Chapter II: Introduction (2)

The best and most efficient switch adopted generally by the commercial stations is the "T" type, consisting of a double pole, double throw switch having very long blades. One set of contacts is mounted on the switch base and the second are carried on a "T"-shaped support from which the switch derives its name. The aerial and ground are connected to the blades of the switch.

The lower contacts lead to the transmitting apparatus and the upper ones to the receiving instruments. By simply moving the switch up or down the aerial and ground may be connected to either the transmitter or the receptor at will.

A third blade, much shorter than the other two is usually provided and connected by means of an insulating bar to the other blades so that when they are moved it also moves. It connects with a contact arranged so that when the switch is thrown into position for transmitting the two come together. This blade and contact are made a part of the circuit supplying current to the primary of the coil or transformer so that in case the key should be accidentally touched while receiving the powerful discharge of the transmitter would not destroy the adjustment of the detector.

LESSON TWENTY-ONE. ANCHOR GAPS.

Certain types of aerial switches require the use of what is known as an _anchor gap_.

An anchor gap consists of a small insulating ring, usually hard rubber, having two and sometimes three electrodes set in the periphery and almost touching each other at the sparking points.

Anchor gaps having two electrodes are used in the aerial circuit of most Break-in-Systems to prevent the receiving currents from flowing directly into the ground through the transmitter without passing through the detector.

A Break-in System enables the operator to hear the signals of any other station which may be transmitting at the same time when he is operating his own key.

The three-electrode anchor gap is commonly used on loop aerial systems. Two of the points are connected to the aerial, one to each half and the other to the lead from the helix. The high potential currents from the helix easily leap across the little gap and divide between the two halves of the aerial.

LESSON TWENTY-TWO. DETECTORS.

The little bobbins of the telephone receivers exert a very powerful choking action upon the currents of high frequency which effectually blocks their passage and prevents them from having any action upon the receiver.

The purpose of the detector is to change these currents into such as will flow readily through the magnets of the telephone receiver and manifest themselves as sounds recognizable from their duration and periodicity as signals of the telegraph code.

Probably the most well known form is the electrolytic detector which consists of an exceedingly fine platinum wire dipping into a cup of dilute nitric acid far enough to just touch the surface of the liquid. The telephone receivers are connected to the detector, in series with a battery. The current from the detector causes bubbles to continuously form on the end of the wire and insulate it from the liquid so that the current cannot flow. When the aerial is struck by a wave, the feeble alternating currents break down the bubbles and permit the currents to flow, causing a sound in the telephone receivers.

The detectors in most common use to-day are of the crystal or rectifying type. There are a great many different forms of this type of detector, each one of which possesses certain features making it peculiarly adaptable under certain circumstances.

The silicon detector consists of a flat surface of highly polished silicon upon which rests a brass point.

The Pyron detector is composed of a crystal of iron pyrites embedded in a cup of fusible metal. A small wire spring bears against the surface of the crystal. The Pyron detector is somewhat harder to adjust than other forms of crystal detector, but remains in a sensitive condition much longer.

The Perikon detector consists of a cup of fusible alloy in which are imbedded several pieces of a mineral called zincite. Another cup containing a fragment of chalcopyrites or bornite is held in a cup carried on the end of a rotating rod. The chalcopyrites is brought into contact with one of the crystals of zincite and the pressure adjusted by means of a spring. The Perikon detector will operate without a battery, but that latter is necessary in order to obtain the best results when receiving faint or far away signals.

The Perikon Electra detector is a very sensitive form of the regular Perikon detector fitted with a micrometer adjustment.

The Galena detector consists of a crystal of that material to which contact is made by means of a fine wire spring exerting very light pressure.

Crystal detectors act as rectifiers and change the alternating currents Into direct currents, which will pass through the telephone receivers. Minerals used for this purpose are said to possess _unilateral conductivity_, that is, they conduct currents better in one direction than the other and act much the same as a valve which allows water to flow in one direction, but not in the other.

Another well known detector of the "valve" type is that known as the _Audion_, consisting of a small incandescent lamp containing a small grid and plate of nickel. When the lamp is lighted by connecting a battery to the filament, a flow of ions passing from the hot filament through the grid to the plate is set up. The grid and plate form part of the receiving circuit containing the telephones. The flow of ions carries the oscillatory currents from the grid to the plate, but does not allow them to pass back again. In this manner, the alternating oscillatory currents are converted into direct currents, which will pass through the telephone receivers.

The Carborundum detector, as its name implies, is a device making use of the _unilateral conductivity_ of carborundum. This form of detector is very sensitive and has been employed for a number of years in all the installations of the United Wireless Telegraph Co.

It consists of a small crystal of carborundum clamped tightly between two carbon electrodes. It may be used with or without a battery. The battery is preferred.

The Magnetic detector is a very sensitive device utilizing the changes in the magnetic state of iron, which are caused by rapidly oscillating currents. If a core of iron wires be placed in a varying magnetic field, the magnetization of the iron will lag behind the magnetizing force on account of _hysteresis_ or "magnetic friction."

But if a rapidly oscillating current is passed through a coil surrounding the iron, a sudden change in magnetization occurs, sufficient to induce an E. M. F. in a second coil surrounding the core and thus operate a telephone receiver in series with this coil.

The usual form of magnetic detector consists of a belt of fine iron wires passing over two pulleys which are driven by clockwork. A pair of permanent magnets supply the field which induces a continuously varying magnetization in the moving core. The core passes through the centre of a double coil, one part of which is connected to the telephone receivers and the others to the aerial and ground.

LESSON TWENTY-THREE. TUNING COILS.

The tuning coil is a device consisting of a large number of turns of wire wound in the form of a cylinder and provided with one or more sliding contacts which can be brought into touch with any one of the turns at will in order to increase or decrease the electrical length or period of the circuit to suit the incoming waves.

A circuit containing a certain amount of inductance, capacity and resistance tends to oscillate at a certain frequency. Therefore, the oscillations in every transmitting set have a certain frequency depending upon these factors. It is necessary to adjust the receiving apparatus so that it possesses the same frequency as the transmitter. The electro magnetic waves from the transmitting station will strike the aerial of the receiving station at a certain frequency and induce currence in it. If the receiving station is _tuned_ to the same _period_ as the transmitter each wave will give a slight impulse to the readily excited oscillations, which will grow in intensity just as small impulses given to a pendulum at the right times will make it swing violently.

The purpose of the tuning coil is to adjust the receiving circuit to the same period as that of the transmitter.

Tuning coils are wound of bare copper wire over a core composed of a specially treated cardboard tube. The wires are spaced apart so that they do not touch one another. Either one, two or three variable contacts or sliders are provided. The coils are consequently known as "single," "double" or "three" slide tuners.

A loading coil is a supplementary coil sometimes placed in series with the regular tuning coil to give a greater inductance to the circuit so that it may be given a much lower frequency in order to receive waves of greater length.

LESSON TWENTY-FOUR. LOOSE COUPLERS.

A Loose Coupler or Receiving Transformer is a tuning coil in which the _coupling_, as well as the inductance, is variable. We have already explained that an ordinary transmitting set throws off two sets of wave trains of slightly different length, one being somewhat weaker than the other.

The purpose of the loose coupler is not only to adjust the receiving set to the period of the transmitter in the manner of the tuning coil, but by varying the coupling to attract the apices of the weaker trains of waves to the same apex as the stronger waves and so really create a _pure_ wave out of the other two.

This may be more easily understood from the accompanying illustration which represents diagrammatically a double train of waves and a pure train.

In construction, the loose coupler consists of a primary winding much the same as an ordinary tuning coil provided with a single slider.

A second winding called the secondary, divided into a number of sections and adjustable by means of a multi-pointed switch mounted on one end, slides in and out of the primary.

LESSON TWENTY-FIVE. FIXED CONDENSERS.

A fixed condenser usually implies the condenser used in the receiving circuit to furnish part of the necessary _capacity_ and to shunt the telephone receivers, or as in cases where a battery is used in connection with the detector to force the current to choose a path through the comparatively low resistance turns of the tuning coil.

A fixed condenser, as its name implies, has a fixed value or capacity. It is usually constructed of sheets of tinfoil interposed between sheets of thin paraffined paper or mica. The capacity of a fixed condenser usually varies from .002 to .005 microfarads.

An alternating current passes readily through a condenser but a direct current is effectually blocked.

When a direct current is led into a condenser as shown in the diagram, the half of the condenser represented by A becomes positively charged. When A receives a positive charge it repels the positive charge from B and attracts the negative thus making B negative. There is no change in the direction of the current after the first connection and the charge remains fixed and no currents pass.

If an alternating current is applied to the condenser when A receives a positive charge, B becomes negative. When A reverses and becomes negative B becomes positive. This process goes on, the two halves constantly changing their charge with the result that the current continues to flow.

A fixed condenser may occupy one of two places in a receiving circuit, either in series with the tuning coil and detector or directly across the telephone receivers. In the illustration A shows a detector requiring a battery with a fixed condenser in series with it and the coil. The oscillations set up in the circuit by the incoming waves can readily pass through the condenser and effect the detector because they are _alternating_. If it were not for the condenser the _direct_ battery current would pass through the tuning coil instead of the detector because of the comparatively low resistance of the former.

Crystal detectors do not require a battery and may be connected to a tuning coil with a condenser in series and the telephone receivers either across the terminals of the detector or across the terminals of the condenser. When in the latter position, the proper capacity for the fixed condenser will depend upon the resistance of the telephone receivers, the higher the resistance the less the capacity that will be required and vice versa.

LESSON TWENTY-SIX. VARIABLE CONDENSERS.

The point of sharpest resonance does not always happen to come on a turn of the tuner where it can be reached by the slider. The variable condenser makes it possible to adjust the circuit to the exact point of resonance.

Variable condensers are of two general types, the Sliding Plate and the Rotary Variable. The rotary variable is the most convenient and easy to manipulate. It consists of a number of fixed semi-circular metal plates between which swings a set of smaller movable semicircular plates. The fixed plates form one half of the condenser and the movable plates the other. In this way the capacity of the condenser is very closely adjustable. The movable plates are provided with a pointer moving over a graduated scale so that the comparative amount of capacity in the circuit is indicated.

The sliding plate type of condenser consists of a number of rectangular fixed plates between which slide a set of movable plates.

The dielectric between the plates of a variable condenser is air. There are no losses of energy due to hysteresis in a condenser having an air dielectric. Rotary condensers employing silk or some such material are not to be recommended.

LESSON TWENTY-SEVEN. TELEPHONE RECEIVERS.

Telephone receivers employed for wireless telegraphy are the same in principle as the ordinary telephone receiver but differ in construction and detail slightly.

They are always of the watch case type, this style being small and light, and consist of a ring or horseshoe shaped permanent magnet upon the poles of which are mounted two small bobbins containing many turns of fine insulated wire. Over the magnets, very close to but not quite touching, is placed a circular diaphram of thin sheet iron. The lines of force created by the permanent magnet pass through the cores of the little bobbin and exert a constant pull on the diaphram.

The little bobbins of wire or electromagnets are connected in series. If a current of electricity is sent through them they will create a little field of force of their own which will strengthen or decrease that of the permanent magnets according in which direction the current flows. Each change in the pull exerted on the diaphragm causes it to move and send out little sound waves which may be heard when the receiver is held close.

We have already learned that the strength of a magnet depends upon the _ampere_ turns. Suppose that a current of one ampere passed through a coil containing 100 _turns_ x 1 _amp._ = 100 _ampere turns_. If only one-tenth of an ampere was available and we wished to retain the same magnetic strength in the coil, the number of turns would have to be increased to one thousand in order for the ampere turns to remain equal; 1/10 _amp._ x 1.000 _turns_ = 100 _ampere turns_.

The currents passing through the receiver from the detector are exceedingly weak, and so in order to produce the maximum effect on the diaphragm, the electromagnets must be wound with a large number of turns of very fine wire. The resistance of fine wire is very great and for this reason wireless telephone receivers are usually termed _high resistance receivers_.

Winding a receiver with many turns of fine wire does not make it more sensitive in the true sense of the word or from the standpoint of efficiency, but makes it better suited to the minute fluctuations of a weak current.

The classification of receivers, according to their resistance is a method of indicating the comparative number of turns and the finess of the wire used in winding the electromagnets. Receivers should be wound with copper wire only.

Wireless receivers come in pairs provided with a head-band so that they may be securely clamped on the ears.

The receiver cases are made of rubber, composition, brass and aluminum depending upon the design and manufacture. It is immaterial which.

LESSON TWENTY-EIGHT. THE HOT WIRE AMMETER.

The hot-wire ammeter is a device for indicating when the transmitting circuits are properly adjusted and arranged to emit the maximum amount of energy. It is placed in series in the aerial circuit so that the high frequency currents surging in the latter must pass through the meter and indicate their strength by moving the pointer a certain distance over a graduated scale.

When a current of electricity flows through a wire it develops a certain amount of heat therein. If the wire is of high resistance the heat will be great enough to cause the wire to expand. Advantage has been taken of this fact in the construction of the hot-wire ammeter. This device consists of a piece of platinum wire or a platinum alloy stretched taut between two posts. The wire is included in the aerial circuit. The platinum wire is connected to a spindle carrying a pointer in such a manner that when the heat causes the wire to expand the expansion is conveyed to the spindle and the pointer moves over the scale magnifying the motion. The greater the current flowing through the wire the greater will be the deflection of the pointer. The scale is calibrated by comparison with a standard meter to read in amperes.

When a hot-wire ammeter is placed in circuit the latter is tuned by moving the position of the helix clips on the helix, altering the length of the spark gap and the condenser capacity until the maximum deflection is indicated. It is then removed from the circuit.

LESSON TWENTY-NINE. POTENTIOMETER

The potentiometer is an instrument for carefully regulating the voltage of the battery supplying a detector of the electrolytic or carborundum types with current.

It is necessary to bring the potential of the battery to a certain critical point where it is just insufficient to "break down" the detector, that is, overcome the resistance which it offers to the oscillatory currents. In construction, the potentiometer usually consists of a small rod wound with German silver wire and provided with an adjustable contact. Graphite resistance rods are merely a cheap method of making a potentiometer and are to be avoided as entirely unsatisfactory for the purpose.

LESSON THIRTY. DEAD END LOSSES AND "NO DEAD END" SWITCHES.

Practically every radio circuit includes an adjustable inductance of some sort, usually consisting of a layer of wire wound over a tube and arranged so that the amount of wire in the circuit can be varied by means of a switch, a plug or a slider. These methods of variation are familiar in the ordinary tuning coil, loose coupler, loading coil, etc.

If the plug, switch or sliding contact, depending upon the method of variation employed, is at E as in Fig. 60 so that only the portion of the coil A E B is in the circuit, then the portion E F together with A E may form an oscillator which, in order for the reader to obtain a better conception, may be likened to a sort of secondary winding, with A E considered as the primary. The oscillations of this part of the system may produce some very undesirable disturbances, especially so when the frequency of the currents in the circuit A E bear a certain relation to the natural frequency of the oscillator or E F. The losses due to the disturbance of these undesirable oscillations and also those resulting from eddy currents induced in the free portion or oscillator E F by the magnetic flux of A E are known as "dead-end effects."

These losses are very much more noticeable in receiving circuits than in transmitters on account of the very weak currents in the former and the importance of preserving all the energy when it is already very small.

Dead end losses take place principally in receiving transformers, loading coils and tuning coils. The losses are much more marked on short waves than long waves.

The presence of these highly objectionable losses, and they are large enough to not only seriously decrease the strength of signals but also to make selective tuning impossible, may be avoided by only using coils which are just the right size so that they can be entirely included in the circuit.

This is a very easy matter when only one wave length or at the most, two or three wave lengths are to be received, because it is then easily possible to quickly connect the coil of the proper size in the circuit. It is desirable however in most stations, and especially so in amateur stations that the apparatus be universal so as to be quickly and easily tunable to any wave length within its range.

Many amateurs build large loose couplers having a very wide wave length range under the impression that they have an ideal instrument. The truth of the matter is however that such an arrangement is decidedly inefficient especially on the shorter waves when only a portion of the windings are in circuit and there is a large dead end portion.

The better types of receiving transformers are now provided with "no dead end loss switches" which automatically break the windings up into a number of groups so that only that portion which is actually required to tune the circuit to a certain wave length is in circuit and the remainder of the coil is entirely disconnected.

These switches are located at certain definite points as previously determined by measurements of the coil with the aid of a wave meter.

The diagram in Fig. 61 illustrates the principle of such an arrangement. The points marked 1, 2 and 3 are the places in the coil where the switches are located so as to divide the winding up into separate parts. Suppose that it is necessary to move the slider or switch to such a point on the coil as represented by its position in the illustration marked E. The switch located at 1 would then automatically close as the slider or switch moved past 2 and 3 would however still remain open because that part of the winding which they connect would not be required. If it became necessary to include more of the winding in the circuit, 2 and 3 would automatically close as the slider or switch was moved along the coil and open again as it was moved back.

The automatic arrangement of the switches is easily accomplished in a number of different manners by means of levers, cams, trips, or some other mechanical means.

LESSON THIRTY-ONE. DISTRIBUTED CAPACITY AND CAPACITY LOSSES.

Every coil of wire possesses the property, not only of carrying a current of electricity but of _holding a charge_ of electricity as well. This property is called capacity. The _capacity_ of a condenser is its property for holding a charge of electricity. The capacity of a coil is termed its "distributed capacity" in order to distinguish it from the capacity of a condenser. The distributed capacity of a coil is due to the condenser effect which exists between the adjacent turns of the wire. The effect of this distributed condenser is exactly the same as if a small condenser was connected across the ends of the coil as shown in the accompanying illustration.

Distributed capacity is very objectionable in most receiving circuits because a radio detector depends upon voltage for its operation and when a circuit contains an appreciable amount of distributed capacity the voltage is considerably lower than it would be otherwise.

The usual method of reducing the distributed capacity of a coil is to use wire having comparatively thick insulation so that the wires are spaced farther apart. Certain shellacs and varnishes used in impregnated windings increase the specific dielectric capacity of the space between the turns and increase the distributed capacity of the winding.

The same objection to distributed capacity also holds good in the case of what might be termed capacity losses which are due to improperly arranged connections, contact points, etc. Every pair of leads or taps from a coil possesses capacity. They really form a miniature condenser, the wires corresponding to the tinfoil or metal sheets of the condenser and the air between being the dielectric.

For that reason the leads should always be as far apart from one another as possible and contact points should be as small as possible. It is unwise to use "double conductor" having two parallel conductors bound together for leading out connections or connecting radio apparatus.

If capacity losses and distributed capacity are reduced to a minimum in a circuit, it is possible to employ more inductance than would be otherwise in order to tune the circuit to a certain frequency and the voltage is thereby preserved and full benefit derived therefrom by the changes which it produces in the detector.

LESSON THIRTY-TWO. THE POULSEN ARC OR GENERATOR.

*Method of Producing Undamped Oscillations for Radio Telegraphy and Telephony.*

A radio transmitter whose waves are generated by undamped oscillations has many advantages over the ordinary spark transmitter, the oscillations of which are necessarily damped.

The efficiency of an undamped wave transmitter is far greater in almost every respect. The selectivity at a receiving station listening to undamped wave signals is very marked in comparison to that when spark signals are received.

The problem of producing undamped oscillations by means of an arc was first solved by Poulsen and is known as the Poulsen arc or generator. This type of generator is used for radio work in this country, by the Federal Telegraph Co., in the stations at Sayville and Tuckerton, in many U. S. Naval stations and on board all the U. S. first line battleships.

An arrangement by which such oscillatory currents may be produced is shown in its simplest form in Fig. 62. It consists of an arc, around which is shunted a condenser in series with an inductance. The arc is connected to a source of direct current, preferably having an E. M. F. of 500 volts or more.

The positive electrode of the arc is copper, kept cool by circulating water through a hollow interior or a water jacket. The gap in itself is enclosed in a chamber filled with hydrogen gas or a gas containing hydrogen. The arcs in practical use for generating undamped oscillations are arranged so that they operate in a strong magnetic field. The carbon electrode is constructed so that it is slowly revolved by a small electric motor.

The hydrogen gas atmosphere in which the arc is enclosed is produced by a small feed cup, similar to the ordinary lubricating oil cup, located over the case and filled with alcohol which continuously drips into the flame chamber, where it is vaporized by the heat.

Arc transmitters of large capacity are not as expensive or as bulky as spark transmitters of equal power. The difficulties of handling and controlling a large amount of power in connection with a transmitter of this sort are also not as great as in the case of a spark transmitter. The condenser used with an arc is not nearly so large as that required for a spark transmitter of equal capacity and the voltage of the current is much lower. Condenser breakdown, leakage and insulation problems are therefore not as great.

For telegraphing with damped transmitters, a key which alternately makes and breaks the primary circuit is sufficient. This is not possible, however, with an arc. The distance between the arc electrodes is usually greater than the gap length which the dynamo voltage would jump and form an arc whenever the key should be closed. It is therefore usual to arrange a key or relay so that it short circuits a portion of the aerial inductance or helix when closed. This short circuit is sufficient to throw the circuit out of tune so that it cannot be heard at the receiving station without readjusting the instruments.

The Poulsen arc may be used for radio telephony. A telephone receiver is arranged so as to vary the currents and impress the vibrations of the voice upon the oscillations set up by the arc.

LESSON THIRTY-THREE. RECEIVING UNDAMPED WAVES. THE TICKER.

A decided difference is encountered between damped and undamped oscillations when receiving signals. The ordinary detector cannot be used for receiving undamped oscillations without first being properly modified.

When telegraphing the dots and dashes of the code by undamped oscillations the change taking place in the detector circuit would merely move the telephone receiver diaphragm from its normal position at the beginning of each dot or dash, causing a click to be heard and nothing more. The telephone receiver diaphragm would remain in a fixed position just as long as the waves from the transmitter kept coming in during each signal. Both dots and dashes would be heard simply as clicks and not appear distinguishable from one another.

The most common and perhaps also the best method is to employ a device called a "ticker" in place of the detector for receiving undamped oscillations.

This arrangement is illustrated in Fig. 63. The left hand part of the illustration is the circuit diagram. A detail of the "ticker" wheel is shown at the right.

The condenser F C is of comparatively large capacity and is fixed. The condenser C is also fixed but is of much smaller capacity. F C is usually a condenser having a capacity of several tenths of a microfarad while C has only a few thousands of a microfarad capacity.

T is the ticker wheel and consists of a small brass wheel having a groove in the periphery like a pulley. This wheel is mounted on the shaft of a small motor so that it can be revolved at high speed.

A fine wire is arranged to rub against the groove in the wheel and make contact with the latter.

When the wheel is revolving at high speed, the wire does not make perfect contact at all points but tends to vibrate and to act as the equivalent of a very high speed interrupter by rapidly opening and closing the circuit.

The basic idea in employing a device and a circuit of this sort in receiving undamped waves is as follows:

When the contact is broken at the ticker wheel and the condenser F C is disconnected from the oscillating circuit formed by the condenser C and the secondary of the receiving transformer, the condenser C accumulates a relatively large amount of energy.

Then when the ticker connects the condenser F C in parallel with C, F C takes the major part of the stored energy and discharges it through the telephones P, causing a click to be heard in the latter.

The interruptions of the "ticker" are very rapid, a great many taking place during the duration of a dot or a dash, so that the resultant clicks occur very close together and the dots and dashes sound very similar to the spark signals of a transmitter sending forth damped waves.

The sensitiveness of the ticker arrangement is very great, in fact much greater than that of any detector.

LESSON THIRTY-FOUR. THE AUDION AMPLIFIER.

The audion amplifier is an arrangement whereby an A audion bulb such as that which has already been described in the Lesson on Detectors is so connected that it acts as a relay and also amplifies minute pulsating electric impulses. An ordinary audion detector bulb will serve as an amplifier bulb but it is usual to modify it somewhat and provide a grid and a wing on both sides of the filament as this arrangement gives the best results.

The audion amplifier is of especial advantage in amplifying weak wireless signals from a detector which would otherwise be unreadable. It is not necessary that the audion amplifier be used in connection with another audion serving as a detector. It will amplify the signals of any other form of detector such as an electrolytic, crystal, magnetic, etc.

Figure 64 shows an audion amplifier connected to an audion amplifier connected to an audion detector so that the signals from the latter will be greatly increased in strength.

L C is a loose coupler connected to the aerial and ground in the ordinary manner. P and S are respectively the primary and secondary of the loose coupler. B is the "wing" battery of the detector circuit and B¹ is the "wing" battery of the amplifier circuit. T is the telephone receiver headset in which the amplified signals are heard.

P¹ and S¹ are the primary and secondary of a small open core transformer called the "Amplifier Coil." The windings contain a great many turns of very fine wire. The primary of the transformer is connected so as to be included in the wing circuit of the detector. It should be noticed that only one terminal of the secondary is connected to the amplifier circuit, this one terminal being connected to the grid of the amplifier bulb.

An arrangement of this sort, where one amplifier bulb is used is called a "one step amplifier." Amplifiers having two and three bulbs, respectively known as "two step" and "three step" amplifiers give much greater amplification than a one step amplifier and are often used.

LESSON THIRTY-FIVE. "HOOK-UPS."

*Or Methods of Connecting the Instruments.*

"Hook-ups" or circuit diagrams showing the manner of connecting various instruments are well worth considerable study if one is desirous of securing the greatest selectivity and distance from his apparatus.

There are almost an endless number of ways and combinations of ways of connecting apparatus, and strange to say, different people seem to be able to secure the best results with widely different methods. In spite of the fact that circuits of this kind are very numerous they can all be reduced to a few fundamental forms and an understanding of these forms will enable a person to devise his own "hook-ups" at will.

Transmitting circuits are fundamentally almost the same. The only real difference in arrangement is made by interchanging the condenser and spark gap. Either one may be placed across the terminals of the induction coil or transformer. There is no difference in the results.

Consider the circuit shown in the accompanying illustration. The action of the transformer is to charge the condenser to such a point that the voltage is sufficient to leap the spark gap and cause a discharge. The rush of current which is oscillatory takes place through the condenser, spark gap and _primary_ turns of the helix, or in other words through the _closed_ circuits. The _secondary_ turns of the helix, which are those forming part of the aerial circuit, are larger in number than those of the primary, and because of this ratio cause currents of higher voltage than those of the condenser to be impressed upon the aerial system. The currents in the aerial system surge up and down the aerial through the helix into the ground.

A shows a simple receiving circuit wherein a single slide tuning coil is connected to a detector. The high frequency currents generated in the aerial surge up and down the system and pass through the detector on their way to the ground. By moving the slider back and forth the electrical length of the circuit may be varied to suit the length of the incoming waves. Oscillations may be _forced_ upon such a circuit, that is, if the waves are very powerful they will pass through the system and effect the detector no matter whether the slider is adjusted to suit them or not. This would cause interference and confusion in case more than one station were operating at a time.

By adding a second slider and a condenser as shown in B, this may be avoided to a considerable extent, for slider No. 1 may be adjusted to the desired signals and slider No. 2 placed in a position such as will give the branch of the circuit from the aerial, through the coil and into the ground of which it is a part, a period suited to the objectionable wave and so _carry off_ the latter into the ground without effecting the detector. The desired signals will pass into the ground through the other branch of the circuit and operate the detector which lies in their path. The selectivity of the outfit may be further increased by the addition of a variable condenser.

A variable condenser may be placed in one or more of a great many positions. The accompanying illustrations show several. The effect of a condenser placed in series with the ground or aerial is just the opposite of that of a loading coil. It decreases the period and shortens the wave length to which it is adapted.

The Amateur’s Wireless Handy Book shows over one hundred wiring diagrams starting from the simplest and going to the most complicated in a natural sequence.

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*With full-page Illustrations and 324 Working Drawings and Diagrams*

*by the author. 8vo., Cloth, Net Price, $2.00.*

This is the age of electricity. The most fascinating of all books for a boy must therefore be one dealing with the mystery of this ancient force and modern wonder, even a mere list of whose services is impossible. The best qualified of experts to instruct boys, Alfred P. Morgan, has in a book far superior to any other of its kind told not only how to make all kinds of motors, telegraphs, telephones, batteries, etc., and to do so economically, but has explained the principles upon which these depend for operation, and how the same thing is done in the every-day world be well presented and so attractive is this really great book that it will be an education for any bright boy to have it, as well as the best kind of a moral safeguard, by leaving no time or thought for evil, and a means of future benefit beyond the power of any one to reckon. Glancing over the pages of this book, one cannot but be impressed by the excellent illustrations, clearness of expression and the large number of subjects that are covered. It is beyond doubt the best book in this line that has ever been written or published. It is a book that will delight every boy who has a leaning towards electrical experiments. The author writes in a clear and chatty style and while he has a thorough technical knowledge of his subject he has succeeded in treating it in a simple manner so that it is readily intelligible to his young readers.

*Among the Chapter Headings and Contents are:*

Magnets and Magnetism—Static Electricity—Static Electric Machines—Cells and Batteries—Electro-Magnetism and Magnetic Induction—Electrical Units—Electrical Appurtenances—Electrical Measuring Instruments—Bells, Alarms and Annunciators—Electric Telegraphs—Microphones and Telephones—Induction Coils—Transformers—Wireless Telegraphy—Wireless Telephony—Electric Motors—Dynamos—An Electric Railway—Miniature Lighting—Miscellaneous Electrical Apparatus.

*READ WHAT HAS BEEN SAID OF IT.*

"Even a casual glance through the many pages of the book does not fail to emphasize the fact that Mr. Alfred P. Morgan has indeed succeeded well in giving the juvenile electricians a work that has long been sought."—Popular Electricity.

"We have no hesitation in commending the book to the attention of the juvenile audience for which it is intended."—Boston Post.

"A great book for enterprising boys. Bright boys will highly appreciate it and feel like thanking the wideawake publishers for putting such a reliable and interesting work in the field."—New Haven Journal.

"The book covers the subject of electricity thoroughly in all its phases and is a splendid acquisition to any boy’s library."—Detroit Times.

"In this age of electricity a book like the present one is both fascinating and valuable especially to boys. The book is attractive with its many illustrations and will prove of much educational value for any bright boy."—Zion’s Herald.

"This is an admirably complete and explicit handbook for young boys who fall under the spell of tinkering with electrical apparatus."—Boston Transcript.

"Well presented and attractive this book will be a source of great benefit and delight for any bright boy."—New Orleans Times-Picayune.

*Price, $2.00, Postpaid*

COUNTLESS OTHER MAGAZINES, NEWSPAPERS AND LIBRARIES HAVE

ENDORSED THIS GREAT BOOK. SEND FOR A COPY NOW.

*If you are interested in this great book, write for our 8-page special*

*descriptive circular.*

*Wireless Telegraphy and Telephony Simply Explained*

By ALFRED P. MORGAN.

*A NEW BOOK by the author of "Wireless Telegraph Construction for
Amateurs."*

This is undoubtedly one of the most complete and comprehensive treatises on the subject ever published, and a close study of its pages will enable one to master all the details of the wireless transmission of messages. The author has filled a long-felt want and has succeeded in furnishing a lucid, comprehensible explanation in simple language of the theory and practice of wireless telegraphy and telephony. The book treats the subject from an entirely new standpoint. Several very novel and original ideas have been carried out in its making. It is well illustrated by over one hundred and fifty interesting photographs and drawings. All diagrams have been made in perspective showing the instruments as they actually appear in practice. The drawings are carefully keyed and labeled. Many of the photographs are accompanied by phantom drawings which reveal the name and purpose of each part.

It is a book which the wireless experimenter cannot afford to be without. It will prove even more valuable to the layman.

Among the contents are: Introductory. Wireless Transmission and Reception. The Ether. Electrical Oscillations. Electromagnetic Waves. The Means for Radiating and Intercepting Electric Waves. Aerial Systems. Earth Connection. The Transmitting Apparatus. Current Supply. Spark Coils and Transformers. Condensers. Helixes. Spark Gaps. Anchor Gaps. Aerial Switches, Etc. The Receiving Apparatus. Detectors, Etc. Tuning Coils and Loose Couplers. Variable Condensers. Tuning and Coupling. Directive Wave Telegraphy. The Dignity of Wireless. Its Applications and Service. Wireless in the Army and Navy. Wireless on an Aeroplane. How a Message is Sent and Received. The Wireless Telephone. The Ear. How We Hear. Sound and Sound Waves. The Vocal Cords. The Structure of Speech. The Telephone Transmitter and Receiver. The Photophone. The Thermophone. The Selenium Cell.

Handsomely Bound in Cloth with Embossed Cover. (Postpaid, $1.00)

Build Your Own Wireless Instruments

Complete Up-to-the-Minute Authentic Practical

WIRELESS TELEGRAPH CONSTRUCTION FOR AMATEURS

By ALFRED POWELL MORGAN

3d EDITION

220 Pages 163 Illustrations

*Price*, $1.50, *Postpaid*

*Handsomely Bound in Silk Cloth*

Thoroughly up to date and unusually complete. Gives in minute detail, full directions for constructing wireless apparatus and various outfits capable of receiving from 100 to 1,500 miles and transmitting 3 to 100 miles. Also clearly explains the purpose and action of each instrument. Directions for Operating and Adjusting, etc.

*A SPLENDID TREATISE OF WIRELESS ALONG*

*CONSTRUCTIVE LINES*

_Price_, $1.50, _Postpaid_

The value of this book has been greatly increased by the addition of much new subject matter and many illustrations of recent interest.

The new text explains fully how to build the most recent forms of Quenched Gaps. Rotary Gaps, Dough-Nut Tuners, Kick-back Preventers, Audion Detectors and numerous other instruments, accompanied by dimensioned working drawings. Several very interesting and instructive photographs have been included.

I.—Introduction. II.—The Apparatus. III.—Aerials and Earth Connections. IV.—Induction Coils. V.—Interrupters. VI.—Transformers. VII.—Oscillation Condensers and Leyden Jars. VIII.—Spark Gaps or Oscillators. IX.—Transmitting Helixes. X.—Keys. XI.—Aerial Switches and Anchor Gaps. XII.—Hot Wire Ammeter. XIII.—Oscillation Detectors. XIV.—Tuning Coils and Tuning Transformers. XV.—Receiving Condensers. XVI.—Telephone Receivers and Headbands. XVII.—Operation. XVIII.—The Amateur and the Wireless Law. How to Secure a License. Oscillation Helix. Quenched Spark Gap. Rotary Gaps. Kick-Back. The Variometer. New Crystal Detectors. The Audion.—Appendix.

ENDORSED BY WIRELESS CLUBS THROUGHOUT THE COUNTRY AS BEING

THE MOST PRACTICAL BOOK PUBLISHED ON WIRELESS.

IF YOU ARE INTERESTED IN WIRELESS YOU NEED THIS BOOK

*Model Flying Machines*

*HOW TO BUILD AND FLY THEM*

Will prove interesting and valuable.

Have you ever built and flown a Model Racer?

If not, you have missed something.

Price, 25 Cents, Postpaid.

Model Aeroplaning is one of the most fascinating and instructive of sports.

Thousands of young men and boys have formed Model Aero Clubs and organized Flying Contests throughout the country.

"MODEL FLYING MACHINES" of the _Arts and Sciences_ series is the only book giving reliable data and instructions for the construction of practical Model Aeroplanes.

IF YOU ARE A BEGINNER, this is the book that you ought to have. It will start you right. It tells how to build seven different types of machines, starting with the simplest Monoplane and finishing with several Long Distance Racing Models.

IF YOU ARE INTERESTED IN MODEL AEROPLANING, this book will prove the one you have been looking for. Gives valuable "Kinks". Tells how to carve propellers, make winders, adjust and fly machines, etc. Fully illustrated with large size, detailed working drawings, showing the exact size of each part. Twelve full-page plates.

Printed on first-class paper. Heavy cover in three colors.

Sent postpaid by return mail upon receipt of 25 cents.

*EVERY MODEL AVIATOR OUGHT TO HAVE A COPY*

*Experimental Wireless Construction*

*EIGHTY-SIX PAGES NINETY-THREE ILLUSTRATIONS*

*Only 25 Cents, Postpaid*

Here at last is the book which every young experimenter interested in constructing his own wireless apparatus has been looking for.

A book which tells how to build apparatus which anyone would be proud to own. It is a more advanced book than "Wireless Construction and Installation for Beginners," and describes apparatus which is much more elaborate and sensitive. The instruments have all been the subject of considerable experimental work and study. All the apparatus has been put to practical test and carefully improved by clever experts. By purchasing this book you get the benefit of vast knowledge and experience and are enabled to build far better instruments than by following your own designs and haphazard methods.

THE TREMENDOUS POPULARITY OF THIS VALUABLE LITTLE BOOK IS ONLY AN INDICATION OF ITS GREAT WORTH.

It has only been on the market a short time, yet the sales will undoubtedly soon reach a point which would indicate that experimenters unquestionably consider, that in proportion to its size, it is the best book on the market.

It does not describe any old or obsolete forms of wireless apparatus but only the latest types of aerials, spark coils, keys, gaps, condensers, helixes, oscillation transformers, loose couplers, tuning coils, detectors, loading coils, variable condensers, aerial switches, etc.

IT IS ONE OF THE MOST DETAILED AND THOROUGH BOOKS EVER PUBLISHED.

The information is all intensely practical. Complete directions and dimensions are given. Nothing is left to be guessed at. The book must really be seen to be appreciated.

*Partial Contents*

Chapter I.—THE AERIAL. The Location of the Station. The Construction of an Operating Bench. The Aerial and Ground. The Supports or Masts. Types of Aerials. How to Erect an Aerial. Protection from Lightning, Etc.

Chapter II.—SPARK COILS. The Construction of Spark Coils. A 1/4-inch Spark Coil. A 1/2-inch Spark Coil. A 1-inch Spark Coil. A 1 1/2-inch Coil. A 2-inch Coil. Sources of Current. Dry Cells. Storage Cells. Wireless Keys, Etc.

Chapter III.—TRANSMITTING APPARATUS AND ITS CONSTRUCTION. Step-down Transformers. Spark Gaps. The Oscillation Condenser. Leyden Jars. Helixes. Oscillation Transformers, Etc.

Chapter IV.—THE RECEIVING APPARATUS AND ITS CONSTRUCTION. A Silicon Detector. A Galena Detector. The Double Slide Tuning Coil. How to Make a Fixed Condenser. Building a Loose Coupler. The Loading Coil. How to Make a Variable Condenser, Etc.