Going Wireless

An Old Radio and turned it on. We saw the ancient tubes We had a Philco radio that was about six light up with a dim glow and smelled the feet tall. It had 287 knobs on it, of which characteristic odor produced by a warm cir- only two worked: off-on-volume and the sta- cuit and carbonizing dust particles. We tion selector. -Bill Cosby, The Chicken Heart Routine checked the tubes to make sure that they were not loose and even replaced tubes that I grew up in an extended family in Tul- seemed to be going bad. Static was all that sa, Oklahoma. Often, I found myself in the we got for our reward. After a time we gave breakfast room of my grandparent’s house at up and let it sit there as an enigmatic muse- dinner or breakfast. I loved to eat there. It um piece that must have worked at least dur- was a fairly open room, dominated by a ing “the war”. large table in the center. Besides the tele- Although I was very unsuccessful with phone table, there was almost no other furni- that radio, I was fascinated by the idea of ture except a large Philco radio. It was a information arriving through the air. I or- floor model with beautiful veneer work and dered circuit boards and made circuit boards several knobs and a station selector panel. in many electronic projects that I attempted, That radio was witness to some of the best most of which were failures. However, I did meals and family stories, both of which not give up and did manage to make a sev- seem to grow better as memory dims. I also eral crystal radios, which included making remember that the radio never worked, at my own speakers. Mostly, I heard static, but least within my memory. Several times, my occasionally I heard words and music. cousins and I moved it away from the wall

Figure 1. A diagram of the electromagnetic (EM) spectrum which depicts the relative lengths of its component members. Note that visible light occupies a very small band and the range in wavelength goes from less than 10-13 cm to more than a kilometer. From nasa.gov. TABLE 1. Descriptions of the Electromagnetic spectrum. Note that radio waves have the longest wavelengths, the lowest frequencies, and the lowest energies of the components of the EM spectrum. http://imagine.gsfc.nasa.gov/docs/science/know_l1/spectrum_chart.html

Wavelength (m) Frequency (Hz) Energy (J)

Radio > 1 x 10-1 < 3 x 109 < 2 x 10-24 Microwave 1 x 10-3 - 1 x 10-1 3 x 109 - 3 x 1011 2 x 10-24- 2 x 10-22 Infrared 7 x 10-7 - 1 x 10-3 3 x 1011 - 4 x 1014 2 x 10-22 - 3 x 10-19 Visible 4 x 10-7 - 7 x 10-7 4 x 1014 - 7.5 x 1014 3 x 10-19 - 5 x 10-19 UV 1 x 10-8 - 4 x 10-7 7.5 x 1014 - 3 x 1016 5 x 10-19 - 2 x 10-17 X-ray 1 x 10-11 - 1 x 10-8 3 x 1016 - 3 x 1019 2 x 10-17 - 2 x 10-14 Gamma-ray < 1 x 10-11 > 3 x 1019 > 2 x 10-14

The EM Spectrum to measure the relative temperatures of a Rattlesnakes May Inject Venum Under light beam that was separated into its com- Xtreme aGitation. ponent colors by a prism. The highest tem- –a mnemonic for remembering peratures were in the red end of the visible the Electromagnetic Spectrum. light spectrum. However, when he placed Radio waves and microwaves range the thermometer beyond the red band, the from about 3 cm to more than 300 m long temperature was even higher. He called the (Table 1). The relative energy of the waves invisible light, calorific ray. Today, we call of the EM spectrum is the inverse of the it infrared light. The real importance was wavelength through the whole spectrum that he had demonstrated the existence of from gamma-rays to very long-wave radio. rays of “light” that exist, but are invisible to Only a very narrow band occupies the visi- the eye. ble range1; thus, most of the EM spectrum is Johann Ritter (Germany; 1776-1810), invisible and discovered only indirectly. during his short life, piled up a number of Frederick William Herschel2 (Germany inventions, including the dry cell battery and and England; 1738-1822) in 1800 attempted electroplating. Also, in the year following the discovery of infrared radiation, he began to search for an invisible light at the violet 1 The mnemonic for visible light is usually given as end of the visible light spectrum. He used the name, Roy G Biv (for red, orange, yellow, green, blue, indigo, and violet). Red has the longest wave- silver chloride and exposed it to different length and violet has the shortest wavelength. colors of light using the same method as Herschel. He noted that the red end of the 2 Herschel is most well-known for having discovered Uranus. For more about Herschel read The Planets, spectrum was relatively ineffective at de- an essay in Paths of Science by Jack Holt. composing silver chloride compared to the was the earlier development and used the violet end. When he exposed silver chloride activation of electromagnets to send a non- to “light” beyond violet, the breakdown oc- verbal code along a wire. The telephone curred even more effectively. Thus, he built upon the telegraph and utilized a mi- demonstrated that the visible spectrum was crophone to convert the human voice to straddled both above and below by invisible electric impulses through a wire, and the rays with different properties. At first, he impulses then created sound by activating a called this new light chemical ray, which we device similar to a microphone that func- know as ultraviolet radiation. tioned as a speaker. The greatest breakthrough came when Radio was a disputed technology like James Clerk Maxwell (United Kingdom, those of telephone and telegraph. The in- Scotland; 1831-1879) united electricity and vention of radio has been claimed by the magnetism into a set of equations that we Americans, Italians, Russians, and British. know as the Electromagnetic Theory3. His In truth, all participated in the invention. work implied that light was an electromag- Many of the participants were inventors in netic wave and that electromagnetic waves the old style with little mathematical or sci- of shorter and longer wavelengths must ex- entific training. David Edward Hughes (UK ist. Heinrich Rudolph Hertz (Germany; and USA; 1831-1900) and Thomas Alva Ed- 1857-1894) confirmed that electromagnetic ison (USA; 1847-1931) were such inventors. waves with wavelength of 0.66 meters could Indeed, Edison’s achievements were legend- be produced by one electrical circuit and ary, mainly due to his persistence and pa- received by another. The theoretical foun- tience. Both men had created radio trans- dation of wireless communication had been mitters and receivers long before Hertz suc- achieved. ceeded in doing so. However, they were discouraged by a mistaken understanding RADIO, EARLY DEVELOPMENTS that they were just dealing with electromag- I do not think that the wireless waves I have netic induction, thus, so they thought, the discovered will have any practical applica- phenomenon was nothing new. tion. Heinrich Rudolph Hertz Even the casual users of the early tele- phones were aware that if a spark jumped Radio did not emerge as a technology by across a loose wire in another circuit, they itself. It grew upon the technologies of the could hear a moment of static. The spark 4 5 telephone and telegraph . The telegraph had generated electromagnetic waves that were picked up by the telephone. This is the phenomenon that generally was mistaken for 3 Find more about James Clerk Maxwell and the Elec- electromagnetic induction until Hertz con- tromagnetic Theory in Electricity? What Good is It?, an essay in Paths of Science by Jack R. Holt. 5 The telegraph evolved together with successive 4 Although the true inventor of the telephone was developments in the technology of the electromag- disputed, the patent for the Telephone was awarded net. Samuel Finley Breese Morse (USA; 1791-1872) to Alexander Graham Bell (UK –Scotland and USA; was the first to patent a generally useful system to- 1847-1922) in March 1876. gether with a code made of dots and dashes. firmed that it was something different. free electrons in the wire to oscillate, thus Hertz died on January 1, 1894, after having making an alternating current. Because the developed a radio transmitter and receiver. radio waves provide all of the power to the crystal radio, the antenna wires have to be long. In fact, it should be at least one-fourth of the wavelength, which in the case of radio waves can be very long, indeed (see Table 1 and Figure 1). The antenna is not selective in which waves it receives, so if there is more than one radio source, the listener would just hear a cacophony of sounds. The tuner, which is a coil (see Figure 3), uses resonance6 to en- hance particular wavelengths, thus tuning in particular transmitting stations. For exam- ple, The carrying frequency for the local public radio station is 89.9 (89,900 Hertz or vibrations per second). Simple tuners are made of a simple coil with which the chan- nel is selected by running a contact over the wire, thus changing the length of the coil. The tuning coil in Figure 3 is more complex. FIGURE 2. Heinrich Rudolph Hertz. It has two coils that are independent of each Image from Wikimedia Commons. other. The inner coil is attached to the antenna and the outer coil is attached to the SIMPLE RADIOS rest of the radio. By moving the magnetite “Think simple” as my old mentor used to core in an out, the inductance between the say – meaning reduce the whole of its parts coils changes and allows for more selectivity into the simplest terms, getting back to first in tuning. The variable capacitor also allows principles. -Frank Lloyd Wright for the selection of a particular resonant frequency. When I was a boy, I remember making a The diode is an electronic device that very simple radio, one that did not require changes the alternating current that began in batteries. This was the crystal radio that had the antenna to direct current. This conver- a wire antenna, a coil of wire, a crystal (usu- sion is necessary to drive the speaker, ally of galena), and a small earphone. A which, in this case, is a small piezoelectric basic understanding of how these compo- earphone. In place of a diode, I used a crys- nents work together provides what you need to know about radio fundamentals. 6 For an explanation of resonance, read the essay, The antenna is a conductive wire that On a Performance of Durufle in Paths of Science by picks up radio electricity. This causes the Jack R. Holt. tal of lead-sulfide, called galena. It took signal, we have to convert sound waves to some patience to find just the right places to radio waves. This conversion is not just a put the wire leads on the cubic crystals, but simple reversal of what happens in the re- they worked. ceiver. The microphone is connected to a transformer (see Figure 4), which is similar in overall structure to the coil in Figure 3. The current in one coil induces current in another coil. Loud sound makes large vibrations in the microphone that translate to varying power to the transformer, which, in turn, sends varying current by induction to the oscillator. The oscillator causes the direct current to change to alternating current that sets the electrons in motion in the antenna. Thus, radio waves of a particular frequency leave the antenna. FIGURE 3. A simple crystal radio receiver The simple receiver (Figure 3) and showing its component parts. transmitter (Figure 4) were all that was nec- From sci-toys.com. essary to begin the technology of radio. Hertz had managed to make a transmitter and receiver, but they could neither use nor convert to sound. That step required several necessary innovations, which included the invention of the diode and ways to amplify the weak signal received by the antenna.

WHO INVENTED RADIO? Marconi is a good fellow. Let him continue. He is using seventeen of my patents. -Nikola Tesla

The coherer7, developed between 1884 and 1888, was a glass tube filled with iron filings, which functioned as an early ampli- FIGURE 4. A simple AM radio transmitter. fier. Similarly, that certain crystals could From sci-toys.com. change alternating current to direct current was discovered by Ferdinand Braun (Ger- A receiver is just half of the necessary technology. To send or transmit a vocal 7 The coherer was invented by Temistocle Calecchi- Onesti (Italy; 1853-1922) in 1888. many; 1850-1918) in 1874. This was an early diode or rectifier, as it was called then. Later, Braun developed a very small hair- like crystal diode that he called a cat’s whisker. This was the diode used in the early radios. Thus, by the time of Hertz’s death on January 1, 1894, almost all of the necessary components had been created in primi- tive forms. Alexander Stepanovich Popov (Russia; 1859-1906; Figure 5) was a physicist who repeated and augmented the experiments of Hertz. He even independently developed the coherer in 1894. After that, Popov built a radio and receiver and perfected its use as a lightning detector in 1895. At this point,

he had a working radio, which he demon- FIGURE 5. Alexander Stepanovich Popov. strated in March 1896. He expanded its Image in the Public Domain. range to 6 miles in 1898 and then to 30

miles in 1899. Unfortunately for him, Po- pov did not apply for a patent. Nikola Tesla (Croatia and USA; 1856- 1943; Figure 6) did think that electromagnetic waves had a promising future in wireless communication, a view that he present- ed in London in 1892. He claimed to have perfected the radio and used it to send and receive messages between 1895 and 1899. Though some of his claims are questionable, he did develop a reliable high-frequency oscillator, necessary to a reliable transmitter. Tesla was granted two U.S. patents for inventions related to the radio8.

8 Tesla became embroiled in some very public feuds FIGURE 6. Nikola Tesla. with Edison and later with Marconi. Early on he was Image in the Public Domain. quite famous and even declared the real inventor of the radio in a review by the U.S. Patent Office. How- ever, through his life he made increasingly question- Guglielmo Marconi (Italy; 1874-1937; able claims about his accomplishments and possible Figure 7) is generally recognized as the in- fantastic technological developments (like the death ray) and was ostracized at the end of his life. ventor of radio and shared the Nobel Prize in Physics in 1909 with Ferdinand Braun for and began to come to the world’s attention the development of radio technology. Cer- in 1897. He gave numerous demonstrations tainly, he did much to promote that technol- of the usefulness and reliability of his wireless communication system, which culmi- ogy and he marketed it and himself very nated in the first transatlantic transmission – well. He claimed to have read Hertz’s pa- the letter s. pers during 1894 and became introduced to At first, the Marconi system was called the possibility of wireless communication. wireless telegraph and was used for ship to Initially, he replicated the simple transmitter shore or ship to ship communication.. With and receiver of Hertz. improvements to his wireless system, communication became routine. Marconi telegraph was seen as the main reason any pas- sengers survived the sinking of the Titanic in 1912. The recognition by the public was in contrast with those who knew the technology that Marconi employed. Through the first four decades of the 20th Century, Mar- coni and his company fought lawsuit after lawsuit for patent infringement. Finally, the U.S. Supreme Court overturned most of Marconi’s patents. This was, in part a polit- ical move. The Marconi company was based in Fascist Italy, and Marconi himself had died in 1937. Other innovations made by the Marconi company were quite revolutionary. Ferdi- nand Braun had begun to work for the Mar- coni company, and there developed vacuum tube technology. The vacuum tube replaced the crystal rectifier or diode. The same FIGURE 7. Gugliemo Marconi. technology also made a reliable amplifier. Image in the Public Domain. Braun also created the large vacuum tube oscilloscope, which later evolved into the Hertz used a spark gap transmitter, television tube, a technology that lasted 100 which had been improved by Tesla for years. which he received a patent in 1891. This The general development of radio for the was a relatively simple technology in which home took off quickly after WWI. By that a spark between two electrodes generates time radio carrier waves transmitted sound electromagnetic waves in the antenna that is with fairly high fidelity. The public could attached to one electrode. Marconi connect- hear broadcasts of news and music. It was ed this transmitter to a telegraph key and not long before transmitters appeared with commercial wireless was born. He made programming that prompted many homes in some improvements in the coherer, but was the USA to have one for entertainment. able with his design to get increasingly The next great improvement in radio longer ranges. He went to Britain in 1896 technology came with the invention of tran- sistors in the early 1950s. These were semi- waves, and then amplify them10. With conductors, like the crystals that the vacuum shorter wavelengths, water droplets can de- tubes had replaced 50 years earlier. The ad- flect the waves and be used to follow vantage was that radios could be much storms. Now, Doppler radar is a standard smaller and require much less power to op- tool of meteorology. erate.

WHY RADIO WAVES? Although the atomic bomb ended World War II, in many ways radar won it. - Robert Buderi

While wireless communication was perfected through the 1930s, radio and its sib- ling technologies became very important during World War II. Certainly, rapid and accurate communication was vital. Radio began to be employed in other ways. Much earlier, Hertz had observed that radio waves bounced off metallic objects, and Marconi, in 1922, suggested that radio waves might be used as a collision avoidance system, es- pecially in fog-prone areas of the world. This paper, more than anything else, began to catch the attention of world governments for the development of a weapon system. By the beginning of WWII, particularly dur- FIGURE 8. Radar antenna at the Ronald ing the Battle of Britain, Radar9 was used to Reagan Test Site on Kwajalein Atoll. locate flights of German bombers and esti- Image in the Public Domain. mate their direction and speed. Radio waves work for their different ap- The most amazing applications of the plications because they are long waves that technologies of radio have come to fruition are not deflected by airborne particles, or by since the dawn of the Space Age. Now, the atoms in the air. Recall that radio and with radio coupled together with satellites, microwave wavelengths range from 1 cm to we have GPS, cell phones, together with al- > 1 km (see Figure 1 and Table 1). So, most instant communication anywhere in the 11 wavelengths less than half the size of an air- world . craft, but larger than dust particles and fog droplets, should bounce off of aircraft. Most of the energy, however, is deflected, rather 10 than returning to the antenna. Thus, the an- The parabolic surface of the antenna is like the tenna has to be designed to maximize the reflecting mirrors of reflecting telescopes like Hub- capture of the reflected electromagnetic bell. Read about the development of the reflecting telescope in the essay, A Man with a Telescope in Paths of Science by Jack Holt. 11 As an aside, I am writing this on a laptop computer 9 Radar is an acronym for Radio Detection And Rang- in a wireless environment while I sip hot coffee that I ing. heated in a microwave. RADIO TELESCOPES Australia; 1911-2002) built his own radio The real voyage of discovery consists not in telescope according to a parabolic reflector seeking new lands but seeing with new eyes. design (see Figure 10) in 1937 and began to -Marcel Proust map the sky in radio frequencies.

The same criteria that made radio waves useful for radar also make them useful for space exploration. Long wavelength electromagnetic waves pass through regions of dust and gas that are obscured when examin- ing them by the shorter visible light spectrum. In this case, though, the universe is filled with radio and microwave sources. The examination of the cosmos in the long-wave frequencies was first suggested by Karl Guthe Jansky (USA; 1905-1950; Figure 9) in 1933. Earlier, in 1931, he was using a large antenna to check the sky for radio signal that might interfere with radio telephone reception. He used an antenna that was about 100 feet across and reported detecting three kinds of signals. He identi- FIGURE 9. Karl Jansky. fied two of the signals as nearby thunder- Image from Wikimedia Commmons. storms and distant thunderstorms. The third signal was an almost constant hiss and bare- Reber worked almost alone through ly detectable. It was not constant, however. WWII. He moved to Hawaii and then to It was louder when pointed at certain parts Tasmania where the sky was not as cluttered of the sky, and the sequence of loud and soft with radio signals. Reber’s dogged per- hiss repeated on a daily cycle. Thus, he de- sistance paid off, and his work garnered termined that the source of the radio waves much interest during the post-war period. was extraterrestrial. Furthermore, when As with reflecting light telescopes, the pointed at roughly the center of the galaxy, ability to collect electromagnetic energy is a the hiss was loudest. His conclusion was function of the size of the reflecting surface. that radio might be a good medium to ex- The largest single radio telescope is the plore the universe. Arecibo Observatory in Puerto Rico (see Jansky was enthusiastic about his dis- Figure 11). Designed and built in the early covery and submitted a proposal for a large 1960s, the dish is about 300 meters (longest parabolic antenna, but his employer, Bell length of the inner surface) and it sits within Labs, was not. He was taken off of the pro- a depression made by a sinkhole. Thus, the ject and deployed elsewhere so he did no dish cannot be moved. The telescope is di- more work on radio astronomy. Because the rected onto different parts of the sky by world was in the throes of the Great Depres- moving the detector. This huge telescope sion, his work almost was forgotten even has been used for much ground-breaking though it had been widely publicized in the research. During its first 10 years, the popular press. Fortunately, he did inspire Arecibo Observatory was instrumental in others. In particular, Grote Reber (USA & discovering the rotation rate of Mercury, the confirmation of the existence of neutron stars, the discovery of the first binary pulsar, and the first millisecond pulsar. It also has been involved in the effort to map asteroids and near earth objects that pose a threat to the earth. In addition, it has been one of the major sites for the Search for Extraterrestrial Intelligence (SETI) Project.

FIGURE 11. Arecibo Observatory, the world’s largest radio telescope, is in north- western Puerto Rico and sits in a sinkhole. The image is in the Public Domain.

FIGURE 10. This is the first parabolic radio antenna built by Grote Reber in 1937. The radio waves are collected and focused by the parabolic dish onto the detector that is sus- pended above the center of the dish. This is the common design for radio telescopes and FIGURE 12. The center of the Milky Way radar. Galaxy in radio frequencies. It is complete- ly obscured by dust and gas in the visible The Very Large Array (VLA) in New light spectrum. The arrow points to rem- Mexico uses multiple radio telescope dishes nants of a supernova explosion. in a giant Y-pattern. This creates a recep- Image in the Public Domain. tion that could equal a dish with a diameter of 21 km. The dishes, each of which is 25 From its inception at the end of the 19th meters across can move on a rail system so Century, radio and its offspring have made that the diameter can contract to 600 m, us more comfortable. Communication has which is twice the size of Arecibo. The become almost instantaneous and universal. VLA is used to study quasars, pulsars, su- As a technology, radio has allowed many pernovae and their remnants (Figure 12), practical things, but as a tool of science, ra- gamma ray bursts, black holes, among other dio has given us new eyes. astronomical phenomena. -Jack R. Holt, 2010 References: Marconi, G. 1922. Radio Telegraphy. Pro- ceedings of the Institute of radio Engi- Baird, D., R.I.G. Hughes, and A. Nordmann, neers. 10: 215–238. eds. 1998. 'Heinrich Hertz: Classical Page, R. M. 1962. The Origin of Radar. Dou- Physicist, Modern Philosopher. Springer- bleday Press. New York. Verlag. New York. Radovskii, M. I. 1957. Alexander Popov, Inven- Birch, B. 2001. Guglielmo Marconi: Radio Pio- tor of Radio. Foreign Language Pub. House. neer. Blackbirch Press. Woodbridge, CT Moscow. Bodanis, D. 2006. Electric Universe: How Elec- Seifer, M. J. 1998. Wizard, The Life and Times tricity Switched on the Modern World. Three of Nikola Tesla. Biography of a Genius. Rivers Press. New York. Citidel Press. New York. Bryant, J. H. 1988. Heinrich Hertz, the Begin- Spadley, J. L. 1988. The First True Radio Tele- ning of Microwaves: Discovery of Electro- scope. Sky and Telescope. 76(1): 28-30. magnetic Waves and Opening of the Elec- Tesla, N. 1892. Experiments with Alternating tromagnetic Spectrum by Heinrich Hertz in Currents of High Potential and High Fre- the Years 1886-1892. IEEE (Institute of quency. Delivered before the Institution of Electrical and Electronics Engineers). New Electrical Engineers, London, February York . 1892. Buchwald, J. Z. 1994. The Creation of Scientific Tesla, N. 1893. On Light and Other High Fre- Effects : Heinrich Hertz and Electric Waves. quency Phenomena. Delivered before the University of Chicago Press. Chicago. Franklin Institute, Philadelphia, February Buderi, R. 1996. The Invention That Changed 1893, and before the National Electric Light the World, How a small group of Radar Pi- Association, St. Louis, March 1893. oneers won the Second World War and Trinkaus, G. 1988. Tesla: The Lost Inventions. launched a technological revolution. Simon High Voltage Press. Portland, OR. & Schuster. New York. Feldman, P. A. 1988. Grote Reber: Yester- Ruling of the U. S. Patent Office regarding the day and Today. Sky and Telescope. patent infringement lawsuit Tesla vs Marconi: 76(1): 31. Many of the claims are not patentable over Jansky, K. G. 1933. Radio waves from outside Tesla patent numbers 645,576 and 649,621, the solar system. Nature 132: 66. of record, the amendment to overcome said Kraeuter, D. W. 1992. Radio and Television Pi- references as well as Marconi's pretended oneers: A Patent Bibliography. Scarecrow ignorance of the nature of a "Tesla oscilla- Press. Metuchen, NJ: tor" (a.k.a. Tesla Coil) being little short of Kraus, J. D. 1988. Grote Reber - Founder of absurd... the term "Tesla oscillator" has be- Radio Astronomy. R.A.S. Canada. Jour- come a household word on both continents nal. 82(3/Jun): 107. [Europe and North America]. Kruger, Albrecht. 1979. Introduction to Solar Astronomy and Radio Physics. Geophysics –U.S. Patent Office, 1903. and Astrophysics Monographs, vol. 16. D. Reidel Publishing. Co. Dordrecht; Boston. pp. 1 - 2. Lodge, O. J. 1900. Signalling across space without wires: Being the description of the work of Hertz and his successors. Reprint 1974, Arno Press Inc. New York. Manly, P. 1995. Unusual Telescopes. Cam- bridge University Press. Cambridge.