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Tactical Wireless Communications and Networks: Design Concepts and Challenges by George F. Elmasry

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6.6 Historical Perspective

We have come a long way from the days of using carrier pigeons and smoke stacks to send coded messages in the War Theater. The discovery of modulated RF signals opened the door for making military communications the ever-evolving field it is today. The transformation of radio from a scientific curiosity to a practical communications technology was the result of incremental improvements in a wide range of areas. One can say that the micrometer spark gap used by Heinrich Hertz, followed by various magnetic, electrolytic, and crystal detectors, and finally the very important improvements in three-electrode vacuum tubes made RF signal amplification practical.

One of Marconi's most important discoveries was “groundwave” radio signals, signals that resulted from the addition of a ground connection to the transmitter, which led to greatly increased transmission ranges. This was made possible by the discovery that “earthing” the transmitter antenna resulted in the ground being used as a waveguide; the signals followed the earth's plane, and spread out in only two dimensions. This was unlike a free-space transmission, such as light, which dispersed in three dimensions. This discovery, led people to see that groundwave signal strength tended to drop inversely with the distance covered. This was contrary to free-space signals, where the signal strength is proportional to the square of the distance.

Military radio communications have been around for over 100 years. ...

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