This type of modulation transmits data by varying the frequency of the carrier. In this modulation, the carrier has two predefined frequencies. Problem: Certain types of data such as voice, video, and bit streams from computers have lower frequency bands and therefore they cannot travel very far wirelessly because they cannot propagate through space.
Solution: When using modulation, the carrier wave which has a much higher frequency is used to carry the signal, meaning it can travel further and more quickly through space.
Problem: Antenna length would be impractical for voice, video and bit streams without modulation. Solution: By using the high frequency carrier waves, the necessary antenna size is greatly reduced. Problem: Without modulation, transmission of video, voice or data bit streams being sent on the same frequency range would cause overlapping of channels resulting in interference. Solution: Carrier radio waves have a wide range of frequencies which allow you to select individual non-overlapping channels to carry the information.
Lost your password? Search for:. What is Modulation in Telecommunications? January 9, What is modulation? The problem here is that the free electrons are oscillating in an extremely complex pattern.
You see, there are many radio stations and each one is sending out a modulated wave. The free electrons are affected by each of these waves. At the receiving end of the radio signal, the antenna is connected to an oscillator which uses a variable capacitor and an inductor electromagnet to "tune" to one specific frequency of radio wave. This is sometimes called a " tank circuit ". You can think of this tank circuit as a "filter" which is used to isolate the carrier wave you want to pick up the radio station you want to hear from all the other radio stations in the area.
As an analogy, think of a simple pendulum where the bob swings and converts potential energy to kinetic energy and then back to potential energy again. The "tuner" is the length of the string. A long string will make the system oscillate with a low frequency it takes more time to swing , but if you shorten the string, the bob takes less time to swing The tank circuit works the same way.
An electric signal will bounce between the capacitor where it is charged up and then discharges and inductor remember the metal detector? A pulse goes in and a "back emf" comes out. A returned signal is sent back to the capacitor Just as the pendulum is constantly converting energy from potential to kinetic and back to potential, It takes a certain amount of time to complete the cycle, so only one frequency of AC current is allowed to "oscillate" in this manner.
That is, the circuitry is adjusted so that only one specific type of wave will resonate within it. This is how the tank circuit works to only let one wave through If you move the channel tuner, you are changing the properties of the capacitor This means a carrier wave with a different frequency from another radio station will oscillate in the tank circuit.
Let's take the pendulum analogy one step farther. A simple playground swing-set is nothing more than a pendulum. All kids know that gentle pushes at the right time can provide for a great ride. Think of the pushes as the input energy into your swing-set "tank circuit". For any given swing, there is only one frequency of pushes that will work for that particular swing. If the incoming energy is timed perfectly and comes in at the right part of the oscillation, you can set your swing-set "tank circuit" into resonance.
In the case of the radio tank circuit, the input energy are radio waves of all kinds of frequencies all the radio stations in town , but only one specific frequency is able to oscillate in resonance in your tank circuit. Click link 6.
When you play with this applet, you will see that only one specific wave frequency will "oscillate" in the tank circuit. Finally the radio must "decode" the signal by extracting the modulated signal imprinted on it. That is, you need a way to eliminate the carrier wave and only allow the original voice signal to the speakers. In AM transmission this can be done with a diode, capacitor, and resistor. A simple diode will extract only half of the sine wave.
This process, called rectification, essentially converts the AC signal to a DC signal. The circuit looks like this: This arrangement is sometimes called a "peak detector" because it only detects the peak voltage of any signal. Essentially it filters out the smaller carrier wave.
The reasoning goes something like this in case you are interested DC currents do not normally pass through capacitors very well. They will charge to the peak voltage and then block the passage of current after that. Both AM and FM signals must be decoded at the receiving station. In either case, the carrier wave is electronically subtracted from the radio wave that is picked up by the receiving antenna.
What remains after this process is the original sound wave, encoded, of course, as an electrical signal. All broadcasting stations are assigned characteristic carrier frequencies by the Federal Communications Commission. This system allows a number of stations to operate in the same area without overlapping.
Thus, two stations a few kilometers apart could both be sending out exactly the same program, but they would sound different and have different electric signals because each had been overlaid on a different carrier signal. Receiving stations can detect the difference between these two transmissions because they can tune their equipment to pick up only one or the other carrier frequency.
When you turn the tuning knob on your own radio, for example, you are adjusting the receiver to pick up carrier waves from station A, station B, or some other station. Your radio then decodes the signal it has received by subtracting the carrier wave and converting the remaining electric signal to a sound wave. Radio Academy. Login Register Search.
Topic Progress:. Course lessons. Introduction to Radio Communications Principles. What is Communication? What is a radio wave? What is propagation? How do repeaters work? Modulation and Radio Building Blocks. How does modulation work? Communications Systems. How do repeater systems work?
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