The initial long distance transmissions had been made using very long wavelengths, typically in excess of 2000 metres. Then in the early 1920s the short wave bands were starting to be exploited. Many professionals including Marconi started to experiment with these bands carrying out many experiments.
With proof that the short wave bands could provide reliable communication over long distances the British Government decided that it needed to install an Imperial Wireless Network. The Marconi Company approached the British Government and offered to link up the Empire with short wave stations in England, Canada, India, South Africa and Australia. As the technology was very new and there was a high risk of failure the Government insisted that Marconi bore all the risk of failure. Once installed the system was very successful, and very reliable.
Marconi 7777 patent
One of Marconi's most famous "inventions" was that of tuning. The famous Marconi 7777 patent for Improvements in Apparatus for Wireless Telegraphy was granted on 26 April 1901. It arose out of the need to separate signals from each other because one of the major problems Marconi faced was that of interference between different transmitting stations. Using the concept behind the Marconi 7777 patent tuning of the transmitter, receiver and antenna enabled interference to be considerably reduced.
The new invention was based in part on earlier work by Sir Oliver Lodge where Lodge had tuned the sending and receiving aerials. Lodge was unhappy as he felt it infringed his work and litigation followed. However the 7777 patent gave Marconi a significant edge over the competition: Using concept of the patent allowed simultaneous transmissions on different frequencies - something which was revolutionary in these early days of radio communications.
The result was that radio communications stations close to one another were able to operate with reduced levels of interference and as a result ranges could be increased.
The coherer had long been used but was a particularly insensitive element within the overall radio communications system. It needed a very large spark discharge to cohere. As a result new forms of detector were investigated and after much work Marconi patented the magnetic detector as an invention.
From around 1902 ships that had Marconi radio communications equipment installed on them used the magnetic detector. It provided a higher level of sensitivity, better discrimination of interference, and faster signalling speeds.
The magnetic detector had been developed by Marconi from an original experimental detector that had been used by Rutherford in 1985 as part of his radio communications experiments.
Marconi business growing pains
The business model Marconi used for his radio communications equipment was to charge a rental fee. This also included the fees for the use of a trained radio operator and the use of the Marconi shore based stations. In this way he did not infringe the monopoly held at that time by the British General Post Office.
This arrangement also enabled the company to restrict competition as users with equipment from competitors could not use the shore stations except for emergency communications.
With the Marconi company possessing a large number of strategically located stations, this provided a strong incentive for ships to use the Marconi equipment rather than that of a competitor.
There was a growing call for international cooperation and legislation in view of the degree of chaos on the radio bands with some operators even deliberately jamming or interfering with the transmissions of others. International agreements were drawn up and it became necessary for all radio communications stations to be licensed by the various countries of origin.
As a result, on 1 January 1905 radio communication within Great Britain came under the control of the Wireless Telegraphy Act 1904. All radio communications stations were licensed including the shore stations which were given a licence for eight years.
Under the terms of the agreement telegraph messages or "Marconigrams" could be sent to and from the ships at sea and then relayed through the standard land based telegraph system operated by the British General Post Office or GPO.
Ultimately the government owned GPO required that the shore stations were sold to them, and this meant that Marconi had to further improve his commercial offerings.
Early transmitter technology used a spark discharge connected to an aerial to provide the signal. Today this seems a particularly crude form of radio communications technology. Marconi had noted that the technology had been in use for a number of years and needed improving to ensure the continued development of the overall radio communications technology.
One of the key issues was that once the spark was struck, and remained conductive, the radio frequency energy created by the spark transferred from the spark circuit to the antenna and back many times with much of the RF energy being absorbed in the spark rather than being radiated.
In addition to this the signal was very broadband in nature and also gave a very rough sound in the operator's headphones.
To improve the overall efficiency of these early radio communications transmitters, Marconi invented a system whereby the spark was struck and extinguished in a more controlled manner using a studded disc to vary the length of the spark.
As each stud on the wheel came towards the stationary electrode, the gap narrowed and the spark struck. As it then moved away the length of the spark increased and eventually it extinguished.
This development or invention had a number of advantages. Firstly, the signal received by the operator had a far more musical note and was easier to copy. Secondly the extinction of the spark was timed to occur as the reflected power was returned from the aerial circuit. As the oscillations from the spark were unable to return to the now extinguished spark, the oscillations reduced slowly increasing the efficiency and also reducing the signal bandwidth.
The result was that Marconi introduced the system onto his transatlantic transmitters in 1907 thereby increasing the reliability, although in reality, messages often needed to be transmitted several times to prevent errors.