The Science Notebook
Gilbert Signal Engineering - Part 5

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NOTE:  This book was published in 1920, and while many of the experiments and activities here may be safely done as written, a few of them may not be considered particularly safe today.  If you try anything here, please understand that you do so at your own risk.  See our Terms of Use.   

NOTE # 2:  Some of the codes in this book have changed slightly.  For example, the International Morse Code, known at the time as the "General Service Code is still used today and is as shown in this book.  (See p. 15.)  However, some of the "conventional signals" have changed.  (See p 17.)  Learning to send or receive Morse code by sound, light or semaphore might be a little hard, but it can be a lot of fun, but before you attempt to learn it, be sure you are using the correct code and signals for today.  You should be able to get the current version of the code or sending method you want to use online.  Check out our Downloads and Useful Links pages for additional information.

 Pages 101 - End


No. 1 of Chart 16 shows the proper way to lay out a wigwag flag. The cloth can be tacked to any flat surface and, with a ruler and pencil, a square can be marked off the exact size wanted. Lines can then be drawn from corner to corner as shown. This serves to help; get the square in the exact center. The cloth can then be cui around the dotted lines, which should be about 1/4 or 1/2 inch. from the edge of the flag. This gives enough margin for hemming . The next step is to turn down the edges of flag and pin. A selvedged edge can then be made by hemming on a sewing machine or stitching by hand. After this is done another small piece of cloth of opposite color is marked off as pictured in No. 2. The size of square being same as the square in center of flag. The smaller piece of cloth is then cut around on the dotted lines and hemmed around the edge, after which it is placed over the square of the larger piece of cloth and sewed on. Be careful to stitch as close to edge as possible. After this the flag can be turned over and cut out on inside of stitching with a pair of scissors. This brings the square through and makes flag the same on both sides. The flag is now complete except for a staff and the fastenings necessary.

Ties can be sewed on flag as shown in No. 3, using flat binding tape. Three ties will be enough one in center and one at each end, as seen in No. 4 on the completed flag. For a staff a bamboo fishing pole can be used or any round pole of 3/4 to 1 inch in diameter.

No. 5 suggests several ways of making a jointed pole if one is wanted to make flag staff convenient to carry on a hike.


No. 6 suggests a disc for wigwagging. The disc can be either cut out of a piece of tin or heavy cardboard, painted in colors black and white or red and white and then tacked to a


slender stick or pole. This piece of signal apparatus is easily made and has the advantage over the flag on a windy day as flag is very apt to foul while the disc is not open to this objection.


Semaphore flags can be made exactly like wigwag flags except for size, which vary from the 10 and 15-inch sizes used in Navy to 24-inch size which is the largest used by the Army.

For all around semaphore signaling the 12 to 18-inch size will be found most adaptable. The flags are always made square in shape and usually of a design like the wigwag flags, with square center or the diagonal type illustrated. (No. 8.)

No. 7 shows the way to mark off cloth for cutting out the diagonal flag.

The ties for fastening flag to stick can be made the same way as in the case of the wigwag, but need not be as strong. The darkest portion of flag goes next to stick and the stick should be only long enough to allow a hand hold below the flag. The stick can be notched to keep ties in place ; or another way which makes a neat effect is to make eyelets as shown in No. 9. This is done by shaping the eyelets out of a piece of copper wire, flattening the ends and binding them to the stick with fine wire or heavy thread, after which a coat of varnish, if added, will put on the finished appearance.


The field buzzer is an instrument used by Boy Scouts and armies for sending and receiving signals between temporary stations. It is strictly a portable instrument. The one used by the United States Army can be used for many kinds of signaling. It will work as a telephone or as a telegraph. Of course it is used as a telephone whenever possible ; but when the connecting lines are broken, it is possible to use the sets as tele-


graph stations, and messages are sent and received in the form of a high pitched hum very much like that of a radio signal.

In actual field use, these messages have been sent and received when the lines were cut off but both ends of the line slightly grounded. It is not hard to make an instrument similar to the United States Service Buzzer which will give the Gilbert Signal Engineers lots of sport as well as practice in telephone and telegraph work. This amateur set will not, of course, be so elaborate as the army set, because the latter is made for use in all sorts of weather, in all sorts of places.

But for practice work, the little sets described below will serve you just as well and will be cheaper and easier to build.


This instrument can not be used as a telephone set, but can send and receive Morse and Continental Code telegraph messages.

Parts Required

1. Panel - This should be about 1/8 of an inch thick and can be made of hard black rubber, black fibre, or even thin wood painted or stained to make it look well. This panel should be 6 inches long and 3 1/2 inches wide.

2. Battery - Purchase five flash light batteries and connect them in series. The batteries used in the set described here measure 1 3/8 wide, 11/16 inches thick and 2 1/4 inches long. But batteries of other size can be used if necessary, and the only change in the set required will be in the wooden box enclosing the set and in the size of the panel.

3. Key or Button - For this set an ordinary doorbell push button will do very well.

4. Telephone Receiver - Purchase a 75 ohm telephone receiver of the watch case type.



FIG. 28


5. Vibrator and Vibrator Coil - You can buy a buzzer such as is used for sending practice in wireless telegraphy, or, if you prefer to make one yourself, you will find the following instruction helpful.

Cut two cardboard or fibre discs; these should be about 24 inches in diameter. Put a hole through the center 3/16 inches in diameter and two small holes for the wire to pass through as near the edge as possible and on opposite side of the large center hole. These small holes can be made with a small nail or an awl. (See Figure 29.)

Make two supports for the buzzer, using 1/16 inch steel and a vibrator of springy steel about 1/64 of an inch thick.

Place an 8-32 round head steel machine screw  1 1/8 inches long through one of the supports and washers, holding the latter tightly against the screw head. Wrap six or seven layers of writing paper around the body of the screw. Make the width of this paper 24 of an inch. Place the other washer on the screw and tighten it against the end of the paper wrapper, by means of a steel nut. Wind over the paper 25 feet of No. 24 B&S Gauge copper wire insulated either with enamel or cotton.

Start this winding by pushing a beginning of the wire through one of the small holes in the end washer, leaving about 2 l / 2 inches of wire sticking through the hole for a connecting lead. When the coil is complete, stick the end through one of the other small holes and your magnet is complete.

Next you will need a support for the adjusting screw, which should be of brass 8-32 and about l/2 inch long. This is locked in place by an adjusting nut.

6. Box - This should be a well-made box with a hinged cover and clasp. (See Figure 30.) Make the inside dimensions of the box 6 inches long, 3 l/2 inches wide and 2 inches deep. The cover should be 6 inches by 3 l/2 inches by 1 inch deep. If you plan to


FIG. 29


use the buzzer on hikes, it will be well to put a carrying strap of leather or webbing on the box.

The batteries should be held in place by end blocks of wood and also by the two brass terminal strips shown in Figure 28. The battery terminals should be placed so they make good contact with these brass strips so that the first battery on the right


FIG. 30

has the outside terminal against the upper strip, the next will have the outside terminal against the lower strip. Alternate these connections until all the batteries are in place.

Make the connections as shown in the diagram (Figure 28), fasten the panel in place, attach the telephone receiver to the binding screw and the instrument is ready for use. It will be a great help if you make an iron pin to push into the ground for one side of the line circuit. The other side should be a copper wire at least as large as No. 24 B&S Gauge.


If in the above instrument we had used a telephone receiver connected, as shown in the next diagram (Figure 31), with this


circuit when the key is closed, a single click would have been heard in the receiver.

If the key is held down, no further sound will be heard unless some one speaks into the transmitter. The set will then act as a telephone. We will not take the time here to explain the telephone theory. It requires a book by itself.

FIG. 31

Now we can combine the telegraph and telephone instruments in one by the addition of a second push button or key and a transmitter. Study the connection diagrams shown (Figures 32 and 33) and you will have very little trouble in understanding how to build this set.

When you wish to use this outfit as a telephone, you press Key No. 2, holding it closed. A current will then flow from the + side of the battery to the ground, from the ground it will pass through the grounded side of the listening station, around the buzzer winding, through the listening station receiver to the line back to the sending station, through the sending station receiver to the telephone transmitter, from the transmitter to Key No. 2 and from Key No. 2 to the battery, thus completing


FIG. 32

the Circuit. Note the whole battery is not used for this circuit but only two batteries are connected by a tap for the telephone use.

When the speaker at the sending station talks into the transmitter, his voice sets the little granules of carbon in motion, thus varying the resistance of the circuit. This causes the current to

FIG. 33


fluctuate, causing the magnet in the receiver to vibrate the diaphragm for every tone the sender utters. This is heard as a telephone message by the listener at the receiving end.

To use the telegraph circuit, Key No. 1 is pressed. When it closes the circuit, the current flows from the positive side of the battery to the buzzer coil, to the vibrator. From the vibrator it passes to the brass contact screw, but at this point the circuit is rapidly opened and closed due to the action of the magnet and
vibrator. From the contact screw, the current passes to the Key No. 1, from the key back to the negative side of the entire battery.

But in addition to this there is also a current flowing from the ground to the receiving station ground, through the receiving station buzzer coil, from the coil to the receiving station telephone receiver where a high pitched hum is heard, from the receiver to the line back to the line side of the sending instrument receiver to sending station buzzer coil and back to the ground.

When the sending station buzzer starts vibrating, it sets up a pulsating current in the second circuit which can be heard as dots and dashes in the receiving station receiver when the sending key is operated properly.

With two of these instruments it is possible for two boys to have lots of fun and, at the same time, learn many of the elements of electric signaling.

In the Army Service Buzzer there are other parts such as the condenser, so that the soldiers can attach the instruments to any telegraph lines in the country where they happen to be. This allows them to operate without interfering with the regular telegraph work of the line.

But these things make the set a little more complicated and are not necessary for the average boy, so we will not describe them.



Before trying to make the heliograph outfit illustrated on Chart 17 read over carefully the theory of heliographing in Chapter V, page 50, and with these principles thoroughly fixed in your mind the making and operating of the heliograph will be very easy.

To make heliograph as shown the station mirror and the two diaphragms L (Nos. 2 and 3) are supported on a tripod, made by using a 2x4 or 4x4 inch upright. This can be sharpened and driven in the ground about 1 1/2 or 2 feet, after which a 2x4 inch piece 6 1/2 feet long can be fastened through the flat side at the center to the post by a large screw. This will allow the instrument to turn so as to face in any direction desired.

The station mirror can be made as pictured by using a plate glass mirror 4 inches square. The mirror is set in a frame made of picture moulding. The framed mirror is then mounted in a U-shaped easel. The easel can be made out of 1x1 inch lumber and strengthened by using small angle irons at corners. (These can be purchased at any hardware store.) The mirror frame can be suspended in the easel by attaching it to large size nails inserted in the holes that have been drilled through the center of the frame and the upright ends of the easel. A spring arrangement is then placed on each side of the mirror frame between the uprights of the easel. This can be worked out so that the mirror will set rigid at any angle.

The easel is bolted to one end of the tripod, using several washers on the bolt, between the 2x4 and easel. The station mirror can then be turned to right or left.

The diaphragms, Nos. 2 and 3, can be made out of tin, cardboard or light wood. Both of them can be made the same size, about 8x12 inches, with the 8-inch side at top. The diaphragms are cut out so as to slide on the 2x4 piece. They are balanced and supported by a piece of wood to which several





blocks are nailed on each side as shown. The diaphragm is of course tacked to the wood supports; this allows the completed diaphragm to slide on the 2x4 piece of the tripod.

The diaphragm shown in No. 2 has a square hole 3x3 inches at center, with cross wires. That shown in No. 3 has a square hole 2x2 inches, with cross wires or thread.

In making the diaphragms a great deal of care must be given to obtaining the right size hole in each and also that in the center of the station mirror. (Make the hole in the exact center of station mirror by scratching off a little of the silver.) The cross wires in each diaphragm must be exactly in line.


The advantage of this type of heliograph over the open mirror type is that it reduces the beam of light down to a direct flash by means of the two diaphragms. The result of which is shown on Chart 17 by the dotted line which represents the straight course of the rays coming from the second diaphragm (No. 3).

The first diaphragm should be placed about 1 foot from the station and the second diaphragm (No. 3) about 3 l /2 to 4 1/2 feet distant from the first; as both slide they can be adjusted easily to the proper distance.

By lining up the receiving station through peep hole and cross wires of both of the diaphragms and the station mirror angled so as to catch the sun's rays, the apparatus is ready to send the message.

The flashes can be intercepted by using a piece of tin or wood about 12x12 inches square, to which several pieces of 1x1 inch wood can be nailed, as pictured at lower right hand corner of Chart 17. This gives a good hand, hold and perfect control of your shutter. 


An additional mirror will be necessary should the sun be behind the sender. The extra mirror can be held by another boy in this case so as to deflect the sun's rays into the station mirror.

A little practice will be necessary to get accustomed to the adjustment required when the angle which the sun's rays make with the mirror changes at different times during the day. When the knack of arranging the mirror is acquired you will have no trouble in sending a message up to twenty-five miles, if that distance is required with this outfit.


The semaphore at center of Chart 18 needs little explanation as it is simply two cross arms with paddles which can be painted in conspicuous alternating colors so as to be readable at a distance.

The post which carries the semaphore arms can be any height desired. The arms to which paddles are nailed should be made of 1x1 inch light pine wood and the paddles about  1/4 or 3/8 inches thick by 2 1/2 feet in length and 6 to 8 inches in width.

The semaphore arms are bolted or nailed below the other arms so as to fold back to post when not in use. This extra arm indicates to receiving station the sender's right or left.

Messages are transmitted by pulling the semaphore wings up by means of the cord to a position at right angles to the upright post and then dropping same immediately to a position parallel to and in back of the post.

The, right wing when pulled up to the position mentioned will indicate the dot of the General Service Code and the left wing will indicate the dash. The end of word can be indicated by raising both arms at same time and the end of sentence by swinging the arms a little.






Two types of blinker lights for sending messages by General Service Code are pictured on Chart 18.

The blinker at the right on the chart is made with a lantern and operated by a cord passing over two small pulleys. The lantern is so suspended as to make it possible to drop it in a bucket, which of course "douses the glim." By pulling the lantern up and letting it drop back into the bucket, a dot or dash can be made by timing the length of lantern's exposure.

The blinker on the left of Chart 18 is operated electrically by using a telegraph key. A miniature receptacle can be purchased at any electrical shop. This can be mounted on a wooden block and nailed to top of a pole or in fact any other suitable place. A small 2 or 3 candle power light can be used in the receptacle for the light. (A 3 candle power light is good for a distance of 3/4 of a mile without the use of binoculars.) One light copper insulated wire is run from one terminal of receptacle to the dry cell batteries, which are connected in series. Another wire is run down from the other terminal of receptacle to the key and then to the batteries.

Two dry cell batteries will be strong enough to cause a 3 candle power lamp to work satisfactorily.


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