2-10
Q6. It is known that WWV operates on a frequency of 10 megahertz. What is the wavelength of WWV?
Q7. A station is known to operate at 60-meters. What is the frequency of the unknown station?
POLARIZATION
For maximum absorption of energy from the electromagnetic fields, the receiving antenna must be
located in the plane of polarization. This places the conductor of the antenna at right angles to the
magnetic lines of force moving through the antenna and parallel to the electric lines, causing maximum
induction.
Normally, the plane of polarization of a radio wave is the plane in which the E field propagates with
respect to the Earth. If the E field component of the radiated wave travels in a plane perpendicular to the
Earth's surface (vertical), the radiation is said to be VERTICALLY POLARIZED, as shown in figure 2-5,
view A. If the E field propagates in a plane parallel to the Earth's surface (horizontal), the radiation is said
to be HORIZONTALLY POLARIZED, as shown in view B.
Figure 2-5.—Vertical and horizontal polarization.
The position of the antenna in space is important because it affects the polarization of the
electromagnetic wave. When the transmitting antenna is close to the ground, vertically polarized waves
cause a greater signal strength along the Earth's surface. On the other hand, antennas high above the
ground should be horizontally polarized to get the greatest possible signal strength to the Earth's surface.
Vertically and horizontally polarized antennas will be discussed in more detail in chapter 4.
The radiated energy from an antenna is in the form of an expanding sphere. Any small section of this
sphere is perpendicular to the direction the energy travels and is called a WAVEFRONT. All energy on a
wavefront is in phase. Usually all points on the wavefront are at equal distances from the antenna. The
farther the wavefront is from the antenna, the less spherical the wave appears. At a considerable distance
the wavefront can be considered as a plane surface at a right angle to the direction of propagation.
