the dawn of amateur radio in the u[1].k.(收音机雏形的诞生)-第2章
按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
caused the magnetic lines of force surrounding one coil to rise and fall by
interrupting or varying the flow of current； a similar current was induced
6
… Page 7…
The dawn of amateur radio in the U。K。 and Greece ： a personal view
in a neighbouring coil closely coupled to the first。
The colossal importance of Faraday's discovery was that it paved the
way for the generation of electricity by mechanical means。 However； as
can be seen from the drawing； the basic generator produces an alternating
flow of current。（A。C。）
Rotating a coil of wire steadily through a complete revolution in the
steady magnetic field between the north and south poles of a magnet
results in an electromotive force （E。M。F。） at its terminals which rises in
value； falls back to zero； reverses in a negative direction； reaches a peak
and again returns to zero。 This completes one cycle or sine wave。 （1Hz in
S。I。units）。
In recent years other methods have been developed for generating
electrical power in relatively small quantities for special applications。
Semiconductors； which combine heat insulation with good electrical
conduction； are used for thermoelectric generators to power isolated
weather stations； artificial satellites； undersea cables and marker buoys。
Specially developed diode valves are used as thermionic generators with
an efficiency； at present； of only 20％ but the heat taken away from the
anode is used to raise steam for conventional power generation。
Sir Humphry Davy （1778…1829） one of Britain's leading chemists of
the 18th century； is best remembered for his safety lamp for miners which
cut down the risk of methane gas explosions in mines。 It was Davy who
first demonstrated that electricity could be used to produce light。 He
connected two carbon rods to a heavy duty storage battery。 When he
touched the tips of the rods together a very bright white light was
produced。 As he drew the rods apart； the arc light persisted until the tips
had burnt away to the critical gap which extinguished the light。 As a
researcher and lecturer at the Royal Institution Davy worked closely with
Michael Faraday who first joined the institution as his manservant and
later became his secretary。 Davy's crowning honour in the scientific world
came in 1820； when he was elected President of the Royal Society。
In the U。S。A。 the prolific inventor Thomas Alva Edison （1847…1831）
who had invented the incandescent carbon filament bulb； built a number of
electricity generators in the vicinity of the Niagara Falls。 These used the
7
… Page 8…
The dawn of amateur radio in the U。K。 and Greece ： a personal view
power of the falling water to drive hydraulic turbines which were coupled
to the dynamos。 These generators were fitted with a spinning switch or
commutator （one of the neatest gadgets Edison ever invented） to make the
current flow in unidirectional pulses （D。C。） In 1876 all electrical
equipment was powered by direct current。
Today mains electricity plays a vital part in our everyday lives and its
applications are widespread and staggering in their immensity。 But we
must not forget that popular demand for this convenient form of power
arose only about 100 years ago； mainly for illumination。
Recent experiments in superconductivity； using ceramic instead metal
conductors have given us an exciting glimpse into what might be achieved
for improving efficiency in the distribution of electric power。
Historians of the future may well characterise the 20th century as ‘the
century of electricity & electronics'。 But Edison's D。C。 generators could
not in themselves； have achieved the spectacular progress that has been
made。 All over the world we depend totally on a system of transmitting
mains electricity over long distances which was originally created by an
amazing inventor whose scientific discoveries changed； and are still
changing； the whole world。 His name was scarcely known to the general
public； especially in Europe； where he was born。
Who was this unknown pioneer？ Some people reckon that it was this
astonishing visionary who invented wireless； remote control； robotics and
a form of X…ray photography using high frequency radio waves。 A patent
which he took out in the U。S。A。 in 1890 ultimately led to the design of the
humble ignition coil which energises billions and billions of spark plugs in
all the motor cars of the world。 His American patents fill a book two
inches thick。 His name was Nicola Tesla （1856…1943）。
Nicola Tesla was born in a small village in Croatia which at that time
formed part of the great Austro…Hungarian Empire。 Today it is a northern
province of Yugoslavia； a state created after the 1914…1918 war。 Tesla
studied at the Graz Technical University and later in Budapest。 Early in his
studies he had the idea that a way had to be found to run electric motors
directly from A。C。 generators。 His professor in Graz had assured him
categorically that this was not possible。 But young Tesla was not
8
… Page 9…
The dawn of amateur radio in the U。K。 and Greece ： a personal view
convinced。 When he went to Budapest he got a job in the Central
Telegraph Office； and one evening in 1882； as he was sitting on a bench in
the City Park he had an inspiration which ultimately led to the solution of
the problem。
Tesla remembered a poem by the German poet Goethe about the sun
which supports life on the earth and when the day is over moves on to give
life to the other side of the globe。 He picked up a twig and began to
scratch a drawing on the soil in front of him。 He drew four coils arranged
symmetrically round the circumference of a circle。 In the centre he drew a
rotor or armature。 As each coil in turn was energised it attracted the rotor
towards it and the rotary motion was established。 When he constructed the
first practical models he used eight； sixteen and even more coils。 The
simple drawing on the ground led to the design of the first induction motor
driven directly by A。C。electricity。
Tesla emigrated to the U。S。A。 in 1884。 During the first year he filed
no less than 30 patents mostly in relation to the generation and distribution
of A。C。 mains electricity。 He designed and built his ‘A。C。 Polyphase
System' which generated three…phase alternating current at 25 Hz。 One
particular unit delivered 422 amperes at 12；000 volts。 The beauty of this
system was that the voltage could be stepped down using transformers for
local use； or stepped up to many thousands of volts for transmission over
long distances through relatively thin conductors。 Edison's generating
stations were incapable of any such thing。
Tesla signed a lucrative contract with the famous railway engineer
George Westinghouse； the inventor of the Westinghouse Air Brake which
is used by most railways all over the world to the present day。 Their
generating station was put into service in 1895 and was called the Niagara
Falls Electricity Generating Company。 It supplied power for the
Westinghouse network of trains and also for an industrial complex in
Buffalo； New York。
After ten years Tesla began to experiment with high frequencies。 The
Tesla Coil which he had patented in 1890 was capable of raising voltages
to unheard of levels such as 300；000 volts。 Edison； who was still
generating D。C。； claimed A。C。 was dangerous and to prove it contracted
9
… Page 10…
The dawn of amateur radio in the U。K。 and Greece ： a personal view
with the government to produce the first electric chair using A。C。 for the
execution of murderers condemned to death。 When it was first used it was
a ghastly flop。 The condemned man moaned and groaned and foamed at
the mouth。 After four minutes of repeated application of the A。C。voltage
smoke began to come out of his back。 It was obvious that the victim had
suffered a horribly drawn…out death。
Tesla said he could prove that A。C。 was not dangerous。 He gave a
demonstration of high voltage electricity flowing harmlessly over his body。
But in reality； he cheated； because he had used a frequency of 10；000
cycles （10 kHz） at extremely low current and because of the skin effect
suffered no harm。
One of Tesla's patents related to a system of lighting using glass tubes
filled with fluorine （not neon） excited by H。F。voltages。 His workshop was
lit by this method。 Several years before Wilhelm Roentgen demonstrated
his system of X…rays Tesla had been taking photographs of the bones in his
hand and his foot from up to 40 feet away using H。F。currents。
More astonishing still is the fact that in 1893； two years before
Marconi demonstrated his system of wireless signaling； Tesla had built a
model boat in which he combined power to drive it with radio control and
robotics。 He put the small boat in a lake in Madison Square Gardens in
New York。 Standing on the shore with a control box； he invited onlookers
to suggest movements。 He was able to make the boat go forwards and
backwards and round in circles。 We all know how model cars and aircraft
are controlled by radio today； but when Tesla did it a century ago the
motor car had not been invented； and the only method by which man could
cover long distances was on horseback！
Many people believe that a modification of Tesla's ‘Magnifying
Transmitter' was used by the Soviet Union when suddenly one day in
October 1976 they produced an amazing noise which blotted out all radio
transmissions be
