It is generally the receiving apparatus which first attracts the
attention of the amateur operator, and so it will be considered first
here. An efficient receiving set consists of some form of _Detector,
Tuning Coil, Telephone Receivers_, and _Condenser_.
Other accessories such as adjustable condensers, potentiometer, battery
and testing buzzer improve the outfit and make it more complete.
The choice of the type of instruments must be left entirely to the
person who is constructing them. His resources will determine whether he
is to use 1,000 ohm telephone receivers built especially for wireless
work or ordinary ones having a resistance of only 75 ohms. It is
therefore best to read carefully the chapters devoted to the different
pieces of receiving apparatus and select the type of detector, tuning
coil, etc., which it is desirable to use before commencing the
construction of any.
For beginners, I would recommend an outfit consisting of a silicon
detector, a double slide tuning coil, a condenser of fixed capacity and
75-ohm telephone receivers. Such an outfit with a 50-foot aerial will
receive messages about 150 miles. If 1,000 ohm telephone receivers are
used, messages may be read up to 400 miles. Much depends upon the
location of the station and the ability of the operator.
A more elaborate and efficient set consists of an electrolytic or
"Perikon" detector, a transforming tuner, two adjustable condensers, a
potentiometer and a pair of 1,000 ohm telephone receivers. This outfit
and a 75-foot aerial could be made to receive 500 to 1,000 miles by a
careful operator.
Several cuts of wireless apparatus built for private installation are
shown both in this chapter and further through the book, to give an idea
of how the better instruments of this type are constructed and finished.
[Illustration: Fig. 10. Long-distance Receiving Set.]
Fig. 10 illustrates a selective receiving set built by the Long Distance
Wireless Company. The set is mounted on a mahogany base and the
instruments are finished in polished hard rubber and lacquered brass.
They comprise a detector stand so arranged that any of the sensitive
minerals used in wireless work may be used. The tuning coil is of the
double slide type. The condenser is sealed up in a square lacquered
brass tube fitted with hard rubber ends and binding posts. The
arrangement and construction of the outfit may be readily understood
from the cut.
[Illustration: Fig. 11. Murdock Receiving Set.]
Fig. 11 illustrates a receiving set manufactured by the Wm. J. Murdock
Company. The tuning coil is fitted with hard rubber composition ends and
is wound on a special core which is not affected by temperature changes.
The detector is of the crystal type and is of rather unique
construction, since the small fixed condenser is mounted in the base of
the detector itself.
The Clapp-Eastham set in Fig. 12 employs a receiving transformer which
makes great selectivity possible. The detector is mounted at the
left-hand side of the outfit. A very sensitive mineral called "Ferron"
is used in the detector. The fixed condenser is enclosed in a brass tube
fitted with hard rubber ends and is located on the front of the base,
directly in the center. A variable condenser of the rotary type is
placed at the right-hand corner.
[Illustration: Fig. 12. Clapp-Eastham Receiving Set.]
The Prague Electric Company manufacture the apparatus shown in Fig. 13.
The cabinet is mahogany and is fitted with a hard rubber cover. A fixed
condenser and a double slide tuning coil are mounted within the cabinet.
The sliders of the tuning coil project through two long slots in the
cabinet. A universal detector mounted on top of the cabinet is so
designed that any material may be experimented with or tested.
[Illustration: Fig. 13. Prague Receiving Set.]
Fig. 14 shows a receiving set built up from apparatus described in this
book. The cabinet is 12 x 16 inches and 4 inches deep. The wood should
be 1/2 inch thick, and in order to present a good appearance is
preferably of mahogany. As mahogany is sometimes very hard to procure
and expensive, some may find red birch an excellent substitute. When
stained with a mahogany stain it presents a fine appearance.
[Illustration: Fig. 14. Receiving Set.]
Varnishing and polishing are wasted time when applied to the average
amateur’s instruments in view of the rough handling and scratching which
they receive. The best plan is to stain the wood with an oil stain and
give it a wax finish. An oil stain contains no varnish but is merely
coloring matter and oil. A good coat should be applied with a wide brush
and the surplus stain immediately wiped off by rubbing the whole surface
with a piece of cheesecloth. As soon as the stain is thoroughly dry the
wood is waxed.
Cut up some beeswax into fine shreds and place it in a jar. Pour some
turpentine over the beeswax and let the mixture stand for five or six
hours, giving it an occasional stir. Allow it to stand further if
necessary until the wax melts and then add enough turpentine to give the
mixture a consistency similar to that of thick cream. Apply the
preparation to the wood with a rag, and then rub with a piece of clean
cheesecloth until the finish is hard and dry. Waxing produces a gloss
which is not so bright as a French polish but yet is more durable and
not so easily scratched or marred.
A double slide tuning coil made as described in Chapter XIV is mounted
on top of the cabinet in the rear. A "universal" detector is mounted in
the center, directly in front of the tuning coil. A tubular condenser of
fixed capacity is placed on the left-hand side of the detector, and a
potentiometer on the opposite side. A double point switch placed
directly in front of the detector enables the potentiometer to be
brought into play when a battery is used. Four binding posts are mounted
on the front of the cabinet. The ground and aerial are connected to the
left-hand pair and the telephone receivers to those on the right hand.
The wiring diagram is shown also in Fig. 14. By placing the switch _A_
on contact 1, the potentiometer is brought into use. When on contact 2,
the potentiometer is cut out. The switch _B_ must be opened when the
detector is not in use so as not to run down the battery.
[Illustration: Fig. 15. Receiving Set.]
Fig. 15 shows a receiving set somewhat similar to that shown in Fig. 14
but more elaborate and efficient. The cabinet in this case measures 14 x
22 inches and is 6 inches deep. A loosely coupled or transforming tuning
coil is used in place of the closely coupled double slide type. Two
variable condensers are mounted on either side of the tuning coil. The
detector and potentiometer occupy the space directly in front of the
tuning coil, while a fixed condenser is placed at their right. The two
switches for breaking the battery circuit and disconnecting the
potentiometer are in front of the detector. The aerial, ground and
telephone receiver leads are connected to binding posts mounted on the
front of the cabinet.
The batteries, in both cases, are placed inside the cabinet. The details
and construction of all the separate instruments will be found in the
respective chapters as denoted by the titles.
*Transmitting Range.*—A simple transmitting outfit capable of sending
about two miles consists of the necessary batteries, a one-inch spark
induction coil, a small zinc spark gap and a key. The connections of
such a transmitting outfit are shown in Fig. 4.
If the same coil is used with a transmitting helix and a condenser, the
range may be increased from 3 to 5 miles.
A 1 1/2-inch spark induction coil using a condenser and a transmitting
helix will send about 10 miles, and a 3-inch coil under the same
conditions about 20 miles. A 4 and a 6 inch coil will transmit about 30
and 40 miles respectively.
[Illustration: Fig. 16. Murdock Transmitting and Receiving Set.]
The one quarter kilowatt transformer with a helix and four two-quart
leyden jars or an equivalent condenser will transmit at least 50 miles
with a suitable aerial. Used as a one half kilowatt transformer with a
helix and eight two-quart leyden jars, it will send about 100 miles.
Of course, as in the case of the receiving outfits, these distances are
approximate and depend upon the location of the station, the nature of
the ground over which the messages are transmitted, the kind of receptor
used at the receiving station and the efficiency of the operator
himself.
Fig. 16 illustrates a complete Murdock transmitting and receiving set.
The transmitting outfit consists of a 15-watt induction coil giving
about a one-inch spark, a sending helix, oscillation condenser, a key
and a double pole double throw switch for changing the antenna and
ground from the transmitting to the receiving instruments or vice versa.
The spark gap is mounted on top of the coil. The receiving outfit is the
same as that illustrated in Fig. 11.
*A complete wireless station*—outside of the aerial consists primarily
of a source of electrical energy, a transformer or induction coil for
charging the oscillation condenser, an oscillation condenser, a
transmitting helix, a key for breaking the primary current, a spark gap,
an aerial switch, a hot wire ammeter for tuning the transmitting
circuits, a detector, a receiving tuner, auxiliary tuning apparatus such
as fixed and variable condensers, a potentiometer and battery, and a
pair of telephone receivers with a headband.
Other apparatus such as switches, insulators, anchor gaps, testing
buzzers, reactance coils, grounding switches, etc., have been described
in various places throughout the book and their use suggested whenever
it is of any advantage.
The choice of transmitting instruments, as with the receiving apparatus,
is left entirely with the experimenter so that he may suit his ideas and
means. Wherever possible the range and power of the instruments have
been given and suggestions made as to the other apparatus which should
be used in connection with them so that the completed outfit will bear
some sense of proportion.
[Illustration: Fig. 17. United Wireless Portable Outfit.]
Fig. 17 illustrates the portable wireless telegraph set manufactured by
the United Wireless Telegraph Company for army service and exploring
expeditions or isolated camps. The aerial and the mast can be unloaded,
erected, and all parts be ready for operation in fifteen minutes. The
mast is made of interchangeable wooden sections. The current for the
transmitter is furnished by a portable storage battery. The whole outfit
is capable of furnishing efficient service for distances of 25 to 30
miles.