How do antennas create radio waves

These waves travel out at the speed of light , taking your radio program with them. What happens when I turn on my radio in my home a few miles away?

The radio waves you sent flow through the metal antenna and cause electrons to wiggle back and forth. That generates an electric current—a signal that the electronic components inside my radio turn back into sound I can hear. How a transmitter sends radio waves to a receiver. This produces an electric current that recreates the original signal. Transmitter and receiver antennas are often very similar in design. For example, if you're using something like a satellite phone that can send and receive a video-telephone call to any other place on Earth using space satellites , the signals you transmit and receive all pass through a single satellite dish—a special kind of antenna shaped like a bowl and technically known as a parabolic reflector , because the dish curves in the shape of a graph called a parabola.

Often, though, transmitters and receivers look very different. But you don't need anything that big on your TV or radio at home: a much smaller antenna will do the job fine. Waves don't always zap through the air from transmitter to receiver. 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. Photo: This telescopic FM radio antenna pulls out to a length of about 1—2m 3—6ft or so , which is roughly half the length of the radio waves it's trying to capture.

The simplest antenna is a single piece of metal wire attached to a radio. The first radio I ever built, when I was 11 or 12, was a crystal set with a long loop of copper wire acting as the antenna. I ran the antenna right the way around my bedroom ceiling, so it must have been about 20—30 meters 60— ft long in all!

Photo: Antennas that use line-of-sight communication need to be mounted on high towers, like this. You can see the thin dipoles of the antenna sticking out of the top, but most of what you see here is just the tower that holds the antenna high in the air. 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. The antenna you might have to receive satellite television, car radio, or anything else, is a receiver. The size, shape, and scope of these antennas will depend on the purposes of the sender and the distance that the signal is required to go.

In order for a transmitter to send a signal through an antenna, an electrical current must be sent through the antenna and generate a magnetic field.

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.

Signals sent on low frequencies, often times AM stations, rely on the use of ground wave propagation to operate. These ground waves can travel a great distance when used in the lower frequencies of the spectrum. The ionosphere is home to free electrons which help to reflect signals and allow messages to be directed across the entire globe.