Sun. Feb 23rd, 2020

# What are radio waves? | Science

We call radio wave a class of electromagnetic radiation whose frequency is comprised in what we call the radio spectrum that ranges from the frequency 0 to 300 gigahertz. From that frequency we start talking about infrared, visible, ultraviolet …

The electromagnetic field is a wave process similar to when one throws a stone into a pond and a wave is formed that has highs and lows (peaks and valleys) and varies. In the same way, even if we don't see it, the electromagnetic field varies; It has values ​​that are higher first, then lower and so on, undulating.

And what is the frequency? The frequency has to do with how quickly that wave undulates, that is, how fast it goes from a maximum to a minimum or how close are the maximums and minimums in time because the important thing to consider is That value varies. The time between maximum or minimum, that is, between repeated values, we call it period. And the inverse of the period, how many turns to that cycle we have given per second we call the frequency and is measured in hertz (which are neither more nor less than cycles per second). For example, if I have a period of 0.1 seconds it means that in a second I found 10 peaks. If we think of a bus that goes around a circuit we can say that the period of the bus is one hour or we can say the turns that the bus takes in an hour, the turns that the bus takes is the frequency and the time it takes to take One lap is the period.

The frequency of a wave, that is, how fast it makes these variations, will change its characteristics, its behavior. And since we are capable of generating waves of different frequencies, that allows us to organize the spectrum. It allows us to decide, for example, that when we generate a 900 megahertz wave we use it for mobile telephony, or a 2.4 gigahertz wave we use it for Wi-Fi. All are radio waves but with different frequency.

The frequency of a wave, that is, how fast it makes these variations, will change its characteristics, its behavior. And since we are able to generate waves of different frequencies, that allows us to organize the spectrum

We use them for all types of wireless communications and we also use them for communication via cable. But the most popular use is wireless: television, mobile communications, the data that the mobile sends or receives or how we communicate with Wi-Fi, FM radio …, all that goes through radio waves and arrives to us because a receiver with an antenna is able to receive the information and transfer it to us.

What we wanted to convey: image, sound, etc …, first it has been converted to a format suitable for transmission, which is usually a digital format; that information in digital format is transported on the radio wave and upon reaching the receiver, the bits carried by the wave become what they were at the beginning: image or sound.

Radio communications began to be analog. Then the information was sent as is. If I speak to a microphone, the voice produces variations of a current and that is what was used to modify the radio wave and was transmitted directly through the antenna. Now that voice is encoded in bits to transmit it because the digitized information is much more robust.

And how is that information transmitted within the radio wave? We have to change some characteristic of the wave depending on the message you want to send. The easiest to understand is to change the amplitude. The radio wave has an amplitude that increases and decreases between two possible values. I can change those values, make them bigger or smaller, according to the information I want to send. We call that modulation, we modulate the wave with the information we want to transport. If I want to send 1, 2, 3; I send a wave that has amplitude 1 first, then amplitude 2 and then amplitude 3. And when it reaches the receiver, the receiver will look at the amplitude and say: 1, 2, 3. But instead of being 1, 2, 3 can be someone's voice or bits that encode any information. Changing its characteristics the radio wave transports the information that I want along the distance.

We also use radio waves to heat food inside the microwave. They are the same as those of Wi-Fi, what happens is that inside the microwave we put more power than we transmit through the air, because we don't want to warm people, right? And it is that certain frequencies can make the water molecules resonate and heat up.

Radio waves also serve to see beyond what our human capabilities allow, for example the radar can know what we have around even if it is far away, or even hidden. Light is also an electromagnetic wave but of specific frequencies that we see and generally do not call them radio waves, but we speak of visible frequencies. But like me with the light I capture images with a camera, with radio waves of other frequencies I can capture images through walls or through our body.

Ana Garcia Armada She is a telecommunications engineer, professor at the Carlos III University of Madrid and a researcher specializing in mobile broadband communications and 5G technology.

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