Saturday, August 18, 2012

How a radio works?

"Radio waves" transmit music, conversations, pictures and data invisibly through the air, often over millions of miles -- it happens every day in thousands of different ways! Even though radio waves are invisible and completely undetectable to humans, they have totally changed society. Whether we are talking about a cell phone, a baby monitor, a cordless phone or any one of the thousands of other wireless technologies, all of them use radio waves to communicate.

Technologies that depends on radio waves:

  • AM and FM radio broadcasts
  • Cordless phones
  • Garage door openers
  • Wireless networks
  • Radio-controlled toys
  • Television broadcasts
  • Cell phones
  • GPS receivers
  • Ham radios
  • Satellite communications
  • Police radios
  • Wireless clocks

The Simplest Radio:

Radio can be incredibly simple, and around the turn of the century this simplicity made early experimentation possible for just about anyone.
Here a small experiment:
By tapping the terminals of a 9-volt battery with a coin, you can create radio waves that an AM radio can receive!


  • Take a fresh 9-volt battery and a coin.
  • Find an AM radio and tune it to an area of the dial where you hear static.
  • Now hold the battery near the antenna and quickly tap the two terminals of the battery with the coin (so that you connect them together for an instant).
  • You will hear a crackle in the radio that is caused by the connection and disconnection of the coin.
Your battery/coin combination is a radio transmitter! It's not transmitting anything useful (just static), and it will not transmit very far (just a few inches, because it's not optimized for distance). But if you use the static to tap out Morse code, you can actually communicate over several inches with this crude device!

A (Slightly) More Elaborate Radio:

If you want to get a little more elaborate, use a metal file and two pieces of wire. Connect the handle of the file to one terminal of your 9-volt battery. Connect the other piece of wire to the other terminal, and run the free end of the wire up and down the file. If you do this in the dark, you will be able to see very small 9-volt sparks running along the file as the tip of the wire connects and disconnects with the file's ridges. Hold the file near an AM radio and you will hear a lot of static.

In the early days of radio, the transmitters were called spark coils, and they created a continuous stream of sparks at much higher voltages (e.g. 20,000 volts). 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.

Radio Basics: The Parts

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.
Each different radio signal uses a different sine wave frequency, and that is how they are all separated.
Any radio setup has two parts:
  • The transmitter
  • The receiver
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.

 Radio Basics: Real-life Examples

  • Modulation: Amplitude Modulation (AM)
  • Frequency range: 49 MHz
  • Number of frequencies: 1 or 2
  • Transmitter power: 0.25 watts 
A cell phone is also a radio and is a much more sophisticated device 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:
  • Modulation: Frequency Modulation (FM)
  • Frequency range: 800 MHz
  • Number of frequencies: 1,664 (832 per provider, two providers per area)
  • Transmitter power: 3 watts  
 Hardwork Can Never Ever Fails...
Best Luck...

 



 

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