Telecommunications Notes PDF

**Telecommunications Notes** - ***Specialized Testing (Voltage, Current, Insulation, Signal Strnegth and testing)*** **Voltmeters** Voltmeters are specialised testers which are used to measure the voltage of a circuit. Voltmeters are measured in parallel to the circuit. The voltmeter works...

**Telecommunications Notes** - ***Specialized Testing (Voltage, Current, Insulation, Signal Strnegth and testing)*** **Voltmeters** Voltmeters are specialised testers which are used to measure the voltage of a circuit. Voltmeters are measured in parallel to the circuit. The voltmeter works where the instrument measures the potential difference between two points of the component. **Ammeter** Ammeter is used to measure the flow of electrons within a circuit. Amneters have very low resistance to give an accurate reading. The Ammeter must be set up in series. **Insulation Testing** Insulation is used to ensure that insulation has not broken down to allow leakage current. Insulation Testers such as the megohmmeter testers allow insulation to be tested by passing through voltage and checking there is no leakage. Low resistance readings indicate there is a leakage. They will supply voltage of 3300V and leave, if there is **no** **broken insulation**, it will stay at 3300V. However, if there is a leakage in insulation and voltage drops to 200V, insulation is **therefore broken.**  - ***Copper and its alloys used in telecommunications including copper beryllium, copper zinc, electrolytic tough pitched copper.*** Copper and its alloys used in telecommunications is used in alloyed or unalloyed form. They are used since they are ductile (able to be drawn into a thin wire) **Copper Beryllium** Beryllium is a light metal, offers excellent strength to weight ratio, and stiffness. Beryllium is alloyed with copper between amounts (0.5%-4%) Be. Where Beryllium gives significant strength over pure copper. Advantages: - Good electrical and thermal conductivity - Able to be hardened through precipitation hardening. They are worked and formed. Beryllium precipitates lead, to then a higher strength-to-weight ratio. - Good Tensile Strnegth and hardness with the trade off for conduvity. Higher Strength = Lower Conductivity **Copper Zinc** Harder and stronger than pure copper, due to alloying with copper, used as connector for telecommunications. **Electrolytic Tough Pitch Copper** One of the most conductive copper alloys. With 99.9%, no impurities, no impediments, high ductility. ETPC has a conductivity of 100% according to the IACS (International Annealed Copper Standards) ETPC has 100% conductivity as it is electrolytically refined. Refined pure copper is placed next to refined sold copper anode which has been placed in a tank of sulphuric acid. Then a negative charge is placed on the pure copper. Where the copper anode is transferred to the pure copper, making it **electrolytically refined.** - ***Semiconductors such as transistors, Zener diodes, light emitting diodes and laser diodes*** **Semi-Conductors** Poor conductors which consisting of insulating material which is doped with another atom to give surplus of electrons. If semiconductor has more electrons, it is n-type. If semiconductor has less electrons, it is a p-type. Silicon and Germanium are the most common materials used in semiconductors. - **When Semi-Conductor is placed in the opposite direction this happens** N -- type and P -- Type is butted together so they have perfect electrical contact. When there is a **negative charge** on the **right** of the semiconductor (**p-type side**) and a **positive charge** on the **left** of semi -- conductor (**n-type side**) The P-type protons will be attracted to the negative charge, and the n -type will be attracted to the positive charge.  The Positive in the p-type will be attracted to the negative, and as a result this creates a depleted layer in the middle, resulting in no flow of current. - **When Semi -- Conductor is placed in the same direction of current this happens.** Polarity of charges are flipped. As a result of repulsion, the charges will be pushed towards the middle, where the charges will cancel out due to attractive charges, and there is no depletion zone, as a result current will flow. **Light Emitting Diodes** Light Emitting Diodes work, where the protons and electrons will cancel each other out, which releases energy in the form of light. Conventional Current flows from positive to negative. **Transistor** When there is a double p-n junction, this creates a transistor. For example, This NPN Transistor  The Charges create a depletion zone, and no current flows. The transistor acts either as a **switch** or an **amplifier.** However, if there is a charge on the top of exactly 0.6V this eliminates the depletion zone, and as a result allows current to flow. This **switch** allows current to flow, and higher voltage of third terminal to 1.6 -- 2V, causes increased current to flow in terminal. **Zener Diodes** The Zener diode allows current to flow one way up to a certain point, and then when that voltage limit has been hit. Current is able to flow in both directions. **Light Emitting Diodes** When the depletion zone disappears, and the protons and electrons cancel each other out, this as a result causes the release of light in the form of photons. Finds use in traffic light. They find use due to their efficiency compared to incandescent filament. **Laser Diodes** The Laser diode has a p-n junction, with a layer in the middle (aluminium, yttrium and garnet) which allows the release of laser light, with the disappearing of the depletion zone. Provides light which is one frequency. Laser Diodes finds use in DVD Players, or signal transmitters in fibre optics.  - ***Polymers (Insulation Materials)*** Polymers finds use in telecommunications to insulate copper wires and prevent corrosion and oxidising into copper sulphate, they also prevent shock which can harm individuals For example, polymer casings for mobile phones are made from polycarbonate or acrylonitrile-butadiene-styrene, which is created through injection moulding. - ***Fibre Optics (Types and Applications, materials)*** Fibre Optics transmit electrical information. Fibre Optics works where it converts electrical current into light using a transmitter. The receiver then converts the light into electrical current. Advantages of Fibre Optics: Fibre Optics is much **safer** than copper cables, **might lighter** than copper cables, is able to create a larger bandwidth. However copper cables are MUCH CHEAPER Fibre Optics have a fibre, then cladding (reflective surface), then protection layer. **Materials of Fibre Optics:** Typically inner cladding is made of glass or Perspex. And outer cladding is made of polystyrene **Applications of Fibre Optics** - **Single Mode Fibre Optics** Fibre Optics include single mode and multimode. Single mode fibres have very small core of (8 micro metres), meaning light only passes as a single ray. Single Mode Optical Fibres is the most accurate and massive data transfer but very expensive.  - **Multimode Cables (larger diameter)** Multimode Fibres, have a larger core diameter where light is able to reflect internally off the cladding, compared to single mode fibre optics which travel in straight lines. There are two types of multimode fibre optics (stepped and graded index) Multimodal fibres are created when: 1. They get a tube of pure silica then it is vapour deposit it to change refractive index of inner cladding compared to outer cladding. 2. It is then melted and then placed into a fine tube and then it is drawn - **Stepped Index Multimode Cables** The Cheapest type of cable with a diameter of 62 micro metres. Stepped -- Index Multimodal Cables, works through bouncing the light across the cladding or two refractive indexes. This means that light travels different distances, and hence takes different times for electrical information to be received. This means when light is inputted, then there is a spread of light which is received. A black and white image of arrows and squares Description automatically generated Figure 1: Input and Output of Electrical Signal Disadvantages of Stepped Index Multimode Fibre Optics: - Worser Quality transmission of information - Significant transmission loss - Not able to transmit a lot of information. - **Graded Index** Uses refractive index which is lower on the inside cladding compared to the outside. As a result, all light rays travel at the same speed, **reducing modal dispersion** and **increasing bandwidth**. The refractive index of the core of the cable gradually decreases towards the cladding, which allows light rays to reflect with less angle as opposed to a sharp angle At the centre of the core, the refractive index is the highest and the speed of the transmission is the lowest. When the transmission is at the peak, it is travelling fast as the refractive index is low.  Compared to the Stepped Multimodal, the Graded Multimodal fibre does not reflect suddenly but gradually as a result there is less transmission data loss. - ***Telecommunications including (analogue and digital systems)*** Analogue systems are systems which use a wide span of values. For example, when a person speaks very loudly and in a high tone (amplitude), increases and the pitch (frequency), increases. Whereas Digital Systems are systems which produce either on or off, or '*1'* or '*0',* respectively. This **digital data** is converted into **binary code** and transmitted as **digital electrical signals.** However, most machines are analogue, hence we must use converters to convert one signal to another. Digital signals are used in mobile phones and televisions and are able to be easily compressed. measure of how much space there is to carry information **without distortion.** Bandwidth: measure of how much space there is to carry information. Higher Bandwidth = More transmission of media - **Conversion of Analogue Signals to Digital Signals** Analogue Signals such as temperature or light provide a lot of static noise and must be converted to digital signals in order to be transmitted. Analogue signals created with coil subjected to changing MF, inducing an EMF creating a signal.  Since the graph goes below the x-axis and digital signals can only be 1's and 0's. Therefore, a constant DC voltage is applied to shift it up. A graph on a white board Description automatically generated To convert, you must take a sample at intervals (they take a value of frequency at specific times), called the **sampling rate** to convert to digital signals. Higher Sampling Frequency = less error in conversion  Next is to **Quantise** (Meaning to approximate the amplitude towards a whole number) And 16-bit meaning 2\^16 samples = 65536 samples. Hence, maximum value can be 65536 Giving whole numbers, it is then transmitted. This is done through binary bit.  Get a quantised number, if it is able to be divided with value \>1, minus quantised number from bit number. Keep going until you get to 1. Discs and DVD's are examples which convert Analogue Signals to Digital Signals. Nyquist discovered that the sampling rate must be greater than or equal to two times the bandwidth, hence sampling rate is 44100Hz, as a common factor between Beta and Sony Walkman. - ***Modulation and Demodulation*** Easier to transfer EM waves at higher frequencies due to their low power at **[great distances]**. Hence, **low frequency** signals were **transferred** on **high frequency carrier wave, specifically analogue sine wave.** **Modulation** refers to adding a signal to transmit non -- linear data onto carrier wave (which has constant frequency and amplitude), a **demodulator** which extracts original information -- bearing signal from a carrier wave, before converting to soundwaves. Common forms of analogue modulation is: - Amplitude Modulation (AM) used for radio and picture on television. - Frequency Modulation (FM) used by television and radio. - Phase Modulation (PM) For Digital Modulation it is: - Amplitude Shift Keying (ASK) - Frequency Shift Keying (FSK) - Phase Shift Keying (PSK) - **Amplitude Shift Keying** When the amplitude is high this corresponds to binary of '*1'* When amplitude is low this corresponds to binary of '*0'*  - **Frequency Shift Keying** Low Frequency (spread apart) '*0',* High Frequency (closer together) '*1'.* Advantages: Electrical Noise does not interfere with the frequency of the signal. A diagram of waves Description automatically generated - **Binary Phase Shift Keying**  **Multiplexing** Placing **multple signals** along a **single communication channel**, increasing the amount of information transmitted, where **demultiplexer**, seperates the **multiple signals**. Two types of Multiplexing: - Frequency Division Multiplexing (FDM) Splits different signals which correspond to different frequencies to travel through medium, e.g., TV has multiple frequencies running down cable. - Time Division Multiplexing (TDM) Splits information into discrete packets and reassembled at receiving end. - ***Radio Transmission (AM, FM, digital)*** **Radio Transmission** **Amplitude Modulation (Modulates Amplitude)** Amplitude Modulation acts at 1MHz. Information is sent at large distances. The Amplitude varies to transmit data. As signal wave amplitude increases = amplitude of modulated wave increases. AM Radio is sent through transmitter after being modulated. Then to receive signal, it is then tuned to required **carrier frequency.** Then this is passed through **demodulator** to extract information and **remove carrier wave** The Amplitude is converted into sound. Disadvantages of AM Radio: - AM Radio induces '*noise'* which reduces signal quality, to affect amplitude of modulated wave. **Frequency Modulation (Modulates Frequency)** Where frequency signal is placed onto a carrier wave (modulated). Amplitude of signal wave increases frequency of FM wave increases. Advantages of FM Radio: - Quality of signal is better. The main difference for FM Radio is frequency is converted into sound. Due to a higher bandwidth (amount of space to supply a carrier wave). **Demodulation Circuit** Antenna: Receives all signals which were transmitted Coil: with a fixed number of turns is able to be fixed to a set frequency to resonate at. Variable Capacitor: Able to make coils variable to tune to set frequency. Diode or Section B: Acts as a demodulator to remove all parts below x-axis of sine wave, to leave rectified half sine wave. Earphones: Convert electrical signals to sound - ***Digital Television Transmission such as (LED, LCD, 3D)*** **Digital Television Transmission** Radio waves which transmit information using either very high frequency (VHF) or ultra-high frequency (UHF). **Black and White Television** Black and White televisions worked by using a cathode ray tube (CRT), by firing electrons from cathode to anode behind glass screen. Coated in a phosphor coating, this would emit light in the visible light range. Similarly, audio signal was transmitted with both a video signal. This produced an audio signal which was **sent via the transmitter, received, demodulated, and produced an output on sound system.** **Colour Television** Colour television is similar to black and white television but instead of one electron beam there are three electron beams which reacted with red, green, and blue phosphor coatings to provide colours such as **white.** Where these colours (red, green, and blue), are placed across screen. To produce **white**, all three colours (red, green, and blue) are all excited by electron guns. To make **black** the electron guns do not hit the three colours. **Digital Televisions** End of 2013, TV was switched to Digital TV. Digital TV works through using digital modulation and multiplexing. Advantages of Digital TV: - Higher transmission of information and resolution due to higher bandwidth - Digital TV was able to run various programs at one frequency at reduced resolution and adjust resolution for a different station. Whereas analogue TV could not display different resolutions. **Display Media** - **Plasma** Plasma occurs in a fluorescent light they use electricity (positive and negative plate) at ends of fluorescent light with gas (noble gases) in vacuum. This splits the atom in electrons and protons. Plasma uses tiny, quick fluorescent light cells to form a picture. Plasma is gas with electrons and protons. These electrons are introduced to **noble gases** such as xenon and neon. Causing acceleration towards positive plate. The electrons will collide with protons to release **photons** or **light** in **UV** to light up each pixel. Advantages of Plasma: - Greater Contrast of Black - Greater Resolution Disadvantages: - Energy Intensive - **LCD (Liquid Crystal Display)** - **LCD (Liquid Crystal Display)** Uses a white backlight which is shone through fluorescent tubes. 1. Shone through millions of LCD shutters arranged on a grid (diffusers) 2. Liquid crystals rotate the polarizers to produce different intensities of light when **subjected to voltage**. 3. There is a coloured sheet with RGB pixels to produce different colours of light.  Disadvantages of LCD TV's - The LCD TV does produce a true black. - **LED TV's** Works through the same principle of LCD TV's, however, instead of fluorescent tubes which creates white light. There is a backlight to produce this. - ***Telephony (Fixed and Mobile)*** **Fixed Telephones** A fixed telephone consisted of a loudspeaker, mouthpiece, earpiece and a main body. When speaking into telephone, sound waves hit metal plate causing vibration. Electromagnetic coil converts this changing magnetic field into current. To move this current or electrical signal to destination. When handpiece was lifted, which connected the telephone to the '*network'*. This in turn, causes automatic switching to take place and connect to dialled number. **Mobiles Phones** Each city or area is broken into small cells. **Each cell has certain frequencies**. More Cells = More Phones. Frequencies of different cells do not affect as mobile phone travels short distances. When mobile phone gets to boundary of cell. The computer realises the **signal** getting weaker from **original cell**, and **another signal** getting stronger from new cell. Network will connect to frequency of different cell. When this doesn't work the mobile data drops out. Making parts of city into cells you are able to duplicate frequency to enhance strength. 4G and 5G run at higher frequencies which increases their bandwidth (space at which is able to transmit signals, this provides stronger transmission of information). However, this high frequency cannot propagate as well. - ***Transmission Media (cable, wireless, infrared, microwave, fibre-optics)*** **Cables** Electrolytic Tough Pitch used in telephone lines to make use of copper cabling to transmit information. Using copper can be affected by electromagnetic interference which creates static noise and reduces quality. Cables are affected by heat which cause the wire to contract - **Twisted Pair Cables** When cables are running a changing current through them, this produces a changing magnetic flux. As a result this influences the current flowing through the coil Taking pair of copper wires and twisting them together in a double helix, DNA molecule structure. Twisting wires causes shielding from electromagnetic interference or induction, whereas one cable **produces a magnetic field**, and the other cable **produces magnetic field** in **opposite direction. Which cancels it out.** Unshielded Twisted Pair: Used in LAN as it is very expensive and complexity. Shielded Twisted Pair: The Second layer, known as primary shield, consists of metal foil and prevents electromagnetic induction, as the metal produces an induced EMF, which produces a MF which opposes original change in flux. Advantages of Twisted Pair: - Lightweight - Low Cost (Except Shielded Twisted Pair) Disadvantages of Unshielded Twisted Pair: - Is affected by electromagnetic induction. - **Coaxial Cable** Coaxial Cables are cables which are together on their axis.  Coaxial Cable works where the copper mesh prevents electromagnetic interference. As a result, the coaxial cable is able to travel further distances without '*breaks'* in the transmission, compared to twisted pair. Disadvantages: - Expensive, specifically the metal sheath. **Infrared** Transmission of media, which is outside visible range, infrared transmission must have a line of sight. And the distance must be less than 10m. Examples include TV Remotes. **Wireless** Wireless is affected by heat, where high temperatures cause the signal become lighter and travel faster through air. However, heat increases energy of signal, as a result distorting direction of signal. - ***Satellite Communication Systems (Geostationary, low orbit satellite and GPS)*** **Satellite Communication Systems** Satillete communication systems provide voice, weather and television. **Geostationary** Satellites which stay at **fixed point** above Earth. They have a period of **24 hours**. Where satellites orbit at an **altitude** of **35,785km** somewhere above the equator. Weahter and communications satilletes are geostationary orbit. Providing same perspective of Earth at same brief intervals. However, Geostationary requires line of sight. Advantages: - Higher Bandwidth - Remote Sensing - Fixed Antenna link - Lower Gravity Pull Disadvantages: - Direct Line of Sight - Increased damage and exposure to closer radiation. **Medium -- Earth Orbit** Altitudes between 2000km and 35,000km. Where most GPS (Global Positioning Systems) orbit here. - ***Scope of the profession (nature and scope of telecommunication engineering, health and safety issues, relations with community, technologies unique to profession, legal and ethical implication)*** **Nature and Scope** **Telecommunication engineers**, responsible for **design** and **development** of **communication** **equipment** and **infrastructure**, they also **improve designs,** these include telephones, satellite systems, television, and radio networks. **Health and Safety Issues** Installation of optical fibres causes them to be exposed to danger, from falling equipment, lightning strikes, electrical hazards on the safety sight. Hence, why Work, Health and Safety comes in.