What makes antennas work

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. To help you visualize the importance of the ionosphere, imagine our world before satellites. Satellites float through our skies and receive then transmit signals back, using their scope to send messages across distances that our ancestors could never have imagined.

When you imagine the journey of the message, it goes up, probably at an angle, is received, then beamed down to the receiver.

It forms a sort of triangle whose base can span more than half of the globe. The ionosphere serves a similar role. Imagine that you had a message that you could send as far as you wanted, but only in a single direction with no effect from gravity.

If the charge is bounced up and down waves will propagate outward along the springs. Yes, the world of electromagnetic radiation is far more complex than our simple analogy but hopefully it gives you some idea of how a moving charge could create a wave. Note that the magnetic field lines are perpendicular to the electric field lines. This is one of the famous characteristics of electromagnetic waves.

Figure 3. It turns out that all the conventions in electricity and magnetism are set up for positive charges. Much of this can be traced back to the work of Benjamin Franklin.

When we talk about current we pretend the positive holes are actually moving in the opposite direction as the electrons. If a variable voltage is applied, it will send an electrical wave up an antenna. Free electrons in the antenna act as the media for propagating the wave. The situation is similar to longitudinal sound waves propagated in a metal rod. The sound wave is carried by alternating regions of tension and compression.

In the tension areas they are pulled a little further apart. Although the molecules barely move, the sound wave can be transmitted great distances. The very slight motion of electrons up and down an antenna is enough to cause electromagnetic waves to radiate out the sides of the antenna at the same frequency as the variable voltage applied to it. These are used for transmitting radio and television signals as well as other forms of wireless communication. Like sound, when electrical waves at a defined frequency hit the end of an antenna they are reflected backwards and form a standing wave in the antenna.

The electrical waves created on antennas typically have a fixed wavelength. The free end of an antenna acts like an open circuit. Voltage drop is maximum across an open circuit and zero across a short circuit.

Hence the end of an antenna forms an anti-node or area of maximum voltage or e-field strength. A node is a point which has zero e-field. Each channel, aside from its main service can be broadcasting additional programming on 1 to 4 sub-channels simultaneously.

Complimenting your television setup with a digital antenna will come in handy the next time your cable or satellite blacks out. During emergencies or bad weather, receiving OTA signals to your TV with an antenna will keep you informed.

Much like a radio, the frequency is more reliable and less subject to interruption. When choosing an antenna, remember that every set up is unique to the location in which you live. Click HERE to learn more about antenna selection. Typically, the higher you have your antenna, the better the reception. While signals pass through walls and other surfaces, the more obstructions the signal encounters, the weaker the signal and this causes signal disruption. The clearest, most unobstructed view to the broadcast towers will allow the antenna to perform at the highest level.

Antennas come in a variety of shapes and sizes, each designed for a specific situation. Some are narrow focused directional antennas; while others are multidirectional both with various range capacities. 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. AM medium-wave radio tends to travel this way for short-to-moderate distances.

This explains why we can hear radio signals beyond the horizon when the transmitter and receiver are not within sight of each other. They can shoot up to the sky, bounce off the ionosphere an electrically charged part of Earth's upper atmosphere , and come back down to the ground again.

This effect works best at night, which explains why distant foreign AM radio stations are much easier to pick up in the evenings. During the daytime, waves shooting off to the sky are absorbed by lower layers of the ionosphere. At night, that doesn't happen. Instead, higher layers of the ionosphere catch the radio waves and fling them back to Earth—giving us a very effective "sky mirror" that can help to carry radio waves over very long distances.

How long does an antenna have to be?