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October 1935 Short Wave Craft
 [Table
of Contents]
Wax nostalgic about and learn from the history of early electronics. See articles
from Short Wave Craft,
published 1930 - 1936. All copyrights hereby acknowledged.
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If you or someone you know
is just starting in the realm of radio and want a really nice pictorial presentation
of the basics of radio wave propagation, then this one-page article from a 1935
edition of Short Wave Craft magazine is just what you need. Formula
phobia will not be an issue for anyone since no equations are
presented.
The fundamentals have not changed in the intervening 89 years, and this same sort
of analogy is still used in introductory physics classes and books today. Note
in Figure 7 that the antenna for the airplane is shown being dragged behind.
Back in the day, a long antenna was spooled out once in the air, and cranked
back in before landing. If the pilot forgot to reel the antenna in, it could get
yanked off by a tree upon landing. CW (Morse code) was the dominant form of
air-to-ground communications in the day, where the pilot would have a code keyer
strapped to his leg and had headphones to be able to hear over the noise of an
open cockpit.
How Radio Waves Are Propagated
 This page of elementary diagrams was prepared
for the benefit of the young student, or the layman, who is just becoming acquainted
with short waves. The diagrams at the top show how waves are produced on the surface
of a body of water, for example, by dropping a pebble or other object into the water,
or else by allowing drops of water to fall from a spigot. Note that the wavelength
or pitch of the waves remains constant, but that the strength of the wave gradually
becomes less at a distance from the central point where the waves originate. Radio
waves behave in the same manner; the signal strength falling off inversely as the
square of the distance. Fig. 3 shows how waves expand spherically from an antenna,
as do also Figs. 4 and 5. Fig. 6 shows transmission of a signal by waves on surface
of water; Fig. 7 shows how an airplane receives signals, also a land station. Fig.
8 shows change in pitch of waves of different lengths. The frequency becomes higher
as the wavelength gets shorter and vice versa.
Posted May 24, 2024
(updated from original post on 1/15/2015)
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