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Mobile Phones - A History
Written by T.Farley
Introduction
 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 are our video watch phones? 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 phone services, their technology equal to whatever America
was producing. Their products enabled several first commercial cellular
telephone systems, starting in Bahrain, Tokyo, Osaka, Mexico City.
Wireless and Radio Defined
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 defines
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 bearing 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.
For voice this is exactly the same way a
telephone works, using the essential principle of variable resistance.
A voice in telephony modulates the current of a telephone line. Compared
to a telephone line, the unmodulated carrier in radio is simply the steady
and continuous current the transmitter generates. When you talk the radio
puts, superimposes, or impresses your conversation's signal on the current
the radio is transmitting. Conversation causes the current's resistance
to go up and down, that is, your voice varies or modulates the carrier.
I illustrate this idea with the diagram below. The only difference between
a telephone and radio is that we call the transmitter a microphone. Now
that we've quickly looked at radio, let's go on to its early development.
Pre-History
As we can tell already, and as with the telephone, 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 .
![mobile phones]() In
1821 Michael Faraday reversed Oersted's experiment and in so doing discovered
induction. 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.
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For more information on Joseph Henry, visit the Joseph Henry Papers
Project at:
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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."
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In 1837 Samuel Morse invented the first practical
telegraph, applied for its patent in 1838, an d
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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This site has a small page on Samuel
Morse:
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http://web.mit.edu/invent/www/inventorsI-Q/morse.html
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