7). This will make an
excellent receiver. It will be necessary to adjust the platinum
points, W W, to suit the distance the message is to be worked. For
a mile or less the points should be about 1/16 in. apart, and
closer for longer distances.
The tuning coil is simply a variable choking coil, made of No. 14
insulated copper wire wound on an iron core, as shown in Fig. 7.
After winding, carefully scrape the insulation from one side of
the coil, in a straight line from top to bottom, the full length
of the coil, uncovering just enough to allow a
[Illustration: Aerial]
good contact for the sliding piece. The tuning is done by sliding
the contact piece, which is made of light copper wire, along the
convolutions of the tuning coil until you can hear the signals.
The signals are heard in a telephone receiver, which is shown
connected in shunt across the binding posts of the lamp holder
with one or two cells of dry battery in circuit, Fig. 7.
[Illustration: Details]
The aerial line, No.6 stranded, is run from binding-post B through
the choking or tuning coil, and for best results should extend up
50 ft.
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