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.
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.
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.
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
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.
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.
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.
To check : The Spark Museum
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).
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.
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.