You may not be aware of it, but antennas are integral to the normal functioning of many of your most cherished appliances; from your cell phone to your garage door to your television, antennas make it possible to make changes in your home environment, even from miles away. As the internet of things ramps up, antennas will become even more crucial to the every day life of the tech savvy home owner. Because of antennas sending and receiving radio signals from far away, it’s now possible to get your coffee brewing before you set foot in your house. More importantly, you can check in on your house’s security while you’re away. Clearly antennas have become an important fixture in life, but how do they actually work? Here’s a brief overview:
As previously mentioned, basically radio you see from car radios to cell phones possess some kind of antenna. Antennas themselves come in all shapes and sizes, the specifics of which are generally determined by the frequency that the antenna has been engineered to receive.
That explains why your smartphone isn’t outfitted with one of those long, stiff, collapsible wires that generally are used by AM/FM cars, much less a satellite dish. Radio transmitters offer yet another permutation of the same basic technology; their extremely high antenna towers allow them to transmit their signals far and abroad, directly into the air.
Antennas can do more than transmit signals obviously; they can also receive them. Receivers are made to pick up as much of the transmitter’s power as possible and then direct that power directly to an electrical component called the tuner. Satellites that send out radio signals from millions of miles away require that NASA use enormous dish antennas up to 200 feet in diameter. If you’re close to the transmitter you want to listen to, however, you can use something as small as a dangling metal cord to pick up enough signal to listen in.
How do engineers understand how large to make radio antennas given the signals they hope to pick up? There’s a particular and optimum size for any radio antenna given the frequency of the signal that the antenna is trying to transmit or receive. This is due to the finite speed of light and the limited distance that electrons can travel given a unit of time as a result.
Here’s how it works: Say you’re going to attempt to make a radio tower for your radio station, which will air on 680 AM. That means your station will transmit a sine wave with a frequency of around 680,000 hertz. Another way of saying that is that, during one cycle of the sine wave, your transmitter is going to need to move electrons in the antenna in one direction, switch and pull them back, switch and push them out and switch them and move them back again (the electrons change direction four times per sine wave cycle). The transmitter is functioning at a frequency of 680,000 hertz, so every cycle completes in .00000147 seconds, meaning electrons spend one quarter of that time moving in the same direction before they switch. The optimal antenna size ends up being about 361 feet, which explains why AM towers are always so tall.