57 
American Agriculturist, January 20,1923 
The Simplicity of Radio 
And How to Make a Simple Crystal Set 
This is the second of the radio sferies by 
Brainard Foote. Readers interested in radio 
should keep every issue of American Agricul¬ 
turist on file, for there will be times when 
instructions in making the radio will refer to 
past numbers. Unless you have these back 
numbers, you will be at a loss to understand 
what Mr. Foote is saying. This is also true 
with the construction diagrams. They are not 
only valuable for the diagram, but each early 
diagram carries the schematic symbols of the 
various parts of the radio. 
F or those situated within 20 miles of 
a broadcasting station, this is both a 
“How-to-make it” article and a discus¬ 
sion of the principles of.radio receiving. 
Readers having no station within this 
distance should look upon it as theory 
alone, for receiving sets capable of cov¬ 
ering greater distances differ from the 
simple outfit illustrated this week only 
in the type of detector used. No “crys¬ 
tal” set will reliably cover more than 
about 20 miles, despite far greater 
claims by some manufacturers, and for 
this reason the construction of a “crys¬ 
tal” set for longer distance is really 
wasted effort. 
Radip impulses precede from the 
aerial pf a broadcasting station in the 
form of waves. Sound waves are vibra¬ 
tions of the air, and therefore there can 
be no sound in a vacuum. Waves of 
light and of radio, however, pass 
through a vacuum without the slightest 
difficulty. Radio waves can also pass 
through the earth, through solid walls, 
and in fact can go almost anywhere. It 
duced in a wire if a magnet is moved 
past it. The magnet is surrounded by 
its magnetic field, which makes itself 
evident by its pulling action on a piece 
of iron. Radio waves are similar to a 
magnetic field, although they are mov¬ 
ing at a very rapid rate.. As the wave 
snaps past the aerial wire of a receiv¬ 
ing set it induces in the wire an elec¬ 
tric pressure, first in one direction, and 
then in the other as the wave moves 
up and then down. 
Comparing It to the Violin 
A violin string is most useful here 
for purposes of comparison. The 
length of a radio wave is determined 
by characteristics of the sending aerial 
and internal apparatus connected with 
it, much the same as the pitch of a 
sound wave set up by a vibrating violin 
string is controlled by the string’s phys¬ 
ical properties. The violin string pos¬ 
sesses inertia or resistance to change of 
motion due to its weight, and elasticity. 
The aerial system, which includes the 
aerial wires, the ^ound connections 
and any coils of wire intervening be¬ 
tween the two, possesses similar char¬ 
acteristics. It has inductance, or in¬ 
ertia, and it has capacity, or elasticity. 
An aerial with a large amount of in¬ 
ductance and a large amount of ca¬ 
pacity sets up a long wave length. In¬ 
ductance is determined by the len^h 
and height of the aerial, while capacity 
IbMrlal lb Ground To Phones 
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Diagram of Simple Crystal Set, Save this for Future Use 
is impossible to imagine a wave with¬ 
out picturing at the same time some 
substance or medium that is vibrating. 
Thus a water wave is a vibration of 
the water. A stone is dropped into a 
pond, and ripples spread forth in all 
directions. 
The “Ether” Theory in Radio 
f 
Scientists have set up the “ether” 
theory to explain radio and light 
waves. The “ether” is an aU-pervad- 
ing medium or substance whose pai’- 
ticles are so minute that they fill the 
“chinks” in all other known materials. 
When a man walks along the street the 
ether pours through his body as water 
pours through a sieve. The ether is 
conceived to fill the universe and to 
bring us the light from sun, moon and 
stars. 
In summary, then, currents in the 
transmitting aerial are the “stone” 
which causes the “splash” in the ether 
“pond.” The waves spread out in every 
direction, .travelling 186,000 miles each 
second as in the case of waves of light, 
the waves being high at first, but grad¬ 
ually becoming smaller as the distance 
from the origin increases, The waves 
are definite in length, although their 
height varies according the strength of 
the current in the sending aerial. Wave 
lengths are measured in meters. When 
it is stated that a station’s wave length 
is 360 meters, it means that from the 
top of one wave sent from that station 
to the top of the next wave measures 
exactly 360 meters, or about 1,300 feet. 
Those who have dabbled in electricity 
know that an electric pressure is in- 
depends upon the area of the aerial 
and its nearness to the earth. A single 
wire aerial, high up, is low in capacity, 
while an aerial with five or six wires, 
has a higher capacity, especially if it 
is near the ground. 
It is common knowledge that a string 
on one violin will be brought into vibra¬ 
tion if a string on another violin not 
far away is tuned to the same pitch 
and plucked or bowed. The sound 
waves from the second violin impinge 
upon the string in just the correct 
sympathetic recurrence until the second 
string is pushed and pulled into vibra¬ 
tion in the same way that a boat on the 
ocean may be rocked by steadily recur¬ 
ring waves of water. Where the elec¬ 
trical conditions of the receiving aerial 
are in a similar state of “sympathy” 
with a passing radio wave, the aerial 
is set into electrical vibration and cur¬ 
rents are induced in the aerial, chang- 
. ing direction rapidly in unison with 
the passing wave. 
How the Radio is “Tuned” 
Of course it would be very incon¬ 
venient were it necessary to change the 
size of the aerial every time one wanted 
to receive a dilferent wave length. To 
obviate this difficulty, the aerial is made 
smaller than required, and a coil con¬ 
nected between the aerial and the 
ground. Fig. 1 shows a common method 
of accomplishing this. By moving the 
contact lever back and forth, more or 
less of the coil of wire is introduced 
into the aerial systenj, and various 
wave lengths may be picked up. Vary- 
(Continued on page 59) 
piii. 
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(1) Radiocraft Two Step Amplifier Type D-5 
(1) UV 200 Tube 
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(l) USL 6 volt 80 hr. Storage Battery 
(3) Ever-ready Dry Batteries (22)4 volts) 
(l) Western Electric Head Set 
(l) Stromberg-Carlson Plug 
(l) Copperweld Antenna Outfit (including 2 insulators, 1 porcelain tube, 
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1 997 BROADWAY, BROOKLYN, NEW YORK | 
I enclose (check)—(money order)—(draft) for $30 for radio set described in American Agri- ■ 
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( Name ------ ■ 
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..... State --- 
