Radio

In the early days, before the word radio became common, the most important use was to allow telegraph messages to be sent long distances without the need for wires to connect the places that wanted to communicate. This was really important for ships at sea, which couldn’t be connected by wires to land. Once out of sight of land there was no way for a ship in distress to call for help. So one of the earliest forms of radio was actually called wireless telegraphy. It wasn’t long before that was shortened simply to wireless. The movie Titanic gave a pretty accurate portrayal of how wireless was used by ships in distress. In fact, in that movie, even the Morse Code you hear is authentic. It is correctly sending the actual message that the Titanic’s wireless operator transmitted as his call for help.

 

Pretty soon people began to think how nice it would be if a fairly new invention called the telephone could also be made to work without wires. It wasn’t long before scientists and engineers produced the radiotelephone. They quickly learned that more than one person could listen at once and broadcasting began. Not long afterwards the commercial was invented, and modern civilization has not been quite the same since.

 

At about the same time another inventor worked out how to press letters on a typewriter in one place, have the identity of the keys that were pressed converted to radio waves, and make another typewriter far away type out the same letters. The radio teletype was born. I’ll bet you can see what’s coming next.

 

Wouldn’t it be great if moving pictures could be sent through the air so lots of people could watch the same movie all at the same time, without even having to leave their home. Well, say hello to television, just another form of radio.  Now we have come full circle and most of us get out television pictures through a wire (cable) instead of plucking them from the air with an antenna like in “the good old days.” But, how many of you have seen a TV dish for picking up television signals from satellites. The dish is just the antenna, which is connected to a special kind of radio receiver that recreates the pictures and sound.

 

So, lets think through a modern example. You are listening to the broadcast of a game being played by your favorite team while riding in your car. What steps have to take place? First, the play-by-play announcer’s voice travels through the air as sound waves until they reach a microphone. The microphone converts the sound wave vibrations into electrical signals (not yet radio waves) which must travel along wires until they reach a radio transmitter. In a process called modulation the transmitter turns the signals it got from the microphone into radio waves which travel along a special kind of wire called a transmission line until they reach an antenna. There the waves are launched into space and travel outward, usually in all directions, at the speed of light. A portion of these waves pass by the antenna on your car. (just where is your car’s antenna? - on some cars it may be hard to find). The passing waves cause electrical currents to flow in the antenna and then along another transmission line to your radio receiver. The receiver, in a process called demodulation, converts the signals back into the announcers voice, but still in to form of electrical signals along a wire. The wire is connected to a loudspeaker that turns them back into sound waves that need only span the short distance to your ears for you to be able to enjoy the game.

What is a Radio

The simplest answer may be that a radio is a device that either makes, or responds to, radio waves. You may have already learned that radio waves are part of the larger group of the electromagnetic waves, the group which also includes light, x-rays, even gamma rays. These waves can travel through materials, like air or wood or glass or concrete, or even through the empty vacuum of space. In fact, they travel best though empty space. Some of the waves, such as light, x-rays, and gamma rays can pass reasonably well through varying amount of water or metal. The radio waves we are interested in don’t penetrate water very well at all, and only a small amount of metal will stop them.

 

If all a radio did was just to make or respond to radio waves it would be a very fascinating scientific curiosity, but maybe only little more than that. It is the ability of radio to permit communications that makes it so vital to out modern society. Try to make a list of as many different ways you can think of for one person to communicate with another person. How many of those ways require the two people to be close to one another? For which kinds of communication may the persons be far apart? Which one happen right away, and which may take hours or even days or weeks? Which ones have to have a wire connecting the places where the people are? Which can take place without wires?

 

A radio transmitter (some just called a transmitter) is a device that can take some kind of information (might be voice, or music, or computer data) and convert it into the right kind of radio waves that can pass through the air or through space, without any wires. The waves are launched into space by an antenna. At another place a radio receiver (often just called a receiver) intercepts the radio waves from the air or space (using its own antenna) and changes the radio waves back into the information that the people need. The receiver doesn’t “use up” the radio waves, in fact, many, many receivers can “listen” to the radio waves produced by a single transmitter.

 

For two-way communications to take place (two-way radio) there must be a transmitter and a receiver at each location. Sometimes the transmitter and receiver are combined into a single box, which can then be called a transceiver. A modern cellular telephone is an example of a transceiver.