15 octubre 2007

Some Interesting Radio History

He recibido este interesante texto de AJ5H:

1820 - Hans Christian Oersted discovers Electromagnetic Induction.

- Andre M. Ampere laid the foundations for the science of

electrodynamics demonstrating that electrical currents

produce magnetic lines.

1826 - Joseph Henry is best known for his discovery of electromagnetic

induction and self-induction. The unit of Inductance, the

Henry was named in his honor.

1831 - Michael Faraday demonstrates the principle of Induction. His

research into electricity lead him into the field of

electromagnetism. That current flowing through a wire produced

magnetic lines of force around that wire.

1836 – Samuel Morse formulates the elements of a communications relay

system. A year later the system is improved and demonstrated

using wires and morse code.

1840 – A telegraph line was constructed between Washington and

Baltimore and the first message sent on May 24, 1844 was “What

hath God wrought?”

1851 - Hans C. Oersted dies in March.

1852 – Thomas Edison invents the automatic telegraph.

1864 - James C. Maxwell developed Maxwell's Equations which were an

extension and mathematical formulation of Faraday's theories of

electricity and magnetic lines of force.

1867 – Michael Faraday dies in August.

1868 – Thomas Edison invents the stock ticker.

- Amos Dolbear while a professor at Bethany College invented the

electrostatic telephone. Dolbear also work on converting

sound waves into electrical impulses.

1873 - James C Maxwell publishes a book on electricity and magnetism.

1875 - Charles Coulomb demonstrates the manner in which electric charges

repel each other.

1877 – Thomas Edison invents the phonograph.

1878 - Joseph Henry dies in May.

1879 - James C. Maxwell dies

1882 – Thomas Edison develops the first central electric light power

station.

- Professor Amos E. Dolbear was able to communicate over a

distance of a quarter of a mile without wires in 1882. It is

interesting to note that Prof. Amos Dolbear preceded Hertz and

Marconi.

1887 - German physicist Heinrich Hertz first discovers Radio Waves. He

transmitted an electrical spark which was heard in a

receiving circuit a few meters away, thus the term Hertzian

Wave.

Hertz demonstrated that the velocity of radio waves equaled the

speed of light. The unit of frequency was named in his honor.

1894 – Guglielmo Marconi first experiments with Hertzian Waves.

Heinrich Hertz dies in January.

1895 - Marconi uses the oscillators of Hertz and Augusto Righi. The signals

were too weak so Marconi connects the oscillator to antenna and

ground to increase power. It is also in 1895 when Marconi sends

his first wireless radio transmission at Pontecchio, Italy.

Three dots(the letter "S") were heard behind the hill three

kilometers away.


1896 - Marconi leaves for London, Marconi performed his first offical

experiment from the terrace of the Post Office to the Salisbury

Plain. He was granted the world’s first radio patent.

1897 - The British Ministry gives Marconi money and technicians to

continue his work. Marconi signals reached 5, 8, 15, 30 and

100km. In July Marconi formed the Wireless Telegraph Trading

Signal Co. LTD.

- Thomas Edison develops the first practical incandescent lamp.

1898 - For the first time telegraph is used to send a help signal from

a lighthouse boat in August. In September Marconi comes to the

US where he carries out a telegraph circuit for the Navy between

the cruisers New York and Massachusetts. U.S. Navy establishes

coastal stations and begins to outfit the fleet with spark

wireless. First wireless used for journalism for the Daily

Express.

1899 - Marconi is granted patent no. 7777 for his Tuning equipment. He

also proved through experiments that the curvature of the Earth

was not an obstacle with his 32 mile connection from England to

France.

1900 - The Wireless Telegraph Trading Signal Co. Ltd changes its' name

to the Marconi Telegraph Co. Marconi gets his English patent

for his Tuning equipment.

1901 - Marconi receives a weak signal, the letter "S", the

first signal to cross an ocean, from Poldhu, Cornwell,

England, to St. John's Newfoundland, Canada. To give you some

idea of the size of the station, power for one of the stations

was provided by a 75 kw alternator driven by a coal-fired steam

engine. The antenna was an inverted pyramid of copper wires

supported by four latticework towers that were 210 foot high.

1902 - Marconi builds a radio station at Glace Bay, N.S. It is during

the trip that he discovers the harmful influence of solar

radiation on tramissions. Thus the creation of the Magnetic

Detector. The station at Glace was set up as the transmitting

station, while the station in Europe at Poldhu was the receiving

station. They would use the cable line as a means to verify

communications between the two stations. On December 15th the

first offical messages came through from Table Head to Poldhu

sayin "we have received some signals".

1903 - Marconi establishes the first press agency between Europe and

America. January 18th the first two-way transatlantic

transmission between Poldhu, England and Cape Cod, Mass. USA.

1904 – John Fleming invents the thermionic valve.

Marconi built the Rotating Oscillator and discovered the

directive properties of horizontal antennas. Starts to use the

Fleming thermoionic valve.

1905 - Fleming developed the first diode known as the Fleming Valve.

- Marconi patented his directive horizontal antenna.

1906 - 27 nations signed the International Wireless Telegraph

Convention in Berlin.

- Greenleaf Pickard invented the silicon detector.

- Reginald Fessenden broacsast the first program of speech and

music transmitted by radio. He was also know for his inventions

of the heterodyne system of radio, sonic depth finder, radio

compass and others.


1907 - Clarence D. Tuska the first Secretary of the A.R.R.L. started

working with the Coherer.

- Marconi, Commerical transatlantic wire service inaugurated

between Glace Bay and Clifton Ireland.

- Lee DeForest invents the audion also known as the triode. He was

granted over 300 patents in the field of wireless, radio,

telephone, sound-on-film, picture transmission and T.V.

1909 - Marconi is awarded the Nobel prize for Physics.

1912 - Marconi invents a new way to generate a continuous wave, known

as the Multiple Spark System.

1913 - Clarence Tuska received his first Amateur station and Commerical

Operators Lic.

- The antenna at the Marconi site at Louisbourg was about 1

kilometer long, and was supported by six tubular steel towers

over 3000 ft high.

The spark coil formed the heart of the earliest radio transmitters. Marconi used a coil invented by Heinrich Rhumkorff. The rising and falling magnetic field of the primary coil induces a high voltage across the secondary. When the voltage is high enough it jumps the gap creating a spark. During the time the spark is present there is a high frequency alternating current field radiated from one pole of the spark gap.

The output of a spark gap transmitter is turned on and off by the operator using a special kind of telegraph key, designed with large contacts to carry the heavy current.


1914 - In the spring a small group of young Amateurs were using short

ranged spark coils.

According to the records, in January Hiram Percy Maxim called to

order the first meeting of the Radio Club of Hartford with some

23 members in attendance. By March the attendance grew to 35

members. It was then that H.P.M. had the idea that messages

could be relayed over great distances. In order to accomplish

this, a network would have to be set up across the country. With

this in mind, the American Radio Relay League was adopted and

formed. In October the newly formedleague published its's first

callbook which listed some 400 stations in 33 states and Canada.

- Marconi experiments successfully using the triode thermoionic

valve, this was the birth of radiophony.

1915 - Control of the A.R.R.L. was taken over by H.P.Maxim and

Clarance D. Tuska, the first Secretary of the League. The

League was incorporated, and the second callbook was issued

containing almost 600 members. The league published the first

issue of QST in December.

1916 - League membership jumped to around 960 members. It was in 1916

that the league made its' attempt at a nation-wide relay. 9XE

of Davernport Iowa, on Washingtons birthday, sent a message from

the Rock Island Arsenal addressed to the goveners of every state

and President Wilson. The relay time wasn't too bad. The

record exhibits that the message got to the Pacific coast in 55

mins,to the Atlantic Coast in 60 mins, to New Orleans and Canada

in 20 mins. By this time Amateurs were establishing reliable

trunk networks across the US. By the end of 1916 six trunks had

been established. Also in 1916 the first transcontinental

attempt was tried and failed due to static.

- Marconi started to develop the first VHF radios.

1917 - A second transcontinental attempt was made in January and was

successful. The message was sent by 6EA took 3 relays to H.P.M.

station in Hartford, Ct. In February a two-way circuit was

accomplished in one night. Amateur Radio closes down due to the

WAR. There were about 6000 amateur radio operators.

1918 - Thousands of Amateurs pound brass for the Army and Navy during

the War.

1919 - Marconi acquires the yacht Electra for radio experiments.

- Amateur Radio resumes after the WAR, and thousands of Hams

renew their A.R.R.L. membership. QSL cards first used.

1920 - QST carries an editorial on CW vs. SPARK as Amateurs take sides.

1921 - The second transatlantic test is run and is a success. This

spells the end of Spark as the Audion tube takes its' place.

1922 - There were over 15,000 licensed Amateur stations. Each country

was given a prefix letter (U-United States; U1AW). Then another

letter was added to designate the continent (NU1AW).

1927 - Legislation curtails spark-gap transmissions.

1931 - Marconi inaugurates the new Vatican Radio Station. He further

demonstrated the possibility of using microwaves communicating

between Santa Margherita Ligure and Levanto 36km away.

- Thomas Edison dies in October with more than 1000 patents to his

credit.

1932 - Marconi builds a permanent radiotelegraph connection between

the Vatican and Castel Gandolfo.

1934 - Marconi establishes a radiotelegraph link between the Electra

and the radio beacon in Sestri Levante. Federal Communications

Commission established in the U.S. Amateur radio licenses were

Class A, B and C.

1937 - July 20th Marconi dies, Radio Transmitters around the world close

down for two minutes in his memory. There were about 50,000

amateur radio operators.

1945 – John Fleming dies in April.

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