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Wednesday, 7 November 2018

Basic Principles of Transmission at High Frequencies






We have learnt a lot about the behavior of electrons with the atom of an element, inside an evacuated valve envelope (vacuum), in conductor materials, in semi conductor materials, and in most electric circuits. Electrons move at very high speed both backward and forward (I.e. oscillating) in a circuit known ad tank circuit or oscillating circuit. It consists of a capacitor and an inductor connected. The name of the circuit can be traces to the behaviour of the electrons with in the circuit which can be explained thus: when the switch is closed, current will flow from the battery to the capacitor and inductor which normally store energy. If the circuit is opened, it would be observed that the energy already passed onto the circuit components will remain there indefinitely with out any reduction. This current will continue to move as indicated by the arrow, I.e from the capacitor again. This is to say that the current will be restricted to that circuit which consists of the capacitor and inductor alone.

Wm.  We can now relate the movement of electrons as explained above to the radio system, which involved the radiation of waves into space from the point of generation, and their reception at another point. The basic elements of radio communication or broadcast casting in transmitting messages, speeches or music from one place to another by radio. For a radio to function at all, it will consist of these principal elements:

1. A micro phone which is used to control the radio waves in accordance with the information to be transmitted.

2. A radio transmitter that will generate the radio frequency waves.

3. A receiving aerial to come across a portion of the radiated radio wave.

4. A transmitting aerial to send out the waves into space.

5. A radio receiver to select and amplify the desired transmitter signal and extract the information out of the radio waves.

6. A loudspeaker to convert the information signals which are in the form of electric current back into sound, which will be a close replica of the original information sent out.

At this stage , we will be interested in studying transmitting and receiving aerials. The electric power we use in our different homes comes from Points of generation, which may be far away, and when the generation process is stopped, there is immediate power failure. The same thing applies to the radio waves, which must first be generated before they can be transmitted and received in radio and television sets which may be located several kilometers away fro. The source of generation.

   The generation if radio waved can be traced back to the movement of electrons in the 'tank circuit' or 'oscillating circuit' previously discussed. The electrons oscillate at a high frequency (measured in Hertz) in the tank circuit. A transmitter sets up electromagnetic waves (I.e. radio waves), which are radiated throughout space.  In previous write up we learnt that the accelerated electric charges, ie. Electrons, always radiate energy in the form of the electromagnetic waves. The charges in the glass rod and capacitor will not radiate since they are static. However, the simple inductor capacitor (L-C) tank circuit, with its accelerated electrons (is. The electron oscillations) will continue to radiate energy in the form of electromagnetic waves. The radiated waves from the oscillating circuit, however are extreme weak. In order to radiate these electromagnetic waves from the tank circuit or receive them effectively, we need an aerial. This aerial is simply an arrangement of conductors of various sizes, which is used to couple or match the transmitter or oscillating circuit or the receiver to the open soave. The open space will them act as the transmission channel through which the radiated electromagnetic waves from the aerial of a transmitter will move to the aerial of the receiver I.e. radio or television set in homes,etc.


   The transmitting aerial we usually set at our transmitting stations, like that of the state or federal broadcasting stations, will have to be connected to the transmitter equipment through a transmission line or leadin'. This transmitting aerial will force the wave radiation into the open space in the atmosphere. Similarly, a receiving aerial Or antenna which us usually connected to a radio receiver or television set, will catch or intercept just a small portion of the transmitted electromagnetic wave energy and pass it yo other points of the radio after which WD can receive the replica of the original signal being sent. These aerials are of  various sizes and many forms. The size and form of the aerial conductors that make them more effective  radiators and absorbers of electromagnetic wave energy.  While one is for transmitting into the space. The other Is for receiving signals. For proper radiation and reception of the electromagnetic waves, the aerial   to be used mist have the proper size. If the sizes of the transmitting aerial conductors are small. Less radiation will be available in the open space. While if large radiation of electromagnetic waves will be available in the open space. The waves travel at the speed of light. This is indeed very fast , as light travels at a speed of 300,000 kilometers per second. Thus.  Transmitted signals can be received almost instantaneously in various places in the world.