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How Radio Waves Are Propagated
October 1935 Short Wave Craft

October 1935 Short Wave Craft

October 1935 Short Wave Craft Cover - RF Cafe[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.

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

How Radio Waves Propagate - RF CafeThis 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.

 

Radio waves spread out on surface of sphere - RF Cafe

3-dimensional depiction of wavefronts - RF Cafe

Radio wavefronts impinging on airborne receiver - RF Cafe

Radio wavelengths illustrated - RF Cafe

Water analogy of radio transmission - RF Cafe

Depiction of radio wavelengths - RF Cafe

 

 

Posted May 24, 2024
(updated from original post on 1/15/2015)

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