How does transmitters work

That's more or less what an antenna sometimes called an aerial does: it's the metal rod or dish that catches radio waves and turns them into electrical signals feeding into something like a radio or television or a telephone system.

Antennas like this are sometimes called receivers. A transmitter is a different kind of antenna that does the opposite job to a receiver: it turns electrical signals into radio waves so they can travel sometimes thousands of kilometers around the Earth or even into space and back.

Antennas and transmitters are the key to virtually all forms of modern telecommunication. Let's take a closer look at what they are and how they work! Suppose you're the boss of a radio station and you want to transmit your programs to the wider world. How do you go about it? You use microphones to capture the sounds of people's voices and turn them into electrical energy. You take that electricity and, loosely speaking, make it flow along a tall metal antenna boosting it in power many times so it will travel just as far as you need into the world.

As the electrons tiny particles inside atoms in the electric current wiggle back and forth along the antenna, they create invisible electromagnetic radiation in the form of 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. Learn how to program PLCs, install and wire industrial devices, and at the same time purchase them online.

Pneumatic vs electrical signal. The standard pneumatic signal is 3 to 15 psi. The standard electrical signals are 1 to 5 volts or 4 to 20 mA. Variables measured by the transmitter. Smart Transmitters. New technologies have spawned the development of Smart Transmitters. You might want to review two of our other articles:. Want to Learn More? Check back with us soon for more automation control topics. The RealPars Team.

Search for:. By Ted Mortenson. The high voltage created big fat sparks like you see in a spark plug , and they could transmit farther. Today, a transmitter like that is illegal because it spams the entire radio spectrum , but in the early days it worked fine and was very common because there were not many people using radio waves.

As seen in the previous section, it is incredibly easy to transmit with static. All radios today, however, use continuous sine waves to transmit information audio, video, data. 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.