Electrical Engineering

Without communication systems there would be no mobile phones, internet, TV or radio. Communication systems are vital to our modern society for business, personal life, entertainment and leisure. Many of us could not imagine life without such commodities. On this course you’ll gain a hands-on introduction to communications and cover a range of topics such as analogue, digital and programmable electronics. Download

In this section we will look at the process of converting an analog signal to be digitally transmitted into a digital format. To transmit digitally we only have a discrete set of symbols that can be sent at a fixed rate. Hence before we can send the signal we need to quantize it in time and amplitude. A process of achieving this quantization is PCM. A general criterion is that the digitally modulated transmitted signal can be demodulated and converted back into an analog form with a tolerable amount of distortion. Generally the specification of“tolerable” is very subjective.For example consider voice quality requirements of a wireless phone. Given distortion tolerance, the objective is generally to optimize the encoding such that a minimum bit rate is consumed with the application.

Introduction Pulse modulation includes many different methods of converting information into pulse form for transferring pulses from a source to a destination. The four dominant methods are: 1. Pulse Amplitude Modulation (PAM) 2. Pulse Width Modulation (PWM) 3. Pulse Position Modulation (PAM) 4. Pulse Code Modulation (PCM) Pulse Amplitude Modulation   Pulse-amplitude modulation, also called PAM, is a form of signal modulation where the signal is encoded in the amplitude of a series of signal pulses. Example: A two-bit modulator (PAM-4) will take two bits at a time and will map the signal amplitude to one of four possible levels, for example −2 volts, −1 volt, 1 volt, and 2 volts. It is widely used in base band transmission of digital data

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 Transmission-Media Transmission Media or Communications media  are the paths, or physical channels, is that, over which information travels from one place to another. A key aspect of communication is the movement of information electronically from one place to another. It may be as simple as sending information from one office to another in the same building, or it may be as far- reaching as sending information around the word. Whatever the case, information/signal must travel over some path from its source to its destination. What are the types of Transmission media? Signals are usually transmitted over some transmission media that are broadly classified in to two categories. Guided Media/bounded : These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use

Band Limited Signal   A signal is said to be a band limited signal if all of its frequency components are zero above a certain finite frequency. i.e it's power spectral density should be zero above the finite frequency. Figure 1 shows a signal g(t) that is band limited. Bandwidth requirements (communications) The channel bandwidths needed to transmit various types of signals, using various processing schemes. Every signal observed in practice can be expressed as a sum (discrete or over a frequency continuum) of sinusoidal components of various frequencies. The plot of the amplitude versus frequency constitutes one feature of the frequency spectrum (the other being the phase versus frequency). The difference between the highest and the lowest frequencies of the frequency components of significant amplitudes in the spectrum is called the bandwidth of the signal, expressed in the unit of frequency, hertz. Every communication medium (also called channel) is c

The superhet radio or to give it its full name the super heterodyne receiver is one of the  most popular forms of receiver in use today. Virtually all broadcast radios, televisions  and many more types of receiver use the superhet or super heterodyne principle. First developed at the end of the First World War, with its invention credited to the American Edwin Armstrong, the use of the superhet has grown ever since the concept was first discovered. 

Modulating signal and carrier Wave   Modulated wave   Frequency spectrum of AM wave   If the equation of modulating signal is

Radio Wave Propagation types

  OUTLINE Modulation and Demodulation Radio Communications Radio Receivers Television Radar