Radio 8: A Brief History of Wireless Communication

This passed forward from Mark Hurwitt of the New Energy Movement.

Introduction

Fields in science and engineering can quickly become specialized as knowledge increases. For example the celebrated textbook “Electronic and Radio Engineering” by Frederick Terman of Stanford University (1955) does not mention Maxwell in the name index of a text over a thousand pages long. And no one in physics would ask a PhD student on an oral exam to explain super-hetrodyne radio receivers.  To illuminate the latter topic this article reviews briefly the history of wireless communication and the contributions of some of the pioneers in the field. Another goal is to try to relate the contributions of physicists to this enormous endeavor.

 

—– Original Message —–
From: Mark Hurwit
Sent: Monday, March 04, 2013 2:38 PM
Subject: History of Wireless Communications

A recent computer client is a retired physicist, who shared with me a paper he’d written.
Still kind of interesting for the non-geeky (just… to see how things go), I thought you might
like to gander at a slightly enhanced version. (It’s a bit like parts of Breakthrough Power.)

Mark

- – - -

Here’s the article. You can also download (2 Mb PDF) it with higher resolution versions of the images shown below.

Radio 8: A Brief History of Wireless Communication

R. E Hershberger and R. J. Donnelly|
Department of Physics. University of Oregon

Introduction

Fields in science and engineering can quickly become specialized as knowledge increases. For example the celebrated textbook “Electronic and Radio Engineering” by Frederick Terman of Stanford University (1955) does not mention Maxwell in the name index of a text over a thousand pages long. And no one in physics would ask a PhD student on an oral exam to explain super-hetrodyne radio receivers.  To illuminate the latter topic this article reviews briefly the history of wireless communication and the contributions of some of the pioneers in the field. Another goal is to try to relate the contributions of physicists to this enormous endeavor.

 

Amateur Radio
The development of wireless was not confined to electrical engineers. The Radio Club of America was founded in 1909 and the American Radio Relay League (ARRL) in 1914. The idea of “relay” owed its inception to the fact that although early transmitters had a quite limited range, relays of stations could transmit messages across the country. Today the ARRL has about 154,000 members.

 

The somewhat derisive term “ham” is often applied to these people, but it just means “Amateur Radio Operator”. The ARRL started publishing the Radio Amateur’s Handbook in 1926. It is a very reliable source of information on electronics and for many physicists was their first contact with practical electronics. The last few pages of the Handbook contained advertisements of vendors of receivers, transmitters and parts. One prominent ad was from the “Radio Shack” in Boston, an enterprise that has evolved into a retail electronics giant.

 

In earliest days communication by radio was done using Morse code as voice transmission was not yet possible. The examination for a license to use amateur radio involved testing the ability to use Morse code as well as some rudimentary electronics. (The Morse code requirement has since been dropped.) On passing the exam the applicant was given a license to broadcast and assigned “call letters”, like W1AW. One favorite occupation was to look for (“work”) or contact with ham operators in distant states and other countries by signaling “CQ” (seek you). Since there was a need for economy of words for beginners especially, a large number of sometimes amusing shortcuts were invented. For example the girlfriend would be the young lady “YL” and the wife would be the “XYL”. On completing such a contact the operators would exchange QSL cards, usually colorful post cards with the call letters and address of the station. The walls of “radio shacks,” often the operator’s bedroom, basement or garage were often covered with QSL cards. One benefit to the country is to have thousands of trained operators available for emergencies and to fill the ranks of communication officers in time of war or national disaster like Katrina.

 

Amateur Radio as a Background to Physics

It is clear that many physicists considered interest in amateur radio a sure path to a technician’s job.  But as the former VE3AXF (RJD) found, designing, building and modifying electronics on a limited budget (from one’s own pocket) is very good training for research in physics where one often has to design and build new instruments with limited funding and very limited time.

 

Physicists born in the 1920s and 1930s often came to the field of physics through amateur radio by at least building radio receivers and audio amplifiers in their own homes. One reason was the happy circumstance that the circuits were simple enough that one could afford to buy the few parts needed with very little expenditure. The chassis were available at modest cost and with electric drills and tube hole cutters one could assemble a radio receiver, audio amplifier or even amateur radio transmitter at home. Learning how to make neat solder joints became a high art for many gifted hams. Tubes and transformers for power supplies were available cheaply, and at the end of WWII quite sophisticated electronic parts were available in surplus stores.

 

fig-01a_Hershberger_500

FIGURE 1a: Appearance of the top of the chassis of a home-made
receiver in the 1960’s. From the Radio Amateur’s Handbook 1968.

 

fig-01b_Hershberger_500

FIGURE 1b: Appearance of the under-chassis of the chassis of a home-made
receiver in the 1960’s. From the Radio Amateur’s Handbook 1968.

Physics students who had amateur radio experience found it relatively easy to build and service their own electronics. While that seems an obvious advantage to a thesis advisor, there was a distinct disadvantage. Some senior physicists actually considered the ability to build and service one’s own electronics as a sure sign of the inability to do fundamental research. One of us (RJD), then teaching at Chicago, was having lunch with the distinguished x-ray metallurgist Charles Barrett and Ernest Lawrence (of Berkeley) when another faculty member joined us. He was furious with one of his graduate students who had spent all night “working” his amateur radio instead of working on his thesis. He announced firmly that he never knew a physicist who was a radio amateur who ever amounted to anything in research. The three of us quickly recited our call letters in Morse code.

 

Heinrich Hertz

Hertz was the first to send and receive radio waves. James Clerk Maxwell had predicted their existence mathematically in 1864.  Between 1885 and 1889, as a professor of physics at Karlsruhe Polytechnic in Germany, Hertz produced electromagnetic waves in the laboratory and measured their wavelength and velocity. He showed that the nature of their reflection and refraction was the same as those of light, confirming that light waves are electromagnetic radiation obeying the Maxwell equations. The unit of frequency is named in his honor.

fig-02_Hershberger_500

FIGURE 2: Heinrich Hertz experiments.  The Leyden jar was an early design of a capacitor.

 

Spark Transmitters

Hertz’s device shown in Figure 2 is essentially the same device used for ship to shore communication in the early 20th century. Physicists experimenting at home in the 1930s used spark coils from the early Ford Model T cars, which could be found at almost any dump yard for about 25 cents. About 20,000 volts was generated with plenty of spectral power in the audio range, and hence could be used with a crystal set receiver.

 

Spark transmitters were messy to use and investigators tried to improve them. Many investigators came to understand the need for sinusoidal waves and improvements on the simple spark transmitter were developed, including the rotary spark gap and the Poulsen arc (a “singing arc: which could work up to 200 kHz and was patented in 1903). The rotary spark gap had a rotating cylinder with a number of electrodes. A spark could be established with one rotating electrode and a fixed electrode, and when the cylinder turned the spark was started between the next electrode and the previous spark tended to stop.

 

Spark gap transmitters were used for ship to shore communications. A typical shipboard spark transmitter is shown below in Fig. 3.

 

fig-03_Hershberger_500

FIGURE 3: Shipboard spark transmitter

 

Guglielmo Marconi and Nicolas Tesla

Guglielmo Marconi and Nicolas Tesla were pioneers in the field of wireless communication. Marconi was born in Bologna of an Italian father and an Irish mother. He shared the 1909 Nobel Prize in Physics with Karl Ferdinand Braun “in recognition of their contributions to the development of wireless telegraphy.” Marconi began experiments in his childhood home in Italy, achieving transmission distances of about 2.4 km. Unable to interest the Italian government, he moved to England in 1896 as he also spoke fluent English. His early success was in demonstrating year by year increasing distances over which messages could be sent, culminating in the first overseas transmission from the UK to Newfoundland in Canada. He became successful as an entrepreneur, businessman, and founder of the The Wireless Telegraph & Signal Company in Britain in 1897.

 

Tesla is best known for developing the modern alternating current (AC) electrical supply system. His many revolutionary developments in the field of electromagnetism in the late 19th and early 20th centuries were based on the theories of electromagnetic technology discovered by Michael Faraday (1791-1867). Tesla is also famous for his invention of the Tesla coil round 1891. The Tesla coil is an electrical resonant transformer circuit producing high-voltage, low current, high frequency alternating current electricity. It is a great improvement over electrostatic machines. Tesla coil circuits were used commercially in spark gap transmitters until the 1920s. The unit of magnetic flux density is named in his honor.

 

Origin of the word Radio

The Oxford English Dictionary has many pages on the word Radio. The earliest is the independent use of radio derived from radio-telephony and radio-telegram in the early 20th century. It is tempting to think of parallels with words like “radius” describing something spreading out, but any connection is unproven.

 

 

 

 

Crystal Radios

Crystal radios are the simplest type of radio receiver and can be handmade with a few inexpensive parts, like an antenna wire, tuning coil of copper wire, crystal detector and earphones. They are distinct from ordinary radios because they are passive receivers, while other radios use a separate source of electric power such as a battery or the mains power to amplify the weak radio signal from the antenna so it is louder. Thus crystal sets produce rather weak sound and must be listened to with earphones, and can only pick up stations within a limited range.

The rectifying property of crystals was discovered in 1874 by physicist Karl Ferdinand Braun (who shared the Nobel Prize in Physics with Marconi, and is also famous for the invention of the cathode ray tube). Crystal detectors were developed and applied to radio receivers in 1904 by Jagadish Chandra Bose, G. W. Pickard and others. Crystal radios were the first widely used type of radio receiver, and the main type used during the wireless telegraphy era. Sold and homemade by the millions, the inexpensive and reliable crystal radio was a major driving force in the introduction of radio to the public, contributing to the development of radio as an entertainment medium around 1920.

 

fig-04_Hershberger_500

FIGURE 4: Rudimentary crystal set

 

 

The Edison Effect.

Thomas Edison,1880, experimenting with his early incandescent lamp, stumbled on the basic principle of the electronic vacuum tube. Seeking to find out why filaments burned out, he inserted a metal plate in the lamp ( Fig. 5 below), connected it with a battery and discovered that a tiny but measurable current flowed across the empty gap from hot filament to plate provided the plate was at a positive potential with respect to the filament.

 

Following J. J. Thomson’s identification of the electron, the British physicist Owen Willans Richardson began work on the topic that he later called “thermionic emission”. He received a Nobel Prize in Physics in 1928 “for his work on the thermionic phenomenon and especially for the discovery of the law named after him.”

fig-05_Hershberger_500

FIGURE 5: Edison effect and the Fleming valve

 

The Fleming Valve

John Ambrose Fleming was born in 1849 in Lancaster, England, and educated at University College School, London and University College, London. As he did not come from a wealthy family, Fleming alternated between paying jobs and more schooling, finally studying with James Maxwell at Cambridge University. Maxwell’s lectures, he remarked, were difficult to follow. Maxwell often appeared obscure and had “a paradoxical and allusive way of speaking”. On occasion Fleming was the only student at those lectures. Eventually he was appointed the first Professor of Electrical Engineering at University College London,

 

In 1904 Fleming, discovered that the Edison Effect could be used to detect wireless signals. He curved Edison’s plate into a cylinder around the filament and called the device a valve. When the plate was coupled with an aerial, as shown in the circuit diagram below, it was rapidly alternated from positive to negative by the incoming waves, causing it alternately to attract and repel the tiny current from the filament, thus reproducing the signals in direct current to the headphones. But the Fleming valve, like the crystal detector, had no means of amplifying these signals. That had to wait for the development of the triode.

 

Mixers

Mixers are nonlinear devices such as crystals and other diodes as well as transistors. It is not hard to show that amplitude modulated sinewaves at frequencies and  in a nonlinear device will contain frequencies  and with frequencies , , . The sum and difference frequencies are sometimes called sidebands, and the multiples are called harmonics. If  is close to (and indeed may be from a local oscillator), then may be called the “carrier”, and the sums and differences are often called “sidebands”.

 

Reginald Fessenden

Reginald Fessenden was born in Canada in the province of Quebec in 1866, and died in 1932. He received an excellent classical education including science, mathematics and languages in various schools. Hoping to increase his technical skills he moved to New York City in 1886 and eventually became chief chemist with Thomas Edison. He went on to teach at Purdue University and the University of Pittsburgh. It was there that he became interested in wireless telephones. In 1900 Fessenden began to work with the United States Weather Bureau to develop a series of wireless stations to transmit weather information thus avoiding land lines.

 

The term “heterodyne” was introduced by Fessenden describing his proposed method of producing an audible signal from the Morse code transmissions of an Alexanderson alternator-type transmitter (see below). With the spark gap transmitters then in use, the Morse code signal consisted of short bursts of a heavily amplitude modulated carrier wave which could be clearly heard as a series of short chirps or buzzes in the receiver’s headphones. However, the signal from an Alexanderson alternator did not have any such inherent modulation and Morse code from one of those would only be heard as a series of clicks. Fessenden’s idea was to run two Alexanderson alternators, one producing a carrier frequency 3 kHz higher than the other. In the receiver’s detector the two carriers would beat together to produce a 3 kHz tone (see mixers above) thus in the headphones the Morse signals would then be heard as a series of 3 kHz beeps. For this, the classically-trained Fessenden coined the term “heterodyne” from the Greek “hetero” meaning “different” and “dyne” meaning “power”.

 

By 1906 Fessenden had two ways of making a (somewhat) sinusoidal carrier wave for broadcast. One was the rotary spark gap and the other was the Alexanderson alternator (described below). Fessenden is often credited with the first voice broadcast. The story goes that on the evening of December 24, 1906, Fessenden used the alternator-transmitter to send out a short program from his laboratory at Brant Rock Massachusetts . The broadcast celebrated Christmas Eve by including a phonograph record of Ombra mai fu (Largo) by Handel, followed by Fessenden himself playing the song “O Holy Night” on the violin. Finishing the broadcast with a passage read from the Bible: “Glory to God in the highest and on earth peace to men of good will.” He petitioned his listeners to write in about the quality of the broadcast as well as their location when they heard it. Surprisingly, his broadcast was heard several hundred miles away. On December 31, New Year’s Eve, a second short program was broadcast. The main audience for both these transmissions was an unknown number of shipboard radio operators along the East Coast of the United States. Fessenden claimed that the Christmas Eve broadcast had been heard as far down as Norfolk, Virginia, while the New Year’s Eve broadcast had reached places in the Caribbean. Although now seen as a landmark, these two broadcasts were barely noticed at the time and soon forgotten. There is also uncertainty as to which carrier device was used for either of these broadcasts.

 

Alexanderson Alternator

In 1904, Reginald Fessenden contracted with General Electric for an alternator that generated a frequency of 100,000 hertz for continuous wave radio. The alternator was designed by Ernst Alexanderson. The Alexanderson alternator was extensively used for long wave radio communications by shore stations, but was too large and heavy to be installed on most ships. In 1906 the first three 50 kilowatt alternators were delivered. One was to Reginald Fessenden at his Brant Rock laboratory in Massachusetts.

fig-06_Hershberger_500

FIGURE 6: Sketch of one model of the Alexanderson alternator. Only the top half of the rotor
is shown. The rotor contains no coils: it has a series of holes on the circumference filled with
non-magnetic material so that the magnetic reluctance is modulated at a frequency given
by the product of the rotation rate and the number of holes.

 

Alexanderson would receive a patent in 1911 for his device. The Alexanderson alternator followed Fessenden’s rotary spark-gap transmitter as the second radio transmitter to be modulated to carry the human voice. Until the invention of vacuum tube (valve) oscillators such as the Armstrong oscillator in 1913, the Alexanderson alternator was an important high-power radio transmitter, and allowed amplitude modulation radio transmission of the human voice. The last remaining operable Alexanderson alternator which is at the very low frequency transmitter at Grimeton in Sweden, was in regular service until 1996.

Lee De Forest

Lee De Forest enrolled in the Sheffield Scientific School of Yale University in 1893 receiving his bachelor’s degree in 1896 and his Ph.D. degree in physics in 1899 with a dissertation on radio waves. For the next two years, he was on the faculty at the Armour Institute of Technology and Lewis Institute (the two institutions merged in 1940 to become the Illinois Institute of Technology) and he conducted his first long-distance broadcasts from the university.

 

In January 1906, De Forest filed a patent for a diode vacuum tube detector, a two-electrode device for detecting electromagnetic waves, a variant of the Fleming valve invented two years earlier. One year later, he filed a patent for a three-electrode device that was a much more sensitive detector of electromagnetic waves. It was granted US Patent 879,532 in February 1908. The device was also called the De Forest Valve, and since 1919 has been known as the triode. De Forest’s innovation was the insertion of a third electrode, the grid, between the cathode (filament) and the anode (plate) of the previously invented diode. The resulting triode or three-electrode vacuum tube could be used as an amplifier of electrical signals, notably for radio reception. Called the Audion, it was the fastest electronic switching element of the time, and was later used in early digital electronics (such as computers). Until the 1948 invention of the transistor, the triode was essential for the development of transcontinental telephone communications, radio, and radar.

fig-07_Hershberger_500

FIGURE 7: “Triode” Audion from 1908. (The 1906 Audion was a 2-element device
with the signal applied to a wire wrapped around the glass envelope.)

 

De Forest did not completely understand how the triode worked. He had initially claimed that the operation was based on ions created within the gas in the tube (hence the name), when in fact it was shown by others to operate with a vacuum in the tube. The device was subsequently investigated by H. D. Arnold and his team at Western Electric (AT&T) and Irving Langmuir at the General Electric Corp, both of whom correctly explained the theory of operation of the device, and provided significant improvements in construction.

 

Edwin Howard Armstrong

The inventions of engineer Edwin Howard Armstrong were so important that to this day every radio or television set makes use of one or more of his developments. Born in New York City, Armstrong earned a degree in electrical engineering from Columbia University in 1913. While in college, he invented the regenerative circuit, which was the first amplifying receiver and the first reliable continuous-wave transmitter.

 fig-08_Hershberger_500

FIGURE 8: Regenerative circuit

In 1918, he invented the superheterodyne circuit (shown in Fig. 9), a highly selective means of receiving, converting, and greatly amplifying very weak, high-frequency electromagnetic waves. Even today it is the most used radio receiver for domestic. There are likely scores of variants available, but the standard AM broadcast band is 535 to 1605 kHz. A tunable local oscillator is used to provide an intermediate frequency of 455 KHz with high gain and a bandwidth of about 10 kHz.  This is followed by a detector and audio amplifier feeding a loudspeaker.

fig-09_Hershberger_500

FIGURE 9: Block diagram of a simple superheterodyne receiver.

A little feedback greatly increased the sensitivity of the circuit, and with some modification can become a oscillator or transmission circuit. Armstrong was mostly interested in receivers did not recognize the importance of the transmission circuit in his parent application, which led to considerable confusion in later patent suits.

fig-10_Hershberger_500

FIGURE 10: Variable capacitor used to tune the local oscillator

in a superheterodyne receiver and hence select the station to be heard.

 

Frequency Modulated Receiver

Atmospheric noise, especially from lightning has frequency components in the audio range. Anyone listening to AM broadcasts in the 1930’s will appreciate how distracting this can be. After a long search for a solution to this problem Armstrong invented the FM receiver in 1933.

 

Broadcast FM covers the frequency range 88-108 MHz and employs an intermediate frequency of 10.7 MHz. The block diagram is much the same for a superheterodyne receiver except for two stages. The limiter circuit cuts off any high amplitude modulation that has been picked up in transmission, and the discriminator which converts frequency variations to amplitude variations.

 

Michael Pupin

In 1874 at age 16, Mihajlo Idvosky Pupin immigrated to the United States from what is now Serbia. Within several years he had mastered English and prepared himself academically to enroll in Columbia College, where he was awarded the B.A. degree in 1883. A brilliant student, he won fellowships to study at Cambridge University and the University of Berlin, where he earned the Ph.D. degree in 1889.

He returned to Columbia and became Instructor of Mathematical Physics, and played a key role in founding the Columbia Department of Electrical Engineering. Apparently Fleming and Pupin, both physicists, decided that electrical engineering deserved to have a separate undergraduate curriculum.
Pupin was very important in Armstrong’s career, and backed him where other faculty were not particularly supportive. It must have been significant in Armstrong’s research to be in constant contact with a first class physicist. Pupin died in 1935. Shortly after his death, the Columbia University Trustees named the university’s new physics laboratory building “Pupin Hall” in his honor.

 

Armstrong had become independently wealthy from royalties on his inventions, and drew neither a salary nor taught many classes as professor of electrical engineering at Columbia University. His idea was to support his research by income from his own inventions. When patent disputes arose (which they did frequently) he was a single person fighting corporations like General Electric, RCA and AT&T. Their relentless attacks eventually ruined his health and he killed himself in 1954.

 

FIGURE 11: Pictures of some prominent people in the history of wireless communication.

Left to right from the top row:

James Clerk Maxwell 1831-1879; Heinrich Hertz 1857-1894; John Fleming 1849-1945;
R. Fessenden 1866-1932; G. Marconi1874-1937; N. Tesla 1856-1943;
Edwin Armstrong 1890-1954; Lee De Forest 1873-1961.

 fig-11a_Hershberger_rd

fig-11b_Hershberger_rd

See also