Instead of simply sending out a signal at a particular frequency , the antenna sends out signals that have either their frequency or amplitude modulated. Frequency modulation FM and amplitude modulation AM are the two most common ways that information is packaged in radio waves. The signal is modulated to contain mono audio information left and right speakers , a pilot tone, AM suppressed carrier information, and text information.
That modulated signal is sent through the air, traveling at very specific wavelengths and received by the antenna you are using. The signal with the information is called a carrier signal. When a signal has been modulated and relayed out into the airwaves, we refer to it as a carrier signal because it carries information along with it.
Just as a signal must be modulated to become a carrier signal, it has to be demodulated when it reaches the receiver. In other words, the signal is reduced down to the pertinent information. When it comes to other kinds of media such as video, the signal must be digitized.
Some waves shoot straight from the transmitter to the receiver. The line of sight transmission was effectively eliminated in the 60s when fiber-optic cables were the primary method of transmitting phone calls.
Directionality — an antenna may be non-directional isotropic , transmitting uniformly in all directions, or directional —transmitting preferentially in one or more directions at a higher power. Enhancement amplification of the antenna — the ratio between the radiation power of an antenna in a certain direction, and the radiation power of an isotropic omnidirectional antenna under identical conditions of transmission distance and input power of the antenna.
Polarization — direction of the electric field radiating from the antenna in areas sufficiently distant from the antenna a distance of a number of wavelengths.
Efficiency — The ratio between the total power radiated by the antenna and the net electric power fed to the antenna. Band width — The width of a range of frequencies at which the antenna transmits its maximal radiation and intensity. Antenna array — A systematic deployment of antennas that operate together. The individual antennas in an array are usually of the same type, and are situated in close proximity and at a fixed distance from one another.
An antenna array enables increasing the directionality and control of the main radiation beams and the lateral beams. Dipole antenna - consists of two wires or rods , usually metallic, placed in a straight line, so that an alternating current flows through the center of the antenna. Monopole antenna Marconi — a single straight wire or rod metallic , mounted perpendicularly over an infinite conductive surface called a ground plane.
In practice, a smaller plane is sufficient. Yagi antenna — consists of an active antenna and a number of passive antennas, serving as directors or reflectors. This type of antenna is used mainly for transmission and reception of FM radio and TV broadcasting. In the past this type of antenna was also used in radar systems. Horn antenna — a funnel-shaped wave-guiding antenna. This type of antenna is used mainly for frequencies greater than 1 GHz.
Printed antenna — an antenna that is composed of a conductive layer etched on an insulating substrate. The back of the substrate is covered by a conductor and serves as the ground plane. Most modern transistor radios have at least two antennas.
One of them is a long, shiny telescopic rod that pulls out from the case and swivels around for picking up FM frequency modulation signals. The other is an antenna inside the case, usually fixed to the main circuit board, and it picks up AM amplitude modulation signals.
If you're not sure about the difference between FM and AM, refer to our radio article. Why do you need two antennas in a radio?
The signals on these different wave bands are carried by radio waves of different frequency and wavelength. Typical AM radio signals have a frequency of kHz kilohertz , while typical FM signals are about MHz megahertz —so they vibrate about a hundred times faster. You need two antennas because a single antenna can't pick up such a hugely different range of wavelengths.
It's the wavelength or frequency, if you prefer of the radio waves you're trying to detect that determines the length of the antenna you need to use. Broadly speaking, the length of the antenna has to be about half the wavelength of the radio waves you're trying to receive it's also possible to make antennas that are a quarter of the wavelength, though we won't go into that here.
Blogs Contact. Blogs Need Help? Search Site. How antennas work Suppose you're the boss of a radio station and you want to transmit your programs to the wider world.
Depending on what kinds frequencies of waves we want to send, how far we want to send them, and when we want to do it, there are actually three different ways in which the waves can travel: Artwork: How a wave travels from a transmitter to a receiver: 1 By line of sight; 2 By ground wave; 3 Via the ionosphere. As we've already seen, they can shoot by what's called "line of sight" , in a straight line—just like a beam of light.
In old-fashioned long-distance telephone networks, microwaves were used to carry calls this way between very high communications towers. They can speed round the Earth's curvature in what's known as a ground wave.
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