CHAPTER 1
Introduction

1.1 BEGINNING OF WIRELESS

WIRELESS TELEGRAPHY-At a time when relations are strained between Spain and this country, nothing could be more welcome than a practical method of carrying on electrical communication between distant points on land, and between ships at sea, without any prearranged connection between the two points. During the last year Guglielmo Marconi, an Italian student, developed a system of wireless telegraphy able to transmit intelligible Morse signals to a distance of over ten miles. It has been left, however, for an American inventor to design an apparatus suitable to the requirements of wireless telegraphy in this country. After months of experimenting, Mr. W. J. Clarke, of the United States Electrical Supply Company, has designed a complete wireless telegraphy apparatus that will probably come rapidly into use.

-Scientific American April, 1898

This announcement appeared near the beginning of radio technology. Webster's dictionary [1] lists over 150 definitions that begin with the word radio, the first being:

1a. . the transmission and reception of electric impulses or signals by means of electromagnetic waves without a connecting wire (includes wireless, television and radar).

This remains today the real definition of wireless and, equivalently, radio. Today the uses of radio communication include not only the broadcast of sound through amplitude modulation (AM) and frequency modulation (FM) radio and video through television, but also a broad collection of radio applications, cordless telephones, cell phones, TV, and VCR remotes, automobile remote door locks, garage door openers, and so on.

There is some question about who actually invented radio as a communicative method. Mahlon Loomis, a dentist, experimented with wireless telegraphy using wires supported by kites and a galvanometer to sense the changes in current flow in a second wire when the ground connection of the first was interrupted. He received a patent in 1873 for this system [2].

James Clerk Maxwell [3], more about Maxwell's equations later, predicted the propagation of electromagnetic waves through a vacuum in about 1862. Nathan Stubblefield, a Kentucky farmer and sometimes telephone repairman, demonstrated wireless telephony as early as 1892, but to only one man, and in 1902 to a group [2].

Alexander Popov is said to have "utilized his equipment to obtain information for a study of atmospheric electricity . On 7 May 1895, in a lecture before the Russian Physicist Society of St. Petersburg, he stated he had transmitted and received signals at an intervening distance of 600 yards" [4]. In 1888 Heinrich Hertz conducted an experimental demonstration in a classroom at Karlsruhe Polytechnic in Berlin of the generation and detection of the propagating electromagnetic waves predicted by Maxwell [2].

Sir Oliver Lodge, a professor at Liverpool University was experimenting with wireless telegraphy in 1888, and he patented a system in 1897. Marconi purchased his patent in 1911 [2].

In the public mind Guglielmo Marconi enjoys the most credit for "inventing" radio. He was awarded patents for it; therefore, the Patent Office believed that he had made radio-related inventions. However, the U.S. Navy report [4] states

Marconi can scarcely be called an inventor. His contribution was more in the fields of applied research and engineering development. He possessed a very practical business acumen, and he was not hampered by the same driving urge to do fundamental research, which had caused Lodge and Popoff to procrastinate in the development of a commercial radio system.

This is perhaps the most accurate description of Marconi's role in developing radio technology, a new communication medium. Nikola Tesla had earlier patents, although the focus of his work appears to have been directed to the transmission of power rather than to communication via radio waves. Tesla, well known for his Tesla coil that generated high voltages, actually detected signals consisting of noise bursts, resulting from the large atmospheric electrical discharges he originated, that had traveled completely around the earth. In 1943 the U.S. Supreme Court ruled that Marconi's patents were invalid due to Tesla's prior descriptions, but by that time both Marconi and Tesla were deceased [2].

From its beginnings around 1900, radio moved out to fill many communicative voids. In 1962 George Southworth, a well-known researcher in the field of microwaves, wrote a book about his 40 years of experience in the field [5, p. 1]. He begins:

One of the more spectacular technical developments of our age has been radio. Beginning about the turn of the century with ship-to-shore telegraphy, radio has been extended through the years to intercontinental telegraphy, to broadcasting, to radio astronomy and to satellite communications.

Today, after an additional 40 years, Southworth could make a much longer list of radio applications. It would include garage door openers, global positioning satellites, cellular telephones, wireless computer networks, and radar applications such as speed measurement, ship and aircraft guidance, military surveillance, weapon directing, air traffic control, and automobile anticollision systems. The frequency spectrum for practical wireless devices has expanded as well. Amplitude modulated radio begins at 535?kHz and television remote controls extend into the infrared.

The advance of wireless applications is not complete and probably never will be. Certainly the last decade has seen an explosive growth in applications. And the quantities of systems has been extraordinary, too. Witness the adoption of the cellular telephone, which today rivals the wired telephone in numbers of applications.

Sending signals over telegraph wires formed the basis for the early wireless technology to follow. Using the Current International Morse code characters for the early Morse code message transmitted over the first telegraph wires, the first message inaugurating service between Baltimore and Washington, D.C., in 1843, would have looked like

Most of the full code cipher is shown in Figure 1.1-1. Morse code remains useful, although fewer individuals can interpret it on the fly. A distress signal using the code in Figure 1.1-1 can be sent using a transmitting radio or even a flashlight. Marconi's early wireless transmissions used pulse code modulation, dots and dashes achieved by keying the transmitter on and off. Some nautical buoys are identifiable by the Morse letter that their lights flash.

Figure 1.1-1 International Morse Code remains a standard for distress signals, S.O.S. is (. - - - .)

(English Characters, [1]). Derived from the work of Samuel Morse (1791-1872).

Today, Marconi would need a transmitting license, and were he to continue with his prior transmission technique, his license almost certainly would be suspended due to the broad spectrum of his transmissions (Fig. 1.1-2). His RF source was a spark gap oscillator (Fig. 1.1-3), likely occupying a very broad transmission bandwidth. Powered by a several horsepower generator, the operating transmitter was audible without a radio receiver for several miles.

Figure 1.1-2 Modulation format for Morse code, illustrated for letter R. Today, pulse shaping, as suggested above, would be employed to reduce transmission spectrum, but Marconi's spark gap transmitter doubtless spanned an enormously wide bandwidth.

Figure 1.1-3 Joel Earl Hudson standing by Marconi's spark gap transmitter in 1907.

(Photo courtesy of Cape Cod National Seashore.)

Marconi had his pivotal triumph in December, 1901, when the Morse character "s" was received at St. John's, Newfoundland (Figs. 1.1-4 and 1.1-5). It was transmitted from Poldhu, Cornwall England, 1800 miles across the Atlantic Ocean [5, p. 13; 6, p. 4]. From the South Wellfleet station, Marconi, himself, transmitted the first trans-Atlantic message on January 17, 1903, a communication from the president of the United States to the king of England.

Figure 1.1-4 Prime power for Marconi's South Wellfleet transmitter.

(Photo courtesy of Cape Cod National Seashore.)

Figure 1.1-5 Marconi's first wireless station in South Wellfleet, Cape Cod, Massachusetts. Local residents predicted that antennas would blow down in first good storm. They did, and he rebuilt them.

(Photo courtesy of Cape Cod National Seashore.)

Figure 1.1-6 Guglielmo Marconi (left) received the Nobel Prize for his wireless communication work. He is shown in a 1901 photo with assistant George Kemp shortly after a successful wireless transmission test.

(Photo courtesy of Marconi, Ltd., UK.)

1.2 CURRENT RADIO SPECTRUM

Today's radio spectrum is very crowded. Obtaining a commercial license to radiate carries the obligation to use bandwidth efficiently, using as little bandwidth as practical to convey the information to be transmitted (Tables 1.2-1 and 1.2-2).

TABLE 1.2-1 General Frequency Band Designations

Source: From Reference [7, Section...