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The
History of Amateur Radio
Marconi : Time for business (III)
Thanks
to Hertz's discoveries and Morse's inventions, in
1894 the young Italian Guglielmo Marconi was convinced that he could
transmit signals by electromagnetic waves, thus without using the support
of a wire connecting stations. He created a "Hertzian oscillator" and
"decoherer" to send a signal in the air over 3. 2 km (2 miles) in Salisbury Plain, England. Quickly
he increased the distance separating the receiver from the transmitter and
was able to transmit a CW signal over water, passing over the Bristol
Channel. In 1895 he invented the "spark gap" transmitter that we
will describe later.
In
July 1897 he formed The Wireless Telegraph & Signal Company
Limited (in 1900 re-named Marconi's Wireless Telegraph Company
Ltd). He gave a demonstration to the Italian Government at Spezia
where wireless signals were sent over a distance of 20 km (12
miles). In 1899 Marconi established the first wireless
communication across the English Channel between France and
England. He erected then permanent wireless telegraph stations at
The Needles on the Isle of Wight, at Bournemouth and later at the
Haven Hotel, Poole, Dorset.
Marconi
also gave a large number of lectures. One of his readers was English man Meade Dennis
that tried successfuly to repeat his experiments. In 1898 Dennis
installed at Woolwich Arsenal on the Dartford to London route what is today considered as the
first amateur experimental radio station. |
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Guglielmo Marconi, 1900s, the man who made the wireless telegraph a business.
Document Nobel. |
The
Englishman Leslie Miller, an advanced amateur, published in the
January 1898 issue of The Model Engineer and Amateur
Electrician the first description of what he called a
simple-to-build transmitter and receiver for an amateur audience.
Next year the US magazine Scientific American published a
long article discussing Marconi's results while the July 1899 issue of American Electrician magazine
gave details on the construction of Marconi's antenna and his
wireless radio equipment.
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These
three articles received a considerable interest not only from
professionals who tried to apply this invention but also from the
experienced amateurs, alway curious and attracted by new technologies, and
the "wireless" counted among them. The French speaking countries
knewn it as "T.S.F", standing for "Télégraphie
Sans Fil" (wireless telegraphy) as printed on the original
drawing displayed at left and sold by Guérin-Boutron chocolates.
In
1900 Marconi took out his famous patent No.7777 for "tuned or
syntonic telegraphy". To be complete note however that in 1943
United States Supreme Court overturned Marconi's patent on radio because
Tesla's work on coils and transport of electricity by air had predated
Marconi's invention.
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Drawing
made in the early 1900s showing the first wireless (TSF)
installation in France on a box of Guérin-Boutron chocolates. |
1901
: First signal transmitted across the ocean
On
December 12, 1901, Marconi was determined to prove that waves were
not affected by the curvature of the Earth and asked an operator to go to
Poldhu, Corwall, England, with a spark gap transmitter and a long dipole
to place about 20 m high. With an assistant, Marconi took his receiver and
went to St. John's, Newfoundland where he launched one more time a large
silk-and-bamboo kite in the air. In spite of the high wind, this time the
wire hold. At 11:30 AM a telegram was hurriedly dispatched to
Poldhu, asking the operator to begin transmission. While keying sparks of
blue electric fire, on the other side of the Atlantic, at about 12:30
Marconi heard three distinct clicks, the Morse letter "S".
Great ! For the first time in history, a radio signal was successfully
transmitted across the ocean and covered a distance of
3360 km (2100 miles). That was a true revolution that the press and experimenters
applaud warmly ! This demonstration launched the commercial use of radio. Ships were equipped with
radio, huge commercial stations were set up to handle intercontinental
messages, and this new technology was soon applied to many other areas. Marconi received the Nobel
prize in Physics in 1909.
The
Birth of Amateur radio
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In
the early days of wireless communications Marconi took
advantage of Tesla discovery on coils that were able to transport
electricity by air. He discovered that a voltage applied inside a
spark coil was able to discharge a capacitor across a gap, creating an
oscillating spark, which was coupled to an antenna. These "spark
gap" transmitters produced RF but were broadband, up to spread the
signal over a few hundreds of kilohertz !
The
first transmitters were powered by either low voltage storage
batteries, or a DC dynamotor generating about 5 to 30 V DC. The low
voltage was fed to one side of a telegraph key. As the key was
depressed, the circuit closed and current flew into the primary
side of an induction coil. This induced high voltage currents to
flow in the secondary windings of the coil. These high currents
charged the antenna, then discharged across the sprak gap
electrodes to ground. This action produced magnetic waves for each
discharge across the spark gap electrodes. The wire antenna was
connected to the induction coil by means of another coil with a
moveable tap. A broad band wave, the word is weak, would then be radiated from the
antenna. The spark was keyed on and off to transmit the code. Later
Marconi employed a low voltage AC that was fed to the primary side
of a transformer. The high voltage alternating currents at the
secondary of the transformer could range from 2000 volts to 25000
volts AC, hence the label "DANGER" sometimes displayed in
vintage hamshacks. |
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Tesla
coils were invented to transmit electricity through the air. This
picture of a high voltage discharge
is known as a "spark gap", a technique reused at a
smaller scale in Marconi's wireless telegraphy. |
In
1905 a "state of the art" spark gap transmitter operated on 400
meters (750 Kc) and generated a signal from about 250 meters (1.2 Mc)
to 550 meters (545 Kc). The receiver was simple unamplified detectors,
generally coherers (small quantity of metal filings lying loosely between
metallic electrodes). This later gave way to the famous and more sensitive
galena crystal sets. Tuners were primitive or nonexistent.
To
check : The Spark
Museum
Although
these wireless stations were terribly inefficient compared to you modern standards, these transmitters were
able to reach distance from as little as 180 m (600 feet) with a 12 mm coil (0.5") coil to about 160 km (100 miles) using a 38 cm (15") spark
coil and a kilowatt station. Professional installations like ships at sea used transmitters up to 5 kW and reached
distances up to 800 km (500 miles), a record for the time.
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At left the simplest spark gap transmitter using a 25 cm (10") coil. The battery and the key are
applied on brass contacts at right of the plate. The tuning coil and antenna are connected ontop of
the right electrode. The system is grounded via the left electrode. At right
a painted picture showing Marconi behind
another model of spark gap transmitter (left) and a magnetic detector
working as receiver (right, hidden in the box). Here is the original
B/W image. Sources unknown. |
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In
1904 the Englishman J.A. Fleming developed the first vacuum diode using a
cathode and an anode, known as the the Fleming Valve and four years later
he invented the tungstene filament. In
1906, Lee de Forest had a genious idea. He took Fleming's valve, added a
third element, called the grid, and named the result the Audion. Placed in
a new circuit the Audion could amplify a signal 5 times. But as it
required much power and was still expensive his invention was not used
by the amateurs until
1912 and the discovery of
Edwin H. Armstrong (feedback) that we will describe on the next page.
In
1908 the magazine Modern Electrics was the first magazine fully dedicated to wireless communication.
In just two years its circulation passed from 2000 to over 30,000 copies ! The
success was resounding. In the same time the first experimenters found on bookstore shelfs the first
radio handbook titled "Wireless Telegraph Construction for
Amateurs".
By
1910 the time of the wired or "no wireless" was practically
over and both professionals and amateurs had well understood the power of
this new "wireless" medium. This year for example the
Belgian Paul de Neck, future ON4UU, did one of the first experimental
wireless transmissions using a spark gap transmitter. Paul de Neck was the
first belgian amateur radio and will be later ('30s) the co-founder of the first
Belgian Network as well as the President of the first Belgian
Radio Clubs Union (URCB).
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This
is in this context that the early experimenters interested in amateur
radio ventured. But at that time their activity was not oriented to
personal communications with other stations, or very few. In fact these
"amateurs" concentrated on technical development, either in the interest of pure science through universities or
personal interests, or more often, for the
simple curiosity to share the first steps of this new "high
tech" medium.
But not
everybody could experiment this new technology. Eveybody didn't go to
school yet and learnt to read, and thus very few people were able to understood how
these systems worked. Most experimenters were thus pioneer stations. Among them name
Harold H. Beverage, the famous inventor of the (very long) longwire of the same name
that we see here at left operating his amateur radio station in 1915,
probably at the University of Maine. |
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Harold H. Beverage, alias "BEV" at work, probably in his ham
shack at University of Maine, in 1915. |
After
the publishing of various designs for
wireless equipment in magazines, many experimenters built their own radio
transmitter and receiver. The modest installation emitted at short
distances, a few tens of kilometers, and were not disturbed by interference
yet, contrarily to their professional colleagues. At that time, where
radio communications were not regulated yet, we estimate the number of "major"
amateur stations capable of communicating over 15 km at 600, while "minor" stations emitting in a 1-3 km range probably
to about 3000, maybe more.
In
parallel, by 1910 they were 488 merchant vessels and yachts active on wireless in
the USA, some tens in european countries, and a handful in Russia, Brazil and Cuba.
These people worked on 300-600 meters (1000-500 Kc) with a power ranging
from 350 watts (most) to 2 kW using a relatively small Marconi antenna. Due to the
spark gap their emissions were broadband and these professionals created already at that time
much, much QRM.
Next
chapter
Ham,
the poor operator
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