Crystal Oscillator
Radio gets Mobile
Radio and Propaganda
Frequency Modulation
Radiotelephony
The first Handheld

Development of Radio Broadcasting

99 Channels for Radio Transmissions

At the beginning of the twenties there were the first stations for radio broadcast programs. When it was possible to acquire radio licenses in America in 1921, there were only two available frequencies. 833 kHz and 619 kHz. A year later, 750 kHz was added. However, the number of broadcasters increased so much that three frequencies were not enough. It was decided to reserve a whole „band“ of frequencies for licenses. At the second American National Radio Conference it was decided that the frequencies 500 kHz to 1500 kHz should be used. These were divided into subtends (channels) of 10 kHz. A license thus referred to a 10 kHz channel in this band. The maximum power was limited to 1 kW so that distant transmitters with the same frequency did not interfere.

Similar paths were followed in Europe. Here, in 1925, a European conference in Basel decided to divide the band from 500 to 1500 kHz into 99 channels. 77 of them were firmly assigned, to just one city. It was possible to work with strong transmitters there. The remaining 22 frequencies could be used several times for smaller transmitters. Because of these limitations, there were only 100 broadcast stations in Europe in 1929, and much resentment because there seemed to be no progress. Even a grid with 9 kHz grids did not result in much relief. The broadcasters in Europe were almost all under state control. Private broadcast stations only existed in the USA.

In 1934, the American government established a commission, the FCC, the Federal Communications Commission, to administer the granting of licenses for radio communications. This powerful commission governs all radio communications issues in the United States to this day.

Crystal Oscillators

A severe problem with radio transmitters was the oscillator. Oscillating circuits were sensitive and deviated from the desired frequency when the temperature changed, etc. One solution for this problem was the application of crystals. The effect that a crystal compresses or expands under electrical voltage was already known in the 19th century. Conversely, a quartz creates an electric voltage under pressure. This effect is called piezoelectricity. In the early 1920s, it was possible to get a crystal like quartz to oscillate in this way. The quartz was coupled to an active oscillating circuit which has the same frequency as the quartz oscillation. It turned out that these oscillations were very stable. In 1934, Bell Laboratories succeeded in building a quartz-powered clock. This was the most accurate clock in the world at that time.

With crystal oscillators it was possible to generate the required stable frequency as required for radio broadcasting.

However, the main application of crystal oscillators was in radio technology, especially in the frequency stabilization of transmitters. Until the 1940s, only natural quartz was used, most of which came from Brazil. It was only after the war, that artificial quartz began to be produced and very small oscillators became possible.

Quarz Crystals became a very critical resource in Word War II since it was required not only for transmitters but also for the upcoming radar systems.

Radio gets mobile

In the 1920’s, the innovation in radio technology went hand in hand with improvement of electronics. New, more efficient circuits emerged and new vacuum tubes came onto the market, cheaper and more economical in power consumption.

At the same time another industry was rising, the automobile industry. Soon the radio receiver technology was combined with the car industry resulting in the first car radios. Initially these were individual prototypes, but in 1930/31 the first products came to the market. Well-known names were e.g. Blaupunkt, which would later become the leading German manufacturer of car radios. In America, the Galvin Manufacturing Corporation manufactured a car radio which they called Motorola. (an artificial word from motor and ola = shaft). The radio became so popular that the company renamed itself Motorola.

Radio and Propaganda

Receiving radio broadcast programs was a hobby for enthusiasts working with crystal detectors and headphones in the 1920s. In the thirties there was progress with complex tube circuits, amplifiers and thus loudspeakers. However, receivers were expensive.

The National Socialists in Germany recognized the value of radio as an instrument of propaganda. Next to newspapers, radio was the best and most effective tool for spreading (fake) news. Therefore, they specifically promoted the development of inexpensive radio receivers for the national reception of broadcasts. The result was the so-called „Volksempfänger“ (people’s receiver). Even workers could afford it. In 1939, practically everyone in Germany could listen to the radio. Tragically, this contributed to the spread of nationalism.

During the Second World War, a radio-supported counter-propaganda was created by England. The BBC World Service which was created in England in 1932, broadcasted information throughout the British Empire. Broadcasts began with the characteristic introduction „This is London Calling“. This service was also distributed in foreign languages, from 1938 onwards also in German. During the war, the BBC was considered a reliable source of the real situation. Listening to BBC was therfore banned in Germany and was consicered a capital crime.

Frequency Modulation

In the 1920s, radio was the technology that people wanted to use. Those who could afford it bought a radio and spent a lot of time listening to the news, concert music and popular music. However, the quality of the programs was rather poor. This was not only because the reduced bandwidth of the audio signals made everything sound dull, but also because the amplitude modulation is very sensitive to interference. Atmospheric disturbances and especially thunderstorms were loud in the radio broadcasts and often obscured the broadcasts from more distant stations.

The great American radio pioneer Edwin Armstrong recognized early on that another type of modulation would bring improvements, frequency modulation. Instead of modulating the amplitudes of the transmission signal, the frequencies were changed. For this purpose, an element was brought into the oscillating circuit, which could vary the capacity, controlled by the modulation frequency of the speech or music signal. There were elements such as varactor diodes for this.

However, there were obstacles. Frequency modulation needed more bandwidth. So it couldn’t just replace the existing AM channels. Frequency modulation required 40 kHz instead of 9 – 10 kHz. There were no public bands for this. However, frequency modulation became a candidate for a new technology developed in the 1930’s, television. This gave Armstrong the opportunity to demonstrate his frequency modulation in the Empire State Building in New York. In fact, the quality was significantly better in a direct comparison and convinced many critics. However, it was not possible to agree on a television standard and the onset of the Great Depression slowed down further steps. Also, there was not much interest from the major radio manufacturers to introduce new radio technology. They wanted to continue to develop amplitude modulation and make money from it.

The emerging television technology was thus in competition with frequency modulation for broadcasting. There was a dispute about the necessary frequency bands around 40 MHz. Radio always lost out as more business was seen in the television industry. Finally, in 1945, there was an agreement with the FCC that allowed frequency modulation to be transmitted in the frequency range of 88MHz -106MHz. This is the so-called VHF (ultra short wave) range, which is still used today for analog radio. In Germany one speaks of UKW (ultra short wave) radio. In the English-speaking countries, the abbreviation FM prevailed for frequency modulation.

Radiotelephony

The 1920s and 1930s were characterized by the development and spread of radio receivers. Radio broadcasting was popular. The idea to use radio technology for telephony as Fessenden has envisioned it was almost forgotten. There was also no real need for it, since the wired telephone network was still being expanded. Furthermore there were no frequencies available for radiotelephony.

The Walkie Talkie

In 1937 it was an Englishman named Donald Hings who managed to fit a complete receiver and a transmitter into a portable box. This was a challenge because of course the electronics contained multiple tubes and their associated batteries. After all, the “talking device” should be mobile and as portable as possible. Hing’s radio should serve pilots in airplanes to communicate with stations on earth.

Hings applied for a patent for the radiotelephone in September 1939 in Canada. As he left the patent office, he heard the news that war had began in Europe. He introduced his radiotelephone to the British military. The benefits became immediately clear and the device was built in large numbers. It could be carried around like a backpack. In 1943 the device was presented to the public in Toronto. A soldier was interviewed. He said that using this radiotelephone he could talk while walking. Thus, it was dubbed „walkie-talkie“ by the press. Ever since, two-way portable radios are called walkie-talkies, even outside England and North America.

Roger, Over and Out

The radiotelephone worked with amplitude modulation and with only one frequency channel. This meant that only one participant could speak at a time and not speak and hear like in usual conversations. On a telephone, this two-way communication was possible. Single channel communication required some discipline. It was necessary, that the speaker formulated short messages and ended them with the word „Over“. If necessary, the recipient confirmed receipt with „Roger“. In English, Roger was the code word for the „R“ which stood for „Received“. When the participants were finished with the communication („hung up“ so to speak), the words „over and out“ stopped the communication. Besides these code words, some kind of spoken word for „SOS“ was required. Such an emergency word was already defined in the 1920s. According to legend, an Englishman had received a voice call from a French transmitter calling for help. The French called „m’aider“ so „help me“. However, the Englishman heard „May Day“ and couldn’t relate to it. When this Englishman was asked to find a code word for SOS, he suggested „May Day“. Since then, anyone in dire danger is using Mayday-Mayday-Mayday to call for help.

The first Handheld

On the American side, the Motorola company was working on a radio for use in World War 2 for the military. They also built a walkie talkie. The SCR300 weighed 16 kg and could be carried by a soldier like a backpack. Like all portable radios, it had two batteries, one 1.5V and one 105V. The second battery was only responsible for heating the tubes. The latest radio technology was used, namely frequency modulation at very high frequencies. It could be used for 8 miles and the batteries lasted about 40 hours.

But Motorola built yet another walkie-talkie that was so small that it could be held to your ear like a telephone receiver. It weighed 2.3 kg and could be easily used in the field. It had special small tubes like those used in popular portable radios. 4 were used for sending, all 5 for receiving. Although the device could work on many channels, it was permanently set to one channel in the field. If the more than 1 meter long antenna was pulled, the device was switched on and receiving. Pressing a large button switched to transmit. „Push-to-Talk“. In the field, this device proved to be of limited use because it was very sensitive and had a range of no more than 1-2 kilometers.