Each of us daily encounters electronic devices - this is a familiar mobile phone, a computer for work and leisure, a TV, a radio, etc. About ten years ago, no one really thought about whether a digital or analog signal was used in a particular device. However, a little time passed and the term “digital”, thanks to a well-thought-out advertising campaign, began to be associated with the words “good, high-quality, reliable”. It is worth recognizing that there is a certain amount of truth in this. An analog signal began to be used to transmit information earlier than digital. This is due to its simpler processing, unavailability of the infrastructure and some other reasons.
To understand what an analog signal is, it is necessary to recall the basics of electrical engineering, in particular, the nature of the electric current. After all, the signal in question is, in fact, directly connected with it - it can be either direct current transfer, or by means of electromagnetic fields. Surely, everyone heard about the "famous" sinusoid.
Mentally draw a horizontal line - this is the axis of time. A continuous wave-like line is strung on it, and the height of the waves below and above the axis is equal. Next, imagine that we are stretching this wave-like line along the time axis. As a result, the number of waves per any period of time will decrease. And now “squeeze” the sine wave - the waves began to go more often. In other words, by these actions we change the frequency. If we continue the thought experiment and “squeeze / stretch” the waves up and down relative to the time axis, then we will be able to change the amplitude. That is how the analog signal is formed.
In radio receivers, these two methods are used - FM (Frequency Modulation) and AM (Amplitude Modulation). Of course, the given example is simplified for understanding. In addition to changing the frequency and / or amplitude of the wave, they undergo other, more specific, changes. You can read more about this on specialized sites or in the literature.
Based on the foregoing, we can formulate a definition: an analog signal is a continuous modulated method of transmitting information over time . One of its drawbacks is exposure to “noise pollution”. Now everyone has mobile phones. And everyone, at least once, left the phone near a working TV or computer speakers. Those strange ordered clicks that sound in the speakers before receiving an SMS or receiving a call are known to everyone. They are an electromagnetic interference wedged into the sound reproduced by a TV or computer. Obviously, this is an undesirable phenomenon.
Crosstalk occurs in the conductors of the columns. In fact, the transmitted modulated wave (analog signal) is exposed to external influences, distortions are introduced into it. Of course, in this case, a person easily distinguishes useful data (sound) from noise, but if logic receives a signal, then a number of difficulties arise. For example, it is impossible to reliably determine where the payload is and where the noise is.
Therefore, the analog transmission method has been replaced by digital. Analog and digital signals are fundamentally different. The second is created as follows: a sinusoid is conditionally divided into many points, the position of each of which is encoded by a certain sequence of pulses and gaps (lack of current). Usually the impulse corresponds to a logical unit, and the interval corresponds to zero (although there may be an opposite way). The receiver decodes the received pulses and restores the original sine wave. Obviously, such a signal is less susceptible to noise, since the decoding unit clearly distinguishes the pulses. However, with excessive noise levels, the digital signal is simply lost.