Slides By: Dr. N. Ioannides (Feb. 2010)CT1037NI - L.02 - Analogue Signal Characteristics - pp 1/43 CT1037NI Introduction to Communications Analogue Signal Characteristics Er. Saroj Sharan Regmi Lecture 02

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 2/43 Introduction to the Module: CT1037NI. Introduction to Telecommunications. Telecommunications have made great progress over the past 150 years. There are a number of organizations responsible for standards. Discussed Social Implications from Telecommunications. Last Lecture: 01 Introduction to Telecommunications

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 3/43 Signal Overview and Definitions. Voltage, Resistance, Current & Power. Characteristics of Sinusoidal Waveforms. Electro-Magnetic Spectrum. International System (SI) of Units. Scientific Notation and Decimal Prefixes in Engineering. Logarithms and Decibel. Signal Attenuation. Power Budget. Noise in Analogue Signals and Types of Noise. Periodic Waveforms. Bandwidth. Today’s Lecture: 02 Analogue Signal Characteristics

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 4/43 Signals Signal: An electrical voltage or current which varies with time and is used to carry messages or information from one point to another.  Analogue signals vary continuously with time:  Digital signals vary abruptly and change between distinct voltage or current levels.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 5/43 Voltage ( V ): an electrical force, or pressure, that occurs when electrons and protons are separated.  The unit of voltage measurement is the Volt (V). Resistance ( R ): the opposition to the movement of electrons through materials.  The unit of resistance measurement is the Ohm (Ω). Current ( I ): Caused by the flow of free electrons in a circuit.  The unit of current measurement is the Ampere (A).  The Ampere is defined as the number of charges per second that pass by a point along a path. Electrons ONLY flow in CLOSED circuits, or COMPLETE loops. Voltage, Resistance & Current

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 6/43 Open vs Closed Circuits Electrons ONLY flow in CLOSED circuits, or COMPLETE loops. Example: The Torchlight. Open Switch / Open Circuit Current does NOT flow ! Closed Switch / Closed Circuit Current DOES flow !

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 7/43 Current Flow Current can flow in one of two ways:  Direct Current (DC): DC always flows in the same direction, and DC voltages always have the same polarity.  Alternating Current (AC): AC varies over time by changing its polarity, or direction. Note: For AC and DC electrical systems, the flow of electrons is always from a negatively charged source to a positively charged source.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 8/43 Current vs Electron Flow For AC and DC electrical systems:  Current Flow: always from a positive terminal to a negative terminal.  Electron Flow: always from a negatively charged source to a positively charged source. Current flow Electron flow

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 9/43 Alternating vs Direct Current The work done by the AC and DC currents is NOT equivalent:  DC performs constant work due to the constant nature of the flow of current.  AC performs variable work due to the alternating / varying nature of the flow of current. Root Mean Square (RMS) Value: the effective value of a varying voltage or current.  RMS is the equivalent DC value which gives the same work.  The following equations hold for sinusoidal waveform signals:

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 10/43 Ohm’s Law Identifies the relationship among Voltage, Resistance and Current:  DC Systems: Note: Ohm’s Law considers the flow of current in the conventional way which sees the current flowing from the positive towards the negative.  AC Systems:

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 11/43 Power Power ( P ): The work performed by an electrical current.  The unit of power measurement is the Watt (W).  DC Circuits:  AC Systems:

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 12/43 International System (SI) of Units The SI is the modern metric system of measurement. A unit is a particular physical quantity, defined and adopted by convention, with which other particular quantities of the same kind are compared to express their value. A physical quantity is a quantity that can be used in the mathematical equations of science and technology. The value of a physical quantity is the quantitative expression of a particular physical quantity as the product of a number and a unit, the number being its numerical value.  Thus, the numerical value of a particular physical quantity depends on the unit in which it is expressed.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 13/43 Scientific Notation Commonly used in Physics, Chemistry and Engineering. A way of separating the range of expressible numbers from their precision: Examples:3.14 =0.314 × 10 1 = 3.14 × =0.1 × = 1.0 × = × 10 4 = × 10 3 f: fraction or mantissa, r: radix or base number, e: +ve or -ve integer called the exponent. The range is determined by the number of digits in the exponent. The precision is determined by the number of digits in the fraction.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 14/43 Decimal Prefixes of Units in Engineering Multiplication Factor PrefixSymbol exaE petaP teraT gigaG megaM kilok millim microμ nanon picop femtof attoa

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 15/43 Logarithm is the power to which a number (base) must be raised to equal a given number. Logarithms By transforming very small or very large numbers into logarithms it makes them easy to work with.  Logarithms are referenced to the base of the number system being used (base 10 logarithms are often abbreviated as log).  Used commonly in calculating decibels (dB): a way of measuring signals on copper, optical, and wireless media. b: the base, n: the given number.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 16/43 Examples on Logarithms Logarithm is the power to which a number (base) must be raised to equal a given number:

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 17/43 Revision on Logarithms Important logarithms:.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 18/43 Decibels (dB) The most frequently used unit in Telecommunications. Defined as: The decibel is a means of logarithmically expressing the ratio between two signal levels (eg: output vs input, or output vs noise).  The result is based on the ratio of a final value (signal strength) to another reference value (input signal or noise value). The decibel is a RELATIVE measure, ie one quantity with respect to another quantity.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 19/43 Decibels (dB) (…2) V out = Signal amplitude at output in Volts V in = Signal amplitude at input in Volts P out = Signal amplitude at output in Watts P in = Signal amplitude at input in Watts Decibels state the amount of gain or loss of power, voltage or current that occurs in a circuit or system. Decibels are expressed as:  Amplification:Gain or + (only one is used, never both).  Weakening:Loss or – (only one is used, never both).

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 20/43 Power vs Voltage Decibel (dB) Values dB Gain/Loss Gain Power Ratio Loss Power Ratio Voltage Gain Voltage Loss

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 21/43 Special dB-based scales define a certain reference signal level as 0 dB (gain of 1) and compare all other signal levels to that defined point. If 0 dB is defined as a particular signal level, then one of the special scales can be defined. Such scales commonly used in electronics / networking are:  dBm: Power ratio related to 1 mW  dBW: Power ratio related to 1 W Special dB-based Scales

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 22/43 Defining the dBm & dBW When we define an output power with respect to 1mW (1 x ) we produce the dBm: When we define an output power with respect to 1W we produce the dBW: Both the dBm and the dBW are ABSOLUTE measures of power. 0 dBm = 1 mW0 dBW = 1 W -3 dBm = 0.5 mW-3 dBW = 0.5 W +3 dBm = 2 mW+3 dBW = 2W

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 23/43 Adding the dB with dBm & dB with dBW Very importantly, we can add these logarithmic quantities and work out an output power ‘absolutely’. Example: 0.5 W x 2 W = 1 W logarithmically: -3 dBW + 3 dBW = 0 dBW Another Example: Input AmplifierAttenuator AmplifierOutput +5 dB -9 dB x dB 1mW (0dBm) 6 dBm 0 dBm + 5 dB – 9 dB + x dB = 6 dBmx = +10dB

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 24/43 Taking Antilogs +5dBW Example: -3dBm Another Example:

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 25/43 The fundamental building block of all communications systems is the sinusoidal waveform. Sinusoidal Waveforms

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 26/43 D: distance t: time Periodic Time (T) Frequency (f) Velocity (v) Wavelength ( ) Characteristics of Sinusoidal Waveforms Displacement (d) Amplitude Peak (A p ) Amplitude Peak-to-Peak (A p-p )

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 27/43

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 28/43 The Electromagnetic (EM) Spectrum Electromagnetic Energy: The energy produced when an electric charge vibrates. Electromagnetic Spectrum: Wavelength continuum. Velocity of EM Wave in free space: 3 x 10 8 m/s = 300,000 km/s = 186,283 miles/s

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 29/43 Signal Velocity c = speed of light = 3 x 10 8 m/s The velocity of a signal depends on the communications medium: Examples:  Air: = 1 v air = 3 x 10 8 m/s  For a coaxial cable, on the dielectric constant ( ) of the insulator:  For an optical fibre, on the refractive index (n) of the glass core:  Fibre:n = 1.46 (glass)v fibre = x 10 8 m/s  Coaxial Cable: = 2.25 (polythene)v coax = 2 x 10 8 m/s

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 30/43 Signals attenuate (weaken) as they travel away from the source. They arrive with less strength than when they started. All transmission media weaken, or attenuate, the strength of the signal. Signal Attenuation

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 31/43 Attenuation is a measure of how much loss a signal experiences when it travels down a communications medium.  All transmission media weaken, or attenuate, the strength of the signal.  As the signal travels down the medium part of the signal is dispersed as heat or absorbed by the transmission medium.  The longer the distance that the signal travels, the greater will be the attenuation that the signal suffers.  If the medium is too long, no signal will arrive at the end, or the signal will be so small that cannot be used (buried in noise). Signal Attenuation (…2)

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 32/43 V out = Signal amplitude at output in Volts (Voltage) V in = Signal amplitude at input in Volts (Voltage) I out = Signal amplitude at output in Amperes (Current) I in = Signal amplitude at input in Amperes (Current) Attenuation is measured in decibels (dB). Signal Attenuation (…3)  If half the signal voltage or current is lost by the time it reaches the destination then it has suffered a 6 dB loss.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 33/43 Signal Attenuation (…4) P out = Signal amplitude at output in Watts (Power) P in = Signal amplitude at input in Watts (Power)  If half the signal power is lost by the time it reaches the destination then it has suffered a 3 dB loss.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 34/43 Power Budget The summation of all gains and losses within a system to determine the overall system output power. Consider the following communications link: Cables (attenuate) Initial Power Amplifier Source Receiver Amplifier Final Power (Amplification)

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 35/43 Power Budget Example Amplifier 20 dB Receiver Amplifier 30 dB Cable l 2 = 30 km Cable l 1 = 45 km Cable l 3 = 35 km Initial Power P in = 15 dBm Source Receiver Amplification P out = 75 dB To find the power budget for the system above simply add the gains and subtract the losses:  System Power Output = + 15 dBm – 22.5 dB + 20 dB – 15 dB + 30 dB – 17.5 dB + 75 dB = = 85 dB Cable Attenuation α = 0.5 dB/km

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 36/43 Noise in Analogue Signals Noise: A usually interferential random frequency current or voltage signal extending over a considerable frequency spectrum and having no useful purpose. Noise Level: The amplitude of ambient electrical noise generated inside or outside an electronic circuit. Signal to Noise Ratio: The ratio of signal amplitude to noise amplitude.  Measured in decibels (dB).

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 37/43 If the transmitting electronics are not properly shielded then signals of other frequency could be superimposed on the signal of interest. This will also be a form of noise. Noise added to the analogue signal can greatly affect the accuracy of the information. Noise is always unwanted and efforts are always taken to minimise its effect but limiting the level of noise is not an easy or inexpensive process. Noise in Analogue Signals (…2)

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 38/43 Types of Noise White Noise: Random noise (acoustic or electric) distributed equally over a given frequency band.  Example: the noise resulting from the random motion of free electrons in conductors and semiconductors. Pink Noise: Electrical noise whose amplitude is inversely proportional to frequency in a limited frequency spectrum. Shot Noise: Caused by random fluctuations in the motion of charge carriers in a conductor. Thermal (Johnson) Noise: Any form of noise generated within a circuit and depends on temperature.  Electrical noise caused by the agitation of electrons in a material due to heat.  Frequency independent.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 39/43 Signal to Noise Ratio (SNR) Signal to Noise Ratio: The ratio of signal amplitude to noise amplitude. V S = Signal amplitude in Volts (Voltage) V N = Noise amplitude in Volts (Voltage) P S = Signal amplitude in Watts (Power) P N = Noise amplitude in Watts (Power) I S = Signal amplitude in Amperes (Current) I N = Noise amplitude in Amperes (Current)

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 40/43 A collection of sinusoidal waveforms can compose any practical signal no matter how complex it may be. All periodic waveforms can be built up from a series of pure sinusoidal waveforms of distinct but related frequencies. These related frequencies are:  Fundamental frequency (the frequency of interest).  Harmonics (integer multiples of the fundamental frequency). The production of such complex periodic waveforms requires electronic circuitry whose bandwidth (BW) is large enough to accommodate the range covering all frequencies involved, i.e. from the lowest to the highest. Periodic Waveforms

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 41/43 Example of a Complex Periodic Waveform

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 42/43 Bandwidth (BW) The range of frequencies that …:  … can be carried across a given transmission medium.  … a telecommunications system is able to support. Examples of Bandwidth:  Telephone Voice Channel:BW = 3 kHz,  Hi-Fi Music:BW = 15 kHz,  CD Stereo Player:BW = 22 kHz,  AM Radio Station:BW = 10 kHz  FM Radio Station:BW = 200 kHz,  TV Channel on CATV:BW = 6 MHz.

Slides By: Dr. N. Ioannides (Feb. 2010) CT1037NI - L.02 - Analogue Signal Characteristics - pp 43/43 Summary Overviewed and Defined Signals. The fundamental building block of all communications systems is the sinusoidal waveform. Sinusoidal Waveform Characteristics: Amplitude, Frequency, Period, Wavelength, Velocity. Periodic Waveforms: A collection of sinusoidal waveforms can compose any practical signal no matter how complex it may be. Bandwidth: the range of frequencies of a system. Electro-Magnetic Spectrum. Signal Attenuation: the weakening of signals. Noise in Analogue Signals and Types of Noise. Noise is always unwanted and efforts are always taken to minimise its effect.