Digital Wireless Basics

This article discusses digital wireless basics. It covers wireless history along with basic radio principles and terms. Digital building blocks like bits, frames, slots, and channels are explained along with details of entire operating systems. Building on my analog cellular article, digital cellular gets treated along with the newest service: personal communication services or PCS.

Where we are now?

Wireless has gone digital, enabling services that analog couldn't easily provide. Like better eavesdropping protection, increased call capacity, decreased fraud, e-mail delivery, and text messaging. But digital has its drawbacks, especially poor coverage and often bad audio quality.We'll compare newer digital systems like GSM and PCS1900 with systems like analog and early digital cellular. We'll better understand where wireless is today and where it's headed.

New and existing wireless services share much in common. They all provide coverage using a cellular like network of radio base stations and antennas. They all use mobile switches to manage that network, allowing calls, arranging handoffs between cells, and so on. They all use use one of two microwave frequency bands. Sometimes both. They all use digital to some extent. But aside from providing basic voice and data handling, the many services differ greatly in features and how they provided. Here's a quick, completely oversimplified list to get us going. More information follows:

AMPS: Advanced Mobile Phone service. Conventional cellular service. Mostly analog, with some digital signals providing call setup and management. A first generation service, now only installed in remote regions.

IS-95: All digital cellular using CDMA, a spread spectrum technique. Sprint PCS uses this technology. Sometimes called by its trade name of PCS 1900. A second generation or early digital service.

IS-136: D-AMPS 1900. Feature rich cellular. Mostly digital, although backward compatible with analog based AMPS. AT&T uses it for their nationwide cellular network. Uses time division multiple access or TDMA. Incorporates the old standard IS-54, an early second generation system at the time. IS-136 operates at either 800 Mhz or 1900 Mhz. AT&T is moving to a transitional technology whereby three standards, in some form, will work together: IS-136, GSM, and the newer General Packet Radio Service or GPRS. Eventually AT&T will stop using IS-136, replace it with GSM, and eventually replace that with a wideband CDMA system.

GSM. European cellular come to North America at 1900 Mhz. Fully digital with advanced features. Each mobile has intelligence within the phone, using a smart card. Uses TDMA. Among others, Pacific Bell uses GSM. Will migrate in a few years to a wideband CDMA technology.

iDEN: Proprietary cellular scheme devised by Motorola and used nationwide by NEXTEL. Combines a cell phone with a business radio. TDMA based.

We'll look soon at each service. For right now, though, to give us some orientation, let's go over recent mobile telephone history. It is quite a L-O-N-G history, so feel free to skip over that series and go on to the next topic, which is about standards.

Click here for this free chapter from Professor Noll's book described below, the selection is an excellent, simple introduction to cellular. (32 pages, 204K in .pdf)

More info on Introduction to Telephones and Telephone Systems (external link to Amazon) (Artech House) Professor A. Michael Noll

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Here's my latest writing on mobile telephone history. 9,000 words, concentrating on developments after World War II. It's much easier to get into than this article if you're just interested in the cellular radio era. You can download it in .pdf format (internal link) or as a Word document (internal link). The .pdf is illustrated. Both versions have dozens of references. Comments are always welcome. Thanks, Tom

Digital wireless and cellular roots go back to the 1940s when commercial mobile telephony began. Compared with the furious pace of development today, it may seem odd that mobile wireless hasn't progressed further in the last 60 years. Where's my real time video watch phone? There were many reasons for this delay but the most important ones were technology, cautiousness, and federal regulation.

As the loading coil and vacuum tube made possible the early telephone network, the wireless revolution began only after low cost microprocessors and digital switching became available. The Bell System, producers of the finest landline telephone system in the world, moved hesitatingly and at times with disinterest toward wireless. Anything AT&T produced had to work reliably with the rest of their network and it had to make economic sense, something not possible for them with the few customers permitted by the limited frequencies available at the time. Frequency availability was in turn controlled by the Federal Communications Commission, whose regulations and unresponsiveness constituted the most significant factors hindering radio-telephone development, especially with cellular radio, delaying that technology in America by perhaps 10 years.

In Europe and Japan, though, where governments could regulate their state run telephone companies less, mobile wireless came no sooner, and in most cases later than the United States. Japanese manufacturers, although not first with a working cellular radio, did equip some of the first car mounted mobile telephone services, their technology equal to whatever America was producing. Their products enabled several first commercial cellular telephone systems, starting in Bahrain, Tokyo, Osaka, and Mexico City.

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Communicating wirelessly does not require radio. Everyone's noticed how appliances like power saws cause havoc to A.M. radio reception. By turning a saw on and off you can communicate wirelessly over short distances using Morse code, with the radio as a receiver. But causing electrical interference does not constitute a radio transmission. Inductive and conductive schemes, which we will look at shortly, also communicate wirelessly but are limited in range, often difficult to implement, and do not fufill the need to reliably and predictably communicate over long distances. So let's see what radio is and then go over what it is not.

Weik defines radio as:

"1. A method of communicating over a distance by modulating electromagnetic waves by means of an intelligence bearing-signal and radiating these modulated waves by means of transmitter and a receiver. 2. A device or pertaining to a device, that transmits or receives electromagnetic waves in the frequency bands that are between 10kHz and 3000 GHz."

Interestingly, the United States Federal Communications Commission does not define radio but the U.S. General Services Administration defined the term simply:

1. Telecommunication by modulation and radiation of electromagnetic waves. 2. A transmitter, receiver, or transceiver used for communication via electromagnetic waves. 3. A general term applied to the use of radio waves.

Radio thus requires a modulated signal within the radio spectrum, using a transmitter and a receiver. Modulation is a two part process, a current called the carrier, and a signal which bears information. We generate a continuous, high frequency carrier wave, and then we modulate or vary that current with the signal we wish to send. Notice how a voice signal varies the carrier wave below:

This technique to modulate the carrier is called amplitude modulation. Amplitude means strength. A.M. means a carrier wave is modulated in proportion to the strength of a signal. The carrier rises and falls instantaneously with each high and low of the conversation.The voice current, in other words, produces an immediate and equivalent change in the carrier.

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As we can tell already, and as with the telephone (internal link), a radio is an electrical instrument. A thorough understanding of electricity was necessary before inventors could produce a reliable, practical radio system. That understanding didn't happen quickly. Starting with the work of Oersted in 1820 and continuing until and beyond Marconi's successful radio system of 1897, dozens of inventors and scientists around the world worked on different parts of the radio puzzle. In an era of poor communication and non-systematic research, people duplicated the work of others, misunderstood the results of other inventors, and often misinterpreted the results they themselves had achieved. While puzzling over the mysteries of radio, many inventors worked concurrently on power generation, telegraphs, lighting, and, later, telephones. We should start at the beginning.

In 1820 Danish physicist Christian Oersted discovered electromagnetism, the critical idea needed to develop electrical power and to communicate. In a famous experiment at his University of Copenhagen classroom, Oersted pushed a compass under a live electric wire. This caused its needle to turn from pointing north, as if acted on by a larger magnet. Oersted discovered that an electric current creates a magnetic field. But could a magnetic field create electricity? If so, a new source of power beckoned. And the principle of electromagnetism, if fully understood and applied, promised a new era of communication.

In 1821 Michael Faraday reversed Oersted's experiment and in so doing discovered induction (internal link). He got a weak current to flow in a wire revolving around a permanent magnet. In other words, a magnetic field caused or induced an electric current to flow in a nearby wire. In so doing, Faraday had built the world's first electric generator. Mechanical energy could now be converted to electrical energy. Is that clear? This is a very important point. The simple act of moving ones' hand caused current to flow. Mechanical energy into electrical energy. But current was produced only when the magnetic field was in motion, that is, when it was changing.

Faraday worked through different electrical problems in the next ten years, eventually publishing his results on induction in 1831. By that year many people were producing electrical dynamos. But electromagnetism still needed understanding. Someone had to show how to use it for communicating.

In 1830 the great American scientist Professor Joseph Henry transmitted the first practical electrical signal. A short time before Henry had invented the first efficient electromagnet. He also concluded similar thoughts about induction before Faraday but he didn't publish them first. Henry's place in electrical history however, has always been secure, in particular for showing that electromagnetism could do more than create current or pick up heavy weights -- it could communicate.

In a stunning demonstration in his Albany Academy classroom, Henry created the forerunner of the telegraph. Henry first built an electromagnet by winding an iron bar with several feet of wire. A pivot mounted steel bar sat next to the magnet. A bell, in turn, stood next to the bar. From the electromagnet Henry strung a mile of wire around the inside of the classroom. He completed the circuit by connecting the ends of the wires at a battery. Guess what happened? The steel bar swung toward the magnet, of course, striking the bell at the same time. Breaking the connection released the bar and it was free to strike again. And while Henry did not pursue electrical signaling, he did help someone who did. And that man was Samuel Finley Breese Morse.

From the December, 1963 American Heritage magazine, "a sketch of Henry's primitive telegraph, a dozen years before Morse, reveals the essential components: an electromagnet activated by a distant battery, and a pivoted iron bar that moves to ring a bell."

In 1837 Samuel Morse invented the first practical telegraph, applied for its patent in 1838, and was finally granted it in 1848. Joseph Henry helped Morse build a telegraph relay or repeater that allowed long distance operation. The telegraph united the country and eventually the world. Not a professional inventor, Morse was nevertheless captivated by electrical experiments. In 1832 he had heard of Faraday's recently published work on inductance, and was given an electromagnet at the same time to ponder over. An idea came to him and Morse quickly worked out details for his telegraph.

As depicted below, his system used a key (a switch) to make or break the electrical circuit, a battery to produce power, a single line joining one telegraph station to another and an electromagnetic receiver or sounder that upon being turned on and off, produced a clicking noise. He completed the package by devising the Morse code system of dots and dashes. A quick key tap broke the circuit momentarily, transmitting a short pulse to a distant sounder, interpreted by an operator as a dot. A more lengthy break produced a dash.

Telegraphy became big business as it replaced messengers, the Pony Express, clipper ships and every other slow paced means of communicating. The fact that service was limited to Western Union offices or large firms seemed hardly a problem. After all, communicating over long distances instantly was otherwise impossible. Morse also experimented with wireless, but not in a way you might think. Morse didn't pass signals though the atmosphere but through the earth and water. Without a cable.

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On October 18, 1842, Morse laid wires between Governor's Island and Castle Garden, New York, a distance of about a mile. [For a complete description click here] Part of that circuit was under water, indeed, Morse wanted to show that an underwater cable could transmit signals as well as a copper wire suspended on poles. But before he could complete this demonstration a passing ship pulled up his cable, ending, it seemed, his experiment. Undaunted, Morse proceeded without the cable, passing his telegraph signals through the water itself. This is wireless by conduction.

Over the next thirty years most inventors and developers concentrated on wireline telegraphy, that is, conventional telegraphy carried over wires suspended on poles. Few tinkered exclusively with wireless since basic radio theory had not yet been worked out and trial and error experimenting produced no consistent results. Telegraphy did produce a good understanding of wireless by induction (internal link), however, since wires ran parallel to each other and often induced rogue currents into other lines. University research and some field work did continue, though, with many people making contributions.

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In 1843 Faraday began intensive research into whether space could conduct electricity. In April,1846 he reported his findings in a speech called "Thoughts on Ray-vibrations." He continued work in this area for many years, with inventors and academicians closely following his discoveries and theories. James Clerk Maxwell, whom we today would call a theoretical physicist, pondered constantly over Faraday's findings, translating and interpreting these field results into a set of mathematical equations. Maxwell often wove these equations into the many papers he published on electricity and magnetism. Scientists knew that light was a wave but they didn't know what made it up. Maxwell figured it out.

In 1864 Maxwell released his paper "Dynamical Theory of the Electromagnetic Field" which concluded that light, electricity, and magnetism, were all related, all worked hand in hand, and that these electromagnetic phenomena all traveled in waves. As he put it "[W]e have strong reason to conclude that light itself -- including radiant heat, and other radiations if any -- is an electromagnetic disturbance in the form of waves . . ." Maxwell found further. If electricity rapidly varied in amount then electromagnetic waves could be produced at will; they would radiate in waves to a distant point. At least he said so. There was no method yet to prove that "other radiations" existed, to demonstrate that waves other than light occurred. How could one see, produce, or detect an invisible wave?

Visible light is only one small part of the omnipresent electromagnetic field or spectrum, that great, universal energy force that constantly washes over and through us. (Illustration, 244K) All matter is in fact a wave (internal link) Radio waves as well as infrared waves lie below the visible spectrum. Things like X-Rays lie above. And because light is a radiated electromagnetic emission, lasers and all things optical qualify, strictly speaking, as a radio transmission.

Maxwell's equations also stated that radiation increased dramatically with frequency, that is, many more radio waves are generated at high frequencies than low, given the same amount of power. Experimenting with generating high frequency waves thus began. This wasn't an easy task since it isn't until 90,000 cycles per second, or 9kHz, that radio begins. The familiar A.M. radio band starts around 560 kHz, or 560,000 cycles a second, with all present day radio-telephone services far, far above this. If you want to define radio, generating a rapidly oscillating, high frequency electromagnetic wave is certainly a prerequisite.

Radio spectrum not to scale, Diagram above modified from here: http://www.jsc.mil/images/speccht.jpg (519K) external link)

Need a different perspective on the spectrum? I have archived a nice NASA diagram. Click here (internal link)

Got Java enabled in your browser? Most folks do. Then try this URL for an excellent demonstration of an electromagnetic wave, it correctly portrays how electric and magnetic fields travel at right angles to each other:

http://micro.magnet.fsu.edu/primer/java/electromagnetic/index.html

Blue stands for the electric field and red for the magnetic field. An electrical current or signal always has a magnetic field associated with it, either in a wire or out in space when it is radiated from an antenna. This modulated signal does NOT go straight up, rather, these big and small loops of electrical energy, depending on how low or high the frequency, are whipped out 360 degrees from an omnidirectional antenna such as the one above. Or focused like a light beam from a directional antenna.

Let's review before we look at how early radio developers developed high frequency waves. At the top of this page we saw how Morse used conduction, to wirelessly pass a signal without using the atmosphere. The second way is to do wireless is by induction, where one wire induces current to flow in another. The third way is radiation, where high frequency, rapidly moving waves get generated by electricity and radiate from a fixed point like an antenna. I want to cover induction just a bit more, to better let us understand the difference between this method and what we now know as true radio.

Don't be put off with phrases like "lines of force" and "electro-magnetic fields." The above is a simple bar magnet with its lines of force. Wrap some wire around it, connect the wire to a battery and you will have an electromagnetic field. Communications often use complex words for simple subjects. For an excellent, authoratative look at electricity and magnetism, visit the IEEE site below:

http://www.ieee.org/organizations/history_center/general_info/lines_menu.html#eandm

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We can define radio as the transmission and reception of signals by means of high frequency electrical waves without a connecting wire. And as we noted before, true radio requires that a signal modulate a carrier wave. Early induction schemes operated at low frequencies and possessed no modulating signal. As I stated above induction was well known to telegraphy, since signals often jumped from one line to another. This same tendency is known as "cross talk" in telephone lines, where one conversation may be heard on another line. In this case the wires are not physically crossed with each other, rather, induction induces one signal to travel on the wire of a nearby line.

An experiment in electromagnetic induction: Two separate but closely set coils of wire are wrapped around a nail. The coils are insulated from the nail itself by several pieces of paper, which you cannot see in the drawing. When the battery is connected current steadily flows in one direction and no sound is produced. Remove a lead from the battery and a clicking noise sounds from the receiver. Current in one wire has been induced to flow in the second wire. Only when the current is turned on or off do you get a change in the electromagnetic field and, consequently, a corresponding click. This is induction.

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In 1865 the dentist Dr. Mahlon Loomis of Virginia may have been the first person to communicate wirelessly through the atmosphere. Between 1866 and 1873 he transmitted telegraphic messages a distance of 18 miles between the tops of Cohocton Mountain and Beorse Deer Mountain, Virginia. Perhaps taking inspiration from Benjamin Franklin, at one location he flew a metal framed kite on a metal wire. He attached a telegraph key to the kite wire and sent signals from it. At another location a similar kite picked up these signals and noted them with a galvanometer. No attempt was made to generate high frequency, rapidly oscillating waves, rather, signals were simply electrical discharges, with current turned off and on to represent the dots and dashes of Morse code. He was granted U.S. patent number 129,971 on July 30, 1872 for an "Improvement in Telegraphing," but for financial reasons did not proceed further with his system.

The text of this sign reads: "T-11: Forerunner of Wireless Telegraphy. From nearby Bear's Den Mountain to the Catoctin Ridge, a distance of fourteen miles, Dr. Mahlon Loomis, Dentist, sent the first aerial wireless signals, 1866-73, using kites flown by copper wires. Loomis received a patent in 1872 and his company was chartered by Congress in 1873. But lack of capital frustrated his experiments. He died in 1866. Virginia Conservation Commission 1848."

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Over the next thirty years different inventors, including Preece and Edison, experimented with various induction schemes. You can read about many of them by clicking here (internal link). The most succesful systems were aboard trains, where a wire atop a passenger car could communicate by induction with telegraph wires strung along the track. A typical plan for that was William W. Smith's idea, contained in U. S. Pat. No. 247,127, which was granted on Sept 13, 1881. Edison, L. J. Phelps, and others came out later with improved systems. In 1888 the principle was successfully employed on 200 miles of the Lehigh Valley Railroad. Now, let's get back to true radio and Maxwell's findings, which lead to intense experimenting.

Maxwells' 1864 conclusions were distributed around the world and created a sensation. But it was not until 1888 that Professor Heinrich Hertz of Bonn, Germany, could reliably produce and detect radio waves. Before that many brushed close to detecting radio waves but did not pursue the elusive goal. The most notable were Edison and David Edward Hughes, who became the first person to take a call on a mobile telephone.

On November 22, 1875, while working on acoustical telegraphy, a science close to telephony, Thomas Alva Edison noticed unusual looking electro-magnetic sparks. Generated from a so called vibrator magnet, Edison had seen similar sparks from other eclectric equipment before and had always thought they were due to induction. Further testing ruled out induction and pointed to a new, unknown force. Although unsure of what he was observing, Edison leapt to amazing, accurate conclusions. This etheric force as he now named it, might replace wires and cables as a way to communicate. Under deadline to complete other inventions Edison did not pursue this mysterious force, although in later years he returned to consider it. Edison's vibrating magnet had in fact set up crude, oscillating electromagnetic waves, although these were too weak to detect at much distance. [Josephson]

An on-line Edison bioghrapy which touches on this subject is here. It is a 376K(!) file: http://www.bookrags.com/books/ehlai/PART32.htm (external link)

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From 1879 to 1886, London born David Hughes discovered radio waves but was told incorrectly that he had discovered no such thing. Discouraged, he pursued radio no further. But he did take the first mobile telephone call. Hughes was a talented freelance inventor who had at only 26 designed an all new printing telegraph (internal link). Like Edison and Elisha Gray he often worked under contract for Western Union. He went on to invent what many consider the first true microphone, a device that made the telephone practical, a transmitter as good as the one Edison developed.

Hughes noted many unusual electrical phenomena while experimenting on his microphone, telephone, and wireless related projects. The telephone, by the way, had been invented in 1876 and plans for constructing them had circulated around the world. Hughes noticed a clicking noise in his home built telephone each time he worked used his induction balance, a device now often used as a metal detector.

From the illustration and explanation on the previous page we know that turning current on and off to an induction coil can produce a clicking sound on another wire. It would seem then that Hughes was receiving an inductively produced sound, not a signal over radio waves. But Hughes noticed something more than just a click. In looking over the balance Hughes saw that he hadn't wired it together well, indeed, the unit was sparking at a poorly fastened wire. What would Sherlock Holmes have said? "Come, Watson, come! The game is afoot."

The spark we see isn't the radio signal, instead, it is light from energy released by excited or charged atoms between the spheres. And the spark does not indicate a single current flowing in one direction, but rather it is a set of oscillating, back and forth currents, too fast to observe.

Fixing the circuit's loose contact stopped the signal. Hughes correctly deduced that radio waves, electromagnetic, radiated emissions, were produced by the coil of wire in his induction balance and that the gap the spark raced across marked the point they radiated from. He set about making all sorts of equipment to test his hypothesis. Most ingenious, perhaps, was a clockwork transmitter that interrupted the circuit as it ticked, allowing Hughes to walk about with his telephone, now aided by a specially built receiver, to test how far each version of his equipment would send a signal.

At first Hughes transmitted signals from one room to another in his house on Great Portland Street, London. But since the greatest range there was about 60 feet, Hughes took to the streets of London with his telephone, intently listening for the clicking produced by the tick, tock of his clockwork transmitter. Ellison Hawks F.R.S., quoted and commented on Hughes' accounting, published years later in 1899:

"He obtained a greater range by setting 'the transmitter in operation and walking up and down Great Portland Street with the receiver in my hand and with the telephone to my ear.' We are not told what passers-by thought of the learned scientist, apparently wandering aimlessly about with a telephone receiver held to his ear, but doubtless they had their own ideas. Hughes found that the strength of the signals increased slightly for a distance of 60 yards and then gradually diminished until they no longer could be heard with certainty." [Hawks]

Since Hughes moved his experimenting from the lab to the field he had truly gone mobile. Although these clicks were not voice transmissions, I think it fair to credit Hughes with taking the first mobile telephone call in 1879. That's because his sparking induction coil and equipment put his signal into the radio frequency band, thus fulfilling part of our radio definition. Modulation, the act of putting intelligence onto a carrier wave such as the one he generated, would have to wait for others. This was an important first step, though, even though his clockwork mechanism signaled simply by turning the current on and off, like inductance and conductance schemes before.

Hughes' experimenting was profound and well researched, it was not accidental discovery. Click here to see a picture of all his radio apparatus.

Now, we can signal using a spark transmitter without a coil. This would be just like a car spark plug. When spark plugs fire up they spew electrical energy across the electromagnetic spectrum; this noise wreaks havoc in nearby radios. It's typical of all unmodulated electrical energy called, appropriately enough, RFI, for radio-frequency interference. Light dimmers, electrical saws, badly adjusted ballast in fluorescent light bulbs, dying door bell transformers, and so on, all generate RFI. If you turn the source of RFI on and off you could communicate over short distances using Morse code. But only by interfering with true radio services and causing the wrath of your neighbors. By contrast to spuriously generated electrical noise, Hughes deliberately formed electromagnetic waves which easily travelled a great distance, were tuned to more or less a specific frequency, and were picked up by a receiver designed to do just that.

Beginning in 1879 Hughes started showing his equipment and results to Royal Society (external link) members. On February 20, 1880 Hughes was sufficiently confident in his findings to arrange a demonstration before the president of the Royal Society, a Mr. Spottiswoode, and his entourage. Less knowledgeable in radio and less inquisitive than Hughes, a Professor Stokes declared that signals were not carried by radio waves but by induction. The group agreed and left after a few hours, leaving Hughes so discouraged he did not even publish the results of his work. Although he continued experimenting with radio, it was left to others to document his findings and by that time radio had passed him by.

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Resources

[Hawks] Hawks, Ellison, Pioneers of Wireless Arno Press, New York (1974) 172. This is a reprint of the original work which was published by Methuen & Co. Ltd. in London in 1927.

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The coil Hughes used raised the audio frequency signal on his line to the lower end of the radio band, providing an essential element of our radio definition. How was the frequency raised? Voice, conversations, music, and all other acoustic sounds reside in the the audio frequency band, far below the radio frequency band. Our range of hearing extends to perhaps 20,000 cycles a second, whereas the radio band starts around 100,000 cycles per second, with normal radio frequencies much higher. Let's stop right here to make a distinction between audio or acoustic signals and radio waves.

Sound waves are acoustic waves, with no electrical component. They are simply vibrations in the air, a physical pressure made by the utterance of a speaker or other sound source. Sounds in the audio and radio band both travel in waves but otherwise they are completely dissimilar. Acoustic waves are sounds made manifest by a physical distrubance, electromagnetic or radio waves are the product of radiated electrical energy. Go to this page to read more about acoustic sounds. And this external link from NASA to learn more about radio waves and the entire electromagnetic spectrum:

http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

When put on a wire a sound occupies the frequency it would normally take up if not on the wire, that is, if a normal conversation is taking place at around 500Hz, then the conversation would naturally set up at 500Hz if put on a wire. That's a simple example, of course, since the telephone system for several reasons limits this baseband or voice band channel on a telephone wire to around 300Hz to 3,000Hz.

As the diagram above show a wire laid flat exhibits only a simple electromagnetic field when current flows. But if you scrunch it together, start running dozens of feet of wire around a core, spacing each loop nearly on top of each other, well, now you've really changed the dynamics of that line. You might have 25 feet or more of wire on a five inch core.

Have you ever seen an A.M. radio antenna in an old style radio? All that wire, wrapped around a ferrite core, is designed to tune frequencies from around 560,000 cycles per second, to about 1,600,000 cycles per second. The length of the wire tries to represent the length of the radio wave itself, although in practice it may be a quarter wavelength in size or less. The closer in size your antenna comes to the size of the wavelength you want to listen to, the better your chances are of receiving it. If you took that same antenna, no core needed, and wired it into a telephone line, you will probably raise the signal on the baseband channel into the low end of the radio band.

Modern radios don't use this principle to produce a high frequency carrier wave, of course, but the point I am making is that an induction coil to produce electromagnetic radio waves was an element which distinguished Hughe's work from more primitive schemes.

So who did complete the first radio telephone call using voice? None other than Alexander Graham Bell, the man who invented the telephone and of course made the first call on a wired telephone to Thomas Watson. Bell was also first with radio, although in a way you probably wouldn't imagine.

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Inductive reactance is the proper term for opposition to current flow through a coil. Resistance of a circuit and inductive reactance, both measured in Ohms, makes up impedance. The other confusing term in radio is AC.

In many radio discussions AC does not mean the alternating current that powers your appliances, rather, it means the way audio signals alternate in a wave like fashion. Huh? As we've just seen above and on the on the previous page , we need a change in current flow through a coil to get radiation. Current must go on and off to release the electromagnetic energy stored within the coil.

AC in radio means the natural alternating current of a voice signal, that is, the normal up and down waveform of the analog signal. In this case the rise and fall of a signal above a median point, that is, the top and bottom of a wave. Alternating current. Get it? A battery powered walkie talkie illustrates the difference between AC signaling current and AC power current.

A battery powered radio transmitter uses direct current to do all things. Including converting your voice, through the microphone, into a signal it can transmit. But the signal it transmits is not called a DC signal but an AC signal. That's because the radio rapidly oscillates (or alternates) the original signal. This is the needed step to get the signal high enough in the frequency band so that it will radiate from the antenna. AC, in this case, is not the power coming out of a wall outlet, it is the alternating current formed by waves of acoustical energy in the voice band converted into electrical waves by the radio circuitry. These terms get clearer as you read more. But if you are really mystified, read this little tutorial on how basic radio circuits work. I think it will help you a great deal and you can always come back here to continue.

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On February 22,1880 Alexander Graham Bell and his cousin Charles Bell communicated over the Photophone, a remarkable invention conceived of by Bell and executed by Sumner Tainter. [Grosvenor] This device transmitted voice over a light beam. A person's voice projected through a glass test tube toward a thin mirror which acted as a transmitter. Acoustical vibrations caused by the voice produced like or sympathetic vibrations in the mirror.

Sunlight was directed onto the mirror, where the vibrations were captured by a parabolic dish. The dish focused the light on a photo-sensitive selenium cell, in circuit with a telephone. The electrical resistance of the selenium changed as the strength of the received light changed, varying the current flowing through the circuit. The telephone's receiver then changed these flucuating currents into speech.

Although not related to the mobile telephony of today, Bell's experimenting was a first: radiated electromagnetic waves had carried the human voice. Despite Bell's brilliant achievement, optical transmission had obvious drawbacks, only now being overcome by firms like TeraBeam. Most later inventors concentrated instead on transmitting in the radio bands, with the period from 1880 to 1900 being one of tremendous technological innovation.

For ruminations on the Photophone and how to improve it go here: http://jefferson.village.virginia.edu/~meg3c/id/id_edin/ph/ph1.html

For a fascinating look at how ham radio operators can communicate optically click here

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Resources

[Grosvenor] Grosvenor, Edwin S. and Morgan Wesson. Alexander Graham Bell : The Life and Times of the Man Who Invented the Telephone Abrams, New York (1997) p.102.
Editor's note: The Photophone photograph that accompanies the text is from Grosvenor's excellent book. I never take pictures from books still in print but I have been unable to find any accurate picture of the Photophone on the net. I will immediately remove this image once I do.

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In 1888 the German Heinrich Hertz conclusively proved Maxwell's prediction that electricity could travel in waves through the atmosphere. Unlike Hughes, the extensive and systematic experiments into radio waves that Hertz conducted were recognized and validated by inventors around the world. Now, who would take take these findings further and develop a true radio?

Dozens and dozens of people began working in the field after Hertz made his findings. It is a miserable job to decide what to report on from this period, with people like Tesla, Branly, and yes, even folks like Nathan B. Stubblefield (external link), claiming to have invented radio. Typical of these events is Jagadis Chandra Bose (external link -- 817K!) demonstrating in 1895 electromagnetic waves "by using them to ring a bell remotely and to explode some gunpowder." While not inventing radio, any more than Edison invented the incadesent light bulb, Marconi did indeed establish the first successful and practical radio system. Starting in 1894 with his first electrical experiments, and continuing until 1901 when his radio telegraph system sent signals across the Atlantic ocean, Marconi fought against every kind of discouragement and deserves lionizing for making radio something reliable and useful.

Don Kimberlin (internal link) now questions Marconi's 1901 claim. It seems likely Marconi did not make a transatlantic radio reception that year. Read Kimberlin's page or download the .pdf file discussing this by clicking here.

Ships were the first wireless mobile platforms. In 1901 Marconi placed a radio aboard a Thornycroft steam powered truck, thus producing the first land based wireless mobile. (Transmitting data, of course, and not voice.) Arthur C. Clarke says the vehicle's cylindrical antenna was lowered to a horizontal position before the the wagon began moving. Marconi never envisioned his system broadcasting voices, he always thought of radio as a wireless telegraph. That would soon change.

Visit Arthur C. Clarke's Time Line of Communication at http://www.acclarke.co.uk/1900-1909.html This link no longer seems to be working.

On December 24, 1906, the first radio band wave communication of human speech was accomplished by Reginald Fessenden over a distance of 11 miles, from Brant Rock, Massachusetts, to ships in the Atlantic Ocean. Radio was no longer limited to telegraph codes, no longer just a wireless telegraph. This was quite a milestone, and many historians regard the radio era as beginning here, at the start of the voice transmitted age.

Coils of wire, induction at work, changing the frequency of a line, crystal receivers demonstrate many electrical principles. I've built small crystal sets myself and you can find the kits in many places. They are fascinating, operating not off of a battery but only by the energy contained in the captured radio wave. Just the power of a received radio wave, nothing more.

As Morgan put it, "Radio receivers with sensitive, inexpensive crystal detectors, such as this double slide tuner crystal set, appeared as early as 1904, and were used by most amateurs until the early Thirties, when vacuum tubes replaced crystals. An oatmeal box was a favorite base upon which to wind the wire coils." (Click here for a much clearer, larger image.)

Visit this site soon, plans to build, kits to buy, good information on crystal radios:
Crystal Radio Connections: blending art and science

http://www.crystalradio.org.uk/ (external link)

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From 1910 on it appears that Lars Magnus Ericsson and his wife Hilda regularly worked the first car telephone. Yes, this was the man who founded Ericsson in 1876. Although he retired to farming in 1901, and seemed set in his ways, his wife Hilda wanted to tour the countryside in that fairly new contraption, the horseless carriage. Lars was reluctant to go but soon realized he could take a telephone along. As Meurling and Jeans relate,

"In today's terminology, the system was an early 'telepoint' application: you could make telephone calls from the car. Access was not by radio, of course -- instead there were two long sticks, like fishing rods, handled by Hilda. She would hook them over a pair of telephone wires, seeking a pair that were free . . . When they were found, Lars Magnus would crank the dynamo handle of the telephone, which produced a signal to an operator in the nearest exchange." [Meurling and Jeans]

Thus we have the founder of Ericsson (external link), that Power of The Permafrost, bouncing along the back roads of Sweden, making calls along the way. Now, telephone companies themselves had portable telephones before this, especially to test their lines, and armed forces would often tap into existing lines while their divisions were on the move, but I still think this is the first regularly occurring, authorized, civilian use of a mobile telephone. More on mobile working below.

Around the middle teens the triode tube was developed, allowing far greater signal strength to be developed both for wireline and wireless telephony. No longer passive like a crystal set, a triode was powered by an external source, which provided much better reception and volume. Later, with Armstrong's regenerative circuit, tubes were developed that could either transmit or receive signals. They were the answer to developing high frequency oscillating waves; tubes were stable and powerful enough to carry the human voice and sensitive enough to detect those signals in the radio spectrum.

More on ho w a triode works and its history is here

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Resources:

[Meurling and Jeans] Meurling, John and Richard Jeans. The Mobile Phone Book: The Invention of The Mobile Phone Industry Communications Week International, London, on behalf of Ericsson Radio Systems (1994) p. 43. ISBN Number 0952403102

More on mobile working: Johan Hauknes points out that "L.M. Ericsson had already developed telephones for military purposes in the field -- mobile -- I would guess of the same kind as Meurling and Jeans describes, tapping into fixed systems. That's according to according to Ericsson's Centennial History which is written in Swedish."

"LME [sold] a large number of transportable field telephones and so called cavalry telephones to South Africa during the Boer War from 1899 to 1902. Several types of transportable telephones for military purposes had been developed by LME during the 1890s, bought by the Swedish Military. This according to Messrs A. Attman, J. Kuuse, and U. Olsson, in LM Ericsson 100 år Band 1 Pionjärtid - Kamp om koncessioner - Kris - 1876-1932 (vol. 1 of 3), published. by LM Ericsson in 1976."

"Finally, the first transportable phone documented in the centennial volume is from 1889 - primarily for 'railroad and canal works, military purposes etc.' There's a facsimile of an ad of this in vol. 3: C. Jakobaeus, LM Ericsson 100 år Band III Teleteknisk skapandet 1876-1976.) Railroad related maintenance and repair work, such as for signbased telegraph systems, was a major source of income for LME in the first years."

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(Please note: treat this material with caution, I am revising the explanation.)

Armstrong's regenerative circuit fed back the input signal into the circuit over and over again, amplifying the signal far more than original designs, building great wireless and wireline transmission signal strength. The feedback circuit could also be overdriven, fed back so many times that supplying a small current to the circuit would develop in it an extremely high frequency, so high it could resonate at the frequency of a radio wave, letting the triode receive or detect signals, not just transmit them. You had a tunable electronic tuning fork, of sorts, a device which detected and amplified the rhythmic energy of the radio wave when set to the frequency desired.

In 1919 three firms came together to develop a wireless company that one day would reach around the world. Heavy equipment maker ASEA, boiler and gas equipment maker AGA, and telephone manufacturer LM Ericsson, formed SRA Radio, the forerunner of Ericsson's radio division. Svenska Radio Aktiebolaget, known simply as SRA, was formed to build radio receivers, broadcasting having just started in Scandinavia. (Aktiebolaget, by the way, is Swedish for a joint stock company or corporation.)

Much unregulated radio experimenting was happening world wide at this time with different services causing confusion and interference with each other. In many countries government regulation stepped in to develop order. In the United States the Radio Act of 1912 brought some order to the radio bands, requiring station and operator licenses and assigning some spectrum blocks to existing users. But since anyone who filed for an operating license got a permit many problems remained and others got worse.

In 1921 United States mobile radios began operating at 2 MHz, just above the present A.M. radio broadcast band. For the most part law enforcement used these frequencies. [Young] The first radio systems were one way, sometimes using Morse Code, with police getting out of their cars and then calling their station house on a wired telephone after being paged. As if to confirm this, a reader recently e-mailed me this paragraph. The reader did not include the author's name or any references, however, the content is quite similiar to Bowers in Communications for a Mobile Society, Sage Publications, Cornell University, Beverley Hills (1978):

"Until the 1920s, mobile radio communications mainly made use of Morse Code. In the early 1920s, under the leadership of William P. Rutledge, the Commissioner of Detroit Police Department, Detroit, Michigan police carried out pioneering experiments to broadcast radio messages to receivers in police cars. The Detroit police department installed the first land mobile radio telephone systems for police car dispatch in the year 1921. [With the call sign KOP!, ed.] This system was similar to the present day paging systems. It was one-way transmission only and the patrolmen had to stop at a wire-line telephone station to call back in. On April 7, 1928, the first voice based radio mobile system went operational. Although the system was still one-way, its effectiveness was immediate and dramatic."

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Resources:

Young, W.R. "Advanced Mobile Phone Service: Introduction, Background, and Objectives." Bell System Technical Journal January, 1979: 7

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A detailed article on the pioneering efforts of the Detroit Police Department with wireless mobile is here:

http://www.detroitnews.com/history/police/police.htm

Police and emergency services drove mobile radio pioneering, therefore, with little thought given to private, individual telephone use. Equipment in all cases was chiefly experimental, with practical systems not implemented until the 1940s, and no interconnection with the the land based telephone system.[FCC: (external link)] Having said this, Bell Laboratories (external link) does claim inventing the first version of a mobile, two way, voice based radio telephone in 1924 and I see nothing that contradicts this, indeed, the photo below from their site certainly seems to confirm it!

http://www.bell-labs.com/history/75/gallery.html

For the difficulty involved in dating radio history, consider this page: http://members.aol.com/jeff560/chrono1.html

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On September 25,1928, Paul V. Galvin and his brother Joseph E. Galvin incorporated the Galvin Manufacturing Corporation. We know it today as Motorola (external link)

In 1927 the United States created a temporary five-member Federal Radio Commission (external link), an agency it was hoped would check the chaos and court cases involving radio. It did not and was quickly replaced by the F.C.C. just a few years later. In 1934 the United States Congress created the Federal Communications Commission. In addition to regulating landline telephone business, they also began managing the radio spectrum. The federal government gave the F.C.C. a broad public interest mandate, telling it to grant licenses if it was in the "public interest, convenience, and necessity" to do so. The FCC would now decide who would get what frequencies.

Founded originally as part of Franklin Roosevelt's liberal New Deal Policy, the Commission gradually became a conservative, industry backed agent for the interests of big business. During the 1940s and 1950s the agency became incestuously close to the broadcasting industry in general and in particular to RCA, helping existing A.M. radio broadcasting companies beat off competition from F.M. for decades. The F.C.C. also became a plodding agency over the years, especially when Bell System business was involved.

The American government had a love/hate relation with AT&T. On one hand they knew the Bell System was the best telephone company in the world. On the other hand they could not permit AT&T's power and reach to extend over every part of communications in America. Room had to be left for other companies and competitors. The F.C.C., the Federal Trade Commission, and the United States Justice Department, were all involved in limiting the Bell System's power and yet at the same time permitting them to continue. It was a difficult and awkward dance for everyone involved. And as for cellular, well, the slow action by the FCC would eventually delay cellular by at least a ten years, possibly twenty.

The FCC gave priority to emergency services, government agencies, utility companies, and services it thought helped the most people. Radio users like a taxi service or a tow truck dispatch company required little spectrum to conduct their business. Radio-telephone, by comparison, used large frequency blocks to serve just a few people. A single radio-telephone call, after all, takes up as much spectrum as a radio broadcast station. The FCC designated no private or individual radio-telephone channels until after World War II. Why the FCC did not allocate large frequency blocks in the then available higher frequency spectrum is still debated. Although commercial radios in quantity were not yet made for those frequencies, it is likely that equipment would have been produced had the F.C.C. freed up the spectrum.

Mobile radio?! A marine radio telephone of 1937 recently up for bid on e-bay.com The seller thought it was a Harvey Wells, Model MR-10. This beast measures 20"X 11"X 8 1/2" and weighs close to 40 pounds. This was probably compact for its time. The tube based radio also needed a big and heavy power supply. The present day SEA digital radiotelephone, by comparison, is a far superior machine and weighs in at 9.1 pounds, and measures only 4" by 10.5" It draws just 13 volts. As is clearly evident, much progress in radio had to await microprocessors and miniaturization.

IMTS authority Geoff Fors checked in recently:

"Tom. Get this -- I just looked at some of your material on your website on early mobile phone history, and saw you have a photo of my Harvey Wells 1941 marine radio telephone! I bought that unit on eBay, I don't recall if anyone else even bid on it, it was very cheap. The seller just threw it in a box with some wadded newspapers, and when it arrived the microphone was smashed to bits along with the porcelain insulators and everything protruding from the rear panel, the cabinet was caved in on top, and there was a baggie with the smashed up knobs in it lying INSIDE the cabinet. I don't know how the knobs were shown in the photo on eBay but then wound up inside the cabinet for shipping. They were shot anyway. It does actually work, although the cabinet was painted a horrible yellow color and should have been wrinkle burgundy. I have already straightened, stripped and primed the cabinet and have a replacement mike lined up from a friend. There is some consternation whether the set is pre or post-war. It uses metal octal tubes, which suggests postwar use, although those tubes were available before 1946. It is definitely pre-1950, in any case."

(Editor's note: I don't mean to confuse you, but these are both principally short wave radios, able to place a phone call through an operator, but they aren't units dedicated to telephony. "Phone" is an old radio term for voice transmission, it doesn't mean, necessarily, that you have a radio-telephone. Photographs simply illustrate radio size.)

Early conventional radio-telephone development and progress towards miniaturization

Radio-telephone work was ongoing throughout the world before the war. This excellent photograph shows a Dutch Post Telegraph and Telephone mobile radio. As the excellent Mobile Radio in the Netherlands web site explains it:

"The NSF Type DR38a transmitter receiver was the first practical mobile radio telephone in Holland. The set was developed in 1937 from PTT specifications and saw use from 1939 onwards. It operates in the frequency range between 66-75 MHz having a RF power output of approximately 4-5 Watts. Change-over from receive to transmit is effected by the large lever on the front panel. The transmitter is pre-set on a single frequency while the receiver is tuneable over the frequency range." I do not know if this set actually connected to their public switched telephone network. It may have been called a radio-telephone, just like the marine radio-telephone described above.

More good details are here. Their page does take a long time to load:
http://home.hccnet.nl/l.meulstee/mobilophone/mobilophone.html

DuringWorld War II civilian commercial mobile telephony work ceased but intensive radio research and development went on for military use. While RADAR was perhaps the most publicized achievement, other landmarks were reached as well. "The first portable FM two-way radio, the "walkie-talkie" backpack radio," [was] designed by Motorola's Dan Noble. It and the "Handie-Talkie" handheld radio become vital to battlefield communications throughout Europe and the South Pacific during World War II." [Motorola (external link) For those researching this time period, see my comments for reading below.

In the July 28, 1945 Saturday Evening Post magazine, the commissioner of the F.C.C., E.K. Jett, hinted at a cellular radio scheme, without calling it by that name. (These systems would first be described as "a small zone system" and then cellular.) Jett had obviously been briefed by telephone people, possibly Bell Labs scientists, to discuss how American civilian radio might proceed after the war.

What he describes below is frequency reuse, the defining principle of cellular. In this context frequency reuse is not enabled by a well developed radio system, but simply by the high frequency band selected. Higher frequency signals travel shorter distances than lower frequencies, consequently you can use them closer together. And if you use F.M. you have even less to worry about, since F.M. has a capture effect, whereby the nearest signal blocks a weaker, more distant station. That compares to A.M. which lets undesired signals drift in and out, requiring stations be located much further apart:

"In the 460,000-kilocycle band, sky waves do not have to be taken into account, day or night. The only ones that matter are those parallel to the ground. These follow a line of sight path and their range can be measured roughly by the range of vision. The higher the antenna, the greater the distance covered. A signal from a mountain top or from an airplane might span 100 miles, by one from a walkie talkie on low ground normally would not go beyond five miles, and one from a higher powered fixed transmitter in a home would not spread more than ten to fifteen miles. There are other factors, such as high buildings and hilly terrain which serve as obstacles and reduce the range considerably."

"Thanks to this extremely limited reach, the same wave lengths may be employed simultaneously in thousands of zones in this country. Citizens in two towns only fifteen miles apart -- or even less if the terrain is especially flat -- will be able to send messages on the same lanes at the same time without getting in one another's way."

"In each zone, the Citizen' Radio frequencies will provide from 70 to 100 different channels, half of which may be used simultaneously in the same area without any overlapping. And each channel in every one of the thousands of sectors will on average assure adequate facilities for ten or twenty, or even more "subscribers," because most of these will be talking on the ether only a very small part of the time. In each locality, radiocasters will avoid interference with one another by listening, before going on the air, to find out whether the lane is free. Thus the 460,000 to 470,000 kilocycle band is expected to furnish enough room for millions of users. . . "

The article was deceptively titled "Phone Me by Air"; no radio-telephone use was envisioned, simply point to point communications in what was to become the Citizens' Radio Band, eventually put at the much lower 27Mhz. Still, the controlling idea of cellular was now being discussed, even if technology and the F.C.C. would not yet permit radio-telephones to use it.

In 1946, the very first circuit boards, a product of war technology, became commercially available. Check out the small board in the lower right hand corner. It would take many years before such boards became common. The National Museum of American History (external link) explains this photo of a 'midget radio set' like this: "Silver lines replace copper wires in the 'printed' method developed for radio circuits . . . One of the new tiny circuits utilizing midget tubes is shown beside the same circuit as produced by conventional methods." These tiny tubes were called "acorn tubes" and were generally used in lower powered equipment. Car mounted mobile telephones used much larger tubes and circuits.

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Resources

My comments for reading: The following three volumes chronicle American military radio development during World War II, focusing on the United States Army. They are indispensable for anyone researching radio, especially those looking at the beginning of F.M. for handheld and mobile operations. Part of a larger series, the United States' official chronicle of World War II, these should be available through any major university. Out of print, used copies exist, figure $25 to $30 a volume; I paid $80 for my set. They have been reprinted a number of times, any edition is serviceable. For used books try ABE below.

Terrett, Dulany. The Signal Corps: The Emergency (to December 1941). Washington, Office of the Chief of Military History, Dept. of the Army, 1956. xiii, 383 p. illus., ports. 26 cm. Series title: United States Army in World War II. Technical services

Thompson, George Raynor. The Signal Corps: The Test (December 1941 to July 1943), by George Raynor Thompson [and others] Washington, Office of the Chief of Military History, Dept. of the Army, 1957. xv, 621 p. illus. 26 cm. Series title: United States Army in World War II : The technical services

Thompson, George Raynor. The Signal Corps: The Outcome (mid-1943 through 1945), by George Raynor Thompson and Dixie R. Harris. Washington, Office of the Chief of Military History, U.S. Army;1966. xvi, 720 p. illus., maps, ports. 26 cm. Series title: United States Army in World War II. Technical services

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On June 17, 1946 in Saint Louis, Missouri, AT&T and Southwestern Bell introduced the first American commercial mobile radio-telephone service to private customers. Mobiles used newly issued vehicle radio-telephone licenses granted to Southwestern Bell by the FCC. They operated on six channels in the 150 MHz band with a 60 kHz channel spacing. [Peterson] Bad cross channel interference, something like cross talk in a landline phone, soon forced Bell to use only three channels. In a rare exception to Bell System practice, subscribers could buy their own radio sets and not AT&T's equipment.

A simplified picture of Radio Telephone Service -- A Non-Zoned System

The diagram above shows a central transmitter serving mobiles over a wide area. One antenna serves a wide area, like a taxi dispatch service. While small cities used this arrangement, radio telephone service was more complicated, using more receiving antennas as depicted below. That's because car mounted transmitters weren't as powerful as the central antenna, thus their signals couldn't always get back to the originating site. That meant, in other words, you needed receiving antennas throughout a large area to funnel radio traffic back to the switch handling the call.. This process of keeping a call going from one zone to another is called a handoff.

The 1946 Bell System Mobile Telephone Service in St. Louis -- A Zoned System
M: mobile R:receiver. PSTN: Public switched telephone network.

As depicted above, in larger cities the Bell System Mobile Telephone Service used a central transmitter to page mobiles and deliver voice traffic on the downlink. Mobiles, based on a signal to noise ratio, selected the nearest receiver to transmit their signal to. In other words, they got messages on one frequency from the central transmitter but they sent their messages to the nearest receiver on a separate frequency.

Placed atop distant central offices, these receivers and antennas could also "be installed in buildings or mounted in weather proof cabinets or poles." They collected the traffic and passed it on to the largest telephone office, where the main mobile equipment and operators resided. [Peterson2]

Installed high above Southwestern Bell's headquarters at 1010 Pine Street, a centrally located antenna transmitting 250 watts paged mobiles and provided radio-telephone traffic on the downlink or forward path, that is, the frequency from the transmitter to the mobile. Operation was straightforward, as the following describes:

How Mobile Telephone Calls Are Handled

Telephone customer (1) dials 'Long Distance' and asks to be connected with the mobile services operator, to whom he gives the telephone number of the vehicle he wants to call. The operator sends out a signal from the radio control terminal (2) which causes a lamp to light and a bell to ring in the mobile unit (3). Occupant answers his telephone, his voice traveling by radio to the nearest receiver (4) and thence by telephone wire.

To place a call from a vehicle, the occupant merely lifts his telephone and presses a 'talk' button. This sends out a radio signal which is picked up by the nearest receiver and transmitted to the operator.[BLR1]

The above text accompanies a Bell Laboratories Record illustration (346K), from the 1946 article that first described the system. It gives you a good idea of how the system worked. Click on the link to view this big, but slow to load graphic.)

Simple block diagrams can be hard to follow. Click here to see another MTS illustration; it is from Bell Labs and my cellular telephone basics article.)

One party talked at a time with Mobile Telephone Service or MTS. You pushed a handset button to talk, then released the button to listen. (This eliminated echo problems which took years to solve before natural, full duplex communications were possible.) Mobile telephone service was not simplex operation as many writers describe, but half duplex operation.

Simplex uses only one frequency to both transmit and receive. In MTS the base station frequency and mobile frequency were offset by five kHz. Privacy is one reason to do this; eavesdroppers could hear only one side of a conversation. Like a citizen's band radio, a caller searched manually for an unused frequency before placing a call. But since there were so few channels this wasn't much of a problem. This does point out greatest problem for conventional radio-telephony: too few channels.

Shortly after this cartoon appeared the July 1948 BLR reported that a taxi cab driver with a mobile phone reported a stuck car on a railroad crossing, thus saving the broken down car and its motorist from disaster. Possibly the first radio-telephone rescue of its kind. This incident happened at a "grade crossing of the Nickel Plate Railroad at Dunkirk, New York." Dr. Scott Savett has found a photograph on the web of a representative Dunkirk rail crossing. The Dr. says, "According to a source on the Web, there were about five grade crossings in Dunkirk, so there's no guarantee that the one shown above is actually the one where the call was made." Still, this photo gives you an idea of the country. Click here to view. I wonder if the county history museum knows of the crossing's place in mobile telephone history.

Art imitating life below. This cartoon is from the April, 1948 issue of The Bell Laboratories Record. It reads, "Hello, Mr. Bunting. I've changed my mind -- I'll take that accident policy!"

Things to come. "All equipped with telephones so that the minute you catch anything you can call all your friends and start bragging." From the September, 1950 Bell Laboratories Record.

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Resources:

Peterson, A.C., Jr. "Vehicle Radiotelephony Becomes a Bell System Practice." Bell Laboratories Record April, 1947: 137

Peterson2 ibid. 140

BLR1"Telephone Service for St. Louis Vehicles." Bell Laboratories Record July, 1946: 267

BLR2 ibid.

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The MTS system presaged many cellular developments. In December,1947 Bell Laboratories' D.H. Ring articulated the cellular concept for mobile telephony in an internal memorandum, authored by Ring with crucial assistance from W.R. Young. Mr. Young later recalled that all the elements were known then: a network of small geographical areas called cells, a low powered transmitter in each, the cell traffic controlled by a central switch, frequencies reused by different cells and so on. Young states that from 1947 Bell teams "had faith that the means for administering and connecting to many small cells would evolve by the time they were needed." [Young]The authors at SRI International, in their voluminous history of cell phones[SR1], put those early days like this:

"The earliest written description of the cellular concept appeared in a 1947 Bell Labs Technical Memorandum authored by D. H. Ring. [but see previous page, the key difference is that Ring describes true mobile telephone service, ed.] The TM detailed the concept of frequency reuse in small cells, which remained one of the key elements of cellular design from then on. The memorandum also dealt with the critical issue of handoff, stating "If more than one primary band is used, means must be provided for switching the car receiver and transmitter to the various bands." Ring does not speculate how this might be accomplished, and, in fact, his focus was on how frequencies might be best conserved in various theoretical system designs."

Here we come to an important point, one that illustrates the controlling difference between conventional mobile telephony and cellular. Note how the authors describe handoffs, a process that Mobile Telephone Service already used. The problem wasn't so much about conducting a handoff from one zone to another, but dealing with handoffs in a cellular system, one in which frequencies were used over and over again. In a cellular system you need to transfer the call from zone to zone as the mobile travels, and you need to switch the frequency it is placed on, since frequencies differ from cell to cell. See the difference? Frequency re-use is the critical and unique element of cellular, not handoffs, since conventional radio telephone systems used them as well. [Discussion] Let's get back to Young's comments, when he says that Bell teams had faith that cellular would evolve by the time it was needed.

Important conventional mobile telephone handoff patents are: Communication System with Carrier Strength Control, Henry Magunski, assignor to Motorola, Inc. U.S. 2,734,131 (1956) and Automatic Radio Telephone Switching System, R.A. Channey, assignor to Bell Telephone Laboratories, Inc. U.S. 3,355,556(1967)

While recognizing the Laboratories' prescience, more mobile telephones were always needed. Waiting lists developed in every city where mobile telephone service was introduced. By 1976 only 545 customers in New York City had Bell System mobiles, with 3,700 customers on the waiting list. Around the country 44,000 Bell subscribers had AT&T mobiles but 20,000 people sat on five to ten year waiting lists. [Gibson] Despite this incredible demand it took cellular 37 years to go commercial from the mobile phone's introduction. But the FCC's regulatory foot dragging slowed cellular as well. Until the 1980s they never made enough channels available; as late as 1978 the Bell System, the Independents, and the non-wireline carriers divided just 54 channels nationwide. [O'Brien] That compares to the 666 channels the first AMPS systems needed to work. Let's back up.

In mobile telephony a channel is a pair of frequencies. One frequency to transmit on and one to receive. It makes up a circuit or a complete communication path. Sounds simple enough to accommodate. Yet the radio spectrum is extremely crowded. In the late 1940s little space existed at the lower frequencies most equipment used. Inefficient radios contributed to the crowding, using a 60 kHz wide bandwidth to send an signal that can now be done with 10kHz or less. But what could you do with just six channels, no matter what the technology? With conventional mobile telephone service you had users by the scores vying for an open frequency. You had, in effect, a wireless party line, with perhaps forty subscribers fighting to place calls on each channel. Most mobile telephone systems couldn't accommodate more than 250 people. There were other problems.

Radio waves at lower frequencies travel great distances, sometimes hundreds of miles when they skip across the atmosphere. High powered transmitters gave mobiles a wide operating range but added to the dilemma. Telephone companies couldn't reuse their precious few channels in nearby cities, lest they interfere with their own systems. They needed at least seventy five miles between systems before they could use them again. While better frequency reuse techniques might have helped, something doubtful with the technology of the times, the FCC held the key to opening more channels for wireless.

In 1947 AT&T began operating a "highway service", a radio-telephone offering that provided service between New York and Boston. It operated in the 35 to 44MHz band and caused interference from to time with other distant services. Even AT&T thought the system unsuccessful. Tom Kneitel, K2AES, writing in his Tune In Telephone Calls, 3d edition, CRB Books (1996) recalls the times:

"Service in those early days was very basic, the mobile subscriber was assigned to use one specific channel, and calls from mobile units were made by raising the operator by voice and saying aloud the number being called. Mobile units were assigned distinctive telephone numbers based upon the coded channel designator upon which they were permitted to operate. A unit assigned to operate on Channel 'ZL' (33.66 Mhz base station) might be ZL-2-2849. The mobile number YJ-3-5771 was a unit assigned to work with a Channel YJ (152.63 Mhz) base station. All conversations meant pushing the button to talk, releasing it to listen."

Also in 1947 the Bell System asked the FCC for more frequencies. The FCC allocated a few more channels in 1949, but gave half to other companies wanting to sell mobile telephone service. Berresford says "these radio common carriers or RCCs, were the first FCC-created competition for the Bell System" He elaborates on the radio common carriers, a group of market driven businessmen who pushed mobile telephony in the early years further and faster than the Bell System:

"The telephone companies and the RCCs evolved differently in the early mobile telephone business. The telephone companies were primarily interested in providing ordinary, 'basic' telephone service to the masses and, therefore, gave scant attention to mobile services throughout the 1950s and 1960s. The RCCs were generally small entrepreneurs that were involved in several related businesses-- telephone answering services, private radio systems for taxicab and delivery companies, maritime and air-to-ground services, and 'beeper' paging services. As a class, the RCCs were more sales-oriented than the telephone companies and won many more customers; a few became rich in the paging business. The RCCs were also highly independent of each other; aside from sales, their specialty was litigation, often tying telephone companies (and each other) up in regulatory proceedings for years." [Berresford External Link

As proof of their competitiveness, the RCCs serviced 80,000 mobile units by 1978, twice as many as Bell. This growth built on a strong start, the introduction of automatic dialing in 1948.]

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Resources

Bullington, Kenneth "Frequency Economy in Mobile Radio Bands." Bell System Technical Journal, January 1953, Volume 32: 42 et. seq.

Douglas, V.A. "The MJ Mobile Radio Telephone System." Bell Laboratories Record December, 1964: 383

Gibson, Stephen W., Cellular Mobile Radiotelephones. Englewood Cliff: Prentice Hall, 1987. 8

McDonald, Ramsey "'Dial Direct'" Automatic Radiotelephone System. IRE Transactions on Vehicle Communications July, 1958: 80 (back to text) As a courtesy to researchers I have scanned this article for you to download and review. These are very large files but they are readable and with some work will be decent for OCR. The first image is the title page for the IRE Transactions publication. The article starts at page 80:

http://www.privateline.com/IRE/IREfrontpiece.jpg
http://www.privateline.com/IRE/page80.jpg
http://www.privateline.com/IRE/page81.jpg
http://www.privateline.com.com/IRE/page82.jpg
http://www.privateline.com.com/IRE/page83.jpg
http://www.privateline.com.com/IRE/page84.jpg
http://www.privateline.com.com/IRE/page85.jpg

[McDonald2] ibid. 84

O'Brien, James "Final Tests Begin for Mobile Telephone System." Bell Laboratories Record July/August, 1978: 171

[SRI1] David Roessner, Robert Carr, Irwin Feller, Michael McGeary, and Nils Newman, "The Role of NSF's Support of Engineering in Enabling Technological Innovation: Phase II Final report to the National Science Foundation. Arlington, VA: SRI International, 1998.

[SRI2] ibid.

Young, W.R. "Advanced Mobile Phone Service: Introduction, Background, and Objectives." Bell System Technical Journal January, 1979: 7 (back to text) Messrs. Carr. Feller, McGeary, and Newman, of SRI, supra, cite the original memo describing cellular as follows: "Mobile Telephony -- Wide Area Coverage" Bell Laboratories Technical Memorandum, December 11, 1947.

[Discussion] Some might say conventional mobile telephones already employ frequency reuse since the same frequencies are used in radio-telephone service some distance away, in other cities perhaps seventy miles or more distant. Broadcast radio and television stations use this same approach to prevent interference, where the same frequencies are used throughout the country and where each station is separated by distance or space. In cellular, though, frequency reuse goes on within the fixed wide area of a cellular carrier, as part of an overall operating system. Within the coverage area of an AM or FM radio station, by comparison, no other station can use the frequency of that station. And there is no connection between other stations to act as a network.

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On March 1, 1948 the first fully automatic radiotelephone service began operating in Richmond, Indiana, eliminating the operator to place most calls. [McDonald] The Richmond Radiotelephone Company bested the Bell System by 16 years. AT&T didn't provide automated dialing for most mobiles until 1964, lagging behind automatic switching for wireless as they had done with landline telephony. (As an aside, the Bell System did not retire their last cord switchboard until 1978.) Most systems, though, RCCs included, still operated manually until the 1960s.

Some claim the Swedish Telecommunications Administration's S. Lauhrén designed the world's first automatic mobile telephone system, with a Stockholm trial starting in 1951. [http://www.telemuseum.se, link, now dead] I've found no literature to support this. Anders Lindeberg of the Swedish Museum of Science and Technology points out the text at the link I provide above is "a summary from an article in the yearbook 'Daedalus' (1991) for the Swedish Museum of Science and Technology http://www.tekmu.se/, link now dead]." He goes on to say, "The Swedish original article is much more extensive than the summary" and that "The Mobile Phone Book" by John Meurling and Richard Jeans, ISBN 0-9524031-02 published by Communications Week International, London in 1994 does briefly describe the "MTL" from 1951. But, again, nothing contradicts my contention that Richmond Telephone was first with automatic dialing.

On July 1, 1948 the Bell System unveiled the transistor, a joint invention of Bell Laboratories scientists William Shockley, John Bardeen, and Walter Brattain. It would revolutionize every aspect of the telephone industry and all of communications. One engineer remarked, "Asking us to predict what transistors will do is like asking the man who first put wheels on an ox cart to foresee the automobile, the wristwatch, or the high speed generator." Sensitive, bulky, high current drawing radios with tubes would be replaced over the next ten to fifteen years with rugged, miniature, low drain units. For the late 1940s and most of the 1950s, however, most radios would still rely on tubes, as the photograph below illustrates, a typical radio-telephone of the time.

Visit the Telecommunication Museum of Sweden!http://www.telemuseum.se/historia/mobtel/mobtfn_2e.html (link now dead)

Let's go to Sweden to read about a typical radio-telephone unit, something similar to American installations:

"It was in the mid-1950's that the first phone-equipped cars took to the road. This was in Stockholm - home of Ericsson's corporate headquarters - and the first users were a doctor-on-call and a bank-on-wheels. The apparatus consisted of receiver, transmitter and logic unit mounted in the boot of the car, with the dial and handset fixed to a board hanging over the back of the front seat. It was like driving around with a complete telephone station in the car. With all the functions of an ordinary telephone, the telephone was powered by the car battery. Rumour has it that the equipment devoured so much power that you were only able to make two calls - the second one to ask the garage to send a breakdown truck to tow away you, your car and your flat battery. . . These first carphones were just too heavy and cumbersome - and too expensive to use - for more than a handful of subscribers. It was not until the mid-1960's that new equipment using transistors were brought onto the market.Weighing a lot less and drawing not nearly so much power, mobile phones now left plenty of room in the boot - but you still needed a car to be able to move them around."

The above paragraph was taken from: http://www.ericsson.com/Connexion/connexion1-94/hist.html Ericsson has since removed this information from their website. You might try Alexa.com to do a Wayback Machine search.

In 1953 the Bell System's Kenneth Bullington wrote an article entitled, "Frequency Economy in Mobile Radio Bands." [Bullington] It appeared in the widely read Bell System Technical Journal. For perhaps the first time in a publicly distributed paper, the 21 page article hinted at, although obliquely, cellular radio principles.

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Resources

Bullington, Kenneth "Frequency Economy in Mobile Radio Bands." Bell System Technical Journal, January 1953, Volume 32: 42 et. seq.

Douglas, V.A. "The MJ Mobile Radio Telephone System." Bell Laboratories Record December, 1964: 383

Gibson, Stephen W., Cellular Mobile Radiotelephones. Englewood Cliff: Prentice Hall, 1987. 8

McDonald, Ramsey "'Dial Direct'" Automatic Radiotelephone System. IRE Transactions on Vehicle Communications July, 1958: 80 (back to text) As a courtesy to researchers I have scanned this article for you to download and review. These are very large files but they are readable and with some work will be decent for OCR. The first image is the title page for the IRE Transactions publication. The article starts at page 80:

http://www.privateline.com/IRE/IREfrontpiece.jpg
http://www.privateline.com/IRE/page80.jpg
http://www.privateline.com/IRE/page81.jpg
http://www.privateline.com.com/IRE/page82.jpg
http://www.privateline.com.com/IRE/page83.jpg
http://www.privateline.com.com/IRE/page84.jpg
http://www.privateline.com.com/IRE/page85.jpg

[McDonald2] ibid. 84

O'Brien, James "Final Tests Begin for Mobile Telephone System." Bell Laboratories Record July/August, 1978: 171

[SRI1] David Roessner, Robert Carr, Irwin Feller, Michael McGeary, and Nils Newman, "The Role of NSF's Support of Engineering in Enabling Technological Innovation: Phase II Final report to the National Science Foundation. Arlington, VA: SRI International, 1998.

[SRI2] ibid.

Young, W.R. "Advanced Mobile Phone Service: Introduction, Background, and Objectives." Bell System Technical Journal January, 1979: 7 (back to text) Messrs. Carr. Feller, McGeary, and Newman, of SRI, supra, cite the original memo describing cellular as follows: "Mobile Telephony -- Wide Area Coverage" Bell Laboratories Technical Memorandum, December 11, 1947.

[Discussion] Some might say conventional mobile telephones already employ frequency reuse since the same frequencies are used in radio-telephone service some distance away, in other cities perhaps seventy miles or more distant. Broadcast radio and television stations use this same approach to prevent interference, where the same frequencies are used throughout the country and where each station is separated by distance or space. In cellular, though, frequency reuse goes on within the fixed wide area of a cellular carrier, as part of an overall operating system. Within the coverage area of an AM or FM radio station, by comparison, no other station can use the frequency of that station. And there is no connection between other stations to act as a network.

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