Radio communication how does it work

The reason that we use continuous sine waves today is because there are so many different people and devices that want to use radio waves at the same time. If you had some way to see them, you would find that there are literally thousands of different radio waves in the form of sine waves around you right now -- TV broadcasts, AM and FM radio broadcasts, police and fire radios, satellite TV transmissions, cell phone conversations, GPS signals, and so on.

It is amazing how many uses there are for radio waves today see How the Radio Spectrum Works to get an idea. Each different radio signal uses a different sine wave frequency , and that is how they are all separated. The transmitter takes some sort of message it could be the sound of someone's voice, pictures for a TV set , data for a radio modem or whatever , encodes it onto a sine wave and transmits it with radio waves. The receiver receives the radio waves and decodes the message from the sine wave it receives.

Both the transmitter and receiver use antennas to radiate and capture the radio signal. A baby monitor is about as simple as radio technology gets. There is a transmitter that sits in the baby's room and a receiver that the parents use to listen to the baby. Here are some of the important characteristics of a typical baby monitor:. Don't worry if terms like "modulation" and "frequency" don't make sense right now -- we will get to them in a moment. A cell phone is also a radio and is a much more sophisticated device see How Cell Phones Work for details.

A cell phone contains both a transmitter and a receiver, can use both of them simultaneously, can understand hundreds of different frequencies, and can automatically switch between frequencies. Here are some of the important characteristics of a typical analog cell phone:. You can get an idea for how a radio transmitter works by starting with a battery and a piece of wire.

In How Electromagnets Work , you can see that a battery sends electricity a stream of electrons through a wire if you connect the wire between the two terminals of the battery. The moving electrons create a magnetic field surrounding the wire, and that field is strong enough to affect a compass. Let's say that you take another wire and place it parallel to the battery's wire but several inches 5 cm away from it. If you connect a very sensitive voltmeter to the wire, then the following will happen: Every time you connect or disconnect the first wire from the battery, you will sense a very small voltage and current in the second wire; any changing magnetic field can induce an electric field in a conductor -- this is the basic principle behind any electrical generator.

One important thing to notice is that electrons flow in the second wire only when you connect or disconnect the battery. A magnetic field does not cause electrons to flow in a wire unless the magnetic field is changing. Connecting and disconnecting the battery changes the magnetic field connecting the battery to the wire creates the magnetic field, while disconnecting collapses the field , so electrons flow in the second wire at those two moments.

To create a simple radio transmitter, what you want to do is create a rapidly changing electric current in a wire. You can do that by rapidly connecting and disconnecting a battery, like this:. A better way is to create a continuously varying electric current in a wire. The simplest and smoothest form of a continuously varying wave is a sine wave like the one shown below:.

By creating a sine wave and running it through a wire, you create a simple radio transmitter. It is extremely easy to create a sine wave with just a few electronic components -- a capacitor and an inductor can create the sine wave, and a couple of transistors can amplify the wave into a powerful signal see How Oscillators Work for details, and here is a simple transmitter schematic.

By sending that signal to an antenna, you can transmit the sine wave into space. If you have a sine wave and a transmitter that is transmitting the sine wave into space with an antenna, you have a radio station. The only problem is that the sine wave doesn't contain any information. You need to modulate the wave in some way to encode information on it.

There are three common ways to modulate a sine wave:. Pulse Modulation - In PM, you simply turn the sine wave on and off. This is an easy way to send Morse code. PM is not that common, but one good example of it is the radio system that sends signals to radio-controlled clocks in the United States. One PM transmitter is able to cover the entire United States!

Amplitude Modulation - Both AM radio stations and the picture part of a TV signal use amplitude modulation to encode information. In amplitude modulation, the amplitude of the sine wave its peak-to-peak voltage changes. So, for example, the sine wave produced by a person's voice is overlaid onto the transmitter's sine wave to vary its amplitude. Frequency Modulation - FM radio stations and hundreds of other wireless technologies including the sound portion of a TV signal , cordless phones, cell phones, etc.

The advantage to FM is that it is largely immune to static. In FM, the transmitter's sine wave frequency changes very slightly based on the information signal. One characteristic of a sine wave is its frequency. The frequency of a sine wave is the number of times it oscillates up and down per second.

When you listen to an AM radio broadcast, your radio is tuning in to a sine wave with a frequency of around 1,, cycles per second cycles per second is also known as hertz. For example, on the AM dial is , cycles per second.

FM radio signals are operating in the range of ,, hertz, so See How the Radio Spectrum Works for details. Here's a real world example. When you tune your car's AM radio to a station -- for example, on the AM dial -- the transmitter's sine wave is transmitting at , hertz the sine wave repeats , times per second.

The DJ's voice is modulated onto that carrier wave by varying the amplitude of the transmitter's sine wave. An amplifier amplifies the signal to something like 50, watts for a large AM station. Then the antenna sends the radio waves out into space. So how does your car's AM radio -- a receiver -- receive the ,hertz signal that the transmitter sent and extract the information the DJ's voice from it? Here are the steps:.

In an FM radio, the detector is different, but everything else is the same. In FM, the detector turns the changes in frequency into sound, but the antenna, tuner and amplifier are largely the same.

In the case of a strong AM signal, it turns out that you can create a simple radio receiver with just two parts and some wire! The process is extremely simple -- here's what you need:.

Here's what you do:. Now if you put the earplug in your ear, you will hear the radio station -- that is the simplest possible radio receiver! This super-simple project will not work if you are very far from the station, but it does demonstrate how simple a radio receiver can be. Here's how it works.

Your wire antenna is receiving all sorts of radio signals, but because you are so close to a particular transmitter it doesn't really matter. The nearby signal overwhelms everything else by a factor of millions. Because you are so close to the transmitter, the antenna is also receiving lots of energy -- enough to drive an earphone! Therefore, you don't need a tuner or batteries or anything else.

The diode acts as a detector for the AM signal as described in the previous section. You always get the strongest signal strength with the best signal quality if you have a completely free line of sight to the antenna of the Wi-Fi router.

Anything that is blocking the signal will always affect it in some way. For that reason, it is always absolutely best to place a Wi-Fi router in an open space with a free line of sight to as many places that you want to cover with your Wi-Fi signal as possible.

You could still end up with a wireless network that works well enough, but it will be considerably worse than if you would move the Wi-Fi router to an open space. A radio antenna can have different appearances depending on what purpose it is designed to fulfil. Antennas also have a different length depending on what wavelength that they are made to transmit and receive radio waves on.

Antennas are manufactured to radiate radio waves in different patterns. The manufacturing process and the design of the antenna can control in which particular directions if any that the antenna should focus its radio wave emissions. The most extreme example is parabolic antennas , where the whole antenna is built to send or receive, or both as much of its effect as possible in one single narrow beam. This design concentrates all of the energy of the radio transmission in one single direction.

Parabolic antennas are used for longer distance communication where you have another single antenna far away that you want to establish communication with. But there are also many other variations on so-called directional antennas that direct radio waves in one or several directions.

The absolutely most common type of antenna for Wi-Fi routers and home networks is the dipole antenna which has an omnidirectional radiation pattern. Such an antenna will be more or less equally powerful in all directions, which is what you usually want in a home network environment.

This is another reason for why you should place your Wi-Fi router in an open area of your house. The router will radiate radio waves more or less equally in all directions. If you place your router in a corner then some of that radio effect will enter the walls and be absorbed right away without producing any positive results for your Wi-Fi network. Many routers are equipped with internal Wi-Fi antennas with a particular antenna alignment , and the router is then meant to be placed in a particular way for the antenna to have the correct alignment.

You should always look at the instructions manual for your router and place it in the correct way standing up or lying down. If the router has an external antenna that can be set in different angles, then you can often choose how you want to place your router, and then pick an angle for the antennas.

Often the manual for the product will have instructions for antenna alignment. Basically, it is best if the antenna alignment of the Wi-Fi router matches up with the antenna alignment of the devices that you want to connect to the Wi-Fi router. Matching antenna alignment is not always as straightforward as one might think.

Also, how will you hold your mobile phone when you are using it? If it is lying down then the antenna is lying down. If you hold it straight up then the antenna is upright. Or perhaps sideways. Luckily a phone rarely needs a high-speed Wi-Fi connection so you will often get away with phone Wi-Fi quality.

But look at your laptop instead. The antenna is often integrated into the screen and is upright when you are using the laptop, but not always. For example, a lot of MacBooks have their antennas integrated into the screen hinge, lying down. If you have multiple antennas on your router you could face some of them straight up and others lying down.

But once again whether or not this is beneficial depends on the type of router you have and what capabilities it supports. Many manufacturers recommend angling the antennas. For three antennas you would have the middle antenna somewhat straight up, and then angle the two side antennas degrees. But check with the router manual to see what their recommendation is for your particular home router. Then you probably also know that those radio channels are operating on different Frequencies that they are allowed to transmit on.

Different countries have different governing bodies that rule on how the radio frequencies can be used. This is necessary because if two channels were to transmit on the same frequency within range of each other then they would disturb one another. There must also be some unused frequency space between the channels.

This is because radio signals are never transmitted just on an exact frequency such as This is called the channel width. So if a radio channel is transmitting on the frequency You can even hear this effect if you have an old radio available. When you tune in a channel you can hear how the channel first appears with some distortions as you close in on the right frequency, and then as you get right on top of the center frequency you get perfect sound quality.

When you listen to the radio in your car or kitchen you often listen to the so called FM band of radio frequencies between about One Hertz Hz means one oscillation per second one wavelength.

In AM Amplitude Modulation radio, the strength amplitude of the signal is changed modulated to make the sounds. In FM Frequency Modulation radio, it is the speed frequency of the signal that is changed. When you tune in your radio, the dial number indicates the kilo or megaHertz at which the signal is being broadcast. Radio signal uses specific frequency, or how quickly the waves of the field move up and down.