SIMPLE TELEGRAPH SENDING SETS
A wireless telegraph transmitting set can be installed for a very
small amount of money provided you are content with one that has a
limited range. Larger and better instruments can, of course, be had
for more money, but however much you are willing to spend still you
are limited in your sending radius by the Government's rules and
regulations. The best way, and the cheapest in the end, to install a
telegraph set is to buy the separate parts and hook them up yourself.
The usual type of wireless telegraph transmitter employs a _disruptive
discharge,_ or _spark,_ as it is called, for setting up the
oscillating currents in the aerial wire system and this is the type of
apparatus described in this chapter. There are two ways to set up the
sparks and these are: (1) with an _induction coil,_ or _spark-coil,_
as it is commonly called, and (2) with an _alternating current
transformer_, or _power transformer_, as it is sometimes called. Where
you have to generate the current with a battery you must use a spark
coil, but if you have a 110-volt direct or alternating lighting
current in your home you can use a transformer which will give you
more power.
A Cheap Transmitting Set (No. 1).--For this set you will need: (1) a
_spark-coil_, (2) a _battery_ of dry cells, (3) a _telegraph key_, (4)
a _spark gap_, (5) a _high-tension condenser_, and (6) an _oscillation
transformer_. There are many different makes and styles of these parts
but in the last analysis all of them are built on the same underlying
bases and work on the same fundamental principles.
The Spark-Coil.--Spark coils for wireless work are made to give sparks
from 1/4 inch in length up to 6 inches in length, but as a spark coil
that gives less than a 1-inch spark has a very limited output it is
best to get a coil that gives at least a 1-inch spark, as this only
costs about $8.00, and if you can get a 2- or a 4-inch spark coil so
much the better. There are two general styles of spark coils used for
wireless and these are shown at A and B in Fig. 18.
[Illustration: (A) and (B) Fig. 18.--Types of Spark Coils for Set. No.
1.]
[Illustration: (C) Fig. 18.--Wiring Diagram of Spark Coil]
A spark coil of either style consists of (_a_) a soft _iron core_ on
which is wound (_b_) a couple of layers of heavy insulated wire and
this is called the _primary coil_, (_c_) while over this, but
insulated from it, is wound a large number of turns of very fine
insulated copper wire called the _secondary coil_; (d) an
_interrupter_, or _vibrator_, as it is commonly called, and, finally,
(e) a _condenser_. The core, primary and secondary coils form a unit
and these are set in a box or mounted on top of a hollow wooden base.
The condenser is placed in the bottom of the box, or on the base,
while the vibrator is mounted on one end of the box or on top of the
base, and it is the only part of the coil that needs adjusting.
The vibrator consists of a stiff, flat spring fixed at one end to the
box or base while it carries a piece of soft iron called an _armature_
on its free end and this sets close to one end of the soft iron core.
Insulated from this spring is a standard that carries an adjusting
screw on the small end of which is a platinum point and this makes
contact with a small platinum disk fixed to the spring. The condenser
is formed of alternate sheets of paper and tinfoil built up in the
same fashion as the receiving condenser described under the caption of
_Fixed and Variable Condensers_, in Chapter III.
The wiring diagram C shows how the spark coil is wired up. One of the
battery binding posts is connected with one end of the primary coil
while the other end of the latter which is wound on the soft iron core
connects with the spring of the vibrator. The other battery binding
post connects with the standard that supports the adjusting screw. The
condenser is shunted across the vibrator, that is, one end of the
condenser is connected with the spring and the other end of the
condenser is connected with the adjusting screw standard. The ends of
the secondary coil lead to two binding posts, which are usually placed
on top of the spark coil and it is to these that the spark gap is
connected.
The Battery.--This can be formed of dry cells or you can use a storage
battery to energize your coil. For all coils that give less than a
1-inch spark you should use 5 dry cells; for 1-and 2-inch spark coils
use 6 or 8 dry cells, and for 3 to 4-inch spark coils use 8 to 10 dry
cells. The way the dry cells are connected together to form a battery
will be shown presently. A dry cell is shown at A in Fig, 19.
[Illustration: Fig. 19.--Other parts for Transmitting Set No. 1]
The Telegraph Key.--You can use an ordinary Morse telegraph key for
the sending set and you can get one with a japanned iron base for
$1.50 (or better, one made of brass and which has 1/8-inch silver
contact points for $3.00. A key of the latter kind is shown at B).
The Spark gap.--It is in the _spark gap_ that the high tension spark
takes place. The apparatus in which the spark takes place is also
called the _spark gap_. It consists of a pair of zinc plugs, called
_electrodes_, fixed to the ends of a pair of threaded rods, with knobs
on the other ends, and these screw into and through a pair of
standards as shown at _c_. This is called a _fixed_, or _stationary
spark gap_ and costs about $1.00.
The Tuning Coil.--The _transmitting inductance_, or _sending tuning
coil_, consists of 20 to 30 turns of _No. 8 or 9_ hard drawn copper
wire wound on a slotted insulated form and mounted on a wooden base.
It is provided with _clips_ so that you can cut in and cut out as many
turns of wire as you wish and so tune the sending circuits to send out
whatever wave length you desire. It is shown at _d_, and costs about
$5.00. See also _Oscillation Transformer_, page 63 [Chapter IV].
The High Tension Condenser.--High tension condensers, that is,
condensers which will stand up under _high potentials_, or electric
pressures, can be bought in units or sections. These condensers are
made up of thin brass plates insulated with a special compound and
pressed into a compact form. The _capacitance_ [Footnote: This is the
capacity of the condenser.] of one section is enough for a
transmitting set using a spark coil that gives a 2 inch spark or less
and two sections connected together should be used for coils giving
from 2 to 4 inch sparks. It is shown at _e_.
Connecting Up the Apparatus.--Your sending set should be mounted on a
table, or a bench, where it need not be moved. Place the key in about
the middle of the table and down in front, and the spark coil to the
left and well to the back but so that the vibrator end will be to the
right, as this will enable you to adjust it easily. Place the battery
back of the spark coil and the tuning coil (oscillation transformer)
to the right of the spark coil and back of the key, all of which is
shown in the layout at A in Fig. 20.
[Illustration: (A) Fig. 20.--Top View of Apparatus Layout for Sending
Set No. 1.]
[Illustration: (B) Fig. 20.--Wiring of Diagram for Sending Set No. 1.]
For the _low voltage circuit_, that is the battery circuit, use _No.
12_ or _14_ insulated copper wire. Connect all of the dry cells
together in _series_, that is, connect the zinc of one cell with the
carbon of the next and so on until all of them are connected up. Then
connect the carbon of the end cell with one of the posts of the key,
the zinc of the other end cell with one of the primary posts of the
spark coil and the other primary post of the spark coil with the other
post of the key, when the primary circuit will be complete.
For the _high tension circuits_, that is, the _oscillation circuits_,
you may use either bare or insulated copper wire but you must be
careful that they do not touch the table, each other, or any part of
the apparatus, except, of course, the posts they are connected with.
Connect one of the posts of the secondary coil of the spark coil with
one of the posts of the spark gap, and the other post with one of the
posts of the condenser; then connect the other post of the condenser
with the lower spring clip of the tuning coil and also connect this
clip with the ground. This done, connect the middle spring clip with
one of the posts of the spark gap, and, finally, connect the top clip
with the aerial wire and your transmitting set is ready to be tuned. A
wiring diagram of the connections is shown at B. As this set is tuned
in the same way as _Set No. 2_ which follows, you are referred to the
end of this chapter.
A Better Transmitting Set (No. 2).--The apparatus for this set
includes: (1) an _alternating current transformer_, (2) a _wireless
telegraph key_, (3) a _fixed_, a _rotary_, or a _quenched spark gap_,
(4) a _condenser_, and (5) an _oscillation transformer_. If you have a
110 volt direct lighting current in your home instead of 110 volt
alternating current, then you will also need (6) an _electrolytic
interrupter_, for in this case the primary circuit of the transformer
must be made and broken rapidly in order to set up alternating
currents in the secondary coil.
The Alternating Current Transformer.--An alternating current, or
power, transformer is made on the same principle as a spark coil, that
is, it has a soft iron core, a primary coil formed of a couple of
layers of heavy wire, and a secondary coil wound up of a large number
of turns of very fine wire. Unlike the spark coil, however, which has
an _open magnetic core_ and whose secondary coil is wound on the
primary coil, the transformer has a _closed magnetic core_, with the
primary coil wound on one of the legs of the core and the secondary
wound on the other leg. It has neither a vibrator nor a condenser. A
plain transformer is shown at A in Fig. 21.
[Illustration: Fig. 21.--Parts for Transmitting Set No. 2.]
A transformer of this kind can be bought either (a) _unmounted_, that
is, just the bare transformer, or (b) _fully mounted_, that is, fitted
with an iron stand, mounted on an insulating base on which are a pair
of primary binding posts, while the secondary is provided with a
_safety spark gap_. There are three sizes of transformers of this kind
made and they are rated at 1/4, 1/2 and 1 kilowatt, respectively, they
deliver a secondary current of 9,000, 11,000 and 25,000 volts,
according to size, and cost $16.00, $22.00 and $33.00 when fully
mounted; a reduction of $3.00, $4.00 and $5.00 is made when they are
unmounted. All of these transformers operate on 110 volt, 60 cycle
current and can be connected directly to the source of alternating
current.
The Wireless Key.--For this transmitting set a standard wireless key
should be used as shown at B. It is made about the same as a regular
telegraph key but it is much heavier, the contact points are larger
and instead of the current being led through the bearings as in an
ordinary key, it is carried by heavy conductors directly to the
contact points. This key is made in three sizes and the first will
carry a current of 5 _amperes_[Footnote: See _Appendix_ for
definition.] and costs $4.00, the second will carry a current of 10
amperes and costs $6.50, while the third will carry a current of 20
amperes and costs $7.50.
The Spark Gap.--Either a fixed, a rotary, or a quenched spark gap can
be used with this set, but the former is seldom used except with
spark-coil sets, as it is very hard to keep the sparks from arcing
when large currents are used. A rotary spark gap comprises a wheel,
driven by a small electric motor, with projecting plugs, or
electrodes, on it and a pair of stationary plugs on each side of the
wheel as shown at C. The number of sparks per second can be varied by
changing the speed of the wheel and when it is rotated rapidly it
sends out signals of a high pitch which are easy to read at the
receiving end. A rotary gap with a 110-volt motor costs about $25.00.
A quenched spark gap not only eliminates the noise of the ordinary gap
but, when properly designed, it increases the range of an induction
coil set some 200 per cent. A 1/4 kilowatt quenched gap costs $10.00.
[Footnote: See Appendix for definition.]
The High Tension Condenser.--Since, if you are an amateur, you can
only send out waves that are 200 meters in length, you can only use a
condenser that has a capacitance of .007 _microfarad_. [Footnote: See
Appendix for definition.] A sectional high tension condenser like the
one described in connection with _Set No. 1_ can be used with this
set but it must have a capacitance of not more than .007 microfarad. A
condenser of this value for a 1/4-kilowatt transformer costs $7.00;
for a 1/2-kilowatt transformer $14.00, and for a 1-kilowatt
transformer $21.00. See E, Fig. 19.
The Oscillation Transformer.--With an oscillation transformer you can
tune much more sharply than with a single inductance coil tuner. The
primary coil is formed of 6 turns of copper strip, or No. 9 copper
wire, and the secondary is formed of 9 turns of strip, or wire. The
primary coil, which is the outside coil, is hinged to the base and can
be raised or lowered like the lid of a box. When it is lowered the
primary and secondary coils are in the same plane and when it is
raised the coils set at an angle to each other. It is shown at D and
costs $5.00.
Connecting Up the Apparatus. For Alternating Current.--Screw the key
to the table about the middle of it and near the front edge; place the
high tension condenser back of it and the oscillation transformer back
of the latter; set the alternating current transformer to the left of
the oscillation transformer and place the rotary or quenched spark gap
in front of it.
Now bring a pair of _No. 12_ or _14_ insulated wires from the 110 volt
lighting leads and connect them with a single-throw, double-pole
switch; connect one pole of the switch with one of the posts of the
primary coil of the alternating power transformer and connect the
other post of the latter with one of the posts of your key, and the
other post of this with the other pole of the switch. Now connect the
motor of the rotary spark gap to the power circuit and put a
single-pole, single-throw switch in the motor circuit, all of which is
shown at A in Fig. 22.
[Illustration: (A) Fig. 22.--Top View of Apparatus Layout for Sending
Set No. 2.]
[Illustration: (B) Fig. 22.--Wiring Diagram for Sending Set No. 2.]
Next connect the posts of the secondary coil to the posts of the
rotary or quenched spark gap and connect one post of the latter to one
post of the condenser, the other post of this to the post of the
primary coil of the oscillation transformer, which is the inside coil,
and the clip of the primary coil to the other spark gap post. This
completes the closed oscillation circuit. Finally connect the post of
the secondary coil of the oscillation transformer to the ground and
the clip of it to the wire leading to the aerial when you are ready to
tune the set. A wiring diagram of the connections is shown at B.
For Direct Current.--Where you have 110 volt direct current you must
connect in an electrolytic interrupter. This interrupter, which is
shown at A and B in Fig. 23, consists of (1) a jar filled with a
solution of 1 part of sulphuric acid and 9 parts of water, (2) a lead
electrode having a large surface fastened to the cover of surface that
sets in a porcelain sleeve and whose end rests on the bottom of the
jar.
[Illustration: Fig. 23.--Using 110 Volt Direct Current with an
Alternating Current Transformer.]
When these electrodes are connected in series with the primary of a
large spark coil or an alternating current transformer, see C, and a
direct current of from 40 to 110 volts is made to pass through it, the
current is made and broken from 1,000 to 10,000 times a minute. By
raising or lowering the sleeve, thus exposing more or less of the
platinum, or alloy point, the number of interruptions per minute can
be varied at will. As the electrolytic interrupter will only operate
in one direction, you must connect it with its platinum, or alloy
anode, to the + or _positive_ power lead and the lead cathode to the -
or _negative_ power lead. You can find out which is which by
connecting in the interrupter and trying it, or you can use a polarity
indicator. An electrolytic interrupter can be bought for as little as
$3.00.
How to Adjust Your Transmitter. Tuning With a Hot Wire Ammeter.--A
transmitter can be tuned in two different ways and these are: (1) by
adjusting the length of the spark gap and the tuning coil so that the
greatest amount of energy is set up in the oscillating circuits, and
(2) by adjusting the apparatus so that it will send out waves of a
given length.
To adjust the transmitter so that the circuits will be in tune you
should have a _hot wire ammeter_, or radiation ammeter, as it is
called, which is shown in Fig. 24. It consists of a thin platinum wire
through which the high-frequency currents surge and these heat it; the
expansion and contraction of the wire moves a needle over a scale
marked off into fractions of an ampere. When the spark gap and tuning
coil of your set are properly adjusted, the needle will swing farthest
to the right over the scale and you will then know that the aerial
wire system, or open oscillation circuit, and the closed oscillation
circuit are in tune and radiating the greatest amount of energy.
[Illustration: Fig. 24.--Principle of the Hot Wire Ammeter.]
To Send Out a 200 Meter Wave Length.--If you are using a condenser
having a capacitance of .007 microfarad, which is the largest capacity
value that the Government will allow an amateur to use, then if you
have a hot wire ammeter in your aerial and tune the inductance coil or
coils until the ammeter shows the largest amount of energy flowing
through it you will know that your transmitter is tuned and that the
aerial is sending out waves whose length is 200 meters. To tune to
different wave lengths you must have a _wave-meter_.
The Use of the Aerial Switch.--Where you intend to install both a
transmitter and a receptor you will need a throwover switch, or
_aerial switch_, as it is called. An ordinary double-pole,
double-throw switch, as shown at A in Fig. 25, can be used, or a
switch made especially for the purpose as at B is handier because the
arc of the throw is much less.
[Illustration: Fig. 25.--Kinds of Aerial Switches.]
Aerial Switch for a Complete Sending and Receiving Set.--You can buy a
double-pole, double-throw switch mounted on a porcelain base for about
75 cents and this will serve for _Set No. 1_. Screw this switch on
your table between the sending and receiving sets and then connect one
of the middle posts of it with the ground wire and the other middle
post with the lightning switch which connects with the aerial. Connect
the post of the tuning coil with one of the end posts of the switch
and the clip of the tuning coil with the other and complementary post
of the switch. This done, connect one of the opposite end posts of the
switch to the post of the receiving tuning coil and connect the
sliding contact of the latter with the other and complementary post of
the switch as shown in Fig. 26.
[Illustration: Fig. 26.--Wiring Diagram for Complete Sending and
Receiving Set No. 1.]
Connecting in the Lightning Switch.--The aerial wire connects with the
middle post of the lightning switch, while one of the end posts lead
to one of the middle posts of the aerial switch. The other end post of
the lightning switch leads to a separate ground outside the building,
as the wiring diagrams Figs. 26 and 27 show.
[Illustration: Fig. 27.--Wiring Diagram for Complete Sending and
Receiving Set No. 2.]