|Radio and Electronics (DED Philippinen, 66 p.)|
|2. PRINCIPLES OF RADIO COMMUNICATION UNICATION|
The basical idea of the term COMMUNICATION is: to transfer an idea (a SIGNAL) from one from one brain of a human being (a SIGNAL-SOURCE) to the brain of another human being (a RECEIVER).
The normal way of communication is of course to speak with each other. But which TECHNOLOGY is used during speaking? Obviously, the idea is translated into words.
The words are produced in terms of voice (or SOUND). This sound in physical sense of the word is nothing else than a special sequence of airpressures. These airpressures will cause vibrations everywhere.
They will hit the inner ear of the receiver and will be retranslated in his brain into the original idea. This normal way of communication is no more possible if the distance between the signalsource and the receiver will make it impossible to understand each other anymore. While the past human beings found different possibilities to overcome this problem.
There are two people who want to communicate with each other but the distance is too far... WHAT CAN BE DONE?
A very old fashioned way to solve this problem was to send a MESSENGER.
Since about 100 years there is a more convenient method of communication: the TELEPHONE.
Since about 50 years there is another - even more convenient method of communication the RADIO TECHNOLOGY.
Since the PROPAGATION of SOUND is very limited in distance for communication across longer distances another means of transporting the SIGNAL is necessary.
As we are reminded to by the sketches above, COMMUNICATION SYSTEMS have been developed step by step through the last century.
All those different technologies are working in between the two ends of the original way of communicating.
Even the most modern communicationsystem is working on the same overall system:
FIRST: there has to be a method to translate sound (air vibrations) into an ELECTRIC OSCILLATIONS (current or voltage oscillations).
SECOND: there has to be a method to transport this electric signal across huge distances Either by wires or by so called ELECTROMAGNETIC WAVES (also called RADIOWAVES)
We agreed already: the AIM OF COMMUNICATION is to transport the IDEA (the SIGNAL) totally correctly from the ORIGIN (the TRANSMITTER) to the ADDRESS (the RECEIVER).
But it is easy to imagine, that even in the original way of communication (speaking with each other) very often the idea was not received properly.
As the possibilities of arising faults are increasing with increasing complexity of the system in use, it is easy to understand, that radio technology is mainly a struggle to get a good or at least a satisfying RECEPTION.
The quality of the equivalence of the signal at the start of the communication (INPUT fig. 7a) and the signal at the end of the communicationline (OUTPUT fig 7b or 7c) is called FIDELITY.
The rate of difference between INPUT and OUTPUT is called DISTORTION.