Chapter XV: Signal Equipment

CLASSIFICATION.

The most important and widely used means of communication used by artillery with their advantages and disadvantages follow:

=(a) Telephone.= The telephone is the quickest and most satisfactory means of communication, and is the most generally used of all means. Near the front, in areas subjected to fire it is often difficult to maintain lines and unless a line be a very carefully insulated and transposed metallic circuit, conversations held over it are picked up by the enemy listening service. To guard against such information being of value to him, telephone codes have been devised, for use in important messages.

=(b) Radio.= Radio provides a reasonably certain means of communication, but such messages are always intercepted by the enemy. Its use requires enciphered messages.

=(c) Projectors.= Projectors afford a very reliable means of communication, but their use depends, to a great extent, on atmospheric conditions, and frequently they may not be used from rear to front and are slow in operation.

=(d) Flags.= Semaphore and wig-wag prove fairly satisfactory only on exceptionally favorable conditions and in open warfare.

=(e) Runners.= Used as a last resort. Slow and wasteful but usually reliable.

In each battalion (F. A.) there are a radio officer, telephone officer, and enlisted personnel for the maintenance of the communication system.

The Camp Telephone.

This telephone, which supersedes the field telephone, was developed by the Signal Corps for use in connection with camp telephone systems and small arms target range systems, and may be installed in tents and structures, or considered a portable instrument for use in the field for testing lines or other purposes. It is of local battery type. The battery employed is one unit of Tungston Type A which is made up of two small cells so placed in a rigid paper that they are connected in series. The combination gives a total voltage of 3—1½ being normal voltage of each cell. The instrument is made as compact as practicable and is contained in an oak case 4¼ × 7 × 10” high. The top consists of a metal hinged cover with circuit diagram on inside, held rigid when closed by a spring snap which can be readily released by depressing a button. The bottom of the case is covered by a flanged piece of metal, the flange projecting approximately one-half inch up sides of case. Through one side of the case are six three-eighths inch holes which are covered on the outside by a close mesh metal screen held in place by a metal frame. These apertures are for the purpose of allowing the ringer to be distinctly heard. The case is equipped with a substantial, adjustable carrying strap, each end of which is fastened to the case by means of hinged metal rings. A small 3-bar magneto generator, small ringer, induction coil, aluminum chamber for the single unit of tungston Type A dry battery, hard rubber block upon which are mounted line binding posts, plug connections for the handset used with the instrument, hook switch and hook operating it and auxiliary battery binding posts, are all mounted on a common base which may be readily removed from case after removing magneto generator crank, metal housing for it and three screws which extend through the case. The instrument may be operated with cover closed which is highly advantageous in inclement weather. To accomplish this there is a suitable opening for leading out the 3-conductor cord to receiver and transmitter, the two latter being mounted in the form of a unit, termed a handset. This handset consists of a transmitter and a receiver mounted on a metal piece and is so designed that when the transmitter is normally placed to the mouth, the receiver is automatically adjusted to the ear. The hook of hook switch is so designed that it protrudes through the case. When it is desired to transport the instrument or to remove the base upon which is mounted all parts of the instrument, it is merely necessary to depress the hook and push it toward the base. By this arrangement the hook is not only held in the down position thereby opening the battery circuit, but it is also protected. The aluminum chamber for housing the single unit of tungston type A battery is equipped with a spring catch so located that when upper hinged piece is depressed to proper position, the battery compresses a helical spring, thereby insuring continual contact. The base is equipped with two screw binding posts which may be used to connect leads to an outside battery in the event of there being no tungston type A batteries available. An aluminum frame which is supported on the base previously mentioned forms a compartment for the handset when instrument is being transported. When the instrument is installed for a temporary period, unless in actual operation, the proper place for the handset is hanging on hook of hook switch, there being a ring on the handset for this purpose. A small screwdriver which will fit practically all the screws used in the construction of the instrument is supported by the metal frame and is furnished with each instrument. The instrument complete weighs about 11 pounds.

The Monocord Switchboard.

The liaison of telephone intercommunication between army units is frequently such that a temporary, quickly installed and flexible type of small central exchange located in the field, is essential. Such an exchange is usually placed in a well protected dugout at the infantry battalion headquarters, artillery battalion headquarters, central artillery observation post, etc., where it will be the central terminal point of from four to twelve or more lines connecting with the headquarters of the higher command, with the several units working with the battalion, and with the joining similar battalions. The switchboard which has been designed to meet these requirements is called the “monocord switchboard” and is made up of either four, eight or twelve of the type EE-2 switchboard units.

The monocord switchboard is made up of unit panels, on each of which is mounted all the apparatus needed for the central exchange end of one telephone line. These panels are made of insulating material and are mounted in special wooden frames in groups of four, eight and twelve units, according to the size of the installation necessary. The two sizes most commonly used in overseas work are the four unit and twelve unit boards. Each unit is removable from the frame, thereby lending flexibility to the board and facilitating repair and replacement. Generally, this type of board is used only for a small number of lines as the operating facilities do not permit speedy connections, and it is always better practice to use only three lines on a four unit board and 11 lines on a twelve unit board in order to have a spare unit immediately available.

The monocord switchboard may be used with either a magneto telephone, camp telephone, field telephone Model 1917, buzzerphone or service buzzer. The operator’s telephone set is not furnished as a part of the switchboard and a separate telephone set of one type previously mentioned must be supplied for this purpose.

=Switchboard Frame.=—The switchboard frame is made of hard wood, varnished in order to make it moisture proof. Its function is to hold the various units together and to protect them from dust and mechanical injury. In the back of the frame there are three horizontal brass bars extending the width of the board. In addition to providing a mechanical support for the various units, the top bar serves as a common ground connection and the middle and bottom bars as common night bell and battery connections for all units. Three Fahnestock clips on American made boards and binding posts on French made boards are installed at the top of the frame and four at the bottom. On the French made boards the upper three binding posts are marked S1, S2 and T, and are used for connecting by independent wires, respectively, the night bell and ground. The two posts at the bottom of the frame marked ZS and CS are used for connecting the two poles of the night bell battery. To the other two marked P1 and P2 are connected the operators telephone and the operators plug. The terminals at the top of the American made boards are marked A, A1 and G, corresponding with the French S1, S2 and T, and those at the bottom are marked B, B1, L1 and L2, corresponding to ZS, CS, P1 and P2, respectively.

If two or more multi-unit boards are connected in parallel for operation at one exchange, the interconnections between boards in order to use one ground, one night bell and one battery for the whole exchange are made. The corresponding binding posts at the top and bottom of the frames are simply connected to each other, as S1 and S2 of No. 1 board to S1 and S2, respectively, of No. 2 board.

=Unit Panel.=—Each unit comprises all the necessary apparatus for the exchange terminals of one line (two wires). The various parts are listed below according to their position on the panel from top to bottom:

Two connecting blocks for the line wires.
Lightning arrester between these blocks.
Two fuses.
Line number plate.
Line drop signal and night bell contact.
Jack.
Cord and line plug.

Each unit is held in the frame by means of two machine screws, one at the top and one at the bottom of the unit, which engages the brass bars in back of the board and hold the unit firmly in place. Rigidity of construction is essential, as constant use and transferring from one place to another tend to loosen the units from the frame and disturb the sensitiveness of the adjustment of the line drop.

=Lightning Arrester.=—The lightning arrester is a simple toothed washer held against the panel by the supporting screw. This screw is grounded through the upper brass bar. If lightning comes in on the line wires, the main portion of it jumps the small air gap from the binding post to the grounded washer and thence passes to the ground, so that only a small portion of the high frequency current flows through the switchboard apparatus. If the latter portion is at all heavy, the fuses burn out, opening the circuit through the switchboard with a much wider gap, and hence higher resistance than that in the circuit to ground across the arrester.

=Line Fuses.=—Two glass enclosed removable fuses, which fit into spring connections, are provided to protect each side of the line from excessive currents. In order that burned out fuses may be readily seen, the panel is painted white behind them. The glass is usually smoked up more or less when a fuse burns out and this against the white background is easily noticed.

=Line Number Plate.=—The line number plate is a small white celluloid strip on which the line number is written. This number may easily be erased if it is necessary to change it.

=Line Drop Signal.=—The line drop signal consists of a shutter held normally in a vertical position by a brass trip latch. This trip latch is attached to the armature of a small electromagnet which is normally connected across the line through the anvil and the jack tip contact spring of the switchboard jack. When the coils of the magnet are energized by a current sent over the wire from a calling station, the armature and trip latch are lifted, thereby releasing the shutter, which falls by gravity to a horizontal position and attracts the attention of the operator. The electromagnet is adjusted to operate on a very small current. For locking the shutter in the vertical position and protecting it from mechanical injury during transport, a flat spring lever is provided which may be turned up from a pivot at one end to press against the shutter.

=Night Bell Spring Contact.=—The night bell contact is located in the back of the panel. The battery and bell circuit through this contact is closed when the line signal drop shutter is released by the electromagnet, this forcing the spring back against the contact point. The night bell spring contact consists of a narrow flat brass spring, screwed at one end to the drop mounting plate. The contact point is mounted on the back of the panel, the rear end of this rod making contact with the night bell bus bar, against which the rod presses when the panel is screwed in place on the bars along the back of the switchboard.

=Switchboard Jack and Line Plug.=—Each unit is provided with a jack and plug. The jack consists of a cylindrical opening in the panel of the unit, behind which are arranged the tip contact spring, the sleeve contact spring and the anvil. The tip spring is connected through one of the fuses to one of the line wires. The anvil is connected to the other line wire through the electromagnet coils and the other fuse. The magnet circuit is normally closed across the line when there is no plug in the jack, as the tip spring and the anvil are then in contact. A current coming in over the line, then, would energize the coil. The sleeve spring of the jack is connected directly to the same line wire as the anvil, the line plug is bridged across the tip and sleeve contact spring. It is a standard two-contact type, the tip and the sleeve making direct connection to the line.

=Operators Equipment.=—Any equipment which is not individual to a line, but which is used in common to all lines in the process of interconnection, is called the operator’s equipment. This consists of an ordinary telephone set, employing either magneto or buzzer and including a transmitter, receiver, induction coil, generator, battery and connection, together with the wiring and the associate parts necessary to co-ordinate them with the rest of the apparatus. An operator’s equipment also includes a night bell and battery.

=Carrying Case.=—Carrying cases made of fiber and provided with hand straps are furnished with monocord switchboards to provide a convenient means of carrying them and to protect them from damage during transportation. These cases are made so that they will hold not only the frame with the assembled unit, but also the switchboard cords. To move the board it is necessary to disconnect the night bell battery, the night bell, the ground connection, the operator’s set and the several line wires.

=Care and Adjustments.=—Care must be exercised when a board is installed to make sure that the frame is in a vertical and level position. When assembled at the factory, all adjustments are made with the board in a vertical position and all operations conductive to satisfactory service depends on this prerequisite being observed. The line signals of the monocord switch boards are of the gravity type and require careful adjustment. Any adjustment further than that done at the factory should be made by an expert who is thoroughly familiar with this work. During transportation and installation of this board, the line drop shutters should be held closely by the flat springs previously described. The burning out of a fuse when excessive current comes in on a line that is detached by an open circuit on that line. A bad fuse generally shows plainly against the white background on the panel. However, if it is not possible to see whether or not the fuse is burned out, the line may be short circuited momentarily by means of a piece of bare copper wire placed across the two line terminals. The operators is then inserted in the jack of the unit under test, and the magneto crank turned. If the fuse is burned out, the crank will turn over easy; if not, it will turn hard, indicating that the open circuit is elsewhere on the line. A burned out fuse should be replaced immediately in order to keep all lines working. Several spare fuses should be kept on hand at all times but in case no fuse is available, a strand of small copper wire may be connected across the upper and lower fuse clips. To remove a fuse, take the bottom metal cap of the fuse between the thumb and finger and push upward against the spring holder on the line terminal block, at the same time pulling outward. To install a fuse, hold it in the same manner and put the other end of the fuse in the upper spring contact, forcing it upward until the bottom ends slip into place. Care should be taken to keep the small air gap between the toothed washer and the line terminal clean. If this precaution is not taken, and the air gap is allowed to clog up with dust and dirt, it will introduce a leak to ground or between wires with resulting poor transmission. All mounting screws and all wire connections should be kept tight. Whenever the unit is damaged, it should be replaced by another one, the damaged unit being sent back to headquarters for repair. In this connection it should be noted that the American unit panels and parts have been made interchangeable with the French to facilitate repair. To remove a unit from the frame, it is only necessary to disconnect the line terminals and remove the top and bottom screws which engage the brass bars behind the board. In handling the switchboard cords, they should be grasped by the plug, not by the cord. The connection of the wires to the tip and sleeve of a plug will break, is subject to undue strain or abuse, and by taking hold of the plug while inserting it and pulling it out, the likelihood of breaking the internal connections and wearing out the wires will be reduced to a minimum.

Disadvantages of the Monocord Switchboard.

1. It does not afford as quick connections as the by-cords switchboard type.

2. It is not self-contained. A self-contained switchboard includes operators, receiver and transmitter and ringing and night alarm circuits.

3. The operator’s telephone is usually equipped with a hand set, (receiver and transmitter) which leaves him with only one free hand for making connections.

4. One switchboard is equipped with but one master, or operators cord, this affords only one means of answering and calling.

Advantages of the Monocord Switchboard.

1. Small, compact, light weight.

2. Simple wiring.

3. Quickly installed.

4. Particularly suited for small central exchanges.

5. Units can be removed quickly, in case of trouble in interior circuits. Any unit can be removed without disturbing other units.

Common Faults and Remedies of the Magneto Telephone.

The most common trouble in telephone instruments are due generally to one of three causes. (1) Loose or dirty connections at the binding posts of the instrument, at the binding posts of the batteries, or in joints of the line wires, (2) exhausted, poor, or weak batteries, (3) crossed, open, or defective wires. These troubles, of course, do not include those arising from inferior or defective instruments. If the connections are dirty, corroded or greasy, scrape the wires and clean out the binding posts, then screw the wires firmly in place. If the telephone does not then work properly, examine the batteries and see whether they are run down or whether the zincs are eaten away. With wet batteries, it may be possible that the water has evaporated; in dry batteries, the zincs may be eaten through or the batteries may be otherwise defective. The simplest way to test a battery is to try a new battery, and see whether it will make the telephone work properly; if it does, the trouble is with the old battery. If the trouble is present after changing the battery, examine the line connections and the line outside; if any loose connections are found, correct them at once. When inspecting the line outside see that it does not touch anything except the insulators, and that it is neither crossed nor broken. On grounded lines—grounded lines are obsolete now in modern warfare on the account of the many means of detecting and picking up messages now employed; in fact the metallic circuit telephone lines are now used within a mile of the front lines except for messages which would be of no value to the enemy—examine the ground connections the first thing and see whether it is in good condition, and if a plate is used see that it is in moist ground. The frequent trouble with transmitters is the frying noise; that is usually caused by induction or static electricity, and may also be caused by loose connections.

1. Open Line. { Effect: Cannot receive a call or get
{ central.
{ Test: Follow line with portable magneto
{ test set and ring; if central gets ring,
{ open is toward station or visa versa.

{ Effect: Can hear and receive central call
{ but cannot talk.
2. Open Battery. { Test: Strap out primary winding or
{ transmitter with test receiver, and
{ leaving the receiver off the hook at
{ station, listen
3. Open primary winding. { in either for click while moving
{ switchhook up and down. If no noise be
{ heard, battery circuit must be open, and
{ circuit should be followed with test
4. Open Transmitter. { receiver, which will click loud where
{ battery is found to be O. K.

{ Effect: No signal will show at magneto
5. Short Circuited { switchboard, and use of station
Line. { instrument will be impaired and magneto
{ will turn hard.
6. Wet or short Circuited{ Test: Open line and ring; if magneto still
Instrum’t. { turns hard open connections one at a
{ time, where available throughout entire
{ winding until magneto turns freely.
{ Effect: Other talking heard on the line
7. Line crossed with { when the receiver is off the hook.
another line. { Test: Ring magneto and with central’s help
{ try to locate other party; then trace
{ line.
8. Open secondary {
winding. { Effect: Can ring and hear central ring but
9. Open receiver. { cannot hear in receiver although can be
10. Receiver diaphragm { heard.
missing or badly { Test: Strap test receiver across open part.
dented. {

{ Effect: Can hear well but cannot be heard
11. Weak battery Cells. { clearly.
{ Test: Use ampere meter and see if each cell
{ be weak.

{ Effect: Can talk and hear in receiver but
12. Open Bell. { bell does not ring.
{ Test: Strap bell coils out with test
{ receiver and listen in.

{ Effect: Bell rings from central but does
13. Open magneto Armature { not ring when magneto handle is turned
Winding. { nor can central be called.
{ Test: Ring with another magneto or test
{ set.

14. Slight Short Circuit { Effect: Can ring operator but cannot hear
(escape) to { nor be heard clearly.
Ground. { Test: Open line, one line at a time, and
{ follow circuit with test set. Escapes are
{ due to wires touching damp walls, metal
{ roof, or other grounded wire where
{ insulation has been rubbed off.

Signaling by Means of Lamps.

Visual signaling by means of the lamp has been found to be very important and efficient. Experience has shown that during the first hours of a battle, particularly in an advance, before it has been possible to establish the telephone systems, the lamp has furnished the most dependable means of communication both by day and night. Even in stationary or trench warfare in sectors with well organized systems of communication, the lamp is most serviceable in transmitting short messages such as calling for a barrage, reinforcements, etc., for which arbitrary signals are used. In fact, this method is more precise than the use of rockets and more rapid than the telephone in transmitting information covered by these arbitrary signals. For these reasons, all important telephone lines near the front are paralleled by the lamp system.

=Description of the Lamps.=—The signaling lamps are made in three sizes called the 14, 24 and 35 centimeter lamps. These dimensions indicate the diameter of the reflector. The 24 cm lamp consists of a portable searchlight, similar in principal to an automobile headlight, but equipped with a sighting or aiming tube on top, a hinged lid to cover the glass reflector, and a two-wire cable used to connect the batteries for operating the bulb. The battery comprises eight dry cells in series, carried in two leather pouches, each holding four cells. These pouches are attached to a leather belt supported by shoulder straps. The belt has also an additional pouch in which three extra lamp bulbs are carried. A brass push button which projects through this pouch is used as a key in completing the battery and lamp circuit to make signals of short and long flashes. Connection between the lamp and battery is completed by the two wire cable and the plug and socket connector. The complete apparatus, comprising the lamp and the belt and three spare light bulbs and eight dry batteries, is furnished in a wooden carrying case. The 14 cm lamp is similar to the 24 cm, but smaller, using a battery of four dry cells and being slightly different in the manner in which it is carried. The 14 cm lamps come three in a wooden case with extra batteries and lamp bulbs. The 35 cm lamp is a larger model of the 24 cm lamp, is not as readily portable and employs a storage battery. it is used only for permanent installations.

=Method of Operation.= The lamp and battery circuit is completed by means of the plug and socket connector. The lid covering the reflector is then opened and the operator sights through the tube to locate the station with which he is to communicate, and signals by means of the push button key. It is essential that the lamp be held rigidly and the sighting tube be continuously aimed exactly at the receiving station during signaling. A slight movement of the lamp makes the signals appear blurred or entirely invisible to the receiving station. A lamp station should always be located in the shade or protected from direct sun rays, which would otherwise produce a continuous glare from the reflector and make the electric light signals invisible. A lamp may be held in the hand while signaling or fastened to anything that will aid stability. In permanent and semi-permanent stations an arrangement for holding the lamp in a fixed position, directed at the receiving station, should be installed. In addition, a wooden tube tapering down in size toward the outer end and being 6 ft. to 9 ft. long and approximately the size of the lamp at the inner end, should be constructed and also permanently aligned on the receiving station. This reduces the diffusion of the rays of the lamp, and also minimizes the possibility of the signals being read where not intended.

=Adjustments of Lamps.=—The reflecting apparatus of a lamp is carefully adjusted before it is issued. However, it is possible that a slightly different adjustment will give better results when a new bulb is inserted. To focus the lamp the light is flashed on some dark background, such as wall a few yards away, and the screws supporting the parabolic mirror carefully turned until the light becomes concentrated in the smallest possible circle. The adjustment screws are then tightened, but they should never be set tight. If the receiving operator is having trouble in receiving signals, he will inform the sending station by sending a series of dots. The sending operator will then examine his apparatus to see if the lamp is properly directed at the receiving station, if the reflector is out of focus, or if the battery has become weak. The receiving operator indicates the manner in which he is receiving the signals by the method in which he sends the dots. If the signals become worse, the dots are made more rapidly. As the adjustment becomes better, the dots are made more slowly. When a good readable adjustment has been obtained, he will signal BR, meaning “go ahead.”

PRECAUTIONS IN LAMP SIGNALING.

Don’t leave the lamp cover open when not in use.

Don’t forget to open it when you start to transmit.

Don’t touch the mirror. If necessary, it should be cleaned by wiping with gauze or cotton or wiped with clean water.

Don’t pull the wire cable fastened to the bottom of the lamp when removing from the box.

Don’t return broken or burned-out globes to the pouch, but throw them away unless ordered to turn them in. Don’t use the lamp for illuminating purposes.

Don’t neglect to keep a constant watch on the stations with which you are supposed to communicate.

SIGNALING RANGE OF LAMPS.

Day. Night.
14 cm 1 to 3 kilometers 2 to 6 kilometers.
24 cm 1 to 6 kilometers 3 to 10 kilometers.
35 cm 5 to 10 kilometers 8 to 15 kilometers.

Signals may be transmitted by using either white or red bulbs, but the range when using red bulbs is reduced approximately 50%.

GENERAL SERVICE CODE AND CONVENTIONAL SIGNALS FOR USE WITH PROJECTORS, BUZZERS AND WIGWAG.

A .- G --. M -- S ... Y -.-- 5 .....
B -... H .... N -. T - Z --.. 6 -....
C -.-. I .. O --- U ..- 1 .--- 7 --...
D -.. J .--- P .--. V ...- 2 ..--- 8 ---..
E . K -.- Q —.- W .—. 3 ...— 9 ----.
F ..-. L .-.. R .-. X -..- 4 ....- 10 -----

Manner of Sending Messages.

Messages are sent by using the General Service Code and should always be as short as possible. Every time a letter can be omitted, the chance of error is reduced. A dot is made by a short flash of about ½ second duration. A dash is a longer flash of about two seconds duration. The interval between dot and dash is about ½ second duration. The interval between letters is about 2 seconds duration. The interval between words is about 4 seconds duration. In order that lamp signals may be easily read, it is necessary that the signals be not too rapid, 15 to 20 characters per minute should be taken as the upper limit. Successive letters must be well spaced. An interval of 2 seconds between letters will enable the receiving operator to call off each letter to his assistant as he receives it. In general, two men for each shift are necessary to operate a lamp station. At the sending station one man dictates the message letter by letter, and watches the receiving station for breaks. The other sends the message. At the receiving stations, one man receives the message and calls it off by letter to his helper who writes it down. To call a station, its call letter should be sent several times and at intervals the station calling should signal its own call letter. As soon as a station observes that it is being called, it will answer by signaling its call letter and the signal BR, “go ahead.” The message is then transmitted and the receiving station acknowledges receipt of each word. By one dot, if it has been understood. By the interrogation mark, if it has not been understood and repetition is desired. (While the interrogation is official, two dots are invariably used for this signal.) At the end of a message the sending station signals AR, meaning, “end of message.” The receiving station sends a dot if the message has been understood.

Signaling by Means of Fireworks.

The use of fireworks in modern battles for sending signals has been greatly developed and is now one of the most important means relied upon to send a few fundamental signals from the front line of the infantry to the supporting artillery within the division and between the ground and the airplanes.

The Fireworks Code.

As the signals that are made by fireworks are always of the most important character, it is essential that the system for their use be so perfectly worked out that there will be no chance of confusion. The smaller the number of signals to be sent by fireworks, the less chance there is of confusion.

Classification of Fireworks.

The fireworks now being used by the American Army are divided into the following classes:

1. Very Pistol cartridges.

2. VB cartridges (commonly called “Tromblons”).

3. Rockets.

4. Flares.

The complete directions for firing these various fireworks are generally attached to the container or box in which they are packed. They are fully discussed in Annex 14, Translation of the 1917 “Instruction on Liaison for Troops of all Arms, A. E. F.”

1. Very Pistol Cartridges.

The Very pistol cartridges are made in two sizes, a 25-mm size, which is issued to the companies of infantry, and a 35-mm size, which is used by the airplanes. These Very pistols fire both signal and illuminating cartridges.

2. VB Cartridges.

The VB cartridges are fired from a cylinder which is attached to the end of a rifle. This cylinder, on account of its resemblance to the old-fashioned blunderbuss (which the French call “Tromblon”) has taken the name of tromblon and now even the VB cartridges, which are fired from this cylinder, are often spoken of as Tromblons.

3. Rockets.

The rockets comprise fireworks which are made in the form of cartridges attached to a wooden stick and fired from a tube or trough. They are used both for signaling and illuminating.

4. Flares.

Flares are used only in the front lines to mark the position of the advanced troops when called for by an airplane.

THE USES OF VARIOUS CLASSES OF FIREWORKS.

It will be seen that the above classification of fireworks is an arbitrary one, made according to the method of projecting them. The same signal can be made by several different means. The means employed depend upon the type of fireworks issued to the particular unit using them and also upon the distance through which the signal must be read.

Flares are not projected at all and consequently have the most limited range of visibility in any but a perpendicular direction.

The 25-mm Very pistol projects its signals about 200 ft. and can be seen from the immediate vicinity.

The tromblon projects its signals to a height of 300 ft. and is next in range of visibility.

The rockets which project a signal at the height of 1000 ft. or over have the maximum range of visibility.

The 35-mm Very pistol projects signals which are larger than those of the 25-mm pistol, but throws them a shorter distance (about 150 ft.). As its use is confined to the airplane this is not a factor in its visibility.

The following are important uses that may be made of fireworks:

1. By the infantry platoon, company or battalion commander in signaling to the artillery for a barrage, or otherwise directing the fire of the artillery.

2. For signaling between the front line troops and the contact airplane in an advance.

3. Warning of enemy gas attack given by the fireworks signaler nearest to where the gas is discovered.

4. As a method of acknowledging various visual signals.

5. Occasionally, during the preparation of an attack and upon orders from the General Staff, fireworks may be used in liaison between the artillery and the artillery airplanes.

Signaling by Means of Panels.

The increasing use of the airplane in modern warfare has necessitated the development of reliable communication between it and the earth. This has gradually been worked out in the following methods:

1. The direct dropping of messages by the airplane.

2. The use of radio apparatus.

3. The use of visual signaling by means of lamps, fireworks and panels.

Panels are pieces of cloth or other materials of various designs which are spread out on the ground in a manner to be easily seen by the airplane. They are for three purposes.

1. To signal to an airplane the identity and location of a unit’s headquarters by the use of its distinctive panel, called its “identification panel.” This is displayed either when the airplane requests it (by means of radio) or when the headquarters desires to attract the attention of the airplane.

2. To signal to the airplane other brief information by the use of rectangular panels known as “signaling panels” and arranged in various ways, either by themselves or in conjunction with the unit’s identification panel.

3. To signal to the airplane the position of the front line in a daylight advance by the use of special panels called “marking panels.” These are displayed only when called for by the airplane.

All panels are removed as soon as an acknowledgment is received from the airplane.

As the use of panels is always in conjunction with airplanes, all panel signallers should understand some of the uses of the various airplanes.

Miscellaneous Methods of Visual Signaling.

=Wig-Wag Flags.=—Flags for use in wig-wagging are now issued to divisions under the name of “kits, flag, combination, standard.” Each kit includes one wig-wag staff and two wig-wag flags, and also two semaphore staff and two semaphore flags. A division is supplied with 1,022 of these kits. The use of the wig-wag flags is already fairly well known in the American Army. Signals are transmitted by describing an arc of 90 degrees to the right and left to form dots and dashes, and spaces by a downward front motion. The general service can be transmitted by this means. Wig-wag flag signaling should be thoroughly understood and practiced by all signal men, as it forms an excellent method for becoming familiar with the code. Signals can be sent by this means merely by the use of the hand, and consequently the system forms an excellent way for troops to put in their time when traveling by train or on shipboard. Its use in the present war has been limited, but it will undoubtedly be used more and more, especially when open warfare is resumed.

=Semaphore.=—Signals by semaphore are transmitted by the arms, either alone or with the semaphore flags that are issued in the standard combination flag kits. It is a standard means of communication in the American Navy and well known in the army. It is not used by the armies of Europe, but it might serve a useful purpose to linemen and others for intercommunication.

Radio Equipment.

The Radio receiving sets, type SCR-53 and SCR-54-A form the standard units for the reception on the ground of signals from airplanes, and in general, of all damped wave signals or modulated wave signals. The use for these sets may perhaps be said to be that in connection with the work of the fire control airplanes in directing the fire of the artillery. But in addition, they are used for so many other classes of radio work, that they may indeed be considered among the most important radio sets.

Type SCR-54 Set.

The type SCR-54 set is very similar to the French type A-1 receiving set. The SCR 54-A set is an improved American product, designed along the same general lines as the type SCR-54 but differing in some respects, both mechanical and electrical, to improve the operating characteristics. The type A-2 and A-2-B antennae are fully described in Radio Pamphlet No. 2. With their use the receiving sets have a wave length range of approximately from 150 to 650 meters. If properly operated, they afford quite sharp tuning. This feature and their compact, rugged and simple construction have made them of very considerable value on the Western Front.

As shown in the wiring diagram, Fig. 1, the type SCR-54A receiving set comprises a primary (antenna) circuit and a secondary circuit, both of which may be tuned by means of the variable capacitance and variable inductance comprised in both circuits. The secondary circuit may also be made aperiodic by placing the switch M on the position marked “AP.” This connects the condenser in or disconnects it from the circuit. A separate buzzer circuit is installed in the cover of the box to excite the set when adjusting the crystal detector.

The adjustable capacitance in each circuit is a variable air condenser which is adjusted by means of an insulating handle, marked “Primary” or “Secondary,” mounted directly on the rotating shaft of the condenser. The relative amount of capacitance in the circuit, corresponding to the various positions of these handles, is indicated by a pointer fastened to the shaft, which moves over a dial graduated from 0 to 90. The position 0 corresponds to the minimum and the position 90 to the maximum capacitance of the condenser. The two condensers are identical in design, and have a maximum capacitance of 500 micro-mfd.

The primary and secondary inductances are varied by means of two dial switches marked “P” and “S,” respectively. The primary inductance comprises 60 turns of wire divided into six steps of 10 turns each, while the secondary inductance comprises 60 turns divided into four steps of 15 turns each. These two inductance coils are wound on separate wooden cylinders so arranged that their relative positions may be readily varied. The coupling of the two circuits, which is accomplished by the mutual induction effect of these two coils, is varied by changing the relative mechanical positions of the coils. The secondary coil may be rotated by means of a handle marked “Coupling,” and a pointer moving over a scale graduated from 0 to 90 indicates its position. When in the 0 position the axes of the two coils are at right angles to each other, and the degree of coupling is 0. When in the position “90” the axes are parallel, and the coupling is a maximum.

The telephone and detector circuit shunts the secondary condenser. This circuit consists of a crystal detector connected in series with the telephone receiver which are shunted by so-called stopping condensers. The latter is a .002 mfd. mica condenser. Two crystal detectors are furnished with a set; one of them is enclosed in a glass tube, which protects the crystal from dust or dirt. The other is open, having no such protecting casing. Either one may be used by screwing it to the two binding posts of the set marked “Detector.”

The buzzer is mounted in a compartment of set box cover, and consists of a small buzzer connected in series with a dry battery type BA-4, and a switch. The buzzer is energized when this switch is closed. A spare dry for the buzzer, a screwdriver, the enclosed detector, some spare wire and spare crystals are normally stored in compartments or metal clips in the cover. Two type P-11 telephone head sets are kept in a special compartment in the box. This set box when closed may be carried by a leather strap attached to it.

Method of Operating.

The first step in putting the set in operating condition is to select a suitable place and set up the antenna. The set box is then installed in a dry and protected place, and the arial and ground (or counterpoise) leads are connected to their respective terminals on the operating panel, and the telephone head set plugged into the jack with the installation thus completed the first step is to adjust the crystal detector. To do this, place the “Coupling” handle near the maximum position, and connect the short piece of wire from the terminal clip in the buzzer circuit to the “Antenna” or “Ground” terminal of the operating panel. Close the buzzer switch to energize the buzzer, and carefully explore the surface of the crystal with the spring contact point until a sensitive spot is found, as evidenced by a good audible sound in the telephone receiver. The short wire running from the buzzer to the panel is then removed and the buzzer stopped by opening the buzzer switch. Care should be taken not to disturb the crystal adjustment by mechanical vibration or shock. This adjustment is very delicate, and if destroyed, it must be restored before any signals can be received. With the crystal adjusted, the set is then ready for tuning. The procedure varies somewhat according to whether the wave length of the station it is desired to receive is known or not.

=(a) Wave Lengths of Signals Unknown.=—The switch M in the center of the panel is thrown to the position “AP” (aperiodic). This disconnects the secondary condenser, and makes the secondary circuit responsive to signals of any wave length. The coupling is made a maximum, and the secondary inductance dial switch S placed at the position “60.” The primary inductance switch P is then placed successively at the positions marked 10, 20, 30, 40, 50 and 60, and, at each point, the handle of the primary condenser is slowly turned over its full range, until the loudest signals are obtained in the telephone. The station is then identified by its call letters, and if it is the station desired, tuning of the set is completed as explained below. It may happen however, that in this search for signals, several stations are heard, simultaneously or for different positions of the handles. The process of searching is kept up until the desired station, as identified by its call letters, is heard with the greatest intensity.

The coupling pointer is then moved toward the minimum position, so that the signals will be just loud enough to be easily read. The switch M is placed in the position T (tune), which connects the secondary condenser in the secondary circuit. The secondary circuit is then tuned by operating the secondary inductance dial switch S and the secondary in the same way that was followed in tuning the primary. The secondary circuit is in tune when the signals are heard loudest. The set is then ready for operation.

If necessary, the strength of the signals may be increased by increasing the coupling, but this should not be done unless the signal become too faint to be read, since increasing the coupling increases the likelihood of interference by other sending stations. When the coupling is changed, some slight adjustments of the primary and secondary condensers will be found to improve the signals.

=(b) Wave lengths of Signals Known.=—When the receiving operator has been advised of the wave length of the signals he is to pick up, the process of tuning in is somewhat facilitated by the use of the table of wave lengths which is pasted in the cover of the box.

The primary circuit of the set is first tuned, as explained above, with the switch on “AP,” the secondary inductance on “60” and with maximum coupling. After the signals have been identified and the primary has been tuned to give maximum loudness, the coupling is reduced as before and the switch M moved to T. The secondary inductance setting to be used is then given in the table. Thus, for a wave length of 280 meters, the setting may be 30 or 45. It is best to use the higher value 45. The final secondary adjustment is then made as before by means of the secondary condenser.

Use of a Vacuum Tube Detector with the SCR-54 Set.

It is sometimes desirable to use a vacuum tube detector in place of the crystal detector supplied with the set. In this case, the telephone stopping condenser of the set must be short circuited by inserting a dummy brass plug in the telephone jack. The crystal detector is then disconnected, and wires are connected from the detector binding posts of the set to the proper terminals of the vacuum tube detector set. The telephone receivers should not be plugged in, as before, in the jack of the set box, but must be connected to the proper terminals or jack of the vacuum tube detector box.

Precautions, Sources of Trouble, Maintenance.

In using this set, care should be taken to always keep it in as dry a place as possible. It should be kept in a clean condition, especially the operating panel, the contacts, binding posts, dial switch studs, and the telephone jacks. Oil or grease on these contacts will make the connections uncertain and unsteady and impair or even prevent the satisfactory operation of the set.

The set should be handled carefully to avoid warping the condenser plates or otherwise damaging the set. No foreign substance should be placed in the set box. Care should be taken that the telephone receiver cords do not get wet, for the resulting leakage of current through them would considerably decrease the strength of signals and introduce an annoying noise. The telephones do not require any adjustment, and the earpieces should always be kept screwed up tight. The telephone receiver should never be taken apart, since their adjustment at the factory is very accurate and permanent. If it becomes necessary to remove the cord connections from either the telephones or the plug, the wires must be connected as found, according to their different colors. This is important since otherwise the permanent magnets will be partially demagnetized and the efficiency of the telephone receivers will be seriously impaired. In packing the set for transportation the telephone head set receivers are placed face to face so that the diaphragms will be protected and kept free of mud and dirt. The telephone cord is then wound around the head band in such a way as to hold the receivers together. The telephone plug is finally slipped inside the coil thus formed by the connection cord, and the entire set is carefully placed in its compartment in the set box. Among the troubles most frequently encountered are those considered below. It may happen that the buzzer does not work. This may be due to a poor adjustment of the buzzer vibrator, or to a run down dry battery. If the radio does not work it may be because the crystal detector is not making contact with the sensitive spot. Readjust it with the aid of the buzzer. No sound in the receiver may be due to the fact that the telephone is not all the way in the jack, or that it is dirty. In this case see that the plug is clear in, or remove it and wipe it off with a clean cloth. Also, the dummy brass plug may be in the telephone jack. This would prevent operation entirely with the crystal detector.

Scratching noises in the telephone may be the result of wet connection cord, or the connection at the plug or either telephone receiver may be loose.

If the antenna or ground connections is loose, or if the ariel or lead in wire is grounded through a branch of a tree, or in some other way, the set will fail to operate. Make sure of good insulation all around. It sometimes happens that a wire will break inside the set box. This generally occurs to one of the wires connecting the secondary induction coils to the various taps to the secondary dial switch. One way to discover this fault is to turn the “Coupling” handle back and forth; the signals may then suddenly stop for a certain position of the handle, although they will be audible with the handle on either side of this position. Finally, a plate of one of the variable air condensers may become warped and short circuit the condenser. This is generally evidenced by the fact that the condenser, when varied over its whole range, does not change the loudness of the signals. In active service, the receiving sets are required to be in continuous working condition. To insure this, spare parts must be kept on hand at all times in order to replace defective parts with the least possible delay. Such spare parts should include spare crystals, telephones and telephone cords. Complete extra set should always be in stock at the central Radio supply station to provide for replacement promptly when sets are destroyed. The sets in use should also be frequently tested to determine and readiness for an intensive and continuous activity. The condenser and inductance circuits should be tested to make sure that each part of each circuit is in perfect working condition. Testing of circuit parts may be simply done with a head phone and dry cell, a click through closed circuits, and the absence of a click through the condenser circuits, being the indication which should be noted.