Radio Waves


Q1: What are the differences between radar and sonar waves? Why in some situations we use radar but in others we use sonar waves?

Q2: In radio waves, there are surface/ground waves, sky waves and space waves. What are their differences?

Q3: Why some space waves can penetrate through the ionosphere but some space waves just travel straightly above the earth's surface from transmitting aerial to receiving aerial? Are they the same kind of waves?



Radar and sonar waves are fundamentally different. Radar waves are electromagnetic, like radio waves, light waves and gamma rays. These waves pass through empty space and through other material that is insulating rather than conducting of electricity. Sonar waves are sound waves which pass through a solid, liquid or to some extent a gas, as pressure variations. The choice of which wave to use to explore our surroundings depends on the nature of those surroundings. If the medium to be penetrated by the wave is a gas like the atmosphere or empty space, a radar wave is used. If the medium is a conductor of electricity like the ocean, then a sonar wave would be used.

The distinction among radio waves of ground, sky or space waves is concerned with the wave's major path between transmitter and receiver. The same wave may be all three types. Ground waves interact with the Earth as they travel and stay close to the ground. The bulk of radio broadcasts are received by ground waves. They are of limited range and quite reliable. Sky waves are reflected by the ionosphere back to Earth, perhaps at a long distance from the transmitter. At certain radio frequencies the ionosphere acts like a dirty mirror which is constantly changing its position and orientation in space. This make the reception of sky waves less reliable than the predictable ground waves but may make possible reception at great distances on the Earth. Space waves are not much affected by the ionosphere. They travel in straight lines from the transmitter to the receiver. In general the frequency of the radio wave will favor one or another path. Low frequency radio waves tend to be ground or sky waves. High frequency waves are more likely to take straight line paths and so radiate out into space.

All space waves, by definition, penetrate the ionosphere. The difference between waves receivable only in low orbit and those receivable at great distances is a matter of power delivered to the receiving antenna. Power at the receiver may be increased by focusing the waves onto a small area as well as increasing the power of the transmitter