Understanding Telecommunications: Signals, Frequency, and Noise
Typically, a message produced by a source is electrical in nature, requiring a device called a transducer to convert it into an electrical signal. This quantity varies over time, representing the message as electricity. At the receiving end, another transducer converts the output signal back to the original format. A microphone and speaker are examples of input and output transducers, respectively, in the case of analog messages.
The transmitter attaches the message to the channel in the form of a transmitted signal. Various signal processing operations can be performed for efficient transmission.
The most common technique is modulation, where the transmitted signal is adapted to the channel properties through the use of a carrier wave.
The transmission channel or medium is the electrical connection between the transmitter and receiver. This can be a pair of conductors, coaxial cable, a radio wave, a fiber optic cable, etc.
The receiver extracts the desired signal from the channel and delivers it to the transducer.
In the transmission path of the signal, there are certain undesirable effects that appear as alterations in the form of the signal. These contaminations are introduced throughout the system, usually referring to the channel, considering the transmitter and receiver as ideal. These contaminations are mainly attenuation and noise (among others).
What are Time and Frequency in Telecommunications?
Frequency is an objective and measurable quantity referring to periodic waveforms.
Its unit of measurement is hertz (Hz). Hertz expresses a frequency referring to cycles per second. Thus, a frequency of 1 Hertz is the same as saying that the cycle lasts 1 second.
What is Bandwidth?
Electromagnetic signals are associated with a term called the frequency spectrum, which is simply a number that represents the range of frequencies, without specifying the lower and upper limits. The bandwidth of a signal is the space it occupies within the range of frequency (highest frequency – lowest frequency), and its value is closely linked to the amount of information it carries. In the sense that the more information, the greater the bandwidth, making it one of the most important aspects to consider in telecommunications systems. In the world of data, bandwidth is defined by the ability of a circuit or channel to carry information (bits/second).
Analog and Digital Signals
Analog Signal: This is a signal type where information is encoded in the amplitude and frequency differences. It can be handled regularly or periodically. These signals are dominant in analog telecommunication systems.
Digital Signal: These are signals where the information is encrypted between two fixed voltage levels, also called logic levels. They are basically pulse trains, which is characteristic of digital systems.
What is Noise?
In a broad sense, noise is any unwanted signal that is added to the intended signal. This may come from:
- Thermal noise (Random): Noise introduced in electronic components or the environment.
- Impulsive noise: Caused, for example, by the operation of electromechanical devices (e.g., relays).
- Crosstalk: Signal crossing from another circuit.
- Certain types of distortion inherent in digital transmission techniques.