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.(A) and (B) Fig. 18.--Types of Spark Coils for Set. No. 1. (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.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.(A) Fig. 20.--Top View of Apparatus Layout for Sending Set No. 1. (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.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.(A) Fig. 22.--Top View of Apparatus Layout for Sending Set No. 2. (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.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.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.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.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.Fig. 27.--Wiring Diagram for Complete Sending and Receiving Set No. 2.