Figure 11. Components of Electromagnetic Wave.
3.
Directivity. Communications over a radio circuit is satisfactory when the received signal is
strong enough to override undesired signals and noise. In other words, the receiver must be within range
of the transmitter. Communications effectiveness can be increased between two radio stations by
increasing the transmitting power, changing the type of emission (for example, changing from a
radiotelephone to CW), changing to a frequency that is not readily absorbed, or using more directional
antenna. In point-to-point communications, it is usually more economical to increase the directivity of
the antenna system. Directional transmitting antennas concentrate radiation in a given direction and
minimize radiation in other directions. A directional antenna may also be used to lessen interception by
the enemy and interference with friendly stations.
Learning Event 2:
MICROWAVE MULTICHANNEL RADIO SYSTEMS.
1.
General. The radios used in microwave multichannel systems are designed specifically for
such use and are not generally used without multiplex equipment. The radios (figure 12) are used in
pairs; one at each end of the line-of-sight or troposcatter path. These radios operate on frequencies
above 30 megahertz (MHz). The frequency range and associated multiplex equipment determine
whether the sets are compatible with each other. Since radio is the least secure means of
communications, transmission security is a constant concern in multichannel operation. The enemy
obtains information through merely knowing that such radio sets are operating. His analysis of the
number and location of radios in operation and their volume of traffic, may produce even more
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