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| Photo courtesy Science Museum, London |
The Marconi 10 inch coil formed the heart of many transmitters during the era of the spark gap . It was used as a ship or shore transmitter from the beginning of the Marconi company( 1898), until they made larger transmitters. It was used as an emergency transmitter on the Olympic and the Titanic. (1912).The British coil used two batteries of eight cells which gave an output voltage of sixteen volts.
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| Photo courtesy Science Museum, London |
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Figure 247 - Parts of the 10 inch coil explained. Click on image to enlarge (From The Handbook of Technical Instruction for Wireless Telegraphists 1925 edition) |
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| Figure 241.
The actual configuration when the 10 inch coil is used as an emergency
transmitter. Click on image to enlarge. (From The Hanbook
of Technical Instruction for Wireless Telegraphists 1925 edition).
The primary winding
of the has a resistance of 19 ohms. It was wound with 360 turns of
No. 12 double cotton covered wire . The secondary was wound with 54,000
turns of No. 34 silk covered wire. The ordinary working current taken
by this coil is about eight amperes at sixteen volts. Eight ``Chloride
`` cells were used , with a capacity of 80 ampere hours. The coil
could transmit for ten hours on these batteries. The normal charging current
of 12 amperes, took about 7 1/2 hours to charge fully the batteries
which have been run down to their safety limit. The average range ws 60
nautical miles on the batteries and 80 on the ships mains, without tuning
coils. On fig. 247, "X" is called a commutator. It was an on-off,
and polarity reversing switch for the primary.
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| This is a typical early spark gap transmitter installation with Layden jars (for tuning ), and a fixed tuning coil. It was fixed rather than variable and was located in in the large teak box. (Photo courtesy Canada Science and Technology Museum, Ottawa) |
Contributors and Credits:1) Lewis Bodkin [05bodkin555(at)gmail.com]
Mar 15 /21