At the turn of the century, in 1901, radio was a scientific curiousity in the laboratory.  Signals could be sent a few feet during demonstrations.  Marconi astounded the world with his first transatlantic transmission of a message across the ocean using no was born out of this experiment.

Immediately commercial and military interests wanted radio equipment built and installed.  These were put aboard ships, at shore stations, and at important coastal stations for continent to continent communications for commercial businesses and military operations.  Radio transmitting equipment occupied the size of a room and cost hundreds of thousands of dollars.

In the 1920's someone had the idea of using radio for broadcasting to the, news, and entertainment radio was born.  Radio circuits had advanced to the point where a radio receiver could be built for a few tens of dollars.  Millions of radio receivers were bought or built by consumers who knew nothing of the technical side of radio, but who were magically enthralled by its power and possibilities.  All these radio interests - commercial, military, broadcasting, and experimenters crowded the air waves, and listening to a radio receiver in those days trying to find a desired station was like listening for a single grasshopper amidst 10,000 of them calling at the same time on a hot summer's night.  Interference? It was bedlam!

All throughout the infancy of radio, scientists and hobbyists were experimenting with radio circuits, inventing improvements to make signals louder and clearer, and just plain enjoying the thrill of communicating with one another of like technical interests.  This two-way communication is amateur radio.  Today, amateur radio allows a person to talk with another amateur or "ham" on the other side of the world.  Equipment can be simple home built affairs not unlike the very early radios, or it can be sophisticated expensive factory bought sets.  Whatever the interest and technical skills of a person, there is something for everyone in amateur radio.  It is the thrill of invisible electromagnetic waves travelling at the speed of light, carrying one's voice, or picture, or data to a distant point, magically, through the air.  It is the fun of "meeting" people and making a new friend, whether across town or in a distant country.  It is the experience and knowledge gained by trying out new radio circuits and antennas.  It is the heroism and service to one's community when a whole network of radio amateurs, using emergency power, are able to help people communicate with loved ones during times of natural disaster when the regular radio, tv, and telephone systems no longer function.  This is amateur radio.

When a radio transmitter is turned on, it generates radio waves.  Like ocean waves, or the expanding circular waves that are produced when a stone is thrown into a pond of water, there is a definite interval of time between crests and troughs, or "cycle" of a passing wave.  The number of times a wave goes up and down in a second as it passes by, or cycles per second, is called its frequency.  Acoustical sound waves that a person hears range from 20 to 20,000 cycles per second.  Electromagnetic radio waves range from 100,000 to over 10,000,000,000 cycles per second!  Radio waves are extremely rapid vibrations of electromagnetic wave energy.

By international agreement, all radio transmitters are licenced to generate waves of one definite frequency.  A radio receiver with proper circuits can be TUNED to respond to only one desired frequency and so "hear" that transmission, without responding to all the thousands of other radio transmitters that may be transmitting at the same time using different frequencies of waves.  In this way more than one radio transmitter can be operated at the same time, and put out its radio waves into the air.

Frequencies of waves used in some common radio applications:
RADIO BAND FREQUENCY, cycles per second
standard broadcasting, AM          535,000 -       1,605,000        (abrev. 540-1600 on radio dials)
shortwave radio       1,800,000 -     30,000,000        (or 1.8 - 30 megacycles, mega = million)
tv channels   2 -   6     54,000,000 -     88,000,000
standard broadcasting, FM     88,000,000 -   108,000,000        (abrev. 88.0-108.0 on radio dials)
tv channels   7 - 13   174,000,000 -   216,000,000
tv channels 14 - 69   470,000,000 -   806,000,000
"800" & "850" U.S. cell phones   824,200,000 -   893,800,000
"900" Europe GSM phones   880,200,000 -   959,800,000
"1800" Europe GSM phones 1710,200,000 - 1879,800,000
"1900" U.S. GSM cell phones 1850,200,000 - 1989,800,000

Amateur radio frequencies are mostly assigned within the shortwave radio band, 1,800,000 - 30,000,000 cycles.  Instead of writing all those 0's, it's easier to work with megacycles.  So 1.8 - 30 megacycles is exactly the same thing. 

It is on these frequencies that one amateur can talk to another amateur using radio:
  1.8 -       2.0
  3.5 -       4.0
  7.0 -       7.3
10.1 -     10.15
14.0 -     14.35
18.068 - 18.168
21.0 -     21.45
24.89 -   24.99
28.0 -     29.7


Radio waves from a transmitter in reality are not of exactly one frequency, but occupy a definite "bandwidth" of frequencies close together.  AM voice transmission typically requires 10000 cycles per second bandwidth, or 0.01 megacycles in width.  You can work out for yourself, for example, in the 1.8 - 2.0 megacycle amateur band, you could "fit in" side by side, only 20 such AM voice transmitters, without overlapping and causing interference. (20 x 0.01 = 0.2) and (2.0 - 1.8 = 0.2).  That is not very many stations that can fit in that band allocation!

That is why many radio amateurs use the morse code.  A morse code signal, although requiring learning a new language so to speak, is so much more efficient than a voice signal.  A typical morse code signal is only 0.0001 cycles in width.  If everyone used only the morse code, you could have 2000 different radio transmitters side by side in frequency filling up the 1.8 - 2.0 megacycle amateur band.

In standard AM broadcasting, there are only 107 stations that can fit on the dial.  107 x 10000 = 1,070,000 cycles per second total bandwidth.  And you can verify that 1,605,000 - 535,000 = the entire allocated AM band range, is in fact, 1,070,000.  Fortunately frequencies can be re-used in different geographical parts of the country.

A single television station occupies 6 megacycles of bandwidth!  That is what is needed for picture transmission with good details.  This is why television stations are on the higher frequencies where there is more space.

As more and more people use wireless devices and portable telephones, bandwidth is going to become a very serious issue, as the amount of radio frequency space is limited.  It is this problem that radio physicists and engineers are employed to solve.  Ways to re-use frequencies, shrink useage bandwidth, and employ digital processing techniques so that multiple users can use the same frequency simultaneously is where the state of the art in radio communications is.