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It is difficult to design a single antenna to receive such a wide wavelength range, and there is an octave gap from 216 to 470 MHz between the VHF and UHF frequencies. So traditionally, separate antennas (outdoor antennas with separate sets of elements on a single support boom) have been used to receive the VHF and UHF channels. [6]
Television broadcast stations are located and assigned to channels so that such events are rare. Readjustment of the receiving antenna may allow more of the distant signal to be rejected, improving image quality. A local signal may travel by more than one path from the transmitter to receiving antenna.
These two separate channels can be received by vertical and horizontal feed antennas at the receiving station. For satellite communications, orthogonal circular polarization is often used instead, (i.e. right- and left-handed), as the sense of circular polarization is not changed by the relative orientation of the antenna in space.
[12] [13] For example, the "receiving pattern" (sensitivity to incoming signals as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator, even though the current and voltage distributions on the antenna itself are different for receiving ...
Many times smaller antennas and receivers such as those in vehicles will receive stations farther than normal depending on how favourable conditions are. While only a limited number of local stations can normally be received at satisfactory signal strengths in any given area, tuning into other channels may reveal weaker signals from adjacent areas.
Antenna diversity is especially effective at mitigating these multipath situations. This is because multiple antennas offer a receiver several observations of the same signal. Each antenna will experience a different interference environment. Thus, if one antenna is experiencing a deep fade, it is likely that another has a sufficient signal ...
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Antennas can be classified in various ways, and various writers organize the different aspects of antennas with different priorities, depending on whether their text is most focused on specific frequency bands; or antenna size, construction, and placement feasibility; or explicating principles of radio theory and engineering that underlie ...