged, a nearby Riess instrument sparked. An accident? No, the behavior was reproducible. But was this phenomenon caused by electromagnetic radiation? To prove this, Hertz built a transmitter with a so-called spark inductor. This was a transformer with a small primary and large secondary coil that could produce very high voltages. This high voltage could be used to generate sparks. The sparks where produced between two small metal balls. Those small metal balls where connected to two rods that ended in metal balls. According to Maxwell equations the rods with the balls which served as capacitors would serve as antennas to produce radiation with a frequency of 80 MHz. This corresponds to a wavelength of 3.75 meters. Now Hertz used a simple ring, that had a small opening with small metal balls serving as „spark gaps“. This was the receiver. When Hertz created electromagnetic waves with the „spark transmitter“ a tiny spark appeared between the two balls of the receiver. This was such a small spark, that it was required to darken the room and watch carefully. Hertz could place the transceiver 20 meters away from the spark transmitter and still could observe the sparks appearing in the receiver. This convinced him that the sparks where created by electromagnetic radiation.

Hertz published his results that same year (1886), setting off a scientific tremor. The postulated electromagnetic waves were verified. Over the next two years, Hertz refined his experiments. In particular, he was able to prove the wave nature of electromagnetic waves by reflecting them on a zinc plate. He was able to generate so-called standing waves and thus determine wavelength, frequency and ultimately the speed of light. He published all this in a lengthy report in 1888.

Heinrich Hertz was satisfied with the discovery of electromagnetic waves. He didn’t think they could be of any use.

Hertz was happy with his results. He himself did not believe in any application of these waves. They were of purely scientific interest. He devoted himself to other research and tragically died very early in 1894. He did not live long enough to see the triumph of „radio technology“. He was honored posthumously by having the unit of frequency named after him. From 1930, one oscillation per second was called Hertz, abbreviated Hz.

Pioneers of radio engineering

Many engineers were well aware of the benefits of Hertzian waves, as they were called at the time, and research was carried to improve the surrounding technology. A practical way of using these waves for telegraphy was sought. There wasn’t much to do on the broadcaster side to make improvements. The technology was only refined to generate sparks and radiate them optimally with antennas. It quickly became clear that different frequencies required different antennas. The bigger problem was a receiver. After all, you couldn’t put receivers in dark rooms and count tiny sparks.

A major success came from a French physicist named Edouard Branly. He experimented with iron filings, which he placed between two electrodes inside a glass tube. Normally the iron filings should conduct electricity and therefore it be expected that current is flowing between the two electrodes. However, this was not the case, as a fine layer of oxidation on the metal chips prevented a short circuit. Branly now found that stronger electromagnetic waves broke through this oxidation layer and created a short circuit. Thus, radio waves could be detected by the apparatus he called „Radio Conductor“.

A Russian scientist named Alexander Stephanovich Popov saw the usefulness of the radio conductor. He used the radio conductor’s short circuit to drive a electromagnet, which in turn attracted a metal rod that struck the radio conductor like an electric bell. This hit was then restoring its resistance. Popow probably used this receiver as early as 1892 to detect distant lightning. Its use was more in warning of an approaching thunderstorms than in telegraphy. Later, in 1896, Popov is said to have given a complete demonstration of a wireless telegraph to the Russian military, overcoming 250 m. Whether this actually happened is disputed. Nevertheless, he is considered the „father of radio“ in Russia and later in the Soviet Union.

A renowned English physicist named Oliver Lodge has been researching electromagnetic radiation since the publication of Maxwell’s wave equation. However, Heinrich Hertz forestalled him with the proof. Lodge made many experiments with electromagnetic waves and also used the radio conductor developed by Branly, which he himself called a „coherer“. When Heinrich Hertz died in 1894, Lodge gave a lecture and demonstrations in his honor at a scientific meeting. Here he showed a coherent receiver in addition to a transmitter with a classic spark inductor. This was connected to a mirror galvanometer to demonstrate detection of waves with the deflection of a light beam. The short in the coherer was cleared by being shaken by a ringer that was turned on manually after a reception.

Dawn of Wireless Communication

Guglielmo Marconi

All previous researchers of electromagnetic radiation were primarily interested in knowledge and, of course, in scientific fame. They were less interested in commercialization.

This was different with Guglielmo Marconi, who, like Alexander Graham Bell before him, had the application and the business in mind. Marconi was an engineer familiar with experiments with electromagnetic radiation through his Italian professor Augusto Righi. He knew different arrangements of spark inductors for sending waves and also necessary elements for detecting electromagnetic waves, above all the coherer.

In the mid-1890s, he began building and experimenting with a spark gap transmitter and receiver himself. He improved the spark inductor with an antenna and triggered the sparks with a Morse key. He also used a coherer on the receiving end. When the coherer started to conduct current when receiving a electromagnetic pulse, he used this current to drive a Morse code writer. At the same time, the coherer’s short-circuit current also flowed through a coil, which attracted a metal rod, which then struck the coherer and canceled the short-circuit. This „armed“ the receiver for the next reception. Marconi’s merit was not the discovery or development of individual elements, but the improvement and pragmatic construction of an electromagnetic telegraph. Nevertheless, Marconi is still incorrectly named as the inventor of radio technology.

Marconi did not invent wireless telegraphy. But like Alexander Graham Bell before him, he recognized the enormous benefits of radio transmission and managed to build an industry around it.

Marconi demonstrated his system to the Italian Post. However, the responsible technicians considered his apparatus a useless gimmick and showed no interest. For this reason, Marconi went to England and filed a patent application for his system there in 1896. At the same time, he demonstrated his invention to the authorities. They were immediately convinced of its usefulness. Marconi was able to demonstrate the usefulness and efficiency of his system in many places and offered his invention to the English Post. This was necessary because the post office had a monopoly on telegraphy. Intentional or not, the Post only offered Marconi the paltry sum of £10,000 for his technology. As a result, the disappointed Marconi founded the Wireless and Telegraf Company in 1897, which later became the Marconi Wireless and Telegraf Company.

In the following years, Marconi and his company were busy improving the performance of their system and increasing the range. In 1903, Marconi finally succeeded in establishing the first public wireless communication across the Atlantic. The greatest need for wireless telegraphy came not from terrestrial use but from seafaring. For the first time in history, it was possible that ships could communicate with the land and also with other ships. This was especially important in the navy. For centuries, a huge problem with warships was that they could only communicate with each other when there was line of sight. Communication with the country was practically impossible. Wireless telegraphy was now revolutionizing sea fleets. It was possible to communicate at any time, over long distances.

Ferdinand Braun

The German Physicist Ferdinand Braun is well known to many. However, it is probably more for the invention a special cathode-ray tube called the „Braun tube“, which later led to the television. He also provided significant contributions to wireless telegraphy, for which he was awarded a Nobel Prize in 1909 together with Marconi. As a professor of physics, Braun was also interested in wireless telegraphy. The range of Marconi’s systems were initially not very high. At the time, critics of the system complained that the sparks from the transmitter could be heard further than the electromagnetic waves could reach. Clear improvements were needed. Braun initially made two essential contributions. The previous spark gap transmitters were built in such a way that the antennas were connected directly to the spark gap. The dimensioning of the antenna also determined the frequency with which a pulse was radiated. Braun inductively separated the transmission antenna and spark gap from each other. The spark circuit consists of a LC resonant circuit, i.e. a capacitance and an inductance. These also largely determine the frequency of the excited vibration. The coil (inductance) is also used for inductive coupling to the antenna, which radiates the oscillation. There is also an oscillating circuit in the receiver to receive the corresponding frequency.

This new approach enabled radiotelegraphy to be significantly improved and Marconi also adopted this arrangement to improve his system. Another discovery was made Ferdinand Braun making him a pioneer in wireless communication and electronic. He dealt with the conductivity of various minerals. For example, crystals were screwed into a metal housing and current was measured directly on the crystal with a fine wire. Braun made an interesting discovery. Certain crystals (later called semiconductors) only let current pass in one direction. The benefit was that alternating currents, i.e. currents that oscillate back and forth at a certain frequency, are “cut” and thus can be transformed to direct current. In contrast to high-frequency alternating current, direct current can be measured (and heard) directly.

Braun realized that the semiconductor rectifiers could be used in receivers and work better and more reliably there than coherers. Around the turn of the century, the coherers were more and more replaced by „crystal detectors“.

Braun could never explain the diode effect of the crystals. This succeeded decades later. Nevertheless, he is regarded as the discoverer of the semiconductor diode.

Telefunken

The Marconi Wireless Telegraph Company developed a virtual monopoly. Marconi managed to sign contracts with the big shipping companies. These contracts were such that the radio telegraphs were leased from Marconi and even the radio operators on board were Marconi employees. These employees radioed exclusively with Marconi stations on land. At that time there were no authorities to prevent this.

According to legend, the German Kaiser Wilhelm II wanted to send a telegram from a steamer while traveling on the north sea. Allegedly, the radio operator (an employee of Marconi) refused to accept the telegram because it was not allowed to communicate with the German radio station in Borkum. This outraged the emperor beyond measure and from then on he made radio regulation a „top priority“.

In Germany there were already two companies developing radio technology around 1900. AEG (General Electricity Company) and Siemens fought over key patents. One excellent radio pioneer named Slaby, worked primarily for AEG, while Siemens primarily used the valuable patents of Ferdinand Braun. The emperor put an end to this by asking the companies to set up a joint venture. This is how the Telefunken company came into being in 1903. This company now focused on breaking Marconi’s monopoly.

Kaiser Wilhelm II passed a law in 1908 that regulated wireless communication. This stated: „Electrical telegraph systems, which transmit messages without metallic lines, may only be set up or operated with the approval of the Reich.“ From now on, regulation of wireless communication became a state matter. To this day, the countries have “sovereignty” over all radio frequencies.

Communication via radio is regulated by the countries and requires a license. Free radio transmission is therefore prohibited.

World Radiocommunication Conference

At the beginning of the 20th century, “radio transmission” resembled the wild west. Even if radio was controlled by the state, like in Germany, it did not stop at national borders and there were no rules at sea. It was fought for dominance by trying to forge monopolies. Rights and patents were fought for and anyone could generate radio waves at will, no matter the frequency. Long-distance trade via ships was particularly affected because, as described, radio communication with ships was the main application of wireless telegraphy up to now.

This situation called for a settlement. The German government, probably on the advice of Kaiser Wilhelm II, hosted a conference in Berlin in 1903, which was attended by Germany, Austria, Spain, the United States of America, France, Hungary, Russia, Italy and Great Britain. They came to a final act of 8 provisions. Great Britain and Italy, however, had reservations as they depended on the Marconi system and saw their supremacy threatened.

In 1906 they met again in Berlin, this time officially under the leadership of the ITU. Now, 27 countries took part and the conference lasted a month. The successful result was the first international radiotelegraph contract. This prohibited the discrimination of manufacturers as it existed under Marconi. The nations agreed on certain protocols, such as how a radio message is recorded and how it is terminated. In addition, the radio spectrum was divided into two bands, 300 meters (1 MHz) was to be used for marine radio, while 600 meters (500 kHz) was intended for public radio.

The electromagnetic spectrum was regulated for the first time and divided into two bands. 300 meters and 600 meters.

Another agreement that was achieved was the standardization of a signal for emergency calls to be send via radio. Marconi and Telefunken used different emergency signals and it was imperative to agree on one. In Germany it was already mandatory to send a certain Morse code in an emergency: …—… so an S an O and an S. This was an acoustically noticeable signal and that was the only reason for using it. It was used to ensure that all stations that heard it immediately stopped transmitting and then received the actual emergency call. The 1906 conference now prescribed the SOS international. Incidentally, the fact that SOS would stand for “Save our Souls” was only interpreted later. Marconi previously had a distress signal CQD dubbed Come Quick Danger. However, this could not be heard from the radio signals as easily as SOS.

Spark or Radio

Meanwhile no radio transmission system is using a spark gap transmitter. However, in Germany, radio transmission is still related to „sparks“. The whole radio technology is still called in Germany „Funktechnology“ which means spark technology. Even today a mobile telephone in German is call a „spark mobile apparatus“ (Mobilfunkgerät).

In English speaking countries the radiation was always the dominating element. Therefore an apparatus for transmitting electromagnetic waves was always called a radio. In Germany a radio is just a receiver for radio broadcasting.