Whenever considering what makes up a communications system, one must first look at the big picture before it’s possible to zoom in on the individual components. The primary purpose of a communication system is to transmit information from a source to a destination. This is accomplished by using some form of transmission, some type of transmitting medium, and some type of receiving system.
In the case of standard computer networking, it is easiest to consider the source as some application being run by the user. This application encrypts the data into whatever form is appropriate, deconstructs the message into packets and frames, and then transmits the information as binary pulses of electricity or light. Another computer will receive the binary pulses and reconstruct the original message.
Similarly, radio communication systems work in the same way. A message is recorded, modulated, transmitted, demodulated, and then reconstructed to play to the listener.
In order for this article to make sense, we must first understand the most powerful tool in our toolbox: The Fourier Transform.
By utilizing the Fourier transform, we are able to deconstruct signals into their individual frequency components. Similarly, by using Fourier coefficient analysis, it is possible to reconstruct any message as a sum of sinusoidal waves.
What is a frequency component?
Consider a simple 60 Hz pure sine wave that is hypothetically coming from your wall outlet. This signal is around 170 Volts in amplitude from peak to trough. It averages at around 120 Volts using the Root Mean Square method of determination. By using the Root Mean Square method, we get a much better idea of the value of a signal since the average value of any pure sinusoid is simply zero.
Going back to our pure sinusoid, we can perform a Fourier transform of this signal. We can either use the integral method or simply look up the result in a Fourier transform table. Regardless of the method, the result will be two Dirac-delta impulses of half of our original amplitude with one sitting at positive 60Hz and one sitting at negative 60Hz.
What does this tell us? Well, nothing that we shouldn’t have expected. If our sinusoid is perfect, we’ll see nothing but the two impulses at the correct frequencies. However, if our 60Hz sinusoid is actually somewhat modulated by another signal, we’ll see harmonics develop further out.
Our next article will look at some basic power conversion methods and how harmonics can come into play. After that, we’ll look at modulation schemes, multiplexing methods, and the associated distortion that sometimes happens.