51 GILBERT SIGNAL
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heliograph
signals can be read up to forty or fifty miles, and even greater
distances are on record. However, the normal range is around
twenty-five miles, and to obtain longer distances it is usually
necessary to operate from a large hill or mountain peak.
The
principal disadvantage to heliographing lies in its dependence upon the
sunlight. The advantages are portability of equipment ; great range
signals can be exchanged ; the rapidity of sending; and most important
of all is the fact that your signals cannot be observed by others
unless they happen to be on the line of flash between the sending and
receiving station.
Heliograph
instruments vary in design according to the organization using them,
but all are alike in principle. The chief parts of the equipment for a
station consist of one sun mirror, one station mirror, a shutter
arrangement of some sort for intercepting the flashes and a device for
directing or sighting flashes on receiving station.
The
Heliograph and Theory. Every boy has at some time taken a small pocket
mirror or bright piece of metal from which he has reflected the sun's
rays on a shadowed wall. The result on the wall is a bright sun spot or
flash which can be moved at will by slightly shifting the mirror. As
this flash is the important factor in heliographing, it must be
produced and directed at the receiving station with a great deal of
skill.
The mirrors used in heliographs are usually
not over 4
or 5 inches square. Two mirrors are made necessary by the position of
the sun at time one is sending. When the sun is at right angles to the
line joining the two stations, only one mirror is used the sun mirror.
With sun at rear of operator, the two mirrors are required.
With
one mirror the flash is reflected directly from it to receiving station
and with two mirrors the flash is reflected from
52 GILBERT BOY
ENGINEERING
the sun mirror to the
station
mirror and thence to the receiving station. (See Figure 11, A and B.)
How Heliograph Operates
With One
Mirror.
The sun mirror has in center a small peep hole or unsilvered spot about
one-quarter inch in diameter. The sighting device is about 6 or 8
inches to front of the mirror. An upright rod is generally employed
which can be moved up and down; the rod sets parallel with edge of
mirror and has a round disc on an arm which when turned at right angles
to rod falls in line with center of mirror.
To
direct the
flash accurately on distant stations, the operator sights through the
peep hole in rear of mirror and adjusts disc so that the peep hole,
disc and distant station are on an exact line. Then the sun mirror is
adjusted on its horizontal axis only, so that the "shadow spot" cast by
peep hole falls exactly on sighting disc. (The shadow spot can be found
by placing a piece of paper between mirror and sighting device.) After
"shadow spot" is located on disc the flash is visible at receiving
station. (See Figure 12.)
How Heliograph Operates
With Two
Mirrors. The sun mirror is faced towards the sun and the
station mirror towards
FIG. 11
53
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FIG. 12
receiving
station. The station mirror has a paper disc pasted on its face at the
center. The sun mirror is adjusted so that the whole of the station
mirror is reflected into it and the unsilvered spot and reflection of
paper disc accurately cover each other.
To sight
flash on
receiving station the reflection of the distant station will be seen in
station mirror and, by adjusting this so the disc covers the reflection
of distant station, the flash will then be accurately in line.
Intercepting
the Flashes. The method of intercepting flashes in heliograph is either
with the improved shutter with leaves operated by a key or with a
single shutter held in the hand. In either case uniformity of movement
should be maintained. Because of the distances it is always advisable
to count slowly three times for a dot and six times for a dash.
Backgrounds.
Dark backgrounds should be selected when possible for heliographing, as
signals can be more readily distinguished.
To
locate a distant station when its position is unknown, take
54 GILBERT BOY
ENGINEERING
the station mirror and
direct
it towards the horizon, playing it in slowly from right to left several
times. If no response is
FIG. 13
U. S. Marines sending a
heliograph message.
Courtesy of U. S. Marine
Corps
received,
direct it at a point near the home station, and repeat this same
process. As a result of this method you will usually locate the
station.
55 GILBERT SIGNAL
ENGINEERING
If
position of each station is known to the other, the station ready first
will direct its flash upon the distant station so that that station may
be able to adjust its flash to answer the signals.
In
heliographing, the sun's movement has to be watched carefully and
adjustments made often. In the case of well trained signalmen these
adjustments can be made without "breaking" a message. The heliograph is
best operated by two men.
Heliograph flashes are
sometimes
very hard on the eyes; therefore it is always a good plan to smoke the
lenses of the telescope a little when its use is necessary.
THE ARDOIS SYSTEM
The
Ardois System for night signaling consists of a display of red and
white incandescent lamps which indicate the characters of the General
Service Code. The lamps are arranged in four units, each unit
consisting of a red and white lamp. The units are placed an equal
distance apart and usually suspended in a vertical position from a
mast, yardarm or staff, in which case characters are read from top
downward. When it is necessary to place lamps horizontally they are
read by sender from right to left, and in case of receiver from left to
right.
A red lamp indicates a dot and a white lamp
a dash. The lamps are operated by a keyboard.
The
letters of General Service Code are made by a single display; for
example, A which is .
-
would be made in the Ardois System by a display of the red light of the
top unit and the white light of the next unit below. The letter B which
is -
. . . would be expressed by a white
light from the top unit and the next three units below would be red.
Chart
8 gives alphabet for the Ardois System, also conventional signals and
numerals.
The numerals of General Service Code
cannot be used in the
56
GILBERT BOY ENGINEERING
CHART 8
57
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Ardois
system as the expression is limited to four lamps. Therefore, numerals
are made by giving secondary meanings to letters of the alphabet as
shown on the chart.
To make a numeral, display the
letter by which it is indicated, and blink or pulsate the upper light.
In
the case of letters which indicate conventional signals the upper light
is pulsated. The letter R is an exception to this. When pulsated it
signifies Number 2, when flashed it is the conventional signal for
"acknowledge."
The interval is made once to
indicate end of
word, twice for end of sentence and three times for end of message.
When interval is displayed and upper lamp pulsated it is a "Designator"
signal.
The general call to attention is a steady
display of
cornet WWWW.
The cornet is not used, however, if call letter of station
desired is known. In answer to a call, display call letter of station,
the calling station then proceeds with message.
To
indicate
that an error has been made in the message make "interval," the
"error," then "interval" and then begin with word in which error
occurred.
The letter R flashed
acknowledges the receipt of a message.
When
the Ardois System is in use, it is advisable to extinguish all nearby
lights which are liable to cause confusion in signals.
The
Ardois System is authorized for use by both Army and Navy.
THE VERY SYSTEM
The
Very System of night signaling is used by Army and Navy, its use is
mainly confined to signals of extreme importance or when distance is
great.
The signals are made by firing red and
green stars in the air by means of a pistol which has a barrel similar
in gauge to
58 GILBERT BOY
ENGINEERING
the shotgun. The
cartridges
firing the stars are like the shells of a shotgun.
This
system is based on the dot and dash code, a red star representing a dot
and a green star a dash. This system, however, is practical only for
use with Army and Navy codes and therefore is not of any service to a
boy.
59 GILBERT SIGNAL
ENGINEERING
Chapter VI
TELEGRAPHY,
RADIO-TELEGRAPHY AND
TELEPHONY
All
of these non-visual forms of signaling are used by the signal corps of
every modern army. They are also the common means of communication in
everyday commercial life.
In all of the above
methods of
signaling the use of electrical currents are necessary along with
special instruments for receiving and transmitting messages. The theory
of electric currents is a study in itself. This subject is covered in
the Gilbert Electrical Manual, and any boy wishing to acquire a
knowledge of electricity and to apply the theory to his apparatus can
do so by consulting Gilbert Manual of Telegraphy or the Gilbert Book on
Radio Engineering. The writer will confine himself to the operative
side of signaling, which includes the code and proper form of handling
messages over these systems.
TELEGRAPHY
An
American, Samuel F. Morse, invented the first working telegraph
instrument in year of 1835. This instrument was the recording or
writing type, that is, it made marks on strips of paper of dots and
dashes which could be spelled into a message. The recording instruments
are now obsolete and all telegraphy is conducted by sounding
instruments, which spell out messages by means of sharp "clicks."
THE AMERICAN MORSE CODE
The American Morse Code
is used
on all land telegraph lines and short cables. It is also the official
code of the Army for
60
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AMERICAN
MORSE CODE.
CHART 9
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electrical
signaling on military telegraph lines, short cables and field lines.
This code is written on Chart 9. Every signalist should familiarize
himself with this code and learn how it differs from the General
Service Code.
The beginner should thoroughly
commit to memory
the signs representing the letters of the alphabet, the numerals and a
few of the principal punctuation marks. The remaining characters can be
learned afterwards as they are not needed by a beginner.
The
Morse Code is composed of seven elements :
(1)
The dot; (2) the dash; (3) the long dash; (4) the space; (5) the space
between letters ; (6) the space between words and (7) the space between
sentences.
The dot is made by pressing the
telegraph key down
for the smallest fraction of a second and then immediately releasing
it. The result on the sounding instrument is a "click-click" very close
together. The making of a dot involves time, therefore the dash is
equal to two dots and to make this the key is held down accordingly. A
"click click" sound results. The long dash is equal to four dots, thus:
"click click."
The ordinary space between elements
of letters
is equal in time to a dot, between the letters themselves it is equal
to two dots. The word space is equal to three dots and the sentence
space is equal to six dots.
Correct Way of Using the
Key.
The most successful manner of operating the telegraph key is to let the
forearm rest easily upon the table, grasping the key as shown in Figure
14. The wrist should be well above the table, the forefinger curved,
but not held rigid. Let the thumb rest on the edge of knob so that a
slight control of the upward motion is obtained. The raising spring
should assist the upward motion but should never be permitted to
control it. Avoid tapping upon the key. The
62 GILBERT BOY
ENGINEERING
skilled operator will
manipulate it by a muscular action of wrist and ringers.
Elementary Practice of
Code.
Constant practice of making dots with uniformity and precision must
first be acquired, then dashes, then grouping of dots and dashes to
form letters and words.
The beginner should
commence by making
letters slowly, giving proper ratio of time to the elements of each
letter. Speed will come in time by persistent drill.
The
most
difficult letters of the code are C
O R Z Y and S,
termed the space
letters; and if spacing in these letters is not carefully timed they
will be readily confused with such letters as H I P and L.
The
letters J
and K, also
numerals 9 and 7, are difficult letters. Care
should be given not to separate J
into a space which would result in a
double N.
The
usual tendency is to make an F
too long and an L
too short.
Practice transmitting from any
miscellaneous manuscript at hand. This will always test the skill of an
operator.
RECEIVING TELEGRAPHY
Receiving
is of course more difficult to acquire than sending and is mastered
best by having an experienced operator send
FIG. 14
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to the beginner slowly,
increasing the speed as learner becomes more proficient.
Proper Form of
Transmission.
A telegraph message like all visual messages must be checked by the
sender. All words and figures written in the address, body of message
and the signature are counted. Of course To and Sig. are not counted as
they are only indicative terms used by operator.
In
counting
the check of a telegraph message, whether in plain English or code,
groups or initial letters are counted as one word.
Abbreviations
for names of places, cities, towns and states are counted as one word,
as if written in full. This rule applies also to any other
abbreviations.
Figures, decimal points, bar of
division and affixes to numbers, such as d, st, nd, th and rd will each
be counted as a word.
RADIO-TELEGRAPHY
Radio-teiegraphy
or wireless, by which term it is more commonly known, was invented
by Marconi in 1901. Since that time there has been developed
many
improvements, which make the transmission of messages by wireless
almost as practical as by telegraph lines or cables.
Wireless
messages are spelled out by use of the International Morse or General
Service Code (see Chart 1), the operator using a key like that used in
telegraphing. The result is somewhat different from telegraphing, as
wireless instruments have a humming or buzzing sound instead of a
"click." The characters of the alphabet are made up of short and long
buzzes. The receiving is done through phones.
While
wireless
is under the control of the Navy in the United States the government
does not have exclusive use of it. A great many commercial stations
have been established and in
64
GILBERT BOY ENGINEERING
FIG. 15
Boy Scouts of Hartford,
Conn.,
learning the theory of wireless.
Courtesy of
Boy Scouts of America
this
country alone there are thousands of boy experts using wireless, and
enthusiasts are being added to the list daily. Note : For conventional
signals other than in General Service Code see Gilbert Book on Radio
Engineering.
TELEPHONY
The
most widely used of all electrical signal systems is the telephone,
invented by Alexander G. Bell, an American. The telephone is so common
in our everyday life that most of us do not stop to consider the
interesting principles involved.
Color Charts
GILBERT
BOY ENGINEERING
INDEX
Chart
10 Flags of the International Code
Chart 11 Ship Call
Pennants Call Flags
Chart 12 Special Flags of the U. S. Navy
Chart 13 Personal Flags
Chart 14 Weather Signal
Flags
GILBERT
SIGNAL ENGINEERING
FLAGS OF THE
INTERNATIONAL CODE
CHART 10
GILBERT
BOY ENGINEERING
CHART 11
GILBERT
SIGNAL ENGINEERING
SPECIAL FLAGS OF THE U.S. NAVY
CHART 12
GILBERT
BOY ENGINEERING
CHART 13
GILBERT
SIGNAL ENGINEERING
WEATHER SIGNAL
FLAGS
CHART 14
65
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In
speaking, the vocal cords cause air vibrations, which, falling upon the
eardrum are recognized by the auditory nerves as speech. When these
vibrations are transmitted into a telephone instrument, they are caught
by the sensitive diaphragm, changed into electrical vibrations, carried
along the telephone wire to the receiving station and reproduced.
Note:
See Gilbert "Sound Experiments" and Manual on Telephone.
THE TELEPHONE FOR SIGNAL PURPOSES
When signal stations are
connected by telephone, messages are of course sent by this means, it
being much more handy.
FIG. 16
U. S. Army Signal Corps
field
radio station somewhere in France.
66
GILBERT BOY ENGINEERING
The
difficulty arising in telephonic messages is the confusion of certain
letters of the alphabet having like sounds when spoken by word of
mouth.
To provide a ready means of distinguishing
similar
sounding letters, a code of conventional signals is authorized for
military purposes and should be used especially when codes are being
sent. These conventional signals are as follows:
A
Able
B Boy
C cast
D Dog
E
Easy
F Fox
G George
H Have
I
Item
J Jig
K King
L Love
M
Mike |
N
Nan
O Oboe
P Pup
Q Quack
R
Rush
S Sail
T Tare
U Unit
V
Vice
W Watch
X X-ray
Y Yoke
Z
Zed |
To
give an example of the proper use of this code we will suppose an
important message is being telephoned to a station and the receiving
operator cannot clearly understand certain words such as directory, or
the word translation. To make these words clear the operator would
spell directory out slowly Dog-Item-Rush-Easy-Cast-Tare-Oboe-Rush-Yoke.
The word translation would be spelled out likewise. From this code a
clear understanding would undoubtedly result.
67 GILBERT SIGNAL
ENGINEERING
THE SERVICE BUZZER
The
Service Buzzer is a portable piece of signal equipment especially
adapted to the needs of the Army Signal Corps. It can be readily
attached to either telephone or telegraph lines and used as a telephone
or for sending Morse or General Service Code telegraphic signals.
When
service buzzer is used in the latter form the signals are received in a
telephone receiver in form of a high-pitched hum very similar to
wireless signals.
Signals have been exchanged
between two
buzzer outfits even after wire connecting the stations has been cut in.
The instruments were, of course, grounded.
The
mechanism of
the buzzer is very simple, so simple in fact that any boy can make a
practical outfit for Field Service Signaling by following the
suggestions given in this book on page 102.
68 GILBERT SIGNAL
ENGINEERING
Chapter VII
THE SIGNAL TOWER
The
Tower of Babel served as a rallying point and in all probabilities was
the first signal station. Later examples of old signal towers are those
built by the Chinese along the wall of China. Today, however, the
modern signalmen do not build such substantial towers, as the
up-to-date armies are mobile and consequently when a signal tower
is required a portable one or a hand-made affair, which can be erected
in a few minutes by field signal troops, is used.
The
boy
signalist wanting to establish a visual station must first select the
site so it is perfectly in view of receiving station and with a uniform
background for all signals. The distant
FIG. 17
Signal tower erected at
a boy
Scout Camp.
Courtesy of Boy Scouts of America
Signals.
69
GILBERT SIGNAL ENGINEERING
station is the best
judge of
the proper location and background for the signal tower.
In
locating a military station secrecy is of vital importance, and for
this reason the tower is usually camouflaged by shrubbery or erected
behind foliage so the platform of tower is barely exposed.
The
following table gives distances of the visible horizon or how far an
object at sea level can be seen. When observer's eye is :
It
can readily be seen from the above table that an observer whose eye is
25 feet above sea level can distinguish an object at a distance of 6.1
miles provided the object is at sea level. Now should the object itself
be elevated 15 feet its visibility would be increased to 6.1 miles and
4.7 miles, equaling 10.8 miles.
To receive visual
signals at the distances given above, a telescope is used.
SUGGESTIONS FOR ERECTING A SIGNAL
TOWER
The height necessary for
building a signal tower should be calculated according to distance
between points of communica-
70 GILBERT BOY
ENGINEERING
FIG. 18
A natural point of
vantage for
signaling.
Courtesy of Boy Scouts of America
tion.
When possible, natural points of vantage should be used, such as the
roof of a building or a platform built in a tree. Sometimes several
trees can be found close together which can be connected by stringers
and a platform laid around, to which a rail can be added. A ladder
would lead up to the staging to complete the arrangement.
Where
no natural supports can be found, it will be necessary to build a
tower. A substantial tower can be erected by using either three or four
uprights for supporting the platform. The uprights can be made of
finished lumber, using 2x4 pieces or heavier ones, depending on height
of tower wanted.
The drawing on page 71 suggests a
tower made
of three selected trees cut to lengths of 18 feet. These are placed in
the ground about 1 l /2 or 2 feet, the arrangement of placing
being
triangular and 8 feet apart. The uprights are leaned in at the top and
tied 4 feet apart, on which a platform is laid which will accommodate
two signalmen. The platform can be made of
71
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FIG. 19
Illustrating method of
constructing signal tower
72
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boards
or else straight limbs of trees spiked to the cross girders. At a
distance of 5 feet apart cross ties should be spiked to make the tower
as rigid as possible.
A row of cleats nailed to
one of the uprights does very well for the ladder.
SECRET CODES AND CIPHERS
Both
the Army and Navy have their code books, which are especially adapted
to military needs and insure both secrecy and economy of words in
signaling. These codes are confidential except to those in service of
the Government.
The land telegraph and cable
companies also issue code books from time to time to their customers,
not so much for the reason
FIG. 20
73
GILBERT SIGNAL ENGINEERING
FIG. 21
of
secrecy, as for economical benefit of the messages. These code books
can sometimes be obtained and will serve very well for all classes of
signals.
So the boy signalman will not be
handicapped for the
want of a secret code, the writer will suggest the cipher disc which is
used by the signal corps and another improvised method of using the
cipher.
THE CIPHER DISC
The
cipher disc used by the signal corps is a simple but ingenious device
pictured in drawing on opposite page. It consists of two circles of
cardboard, one smaller than the other. These are joined at center so as
to revolve. The inner circle is lettered around the edge with small
letters and the outer circle with capital letters of the alphabet.
The
alphabet reads from right to left on outer circle and left to right on
the inner circle.
The
letter A on inner circle indicated by the arrow is the key letter to
the cipher. The purpose of this cipher is only to transpose one letter
of the alphabet for another, thus the message WE BREAK CAMP AT SUNRISE
when read from the disc
74 GILBERT BOY
ENGINEERING
pictured
would be sent and received as: JB
EOBFV DFTQ FM NLSOXNB. It is of
course understood by reader that the letter F would have been agreed
upon by the sending and receiving stations prior to time this message
was sent.
Any letter can be agreed upon between
sending and
receiving station and then the key letter A is set opposite on disc to
encipher the message.
All numbers are spelled out
when sent in a cipher message.
It
is apparent to the reader that this method is not absolutely unreadable
to any one who would take the time to figure out the key; however, when
used in connection with a code, it can be made much more complicated to
any one desiring to read your message.
The above
method of
sending cipher could be used with the General Service Code which was in
existence prior to the adoption of the International Code of dots and
dashes.
The old General Service Code is written as
follows :
75
GILBERT SIGNAL ENGINEERING
The foregoing code is
used with
the various signal systems as follows :
Wigwag or single flag
- one would be to right and two to left, three would be expressed by
the front motion.
Ardois System
- one
would be red light and two white light, a space would be made for end
of word, etc.
Sound
System, by whistle, bell and foghorn - one would be
indicated by a short blast or taps and three likewise.
Telegraph, Wireless and
Flash
Light System - one would be made by one click, buzz or
flash, two by two clicks, buzzes or flashes and three made in same way
using three.
HOW TO MAKE A CIPHER OUTFIT
A
practical, yet simple cipher can be made by first obtaining several
pieces of ordinary flat picture moulding like those shown in Figure 21.
These pieces will slide parallel to each other; one piece should be at
least 14 or 15 inches in length, while the other can be just half that
length.
Next take white ruled paper and paste
along flat
surfaces of moulding, the ruling or lines of paper should be about 1/4
inch apart.
Fifty-two spaces are necessary for the
long piece
and the alphabet is written twice, backwards, in small letters,
starting from top as shown in Figure 22, these letters are numbered
from 1 to 52.
FIG. 22
The
Science Notebook