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# Power Buzzer

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BOX Iq* rI4,l J^NUMBEREB x / jji \u25a0

FOR OF FI( IAL USE ONLY

POWER BUZZERAMPLIFIER

Edited at theARMY WAR COLLEGE

Washington1918

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THE GENERAL SERVICE SCHOOLSeneral.IBRARYDEPARTMENT,'n, January 28, 191S.er Buzzer, Amplifier,"cerned.JOHN BIDDLE,cting Chief of Staff.

NUMBEB.-_..9UOJ rBISCLASSy2l2iAccession Number

CONTENTS.PAGE

I. Theoretical Considerations 311. Transmitting Apparatus. The 8111. Receiving Apparatus. The Amplifier 10IV . Bases 13V. Ranges 15

VI. Compasses 10VII. Preparation of a Power Buzzer Station and powerBuzzer Amplifier Station, for an Assault 15

VIII . Method of Laying Out Stations 20IX . Precautions to be Taken 20X. Hints on Use of Power Buzzer and Amplifier 21

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1

POWER BUZ2ER-AMPLIFIER.I.THEORETICAL CONSIDERATIONS.

If two earth plates, A and B, are sunk into the ground and adifference of potential is maintained between them, whethersteady by means of a battery or alternating by means of a buzzer,the current through the earth cannot be regarded as flowing ina direct path from A to B, but through the whole earth. Thewhole earth may, therefore, be regarded as an infinitenumber ofinsulated conductors joining plate A to plate B.Consider a battery connected up to the two earth plates, A andB, by means of insulated conductors, as in Plate I.The value of the current flowing through C is equal to thearithmetical sum of all the currents flowing through the infinitenumber of insulated conductors of which the earth is consideredto be constituted.The current flowing through each of the infinite number ofconductors is not equal, as the resistances of such conductors aredirectly proportional to their lengths, and it is only necessary toconsider the conductors that lie in the immediate neighborhoodof the direct line from A to B, the currents in the more distantconductors being so small as to be negligible. The dotted linesin Plate Iepresent the nearer insulated conductors.Electrical energy has been dispersed to a considerable distancefrom the source, i. c., the battery, and if itbe possible to tap thisenergy a method of signalling would be obtained ;or, in otherwords, following the same analogy as above, if it were possibleto break one of the infinite number of conductors and lead itthrough a detecting instrument, signaling would be very simple.In fact, it is possible to tap the energy in this manner, forthough it is, of course, not possible to lead one of the infinitenumber of conductors through an instrument, it is possible toshort-circuit a considerable length of it.Imagine a b c d c f (Plate I) to be one of the infinite numberof conductors and that a conductor of very much less resistanceis put across from b to c, as shown in . the chain-dotted line in thefigure, then a far greater proportion of the total current flowingbetween b and f willpass along the chain-dotted conductor thanalong the conductor b c d c.Considering the question from another point of view, there isa difference of potential between b and c, and there are twopaths for the current to flow from b to c, one a low-resistancepath (chain-dotted), and the other a high-resistance path (b c

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d c). The chain-dotted path has practically short-circuited thepath b c d c, and a very large proportion of the total current dueto the difference of potential between b and c willflow along it.In practice, this result is obtained by burying earth plates at band c and connecting these plates by an insulated conductor.In order to employ the electrical energy, it is necessary to insertsuitable transmitting apparatus in the conductor between earthplates A and B, and to provide suitable apparatus for receivingthe current passing through the conductor connecting the earthplates b and c.The most practical and convenient type of apparatus for detecting very small currents is the telephone receiver, but the diaphragm of such a receiver would not be actuated by a constantcurrent except that it would give a click whenever the circuit ofwhich it formed a part was closed or opened, say, by the employment of a signalling key. Consequently, it is necessary to use abuzzer at the transmitting end, which willgive a series of currentimpulses, and willcause the diaphragm of the telephone receiverto vibrate as long as the transmitting key is held down.The range obtainable by means of a simple telephone receiveris far too small to be of any practical value, and some method ofmagnifying the strength of signals is therefore necessary.actually for signallingThe instruments used are :

(i) A special buzzer, known as the Power Buzzer, fortransmitting.(ii) A Valve Amplifier, for receiving and amplifying thesignals received.

(The Valve Amplifier used in this manner is simplya very sensitive relay.)

The earth plates are generally referred to as "earths," and maytake many forms, the usual one being the earth-pin type. Theinsulated conductor connecting the two earth pins is generallyreferred to as an "earth lead," and ithe imaginary straight linedrawn between two earth plates is known as the "base."Referring again to Plate I, there is a fall of potential along'

each of the dotted lines representing a flow of current, and consequently points of the same potential exist on these lines. Forexample, points g, h and fare at the same potential as b. Curvescan, therefore, be drawn through these points of equi-potential,and they aissuime tihe shape of the chain-dotted lines shown inPlate 11.

By considering these chain-dotted lines, it is perhaps easier tosee how signalling can be carried on, for if an earth-plate C beinserted on curve q r s and an earth-plate D be inserted on curve

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x y z, curve q r s being at a different potential to that of x y z,a current willflow along the base connecting C to D.Ithas been assumed above that the mass of the earth is homo

geneous, but as this is not so , the lines representing current flowwillnot be of regular form, but willbe distorted.Ranges depend on the conductivity of the soil. Where thesoil is of bad conductivity, the current flowing willbe so small,owing to high resistance of the earth, that only small ranges willbe obtainable.A strata of non-conducting material below the transmitting basewilltend to prevent the current passing to any depth into theearth ; hence the current intensity through the surface soil willbe greater, there being no alternative path.A path of high conductivity, such as a stream between twobases, may reduce the range considerably. This is due to thefact that the lines of current flow have been short-circuited to a

considerable extent.In Plate 111, if A B is a transmitting base, C D a receivingbase, and E F a stream flowing between them, the current flowrepresented by line a b e f willdivide at point b, one path beingalong the stream from b to c and the other along path b c d c;hence the strength of signals received at base C D willbe considerably diminished. The base C D is not necessarily entirelyscreened.Somewhat similar results are sometimes experienced in wet,boggy soils.At first sight, it might appear that such soils, being of highconductivity, would be admirable for signalling purposes, butwhat often happens is that there are very high conductivitypaths made by small streams, ditches, a series of puddles, orwater-logged strata, etc., and the current concentrates throughthese paths instead of dispersing at a more equal intensitythrough the earth's mass.An extreme case would be if both earths of a transmitting orreceiving base were placed in a stream. The stream would havethe practical result of providing a direct path back from oneearth plate to the other of so low a resistance that almost thewhole current would flow along it, and there would be practicallyno dispersion through the earth's mass.A strata of low.conductivity reaching to the surface of theground between transmitting and receiving bases willgive considerable screening effects.The inferences to be drawn are as follows:(i) The best results willbe obtained in localities where thesoil consists of a comparatively thin layer of lightsoil over a chalky substrata.

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(ii) A thick, damp, loamy soil does not give such goodresults as the soil mentioned in (i), for although thesoil is of high conductivity, the current flow is notconfined to the surface.(iii) Streams, and to a much lesser degree woods, metalfences and walls between transmitting and receivingbases willreduce ranges.(iv) Only short ranges can be obtained in very sandydistricts.(v) Where the surface of the ground is broken up by shell-fire and its conductivity accordingly reduced, especially in chalky districts, ranges willbe reduced.(vi) Never put earths of either transmitting or receiving

bases in places, such as a stream, which have directhigh conductivity paths between them.In order to get good results, the followingpoints have to beconsidered :(i) The lengths of the bases.(ii) The relative position of the transmitting base to thereceiving base.With regard to (i) ::

Itwillbe seen from Plate Ihat the farther apart the points band c are, the greater willbe the potential difference betweenthem, and since the resistance of the earth lead is negligible whencompared with the resistance between earth and earth plates, thegreater willbe the current flowing through the earth lead andthe receiving apparatus.The current intensity at any point will increase if the trans-mitting base is increased.Hence, theoretically, the longer the bases the better; but prac-tical considerations limit the base in a rear station (where facili-ties exi

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