ECE 314B Principles of Communication Systems Learning Module PDF

1 TECHNOLOGICAL UNIVERSITY OF THE PHILIPPINES VISAYAS Capt. Sabi St., City of Talisay, Negros Occidental College of Engineering Office of the Program Coordinator LEARNING MODULE ECE 314B: Principles of Communications Systems...

1 TECHNOLOGICAL UNIVERSITY OF THE PHILIPPINES VISAYAS Capt. Sabi St., City of Talisay, Negros Occidental College of Engineering Office of the Program Coordinator LEARNING MODULE ECE 314B: Principles of Communications Systems DEPARTMENT: ELECTRONICS ENGINEERING COMPILED BY: ENGR. DONNIE SENOMIO 2020 This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  2 LEARNING GUIDE Week No.: __10__ I. TOPIC/S  Sideband o Introduction to SSB o Modulation and demodulation o Types of SB II. LEARNING OUTCOMES  Be able to understand the main purpose of an electronic communications system how to transfer analog or digital information from one place to another.  Be able to explain how electronic communications can be viewed as the transmission, reception and processing of information between two or more locations using electronic circuit/device. III. CONTENT/TECHNICAL INFORMATION SINGLE SIDEBAND  Purpose: to reduce the bandwidth requirement of AM by one-half. This is achieved by transmitting only the upper sideband or the lower sideband of the DSB AM signal. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  3 SSB FREQUENCY SSB MATH This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  4 SSB HILBERT  SSB signal can be expressed in terms of m(t) and its Hilbert transform SSB GENERATOR  Selective Filtering using filters with sharp cutoff characteristics. Sharp cutoff filters are difficult to design. The audio signal spectrum has no dc component; therefore, the spectrum of the modulated audio signal has a null around the carrier frequency. This means a less than perfect filter can do a reasonably good job of filtering the DSB to produce SSB signals.  Baseband signal must be bandpass  Filter design challenges  No low frequency components  Phase shift method using Hilbert transformer  Non-causal filter, approximations This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  5 SSB DEMODULATION  Synchronous, SSB-SC demodulation 𝜑𝑆𝑆𝐵 (𝑡) cos(𝜔𝑐 𝑡) = [𝑚(𝑡) cos(𝜔𝑐 𝑡) ± 𝑗𝑚ℎ (𝑡) sin(𝜔𝑐 𝑡)] cos(𝑛𝜔𝑐 𝑡) 1 = [𝑚(𝑡)(1 + cos(𝜔𝑐 𝑡)) ± 𝑗𝑚ℎ (𝑡)sin⁡(2𝜔𝑐 𝑡) 2 1 A lowpass filter can be used to get 2 𝑚(𝑡). SSB+C, envelop detection 𝜑𝑆𝑆𝐵+𝐶 (𝑡) = 𝐴𝑐𝑜𝑠(𝜔𝑐 𝑡) + [𝑚(𝑡) cos(𝜔𝑐 𝑡) ± 𝑚ℎ (𝑡) sin(𝜔𝑐 𝑡)] An envelope detector can be used to demodulate such SSB signals What is the envelope of? 𝜑𝑆𝑆𝐵+𝐶 (𝑡) = (𝐴 + 𝑚(𝑡))(cos(𝜔𝑐 𝑡)) + 𝑚ℎ (𝑡) sin(𝜔𝑐 𝑡) = 𝐸(𝑡) cos(𝜔𝑐 𝑡 + 𝛳) SSB VS AM  Since the carrier is not transmitted, there is a reduction by 67% of the transmitted power (-4.7dBm). --In AM @100% modulation: 2/3 of the power is comprised of the carrier; with the remaining (1/3) power in both sidebands.  Because in SSB, only one sideband is transmitted, there is a further reduction by 50% in transmitted power This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  6  Finally, because only one sideband is received, the receiver's needed bandwidth is reduced by one half--thus effectively reducing the required power by the transmitter another 50%  (-4.7dBm (+) -3dBm (+) -3dBm = -10.7dBm).  Relative expensive receiver VESTIGIAL SIDEBAND  VSB is a compromise between DSB and SSB. To produce SSB signal from DSB signal ideal filters should be used to split the spectrum in the middle so that the bandwidth of bandpass signal is reduced by one half. In VSB system one sideband and a vestige of other sideband are transmitted together. The resulting signal has a bandwidth > the bandwidth of the modulating (baseband) signal but < the DSB signal bandwidth. FILTERING SCHEME FOR THE GENERATION OF VSB MODULATED WAVE This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  7 VSB TRANSCEIVER  Envelope detection of VSB+C  Analog TV:  DSB, SSB and VSB o DSB bandwidth too high o SSB: baseband has low frequency component, receiver cost o Relax the filter and baseband requirement with modest increase in bandwidth This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  8 (a) Idealized magnitude spectrum of a transmitted TV signal. (b) Magnitude response of VSB shaping filter in the receiver. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  9 COMPARISON: IV. PROGRESS CHECK: 1. A modulating signal 𝑚(𝑡) is given by 𝑚(𝑡) = cos(200𝜋𝑡) + 8cos⁡(600𝜋𝑡). The message is transmitted with AM single side band modulation using a carrier frequency, 𝑓𝑐 = 10𝑘𝐻𝑧. Find a time domain expression for the upper side band signal 𝜑𝑈𝑆𝐵 (𝑡). (10pts) 2. Over an interval |𝑡| ≤ 1, an angle modulated signal is given by 𝜑𝐸𝑀 (𝑡) = 5cos⁡(90,000𝑡). It is known that the carrier frequency is 𝜔𝑐 = 80,000 radians per second. (a) If this is assumed to be a phase-modulated (PM) signal with 𝑘𝑝 = 5000, find an expression for 𝑚(𝑡) over the interval |𝑡| ≤ 1. (b) If this is assumed to be a frequency modulated (FM) signal with 𝑘𝑓 = 10,000, find an expression for 𝑚(𝑡) over the interval |𝑡| ≤ 1. (20pts) 3. Consider the following indirect FM generator. The input to the generator is a narrowband FM signal with 𝑓𝑐 = 20𝑘𝐻𝑧 and 𝛥𝑓 = 10𝐻𝑧. (20pts) Frequency A B Frequency C multiplier Mixer + Filter multiplier X1000 X100 Oscillator 5MHz Give both 𝑓𝑐 and 𝛥𝑓 at the following points in the circuit. a) Point A b) Point B c) Point C This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  10 LEARNING GUIDE Week No.: __11__ V. TOPIC/S  Frequency Modulation o Architecture o Design o Modulation VI. LEARNING OUTCOMES  Be able to understand the main purpose of an electronic communications system how to transfer analog or digital information from one place to another.  Be able to explain how electronic communications can be viewed as the transmission, reception and processing of information between two or more locations using electronic circuit/device. VII. CONTENT/TECHNICAL INFORMATION FREQUENCY MODULATION  FM is a system in which the amplitude of the modulated carrier is kept constant while its frequency and rate of change are varied by the modulating signal.  PM is a similar system in which the phase of the carrier is varied instead of frequency and the amplitude of the carrier remains constant.  The amplitude of the frequency modulated wave remains constant at all times. ADVANTAGES OF FM OVER AM  The amplitude of FM wave is constant. Independent of the modulation depth. All the transmitted power in FM is useful.  FM receivers can be fitted with amplitude limiters to remove the amplitude variations caused by noise. Making FM reception more immune to noise.  Possibility to further increase the deviation. It can exceed 100 percent modulation without causing severe distortion.  Standard frequency allocations by CCIR of ITU. Guard band has been provided between commercial FM stations, for less adjacent-channel interference.  Operates in the upper VHF and UHF frequency range, in which lesser noise than in MF and HF ranges.  Space wave is used for propagation, radius of operation is limited to slightly more than the LOS. Possible to operate several independent transmitters on the same frequency with less interference. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  11 DISADVANTAGE OF FM OVER AM  A much wider channel is required, up to 10 times as large as that needed by AM.  FM transmitters and receivers device are more complex, particularly for modulation and demodulation.  The area of reception is limited due to LOS. This may be an advantages for co- channel allocations but disadvantage for FM mobile communications over wide area. FREQUENCY MODULATION  The deviation of the carrier is proportional to the amplitude of the modulating voltage.  DEVIATION RATIO- the shift in the carrier frequency from its resting point compared to the amplitude of the modulating voltage.  Deviation ratio of 5 is the maximum allowed in commercially broadcast FM. 𝑓𝑑𝑒𝑣 (𝑚𝑎𝑥)  𝐷𝑒𝑣𝑎𝑡𝑖𝑜𝑛⁡𝑟𝑎𝑡𝑖𝑜 = 𝑓𝐴𝐹 (𝑚𝑎𝑥) MODULATION INDEX  If the frequency deviation of the carrier is known and the frequency of the modulating voltage AF is known, we can establish the modulation index, MI. 𝑓𝑑𝑒𝑣  𝑀𝐼 = 𝑓𝐴𝐹 SYSTEM DESCRIPTION  The general equation of an unmodulated wave or carrier is 𝑥 = 𝐴𝑠𝑖𝑛(𝜔𝑡 + 𝜑) Where: 𝑥 = instantaneous value (of voltage or current) 𝐴 = maximum amplitude 𝑟𝑎𝑑 𝜔 = angular velocity, 𝑠𝑒𝑐 𝛷 = phase angle, 𝑟𝑎𝑑 Note: 𝜔𝑡 represents an angle in radians.  If any of the three parameters is varied in accordance with another signal, normally of a lower frequency, then the second signal is called the modulation, and the first is said to be modulated by the second.  AM is achieved when amplitude A is varied.  Alteration of the phase angle phi will yield phase modulation.  If the frequency of the carrier is made to vary, FM waves are obtained.  If any of the three parameters is varied in accordance with another signal, normally of a lower frequency, then the second signal is called the modulation, and the first is said to be modulated by the second. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  12  AM is achieved when amplitude A is varied.  Alteration of the phase angle phi will yield phase modulation.  If the frequency of the carrier is made to vary, FM waves are obtained. FM REPRESENTATION This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  13 FM VOLTAGE  Note that as the modulating frequency decreases and the modulating voltage amplitude (δ) remains constant, the modulation index increases.  Note as well that 𝑚_𝑓 which is the ratio of two frequencies, is measured in radians. EXAMPLE: In an FM system, when the audio frequency (AF) is 500 Hz and the AF voltage is 2.4V, the deviation is 4.8 kHz. If the AF voltage is now increased to 7.2V, what is the new deviation? If the AF voltage is raised to 10V while the AF is dropped to 200 Hz, what is the deviation? Find the modulation index in each case. SOLUTION: This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  14 INSTANTANEOUS FREQUENCY DEVIATION  Instantaneous change in the frequency of the carrier and is defined as the first time derivative of the instantaneous phase deviation. 𝑟𝑎𝑑 𝑖𝑛𝑠𝑡𝑎𝑛𝑡𝑎𝑛𝑒𝑜𝑢𝑠⁡𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦⁡𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛 = 𝛳′ (𝑡) 𝑠 ′ (𝑡) 𝑟𝑎𝑑 𝛳 𝑐𝑦𝑐𝑙𝑒 𝑠 𝑟𝑎𝑑 = 𝑠 = 𝐻𝑧 2𝜋 𝑠 s INSTANTANEOUS FREQUENCY  The precise frequency of the carrier at any given instant of time and is defined as the first time derivative of the instantaneous phase. 𝑑 𝑖𝑛𝑠𝑡𝑎𝑛𝑡𝑎𝑛𝑒𝑜𝑢𝑠⁡𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 = ⁡ 𝜔𝑖 (𝑡) = [𝜔𝑐 𝑡 + 𝛳(𝑡)] 𝑑𝑡 𝑟𝑎𝑑 = 𝜔𝑐 𝑡 + 𝛳′(𝑡) , 𝑠  Substituting 2𝜋𝑓𝑐 for 𝜔𝑐 gives 𝑖𝑛𝑠𝑡𝑎𝑛𝑡𝑎𝑛𝑒𝑜𝑢𝑠⁡𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 = 𝑓𝑖 (𝑡) 𝑟𝑎𝑑 𝑐𝑦𝑐𝑙𝑒𝑠 𝑟𝑎𝑑 𝜔𝑖 (𝑡) = (2𝜋, ) (𝑓𝑐 , ) + 𝛳′ 𝑡 = 2𝜋𝑓𝑐 + 𝛳′ (𝑡), ⁡ 𝑠 𝑠 𝑠  Frequency modulation is angle modulation in which the instantaneous frequency deviation, 𝛳′(𝑡), is proportional to the amplitude of the modulating signal, and the instantaneous phase deviation is proportional to the integral of the modulating signal voltage. DEVIATION SENSITIVITY  For modulating frequency, 𝑉𝑚 (𝑡), the frequency modulation are 𝑟𝑎𝑑 𝑓𝑚 = 𝛳′ 𝑡 = 𝑘𝑓 𝑉𝑚 (𝑡), 𝑠  Where 𝑘𝑓 are constant and are the deviation sensitivities of the frequency modulator.  Deviation sensitivities are the output-versus-input transfer function for the modulators, which gave the relationship between what output parameter changes in respect to specified changes in the input signal. 𝑟𝑎𝑑 𝛥𝜔  Frequency Modulator, 𝑘𝑓 = 𝑠 ( 𝛥𝑉 ) 𝑉 𝑑𝛳  Variation of ⁡produces Frequency Modulation 𝑑𝑡 𝑑𝛳  Frequency modulation implies that is proportional to the modulating signal. 𝑑𝑡 This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  15 FM WAVEFORM  Carrier amplitude remains constant  Carrier frequency is changed by the modulating signal. o amplitude of the information signal varies, the carrier frequency shift proportionately. o modulating signal amplitude increases, the carrier frequency increases. o modulating signal amplitude varies, the carrier frequency varies below and above it normal center or resting, frequency with no modulation.  The amount of the change in carrier frequency produced by the modulating signal known as frequency deviation fd.  Maximum frequency deviation occurs at the maximum amplitude of the modulating signal. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  16  The frequency of the modulating signal determines the frequency deviation rate MODULATION INDEX  Directly proportional to the amplitude of the modulating signal and inversely proportional to the frequency of the modulating signal.  Ratio of the frequency deviation and the modulating frequency. 𝑣𝐹𝑀 (𝑡) = 𝑉𝑐 sin⁡[𝜔𝑐 𝑡 − 𝛽𝑐𝑜𝑠𝜔𝑚 (𝑡)]  𝛽 as modulation index: 𝛥𝑓𝑐 𝑚𝑓 = 𝛽 = 𝑓𝑚 EXAMPLE: Determine the modulation index for FM signal with modulating frequency is 10KHz deviated by ±10kHz. Answer: (20KHz/10KHz) = 2.0 (unitless) The total frequency change, 10kHz x 2 is called the carrier swing = frequency deviation x 2. PERCENT MODULATION  Simply the ratio of the frequency deviation actually produced to the maximum frequency deviation allowed by law stated in percent form. 𝛥𝑓𝑎𝑐𝑡𝑢𝑎𝑙 %𝑚𝑜𝑑𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = 𝛥𝑓𝑚𝑎𝑥 VIII. PROGRESS CHECK: 1. What is the frequency swing of an FM broadcast transmitter when modulated 80% 2. An FM signal has a center frequency of 10MHz but is swinging between 100.01 MHz and 99.999 MHz at a rate of 100 times per second. What is the modulation index of the signal? 3. An FM wave is represented by, 𝑣𝐹𝑀 = 24𝑠𝑖𝑛⁡(7𝑥108 𝑡 + 4 sin(1800𝑡)). Find the power dissipated in an 8Ω antenna. 4. If a given modulating signal produces ±50kHz frequency deviation, and the law stated that maximum frequency deviation allowed is ±75kHz. Find the %modulation. 5. Find the carrier and modulating frequencies, the modulation index and the maximum deviation of the FM wave represented by the voltage equation 𝑣 = 12sin⁡(6𝑥108 𝑡 + 5𝑠𝑖𝑛1250𝑡). What power will this FM wave dissipate in a 10 ohm resistor? This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  17 LEARNING GUIDE Week No.: __12__ I. TOPIC/S  Radio Wave Propagation o Electromagnetic Waves o Electric ang Magnetic Fields o Power Density o Polarization o Attenuation o Propagation o Losses II. LEARNING OUTCOMES  Be able to understand the main purpose of an electronic communications system how to transfer analog or digital information from one place to another.  Be able to explain how electronic communications can be viewed as the transmission, reception and processing of information between two or more locations using electronic circuit/device. III. CONTENT/TECHNICAL INFORMATION INTRODUCTION  Radio waves are one form of electromagnetic radiation  Electromagnetic radiation has a dual nature: o In some cases, it behaves as waves o In other cases, it behaves as particles (photons)  For radio frequencies the wave model is generally more appropriate  Electromagnetic waves can be generated by many means, but all of them involve the movement of electrical charges ELECTROMAGNETIC SPECTRUM This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  18 ELECTROMAGNETIC WAVES  Electromagnetic transmissions move in space as Transverse waves  Waves are characterized by frequency and wavelength: 𝑣 = 𝑓𝜆 ELECTRIC AND MAGNETIC FIELDS  An electromagnetic wave propagating through space consists of electric and magnetic fields, perpendicular both to each other and to the direction of travel of the wave  The relationship between electric and magnetic field intensities is analogous to the relation between voltage and current in circuits  This relationship is expressed by: 𝐸 Where: 𝑍=𝐻 𝑉 E = rms value of field strength, 𝑚 𝐴 H = rms value of magnetic field strength, 𝑚 Z = characteristics impedance of a medium, 𝜇 Where: 𝑍=√ μ = permeability of medium (inductance) 𝜀 ε = electric permittivity of medium (capacitance) For free space: 𝐻 𝜇 = 4𝜋𝑥10−7 = 1.257𝑥10−6 𝑚 1 𝐹 𝜀= 𝑥109 = 8.854𝑥10−12 36𝜋 𝑚 This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  19 POWER DENSITY  Power density in space is the amount of power that flows through each square meter of a surface perpendicular to the direction of travel. 𝐸2 𝑃𝑡 𝑃𝐷 = = 𝑍 4𝜋𝑟 2 PLANE AND SPHERICAL WAVES  The simplest source of electromagnetic waves would be a point in space, with waves radiating equally in all directions. This is called an isotropic radiator.  A wavefront that has a surface on which all the waves are the same phase would be a sphere. POLARIZATION  The polarization of a plane wave is simply the direction of its electric field vector  The wave can rotate in either direction - it is called right-handed if it rotates clockwise This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  20 CIRCULAR  Circularly polarized light consists of two perpendicular electromagnetic plane waves of equal amplitude and 90° difference in phase. The light illustrated is right- circularly polarized. LINEAR POLARIZATION  A plane electromagnetic wave is said to be linearly polarized. The transverse electric field wave is accompanied by a magnetic field wave as illustrated. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  21 ELLIPTICAL POLARIZATION  Elliptically polarized light consists of two perpendicular waves of unequal amplitude which differ in phase by 90°. The illustration shows right- elliptically polarized light. COMPARISON BETWEEN LINEAR POLARIZATION (HORIZONTAL VS. VERTICAL) This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  22 PROPAGATION FREE SPACE PROPAGATION  Radio waves propagate through free space in a straight line with a velocity of the speed of light (300,000,000 m/s)  There is no loss of energy in free space, but there is attenuation due to the spreading of the waves ATTENUATION OF FREE SPACE  An isotropic radiator would produce spherical waves  The power density of an isotropic radiator is simply be the total power divided by the surface area of the sphere, according to the square-law: 𝑃𝑡 𝑃𝐷 = 4𝜋𝑟 2 TRANSMITTING ANTENNA GAIN  In practical communication systems, it is important to know the signal strength at the receiver input  It depends on the transmitter power and the distance from the transmitter to the receiver, but also upon the transmitting and receiving antennas  Two important antenna characteristics are: o Gain for the transmitting antenna o Effective area for the receiving antenna  Antennas are said to have gain in those directions in which the most power is radiated 𝑃𝐷𝐴 Where: 𝐺𝑡 = 𝑃𝐷𝐼 𝐺𝑡 = transmitting antenna gain 𝑃𝐷𝐴 = power density in a given direction from the real antenna 𝑃𝐷𝐼 = power density at the same distance from an isotropic radiator with the same 𝑃𝑡 Effective Isotropic Radiated Power: 𝐸𝐼𝑅𝑃 = 𝑃𝑡 𝐺𝑡 𝐸𝐼𝑅𝑃 𝑃𝐷 = 4𝜋𝑟 2 RECEIVING ANTENNA GAIN  A receiving antenna absorbs some of the energy from radio waves that pass it  A larger antenna receives more power than a smaller antenna (in relation to surface area) This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  23  Receiving antennas are considered to have gain just as transmitting antennas do  The power extracted from a receiving antenna is a function of its physical size and its gain 𝑃𝑟 𝐴𝑒𝑓𝑓 𝑃𝑡 𝐺𝑡 Where: 𝐴𝑒𝑓𝑓 = = 𝑃𝐷 4𝜋𝑟 2 𝐴𝑒𝑓𝑓 = effective area of the antenna in 𝑚2 𝑃𝑟 = power delivered to the receiver in W 𝑊 𝑃𝐷 = power density of the wave in 𝑚2 𝜆2 𝐺𝑟 𝐴𝑒𝑓𝑓 = 𝐺𝑟 = antenna gain, as a power ratio 4𝜋 λ = wavelength of the signal PATH LOSS  Free-space attenuation is the ratio of received power to transmitted power  The decibel gain between transmitter and receiver is negative (loss) and the loss found this way is called free-space loss or path loss Where: 𝐴𝑒𝑓𝑓 𝑃𝑡 𝐺𝑡 𝑃𝑟 = receiver power in 𝑑𝐵𝑚 𝑃𝑡 = 4𝜋𝑟 2 𝑃𝑡 = transmitted power in 𝑑𝐵𝑚 𝐺𝑡 = transmitting antenna gain in 𝑑𝐵𝑖 𝑃𝑟 = 𝑃𝑡 + 𝐺𝑡 + 𝐺𝑟 − (32.44 + 20𝐿𝑜𝑔⁡𝑑 + 20𝐿𝑜𝑔⁡𝑓) 𝐺𝑟 = receiving antenna gain in 𝑑𝐵𝑖 𝑑 = distance between transmitter and receiver, in 𝑘𝑚 𝑓 = frequency in 𝑀𝐻𝑧 PHYSICS OF WAVE BEHAVIOUR  These three properties are shared by light and radio waves  For both reflection and refraction, it is assumed that the surfaces involved are much larger than the wavelength; if not, diffraction will occur  Reflection of waves from a smooth surface (specular reflection) results in the angle of reflection being equal to the angle of incidence This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  24 REFLECTION  Any conducting surface looks like a mirror to a radio wave, and so radio waves are reflected by any conducting surface they encounter.  Radio-wave reflection follows the principles of light-wave reflection.  The angle of reflection is equal to the angle of incidence.  The direction of the electric field approaching the reflecting surface is reversed from that leaving the surface. This is equivalent to a 180° phase shift.  Other types of reflection: Corner reflection Parabolic reflection Diffuse reflection REFRACTION  It is the bending of a wave due to the physical makeup of the medium through which the wave passes. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  25  Index of refraction is obtained by dividing the speed of a light (or radio) wave in a vacuum and the speed of a light (or radio) wave in the medium that causes the wave to be bent.  The relationship between the angles and the indices of refraction is given by a formula known as Snell’s law: 𝑛1 𝑠𝑖𝑛𝛳1 = 𝑛2 𝑠𝑖𝑛𝛳2 Where: 𝑛1 = index of refraction of initial medium 𝑛2 = index of refraction of next medium 𝛳1 = angle of incidence 𝛳2 = angle of refraction DIFFRACTION  It is the bending of waves around an object.  Diffraction is explained by Huygen’s principle: o Assuming that all electromagnetic waves radiate as spherical waveforms from a source, each point on a wave front can be considered as a point source for additional spherical waves. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  26 o When the waves encounter an obstacle, they pass around it, above it, and on either side. o As the wave front passes the object, the point sources of waves at the edge of the obstacle create additional spherical waves that penetrate and fill in the shadow zone. RADIO WAVE PROPAGATION MODES  Most of the time, radio waves are not quite in free space. 𝑍ℎ𝑡 ℎ𝑟 𝐼 𝑉= 𝜆𝑑  The three basic paths that a radio signal can take through space are: o Ground wave or surface wave  Are radio waves that travel or progress along the surface of the earth.  The ground wave must be vertically polarized to propagate from an antenna.  It follows the curvature of the earth and can, therefore, travel at distances beyond the horizon.  Ground-wave propagation is strongest at the low- and medium- frequency ranges.  AM broadcast signals are propagated primarily by ground waves during the day & by sky waves at night. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  27 o Sky wave or Ionospheric Propagation  Are radio waves that are radiated by the antenna into the upper atmosphere, where they are bent back to earth.  When a radio signal goes into the ionosphere, the different levels of ionization cause the radio waves to be gradually bent.  Skip/ Hop/ Ionospheric Wave) is the propagation of radio waves bent (refracted) back to the Earth's surface by the ionosphere.  HF radio communication (3 and 30 MHz) is a result of sky wave propagation.  A radio wave transmitted into an ionized layer is refracted (bent) as it abruptly changes velocity while entering a new medium  Long-range communication in the high-frequency band is possible because of refraction in a region of the upper atmosphere called the ionosphere  The ionosphere is divided into three regions known as the D, E, and F layers  Ionization is different at different heights above the earth and is affected by time of day and solar activity This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  28 o Space wave or Line of Sight wave  It is propagation of waves travelling in a straight line.  These waves are deviated (reflected) by obstructions and cannot travel over the horizon or behind obstacles.  travel directly from an antenna to another without reflection on the ground.  Occurs when both antennas are w/in LOS of each another.  characteristic of most radio signals with a frequency above 30 MHz, particularly VHF, UHF, and microwave signals.  Signals in the VHF and higher range are not usually returned to earth by the ionosphere  Most terrestrial communication at these frequencies uses direct radiation from the transmitter to the receiver Where: 𝑑 = √2ℎ𝑡 𝑑𝑡 = 4√ℎ𝑡 ℎ𝑡 = height of transmitting antenna, ft 𝑑 = distance from the transmitter to horizon, mi This is called the radio horizon 𝐷 = √2ℎ𝑡 + √2ℎ𝑟 The practical transmission distance, D  Other type of radio wave propagation is Tropospheric Scatter o This makes use of the scattering of radio waves in the troposphere to propagate signals in the 250 MHz –5 GHz range This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  29  Ducting o Under certain conditions, especially over water, a superrefractive layer can form in the troposphere and return signals to earth o The signals can then propagate over long distances by alternately reflecting from the earth and refracting from the superrefractive layer o A related condition involves a thin tropospheric layer with a high refractive index, so that a duct forms  Meteor Trail Propagation o Meteors are constantly entering the earth’s atmosphere and being destroyed o The meteors that enter the atmosphere leave behind an ionized trail that can be used for communication. It is not suitable for voice communication IV. PROGRESS CHECK: I. Problem Solving: 𝜇𝑊 a. At 20Km in free space from a point source, the power density is 200. 𝑚2 What is the power density 25Km away from the source? The field strength present in both locations? b. Calculate the power density (a) 500m from a 500 – W source and (b) 36,000Km from a 3-KW source. Both are assumed to be omnidirectional point sources. The field strength present in both locations? c. At 20Km in free space from a point source, the power density is 200 μW/m^2. What is the power density 25Km away from the source? The field strength present in both locations? d. Calculate the power density (a) 500m from a 500 – W source and (b) 36,000Km from a 3-KW source. Both are assumed to be omnidirectional point sources. The field strength present in both locations? e. At 20Km in free space from a point source, the power density is 200 μW/m^2. What is the power density 25Km away from the source? The field strength present in both locations? f. Calculate the power density (a) 500m from a 500 – W source and (b) 36,000Km from a 3-KW source. Both are assumed to be omnidirectional point sources. The field strength present in both locations? This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  30 g. A 150m antenna, transmitting at 1.2MHz (therefore by ground wave), has an antenna current of 8A. What voltage is received by a receiving antenna 40Km away, with a height of 2m? LIST OF REFERENCES  Haykin & Moher. (2009). Communication Systems  Frenzel, Louis. (2016). Principles of Electronic Communication Systems  Rao. (2013). Communication Systems  3G Learning. (2014). Digital and Analog Communication  Carlson. (2010), Communication Systems, 5th ed., Carlson, McGraw-Hill  www.google.com  www.electrical4u.com  www.electronics-tutorial.ws ABOUT THE AUTHOR ENGR. DONNIE SENOMIO o Master of Engineering Major in Electronics and Communication Engineering (MEECE) o College of Engineering – Electronics Engineering Instructor o Electronics Engineering Communications Engineering Subject Matter Expert o Technological University of the Philippines Visayas UITC Systems Administrator o Technological University of the Philippines Visayas UITC Web Administrator o Institute of Electronics and Communications Engineers of the Philippines Resource Speaker o Electronics Engineering Communications Engineering Resource Speaker o Mechatronics and Robotics Society of the Philippines Training Officer This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.