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18-Inch Induction Coil, by Marconi Company, London, 1898
Inventory Number: 81193
Number of documents: 2
Document Type: Miscellaneous Note
Document Heading: Historical Background
Text:
This particular piece of apparatus was used at Marconi's station at The Royal Needles Hotel, Isle of Wight, in 1898 for transmissions, which included the first commercial telegram sent by Lord Kelvin in the June of the same year.
Document Type: Miscellaneous Note
Document Heading: Technical Details
Text:
This apparatus is a step-up transformer. It has two wire windings, a primary of a few turns and a secondary of many turns. If the primary has 10 turns and the secondary 10,000 turns then the turns ratio would multiply the primary voltage one thousand times. The windings have a central soft iron core to concentrate the magnetic field which also works the contact breaker or interrupter. The interrupter rapidly breaks the primary current from the battery creating a high voltage in the primary circuit which is then multiplied by the turns ratio.
Marconi used this equipment (80% more powerful than the 10 inch induction coil) to generate high voltage. This caused ionization of the air between the two brass balls (spark gap) so providing a path for the string of sparks to jump. The oscillations caused by this discharge excite the aerial and earth system into producing wireless waves.
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