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A WIRELESS TELEPHONE ' 283

This experiment may be - tried by- any boy with the
equipment he probably has already around his .shop.
Twenty-five to thirty turns of wire wound. around a card-
board tube five or six inches in diameter will serve as a
coil. Two such coils, an ordinary telephone transmitter, a
telephone. receiver and a couple of dry. cells are all that is
required.

The diagram in the accompanying illustration shows
how the apparatus is arranged. The coils may be used

  
 

R£O£IVER

BATTERY

FIG. 238. —A Simple Wireless Telephone.

Speech directed into the Transmitter can be heard in the Receiver, although there is no direct
electrical connection between the two. ‘

several inches apart 'and the voice will be clearly heard in
the receiver. -

Such ' an outfit is, however, only experimental, and if it
is desired to make a practical set, the coils, etc., must be
much larger in diameter and contain a greater number of
turns.

Larger coils are made by first drawing a circle four feet
in diameter on the floor of the “ shop ” or attic. Then

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