Radio Shack

The Condensers.–For the aerial series condenser get one that has a
capacitance of .002 mfd. and that will stand a potential of 3,000
volts. [Footnote: The U C-1014 _Faradon_ condenser made by the Radio
Corporation of America will serve the purpose.] It is shown at C. The
other three condensers, see D, are also of the fixed type and may have
a capacitance of .001 mfd.; [Footnote: List No. 266; fixed receiving
condenser, sold by the Manhattan Electrical Supply Co.] the blocking
condenser should preferably have a capacitance of 1/2 a mfd. In these
condensers the leaves of the sheet metal are embedded in composition.
The aerial condenser will cost you $2.00 and the others 75 cents each.
[Illustration: (A) Fig. 75.–Apparatus for Experimental C. W.
Telegraph Transmitter.]
[Illustration: Fig. 75.–Apparatus for Experimental C. W. Telegraph
Transmitter.]
Waym 88.7 Mhz In Columbia The Aerial Ammeter.–This instrument is also called a _hot-wire_
ammeter because the oscillating currents flowing through a piece of
wire heat it according to their current strength and as the wire
contracts and expands it moves a needle over a scale. The ammeter is
connected in the aerial wire system, either in the aerial side or the
ground side–the latter place is usually the most convenient. When you
tune the transmitter so that the ammeter shows the largest amount of
current surging in the aerial wire system you can consider that the
oscillation circuits are in tune. A hot-wire ammeter reading to 2.5
amperes will serve your needs, it costs $6.00 and is shown at E in
Fig. 75.
[Illustration: United States Naval High Power Station, Arlington Va.
General view of Power Room. At the left can be seen the Control
Switchboards, and overhead, the great 30 K.W. Arc Transmitter with
Accessories.]
The Buzzer and Dry Cell.–While a heterodyne, or beat, receptor can
receive continuous wave telegraph signals an ordinary crystal or
vacuum tube detector receiving set cannot receive them unless they are
broken up into trains either at the sending station or at the
receiving station, and it is considered the better practice to do this
at the former rather than at the latter station. For this small
transmitter you can use an ordinary buzzer as shown at F. A dry cell
or two must be used to energize the buzzer. You can get one for about
75 cents.
The Telegraph Key.–Any kind of a telegraph key will serve to break up
the trains of sustained oscillations into dots and dashes. The key
shown at G is mounted on a composition base and is the cheapest key
made, costing $1.50.
The Vacuum Tube Oscillator.–As explained before you can use any
amplifying tube that is made for a plate potential of 100 volts. The
current required for heating the filament is about 1 ampere at 6
volts. A porcelain socket should be used for this tube as it is the
best insulating material for the purpose. An amplifier tube of this
type is shown at H and costs $6.50.
The Storage Battery.–A storage battery is used to heat the filament
of the tube, just as it is with a detector tube, and it can be of any
make or capacity as long as it will develop 6 volts. The cheapest 6
volt storage battery on the market has a 20 to 40 ampere-hour capacity
and sells for $13.00.
The Battery Rheostat.–As with the receptors a rheostat is needed to
regulate the current that heats the filament. A rheostat of this kind
is shown at I and is listed at $1.25.
The Oscillation Choke Coil.–This coil is connected in between the
oscillation circuits and the source of current which feeds the
oscillator tube to keep the oscillations set up by the latter from
surging back into the service wires where they would break down the
insulation. You can make an oscillation choke coil by winding say 100
turns of No. 28 Brown and Sharpe gauge double cotton covered magnet
wire on a cardboard cylinder 2 inches in diameter and 2-1/2 inches
long.
Transmitter Connectors.–For connecting up the different pieces of
apparatus of the transmitter it is a good scheme to use _copper
braid_; this is made of braided copper wire in three sizes and sells
for 7,15 and 20 cents a foot respectively. A piece of it is pictured
at J.