the dawn of amateur radio in the u[1].k.(收音机雏形的诞生)-第3节
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！
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 between 6 and 20 MHz。 （The Woodpecker） The B。B。C。； the
N。B。C。 and most broadcasting and telecommunication organisations of the
world complained to Moscow （the noise had persisted continuously for 10
hours on the first day）； but all the Russians would say in reply was that
they were carrying out an experiment。 At first nobody seemed to know
10
… Page 11…
The dawn of amateur radio in the U。K。 and Greece ： a personal view
what they were doing because it was obviously not intended as another
form of jamming of foreign broadcasts； an old Russian custom as we all
know。
It is believed that in the pursuit of his life's ambition to send power
through the earth without the use of wires； Tesla had achieved a small
measure of success at E。L。F。 （extremely low frequencies） of the order of 7
to 12 Hz。 These frequencies are at present used by the military for
communicating with submarines submerged in the oceans of the world。
Tesla's career and private life have remained something of a mystery。
He lived alone and shunned public life。 He never read any of his papers
before academic institutions； though he was friendly with some journalists
who wrote sensational stories about him。 They said he was terrified of
microbes and that when he ate out at a restaurant he would ask for a
number of clean napkins to wipe the cutlery and the glasses he drank out
of。 For the last 20 years of his life until he died during World War II in
1943 he lived the life of a semi…recluse； with a pigeon as his only
companion。 A disastrous fire had destroyed his workshops and many of his
experimental models and all his papers were lost for ever。
Tesla had moved to Colorado Springs where he built his largest ever
coil which was 52 feet in diameter。 He studied all the different forms of
lightning in his unsuccessful quest for the transmission of power without
wires。
In Yugoslavia； Tesla is a national hero and a well…equipped museum
in Belgrade contains abundant proof of the genius of this extraordinary
man。
11
… Page 12…
The dawn of amateur radio in the U。K。 and Greece ： a personal view
CHAPTER TWO
THE BIRTH OF RADIO COMMUNICATIONS
By 1850 most of the basic electrical phenomena had been
investigated。 However； James Clerk Maxwell （1831…1879）； Professor of
Experimental Physics at Cambridge then came up with something entirely
new。 By some elegant mathematics he had shown the probable existence
of electromagnetic waves of radiation。 But it was twenty four years later
（eight years after Maxwell's death） that Heinrich Hertz （1857…1894） in
Germany gave a practical demonstration of the accuracy of this theory。 He
generated and detected electromagnetic waves across the length of his
laboratory on a wavelength of approximately one metre。 His own
photograph of the equipment he had set up can be seen in the Deutsches
Museum in Munich。
To detect the electromagnetic waves Hertz employed a simple form
of oscillator； which he termed a resonator。 But it was not sensitive enough
to detect waves at any great distance。 Before wireless telegraphy could
become practicable； a more delicate detector was necessary。
Credit is due to Edouard Branly （1844…1940） of France for producing
the first practical instrument for detecting Hertzian waves； the coherer。 It
consisted of two metal cylinders with leads attached； fitted tightly into the
interior of a glass tube containing iron or steel filings。 The instant an
electric discharge of any sort occurred the coherer became conductive； and
if it was tapped lightly its conducting property was immediately destroyed。
In practice the tapping was done automatically by a tapper which came
into action the moment the coherer became conductive。
In Russia the physicist Aleksandr Popov （1859…1905） had used a
coherer while engaged in the investigation of the effects of lightning
discharges。 He suggested that such discharges could possibly be used for
signaling over long distances。 Old timers may remember that about 50
years ago Russian amateurs used to send out a QSL card with a drawing of
Popov and a caption which claimed that he was 'the inventor of radio'。
In Italy； a young 22…year…old electrician became interested
