ECE 222 Principles of Communication Systems FREQUENCY MODULATION PDF

University of Southeastern Philippines COLLEGE OF ENGINEERING Electronics Engineering Program ECE 222 Principles of Communication Systems FREQUENCY MODULATION University of Southeastern Philippines COLLEGE OF ENGINEERING 1 Electronics Engineering Progr...

University of Southeastern Philippines COLLEGE OF ENGINEERING Electronics Engineering Program ECE 222 Principles of Communication Systems FREQUENCY MODULATION University of Southeastern Philippines COLLEGE OF ENGINEERING 1 Electronics Engineering Program FREQUENCY MODULATION Principles of Frequency Modulation Carrier amplitude remains constant Carrier frequency is changed by the modulating signal ↑ Modulating Signal Amplitude ↑ Carrier Frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 2 Electronics Engineering Program FREQUENCY MODULATION Principles of Frequency Modulation The carrier frequency varies above and below its normal center, or resting, frequency The amount of change in carrier frequency produced by the modulating signal is known as the frequency deviation (fd) University of Southeastern Philippines COLLEGE OF ENGINEERING 3 Electronics Engineering Program FREQUENCY MODULATION Principles of Frequency Modulation University of Southeastern Philippines COLLEGE OF ENGINEERING 4 Electronics Engineering Program FREQUENCY MODULATION Principles of Frequency Modulation Example: A carrier frequency is set at 150 MHz. If the peak amplitude of the modulating signal causes a maximum frequency shift of 30 kHz, the total frequency deviation is ________? Answer: ±30kHz University of Southeastern Philippines COLLEGE OF ENGINEERING 5 Electronics Engineering Program FREQUENCY MODULATION Principles of Frequency Modulation Note: The frequency of the modulating signal has no effect on the amount of deviation University of Southeastern Philippines COLLEGE OF ENGINEERING 6 Electronics Engineering Program FREQUENCY MODULATION Principles of Phase Modulation When the amount of phase shift of a constant-frequency carrier is varied in accordance with a modulating signal, the resulting output is a phase modulation ↑ Modulating Signal Amplitude ↑ Phase Shift University of Southeastern Philippines COLLEGE OF ENGINEERING 7 Electronics Engineering Program FREQUENCY MODULATION Principles of Phase Modulation University of Southeastern Philippines COLLEGE OF ENGINEERING 8 Electronics Engineering Program FREQUENCY MODULATION Principles of Phase Modulation In an FM wave the maximum deviation occurs at the peak positive and negative amplitude of the modulating voltage In PM, the amount of carrier deviation is proportional to the rate of change of the modulating signal University of Southeastern Philippines COLLEGE OF ENGINEERING 9 Electronics Engineering Program FREQUENCY MODULATION Relationship Between the Modulating Signal and Carrier Deviation In an FM wave the maximum deviation occurs at the peak positive and negative amplitude of the modulating voltage In PM, the amount of carrier deviation is proportional to the rate of change of the modulating signal University of Southeastern Philippines COLLEGE OF ENGINEERING 10 Electronics Engineering Program FREQUENCY MODULATION Relationship Between the Modulating Signal and Carrier Deviation In FM, frequency deviation is proportional only to the amplitude of the modulating signal, regardless of its frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 11 Electronics Engineering Program FREQUENCY MODULATION Relationship Between the Modulating Signal and Carrier Deviation University of Southeastern Philippines COLLEGE OF ENGINEERING 12 Electronics Engineering Program FREQUENCY MODULATION Converting PM to FM The deviation produced by frequency variations in the modulating signal must be compensated for Higher modulating frequencies produce a greater rate of change University of Southeastern Philippines COLLEGE OF ENGINEERING 13 Electronics Engineering Program FREQUENCY MODULATION Converting PM to FM Using a low-pass RC network The result is an output that is the same as an FM signal → Indirect FM University of Southeastern Philippines COLLEGE OF ENGINEERING 14 Electronics Engineering Program FREQUENCY MODULATION Modulation Index and Sidebands Any modulation process produces sidebands In FM and PM (as in AM) sum and difference sideband frequencies are produced In addition, a large number of pairs of upper and lower sidebands are generated University of Southeastern Philippines COLLEGE OF ENGINEERING 15 Electronics Engineering Program FREQUENCY MODULATION Modulation Index and Sidebands University of Southeastern Philippines COLLEGE OF ENGINEERING 16 Electronics Engineering Program FREQUENCY MODULATION Modulation Index and Sidebands The amplitudes depend upon the modulation index (mf) Theoretically, the FM process produces an infinite number of upper and lower sidebands therefore, Theoretically infinitely large bandwidth University of Southeastern Philippines COLLEGE OF ENGINEERING 17 Electronics Engineering Program FREQUENCY MODULATION Modulation Index and Sidebands Practically, sidebands with the largest amplitudes are significant in carrying the information Any sideband whose amplitude is less than 1 percent of the unmodulated carrier is considered insignificant University of Southeastern Philippines COLLEGE OF ENGINEERING 18 Electronics Engineering Program FREQUENCY MODULATION Modulation Index and Sidebands Modulation Index The ratio of the frequency deviation to the modulating frequency 𝐟𝐝 𝐦𝐟 = 𝐟𝐦 Where: fd = frequency deviation (sometimes denoted as δ) University of Southeastern Philippines COLLEGE OF ENGINEERING 19 Electronics Engineering Program FREQUENCY MODULATION Modulation Index and Sidebands Example: If the maximum frequency deviation of the carrier is ±12 kHz and the maximum modulating frequency is 2.5 kHz, the modulating index is ________. Answer: 4.8 University of Southeastern Philippines COLLEGE OF ENGINEERING 20 Electronics Engineering Program FREQUENCY MODULATION Modulation Index and Sidebands In most communication systems using FM, maximum limits are put on both the frequency deviation and the modulating frequency Maximum permitted frequency deviation: 75 kHz Maximum permitted modulating frequency: 15 kHz University of Southeastern Philippines COLLEGE OF ENGINEERING 21 Electronics Engineering Program FREQUENCY MODULATION Modulation Index and Sidebands When the maximum allowable frequency deviation and the maximum modulating frequency are used in computing the modulation index, mf is known as the deviation ratio University of Southeastern Philippines COLLEGE OF ENGINEERING 22 Electronics Engineering Program FREQUENCY MODULATION Modulation Index and Sidebands Example: The FM signal is given as v(t) = 12 cos [(6π106t)+5sin(2π1250t)] V a.) Determine the frequency of the carrier. b.) Determine the frequency of the modulating signal. Answer: a.) 3 MHz b.) 1.25 kHz University of Southeastern Philippines COLLEGE OF ENGINEERING 23 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions 𝐕𝐅𝐌 𝐭 = 𝐕𝐜 𝐜𝐨𝐬(𝟐𝛑𝐟𝐜 𝐭 + 𝐦𝐟 𝐬𝐢𝐧 𝟐𝛑𝐟𝐦 𝐭) Where: fc = carrier frequency fm = modulating frequency mf = modulating index University of Southeastern Philippines COLLEGE OF ENGINEERING 24 Electronics Engineering Program AMPLITUDE MODULATION AMPLITUDE MODULATION Instantaneous Voltage of the Complex Signal 𝐯𝟐 = 𝐯𝟏 𝐬𝐢𝐧(𝟐𝛑𝐟𝐜 𝐭) 𝐯𝟐 = (𝐕𝐜 + 𝐕𝐦 𝐬𝐢𝐧(𝟐𝛑𝐟𝐦 𝐭))𝐬𝐢𝐧(𝟐𝛑𝐟𝐜 𝐭) 𝐯𝟐 = 𝐕𝐜 𝐬𝐢𝐧(𝟐𝛑𝐟𝐜 𝐭) + 𝐕𝐦 𝐬𝐢𝐧(𝟐𝛑𝐟𝐦 𝐭)𝐬𝐢𝐧(𝟐𝛑𝐟𝐜 𝐭) Carrier Modulation x Carrier Expression consists of two parts: Carrier Carrier multiplied by the modulating signal waveform University of Southeastern Philippines COLLEGE OF ENGINEERING 25 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions Equation is solved with a complex mathematical process known as Bessel functions University of Southeastern Philippines COLLEGE OF ENGINEERING 26 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions The amplitudes of the sidebands are determined by the Jn coefficients University of Southeastern Philippines COLLEGE OF ENGINEERING 27 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions University of Southeastern Philippines COLLEGE OF ENGINEERING 28 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions University of Southeastern Philippines COLLEGE OF ENGINEERING 29 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions m=0 University of Southeastern Philippines COLLEGE OF ENGINEERING 30 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions m=1 University of Southeastern Philippines COLLEGE OF ENGINEERING 31 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions m=2 University of Southeastern Philippines COLLEGE OF ENGINEERING 32 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions m=0.25 University of Southeastern Philippines COLLEGE OF ENGINEERING 33 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions Example: State the amplitudes of the carrier and the first four sidebands of an FM signal with a modulation index of 4. University of Southeastern Philippines COLLEGE OF ENGINEERING 34 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions University of Southeastern Philippines COLLEGE OF ENGINEERING 35 Electronics Engineering Program FREQUENCY MODULATION Bessel Functions Example: State the amplitudes of the carrier and the first four sidebands of an FM signal with a modulation index of 4. Answer: J0 = -0.4 J1 = -0.07 J2 = 0.36 J3 = 0.43 J4 = 0.28 University of Southeastern Philippines COLLEGE OF ENGINEERING 36 Electronics Engineering Program  University of Southeastern Philippines COLLEGE OF ENGINEERING Electronics Engineering Program ECE 222 Principles of Communication Systems FREQUENCY MODULATION University of Southeastern Philippines COLLEGE OF ENGINEERING 1 Electronics Engineering Program FREQUENCY MODULATION FM Signal Bandwidth BW = 2fmN N = number of sidebands University of Southeastern Philippines COLLEGE OF ENGINEERING 2 Electronics Engineering Program FREQUENCY MODULATION FM Signal Bandwidth Carson’s Rule This rule recognizes only the power in the most significant sidebands with amplitudes greater than 2 percent of the carrier BW = 2 [fd(max) + fm(max)] Always give a bandwidth lower than that is normally calculated Proven to ensure full intelligibility of the signal University of Southeastern Philippines COLLEGE OF ENGINEERING 3 Electronics Engineering Program FREQUENCY MODULATION FM Signal Bandwidth Example: What is the maximum bandwidth of an FM signal with a deviation of 30 kHz and a maximum modulating signal of 5 kHz? What is the maximum bandwidth using Carson’s rule? Answer: 90 kHz, 70 kHz University of Southeastern Philippines COLLEGE OF ENGINEERING 4 Electronics Engineering Program FREQUENCY MODULATION FM Signal Bandwidth Narrowband FM Modulation → a single pair of significant sidebands FM signal occupies no more spectrum space than an AM signal BW = 2fm University of Southeastern Philippines COLLEGE OF ENGINEERING 5 Electronics Engineering Program FREQUENCY MODULATION FM Signal Bandwidth Narrowband FM Any FM system in which the modulation index is less than π/2 = 1.57 Used when m < 1 Only a single pair of sidebands Values of mf in the 0.2 to 0.25 range → true NBFM University of Southeastern Philippines COLLEGE OF ENGINEERING 6 Electronics Engineering Program FREQUENCY MODULATION FM Signal Bandwidth Narrowband FM The primary purpose of NBFM is to conserve spectrum space Conserves spectrum space at the expense of the signal-to-noise ratio University of Southeastern Philippines COLLEGE OF ENGINEERING 7 Electronics Engineering Program FREQUENCY MODULATION FM Signal Bandwidth Wideband FM m≥1 BW = 2(m+1)fm University of Southeastern Philippines COLLEGE OF ENGINEERING 8 Electronics Engineering Program FREQUENCY MODULATION FM Signal Bandwidth Wideband FM BW = 2fmN m≥1 BW = 2(m+1)fm Narrowband FM Carson’s Rule m < π/2; m < 1; m is in the 0.2 to 0.25 BW = 2 [fd(max) + fm(max)] BW = 2fm University of Southeastern Philippines COLLEGE OF ENGINEERING 9 Electronics Engineering Program FREQUENCY MODULATION Noise Suppression Effects of FM Noise add to a signal and interfere with it FM have a constant modulated carrier amplitude University of Southeastern Philippines COLLEGE OF ENGINEERING 10 Electronics Engineering Program FREQUENCY MODULATION Noise Suppression Effects of FM Spikes are clipped off at the receiver Does not affect the information content of the FM signal Solely within the frequency variations of the carrier University of Southeastern Philippines COLLEGE OF ENGINEERING 11 Electronics Engineering Program FREQUENCY MODULATION Noise and Phase Shift Noise amplitude added to an FM signal introduces a small frequency variation (or phase shift) Noise is usually a short duration pulse containing many frequencies University of Southeastern Philippines COLLEGE OF ENGINEERING 12 Electronics Engineering Program FREQUENCY MODULATION Noise and Phase Shift Maximum phase shift occurs when the noise and signal phasors are at a right angle University of Southeastern Philippines COLLEGE OF ENGINEERING 13 Electronics Engineering Program FREQUENCY MODULATION Noise and Phase Shift Maximum phase shift occurs when the noise and signal phasors are at a right angle −1 N ϕ = sin C S N We can use the input → N S University of Southeastern Philippines COLLEGE OF ENGINEERING 14 Electronics Engineering Program FREQUENCY MODULATION Noise and Phase Shift Determine just how much of a frequency shift a particular phase shift produces δ = ϕ(fm ) Where: δ = frequency deviation produced by noise ϕ = phase shift (radian) fm = frequency of modulating signal S Use δ to compute the output N University of Southeastern Philippines COLLEGE OF ENGINEERING 15 Electronics Engineering Program FREQUENCY MODULATION Noise and Phase Shift Example: The input to an FM receiver has an S/N of 2.8. The modulating frequency is 1.5 kHz. The maximum permitted deviation is 4 kHz. What are (a) the frequency deviation caused by the noise and (b) the improved output S/N? Answer: a) 547.8 Hz b) 7.3 University of Southeastern Philippines COLLEGE OF ENGINEERING 16 Electronics Engineering Program FREQUENCY MODULATION Preemphasis Noise can interfere with an FM signal, and particularly with the high-frequency components Noise – sharp spikes of energy (contains a lot of harmonics and other high-frequency components) Voice – 3 kHz bandwidth, permits acceptable intelligibility Music - many high-frequency harmonics that give them their unique sound University of Southeastern Philippines COLLEGE OF ENGINEERING 17 Electronics Engineering Program FREQUENCY MODULATION Preemphasis High frequency components (low in amplitude) Noise can obliterate them University of Southeastern Philippines COLLEGE OF ENGINEERING 18 Electronics Engineering Program FREQUENCY MODULATION Preemphasis Amplifies the high-frequency components more than the low-frequency components A simple high-pass filter University of Southeastern Philippines COLLEGE OF ENGINEERING 19 Electronics Engineering Program FREQUENCY MODULATION Preemphasis University of Southeastern Philippines COLLEGE OF ENGINEERING 20 Electronics Engineering Program FREQUENCY MODULATION Deemphasis University of Southeastern Philippines COLLEGE OF ENGINEERING 21 Electronics Engineering Program FREQUENCY MODULATION Deemphasis University of Southeastern Philippines COLLEGE OF ENGINEERING 22 Electronics Engineering Program FREQUENCY MODULATION Preemphasis and Deemphasis University of Southeastern Philippines COLLEGE OF ENGINEERING 23 Electronics Engineering Program FREQUENCY MODULATION Preemphasis 1 fL = 2πRC 𝜏 = RC = 75μs fL = 2123 Hz R1 + R 2 fH = 2πR1 R 2 C fH ≥ 30 kHz University of Southeastern Philippines COLLEGE OF ENGINEERING 24 Electronics Engineering Program FREQUENCY MODULATION Frequency Modulation Versus Amplitude Modulation Advantages of FM 1. Noise Immunity (clipper limiter circuits) 2. Capture Effect (takes place when two or more FM signals occur simultaneously on the same frequency) If one signal is more than twice the amplitude of the other, the stronger signal captures the channel, totally eliminating the weaker signal University of Southeastern Philippines COLLEGE OF ENGINEERING 25 Electronics Engineering Program FREQUENCY MODULATION Frequency Modulation Versus Amplitude Modulation Advantages of FM 2. Capture Effect Signal difference of only 1 dB AM – both signals occupying the same frequency is heard University of Southeastern Philippines COLLEGE OF ENGINEERING 26 Electronics Engineering Program FREQUENCY MODULATION Frequency Modulation Versus Amplitude Modulation Advantages of FM 2. Transmitter Efficiency FM signals have a constant amplitude, and it is therefore not necessary to use linear amplifiers University of Southeastern Philippines COLLEGE OF ENGINEERING 27 Electronics Engineering Program FREQUENCY MODULATION FM Applications University of Southeastern Philippines COLLEGE OF ENGINEERING 28 Electronics Engineering Program  University of Southeastern Philippines COLLEGE OF ENGINEERING Electronics Engineering Program ECE 222 Principles of Communication Systems FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS University of Southeastern Philippines COLLEGE OF ENGINEERING 1 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Two Types of FM Circuits: Direct – vary the carrier oscillator according to the modulating signal Indirect – uses phase shifter University of Southeastern Philippines COLLEGE OF ENGINEERING 2 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Frequency Modulator Vary the carrier frequency according to the modulating signal LC Oscillator Vary the inductance and capacitance → vary the frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 3 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Varactors A junction diode operated at reverse-bias mode University of Southeastern Philippines COLLEGE OF ENGINEERING 4 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Varactors University of Southeastern Philippines COLLEGE OF ENGINEERING 5 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Varactors At reverse bias, diode acts like a small capacitor P and N-type material act as the two conducting plates Depletion region acts as a thin layer of insulation University of Southeastern Philippines COLLEGE OF ENGINEERING 6 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Varactors The width of the dielectric determines the capacitance Varactors are designed to optimize this property Variations are made as wide and linear as possible ϵA C= d University of Southeastern Philippines COLLEGE OF ENGINEERING 7 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Varactors University of Southeastern Philippines COLLEGE OF ENGINEERING 8 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Varactor Modulators University of Southeastern Philippines COLLEGE OF ENGINEERING 9 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Varactor Modulators D1 and L1 forms the parallel-tuned circuit of the oscillator C1 is made very large → very low reactance Also blocks DC signal at the base of Q1 Capacitance of D1 is controlled in two ways: 1. Adjusting the DC Bias 2. Modulating Signal University of Southeastern Philippines COLLEGE OF ENGINEERING 10 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Varactor Modulators University of Southeastern Philippines COLLEGE OF ENGINEERING 11 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Varactor Modulators C5 is a blocking capacitor to keep DC signal from the modulating circuits RFC is high at carrier frequency to prevent carrier from going into the modulating circuits ↑ Modulating Signal ↑ Reverse Bias ↑ Carrier Frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 12 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Example: The value of capacitance of a varactor at the center of its linear range is 40 pF. This varactor will be in parallel with a fixed 20-pF capacitor. What value of inductance should be used to resonate this combination to 5.5 MHz in an oscillator? Answer: 14μH University of Southeastern Philippines COLLEGE OF ENGINEERING 13 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators LC oscillators are not stable enough Temperature changes → variation in frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 14 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Frequency-modulating a Crystal Oscillator It is possible to vary the capacitance in series or in parallel with the crystal Crystal frequency can be “pulled” slightly from its resonant frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 15 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators University of Southeastern Philippines COLLEGE OF ENGINEERING 16 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Very small frequency deviation (several hundred Hertz) Deviation can be increased by using frequency multipliers Frequency Multipliers – one whose output frequency is some integer multiple of the input frequency Doubler (×2) Tripler (×3) University of Southeastern Philippines COLLEGE OF ENGINEERING 17 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Voltage Controlled Oscillators VCOs / VXOs Uses silicon-germanium bipolar transistors to achieve operating frequencies near 10 GHz University of Southeastern Philippines COLLEGE OF ENGINEERING 18 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Voltage Controlled Oscillators University of Southeastern Philippines COLLEGE OF ENGINEERING 19 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators Voltage Controlled Oscillators University of Southeastern Philippines COLLEGE OF ENGINEERING 20 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators NE566 VCO University of Southeastern Philippines COLLEGE OF ENGINEERING 21 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS FM Modulators NE566 VCO Schmitt Trigger – a level detector which ensures that input is significant enough to cause a change in output (noise filtering) Output is filtered out University of Southeastern Philippines COLLEGE OF ENGINEERING 22 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Phase Modulators Most modern FM transmitters use PM to produce indirect FM Optimized for frequency stability and accuracy Phase shift is produced by RC or LC circuits University of Southeastern Philippines COLLEGE OF ENGINEERING 23 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Phase Modulators Phase shifters do not produce linear response Total allowable phase shift is restricted to maximize linearity Use multipliers to achieve desired deviations University of Southeastern Philippines COLLEGE OF ENGINEERING 24 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Phase Modulators R R φ= tan−1 XC Depending on the values of R and C, the output of the phase shifter can be set to any phase angle between 0 and 90° University of Southeastern Philippines COLLEGE OF ENGINEERING 25 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Phase Modulators University of Southeastern Philippines COLLEGE OF ENGINEERING 26 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Phase Modulators Signal becomes more positive Reverse bias Capacitance decreases Reactance increases Phase shift decreases There is an inverse relationship between the modulating signal and frequency deviation Use an inverting amplifier to correct condition University of Southeastern Philippines COLLEGE OF ENGINEERING 27 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Phase Modulators Example: A transmitter must operate at a frequency of 168.96 MHz with a deviation of ±5 kHz. It uses three frequency multipliers––a doubler, a tripler, and a quadrupler. Phase modulation is used. Calculate (a) the frequency of the carrier crystal oscillator and (b) the phase shift Δϕ required to produce the necessary deviation at a 2.8-kHz modulation frequency. Answers: 7.04 MHz, 8.53° University of Southeastern Philippines COLLEGE OF ENGINEERING 28 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Circuits that will convert frequency variation of carrier back to a proportional voltage variation Slope Detectors Makes use of a tuned circuit and a diode detector University of Southeastern Philippines COLLEGE OF ENGINEERING 29 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Slope Detectors The same configuration as a basic AM diode detector, but it is tuned differently C1 and L2 form a parallel resonant circuit University of Southeastern Philippines COLLEGE OF ENGINEERING 30 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Slope Detectors The same configuration as a basic AM diode detector, but it is tuned differently C1 and L2 form a parallel resonant circuit University of Southeastern Philippines COLLEGE OF ENGINEERING 31 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Slope Detectors University of Southeastern Philippines COLLEGE OF ENGINEERING 32 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Slope Detectors Set a carrier frequency centered on the leading edge of the response curve Linear only at a very narrow range Never used in practice University of Southeastern Philippines COLLEGE OF ENGINEERING 33 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Pulse-Averaging Discriminators FM is applied to a zero-crossing detector or clipper-limiter Generates a binary voltage level each time FM varies from plus to minus or minus to plus FM Square Wave University of Southeastern Philippines COLLEGE OF ENGINEERING 34 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Pulse-Averaging Discriminators Output is applied to a monostable (one-shot) multivibrator Fixed-width DC Pulses on the Leading Edge of the Cycle Fed to a simple low-pass RC filter University of Southeastern Philippines COLLEGE OF ENGINEERING 35 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Quadrature Detectors A phase shift circuit that produce a phase shift of 90° at the unmodulated carrier frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 36 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Quadrature Detectors FM signal is applied through a very small capacitor C1 to the parallel tuned circuit At resonance, parallel tuned circuit becomes resistive; C1 has a very high reactance University of Southeastern Philippines COLLEGE OF ENGINEERING 37 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Quadrature Detectors The output across the tuned circuit is very close to 90° (leading the input) The carrier frequency deviates above and below the resonant frequency → increasing or decreasing amount of phase shift University of Southeastern Philippines COLLEGE OF ENGINEERING 38 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Quadrature Detectors University of Southeastern Philippines COLLEGE OF ENGINEERING 39 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Quadrature Detectors University of Southeastern Philippines COLLEGE OF ENGINEERING 40 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Quadrature Detectors The output of phase detector is a series of pulses whose width varies with amount of phase shift. University of Southeastern Philippines COLLEGE OF ENGINEERING 41 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Phase-Locked Loops A phase-locked loop (PLL) is a frequency or phase sensitive feedback control circuit used in frequency demodulation. Three Basic Elements: 1. Phase detector to compare FM input to reference signal (output of VCO) 2. VCO frequency varied by the DC output voltage 3. Low-pass filter that smooths output the phase detector University of Southeastern Philippines COLLEGE OF ENGINEERING 42 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Phase-Locked Loops University of Southeastern Philippines COLLEGE OF ENGINEERING 43 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Phase-Locked Loops Compare the two input signals and generate an output signal that when filtered will control the VCO Phase detector output is in proportion to the difference (FM and VCO) The filtered output will adjust the VCO in an attempt to correct for the original frequency Error signal → recovered modulating signal University of Southeastern Philippines COLLEGE OF ENGINEERING 44 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Phase-Locked Loops When there is no input signal phase detector and low-pass filter output is zero VCO operates at free-running frequency When a difference exist at the inputs, the error voltage will force the VCO to move in the direction of the new input frequency (locked condition) University of Southeastern Philippines COLLEGE OF ENGINEERING 45 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Phase-Locked Loops The range by which the PLL can track the input frequency Lock Range The range of frequencies by which error signal forces the VCO to be equal with the input frequency Capture Range University of Southeastern Philippines COLLEGE OF ENGINEERING 46 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators Phase-Locked Loops The error signal is identical to the original modulating signal University of Southeastern Philippines COLLEGE OF ENGINEERING 47 Electronics Engineering Program FREQUENCY MODULATOR AND DEMODULATOR CIRCUITS Frequency Demodulators IC PLL 565 University of Southeastern Philippines COLLEGE OF ENGINEERING 48 Electronics Engineering Program  University of Southeastern Philippines COLLEGE OF ENGINEERING Electronics Engineering Program ECE 222 Principles of Communication Systems RADIO RECEIVERS University of Southeastern Philippines COLLEGE OF ENGINEERING 49 Electronics Engineering Program RADIO RECEIVERS RECEIVER The electronic unit that selects the desired signal transmitted and extracts the original information signal Tuning to accept the desired carrier signal Detecting intelligence from the radio frequency Providing adequate amplification University of Southeastern Philippines COLLEGE OF ENGINEERING 50 Electronics Engineering Program RADIO RECEIVERS RECEIVER CHARACTERISTICS Sensitivity A measure of a receiver’s ability to receive and amplify weak signal Selectivity A measure of the receiver’s ability to select one signal while rejecting all others at nearby frequencies Stability It is the ability of the receiver to be fixed or tuned to a desired frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 51 Electronics Engineering Program RADIO RECEIVERS TRF RECEIVER Tuned Radio Frequency Receiver A.R.D.A.S. University of Southeastern Philippines COLLEGE OF ENGINEERING 52 Electronics Engineering Program RADIO RECEIVERS SUPERHETERODYNE RECEIVER A type of radio receiver that uses a frequency conversion process called heterodyning to convert incoming radio signals to a fixed intermediate frequency (IF) before amplification and demodulation A.R.M.I.D.A.S. University of Southeastern Philippines COLLEGE OF ENGINEERING 53 Electronics Engineering Program RADIO RECEIVERS LOCAL OSCILLATOR RF INPUT IF OUTPUT LOCAL OSCILLATOR (LO) INPUT High-side Injection – tuning the local oscillator frequency above the RF signal by an amount equal to the intermediate frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 54 Electronics Engineering Program RADIO RECEIVERS LOCAL OSCILLATOR RF INPUT IF OUTPUT LOCAL OSCILLATOR (LO) INPUT Low-side Injection – tuning the local oscillator frequency below the RF signal by an amount equal to the intermediate frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 55 Electronics Engineering Program RADIO RECEIVERS RECEIVER’S INTERMEDIATE FREQUENCY = 455 kHz for AM receivers = 10.7 MHz for FM receivers University of Southeastern Philippines COLLEGE OF ENGINEERING 56 Electronics Engineering Program RADIO RECEIVERS IMAGE FREQUENCY Any frequency other than the selected radio frequency carrier that, if allowed to enter a receiver and mix with the local oscillator will produce a cross-product frequency that is equal to the intermediate frequency fimg = fsig ± 2fint University of Southeastern Philippines COLLEGE OF ENGINEERING 57 Electronics Engineering Program RADIO RECEIVERS IMAGE FREQUENCY REJECTION RATIO (IFRR) α= 1 + Q2 ρ2 fimg fsig ρ= − fsig fimg University of Southeastern Philippines COLLEGE OF ENGINEERING 58 Electronics Engineering Program RADIO RECEIVERS Example: An AM receiver is tuned to broadcast station at 600 kHz. Calculate the image rejection in dB, assuming that the input filter consists of one tuned circuit with a Q of 40. Answer: IFRRdB = 38.57 dB University of Southeastern Philippines COLLEGE OF ENGINEERING 59 Electronics Engineering Program  University of Southeastern Philippines COLLEGE OF ENGINEERING Electronics Engineering Program ECE 222 Principles of Communication Systems RADIO WAVE PROPAGATION University of Southeastern Philippines COLLEGE OF ENGINEERING 1 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Once radio signal is radiated by antenna, it propagates through space until received by receiving antenna Energy level decreases rapidly with distance Affected by obstacles: trees, buildings etc. Other factors: signal frequency, atmospheric conditions, time of the day University of Southeastern Philippines COLLEGE OF ENGINEERING 2 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Radio waves act very much as light waves Reflection Light waves are reflected by mirror Radio waves are reflected by conducting surfaces Ex. Metallic objects (especially if at least one-half wavelength) University of Southeastern Philippines COLLEGE OF ENGINEERING 3 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Reflection Angle of Incidence = Angle of Reflection No perfect conductors, reflection is never complete University of Southeastern Philippines COLLEGE OF ENGINEERING 4 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Reflection Reflection reverses wave polarity (180° phase shift) University of Southeastern Philippines COLLEGE OF ENGINEERING 5 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Refraction Bending of wave due to the physical make up of medium Wave slows down as it passes a medium (causes bending) Air of different densities, different degrees of ionization University of Southeastern Philippines COLLEGE OF ENGINEERING 6 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Refraction Degree of bending depends on the index of refraction (n) speed in vacuum n= speed in medium University of Southeastern Philippines COLLEGE OF ENGINEERING 7 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Refraction University of Southeastern Philippines COLLEGE OF ENGINEERING 8 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Refraction Snell’s Law n1 sin θ1 = n2 sin θ2 Where: n1 = index of refraction of initial medium n2 = index of refraction of medium into which wave passes θ1 = angle of incidence θ2 = angle of refraction University of Southeastern Philippines COLLEGE OF ENGINEERING 9 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Diffraction Bending of waves around an object Light and radio waves travel in straight lines; if signal is blocked, a shadow zone is created University of Southeastern Philippines COLLEGE OF ENGINEERING 10 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Diffraction University of Southeastern Philippines COLLEGE OF ENGINEERING 11 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Diffraction Some signal usually gets through diffraction Huygen’s principle: Waves travel as spherical wave fronts Each point can be considered as a point source for another spherical wave front Knife-edge diffraction University of Southeastern Philippines COLLEGE OF ENGINEERING 12 Electronics Engineering Program RADIO WAVE PROPAGATION Optical Characteristics of Radio Waves Diffraction University of Southeastern Philippines COLLEGE OF ENGINEERING 13 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Three Basic Paths: 1. Ground Wave 2. Sky Wave 3. Space Wave University of Southeastern Philippines COLLEGE OF ENGINEERING 14 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Ground Waves Waves remain close to the earth Follows the curvature of the earth Horizontally polarized waves are absorbed by the ground Strongest at low and medium frequency ranges AM broadcast signals University of Southeastern Philippines COLLEGE OF ENGINEERING 15 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Ground Waves University of Southeastern Philippines COLLEGE OF ENGINEERING 16 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Ground Waves Conductivity of the earth determines how well ground waves propagate Beyond 3 MHz, earth begins to attenuate signals University of Southeastern Philippines COLLEGE OF ENGINEERING 17 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Sky Waves Signals radiated into the upper atmosphere and bent back to earth Bending is caused by the refraction of waves in the ionosphere Ionized → atoms take on or lose electrons University of Southeastern Philippines COLLEGE OF ENGINEERING 18 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Sky Waves Layers of the Ionosphere University of Southeastern Philippines COLLEGE OF ENGINEERING 19 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Sky Waves D and E Layers Farthest from the sun Most weakly ionized Absorbs radio signals in the medium frequency range Exist only during the day University of Southeastern Philippines COLLEGE OF ENGINEERING 20 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Sky Waves F1 and F2 Layers Most highly ionized; greatest effect on signals Exist both in day and night Causes the refraction of radio signals (different levels of ionization cause the radio waves to be gradually bent) University of Southeastern Philippines COLLEGE OF ENGINEERING 21 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Sky Waves Angle is large; signals pass through the ionosphere At some critical angle; waves begin to be refracted back Appears that waves have been reflected University of Southeastern Philippines COLLEGE OF ENGINEERING 22 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Sky Waves University of Southeastern Philippines COLLEGE OF ENGINEERING 23 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Sky Waves At very high frequencies (above 50 MHz), signals pass through the ionosphere without bending Except during sun-spot activities or electromagnetic phenomena Reflected waves are sent back to earth at minimum loss Can be propagated over extremely long distances University of Southeastern Philippines COLLEGE OF ENGINEERING 24 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Sky Waves Multiple Skips or Multiple Hop Transmission Signal reflected back to earth is re-reflected back to the ionosphere 20 hops are possible (transmission around the world) University of Southeastern Philippines COLLEGE OF ENGINEERING 25 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Sky Waves University of Southeastern Philippines COLLEGE OF ENGINEERING 26 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Sky Waves Skip Distance – distance between transmitter and point of first reflection Skip Zone – portion where no signal is received University of Southeastern Philippines COLLEGE OF ENGINEERING 27 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Space Waves Also called direct waves Uses line-of-sight communication (does not follow earth curvature) The receiving antenna must be high enough to intercept signal Line-of-sight is used for most radio signals (VHF, UHF, and microwaves) University of Southeastern Philippines COLLEGE OF ENGINEERING 28 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Space Waves d= 2ht Where: ht = height of transmitting antenna, ft d = distance from transmitter to horizon d is called the radio horizon University of Southeastern Philippines COLLEGE OF ENGINEERING 29 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Space Waves University of Southeastern Philippines COLLEGE OF ENGINEERING 30 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Space Waves Practical Transmission Distance D= 2ht + 2hr University of Southeastern Philippines COLLEGE OF ENGINEERING 31 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Space Waves To extend communication distances; repeaters are used Repeater – a combination of receiver and transmitter Receiver receives signal, amplifies it, and retransmits on another frequency University of Southeastern Philippines COLLEGE OF ENGINEERING 32 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Space Waves University of Southeastern Philippines COLLEGE OF ENGINEERING 33 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Space Waves Increases communication range for mobile units University of Southeastern Philippines COLLEGE OF ENGINEERING 34 Electronics Engineering Program RADIO WAVE PROPAGATION Radio Wave Propagation Through Space Space Waves Communication Satellite Ultimate communication receiver Located at a geostationary orbit; rotates exactly 24 h around the earth They act as fixed repeater stations (transponders) University of Southeastern Philippines COLLEGE OF ENGINEERING 35 Electronics Engineering Program RADIO WAVE PROPAGATION Calculating Received Power A transmitted power is radiated at a specific power level (Accurately determined by computation or measurement) Power level is increased due to antenna gain Begins to be attenuated when it leaves the antenna University of Southeastern Philippines COLLEGE OF ENGINEERING 36 Electronics Engineering Program RADIO WAVE PROPAGATION Calculating Received Power Power Density (Isotropic Radiator) Pt Pd = 4πd2 Where: Pd = power density of signal, W/m2 d = distance from point source, m Pt = total transmitted power, W Dipole (Has a gain of 1.64) University of Southeastern Philippines COLLEGE OF ENGINEERING 37 Electronics Engineering Program RADIO WAVE PROPAGATION Calculating Received Power Actual Received Power Pt G1 G2 λ2 Pr = (4πd)2 Where: λ = signal wavelength, m d = distance from transmitter, m Pr , Pt = received and transmitted power Gr , Gt = receiver and antenna gains (referenced to an isotropic source) University of Southeastern Philippines COLLEGE OF ENGINEERING 38 Electronics Engineering Program RADIO WAVE PROPAGATION Calculating Received Power Path Attenuation dB loss = 37 dB + 20log(f) + 20 log(d) Where: f = frequency of operation, MHz d = distance travelled, mi If in km, 37 dB → 32.4 dB University of Southeastern Philippines COLLEGE OF ENGINEERING 39 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Fading Variation in signal amplitude caused by the signal path Four Factors: 1. Variation in distance between transmitter and receiver 2. Environmental characteristics of signal path 3. Multiple signal paths 4. Relative motion between transmitter and receiver University of Southeastern Philippines COLLEGE OF ENGINEERING 40 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Fading Fading is also caused by objects between transmitter and receiver → shadow fading University of Southeastern Philippines COLLEGE OF ENGINEERING 41 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Multipath One of the worst sources of fading Sometimes called Rayleigh fading Transmitted signal takes multiple paths University of Southeastern Philippines COLLEGE OF ENGINEERING 42 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Multipath Signal is usually radiated by a non-directional antenna Some will travel on direct line-of-sight Others will take different paths and strike obstacles Reflected signals take longer paths Causes time delay → phase shift Reflections causes 180° phase shift University of Southeastern Philippines COLLEGE OF ENGINEERING 43 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Doppler Shift Caused by the movement of either the transmitter and receiver Movement causes transmit- ter or receiver to get closer → frequency increases University of Southeastern Philippines COLLEGE OF ENGINEERING 44 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems To overcome fading, most communication have a built-in fading margin Fade Margin Describe the amount by which the received signal strength exceeds the minimum level required for reliable communication Included in system gain equations that considers the nonideal and less predictable characteristics of radio wave propagation University of Southeastern Philippines COLLEGE OF ENGINEERING 45 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Fade Margin Fm = 30 log (D) + 10 log (6ABf) – 10 log (1 – R) – 70 Fm = fade margin (dB) D = distance (kilometers) f = frequency (gigahertz) R = reliability expressed as a decimal (i.e., 99.99% = 0.9999 reliability) 1 – R = reliability objective for a one-way 400-km route A = roughness factor = 4 over water or a very smooth terrain = 1 over an average terrain = 0.25 over a very rough, mountainous terrain University of Southeastern Philippines COLLEGE OF ENGINEERING 46 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Fade Margin Fm = 30 log (D) + 10 log (6ABf) – 10 log (1 – R) – 70 B factor to convert a worst-month probability to an annual probability = 1 to convert an annual availability to a worst-month basis = 0.5 for hot humid areas = 0.25 for average inland areas = 0.125 for very dry or mountainous areas University of Southeastern Philippines COLLEGE OF ENGINEERING 47 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Example: Consider a space-diversity microwave radio system operating at an RF carrier frequency of 1.8 GHz. Each station has a 2.4-m-diameter parabolic antenna that is fed by 100 m of air-filled coaxial cable. The terrain is smooth, and the area has a humid climate. The distance between stations is 40 km. A reliability objective of 99.99% is desired. Determine the fade margin. Answer: 31.4 dB University of Southeastern Philippines COLLEGE OF ENGINEERING 48 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Diversity System Minimizes fading by using multiple transmitters and receivers 1. Frequency Diversity 2. Spatial Diversity University of Southeastern Philippines COLLEGE OF ENGINEERING 49 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Diversity System Frequency Diversity – uses two separate sets of transmitters and receivers operating at different frequencies University of Southeastern Philippines COLLEGE OF ENGINEERING 50 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Diversity System Combiner Network Signals from antennas are linearly mixed resulting to a larger signal University of Southeastern Philippines COLLEGE OF ENGINEERING 51 Electronics Engineering Program RADIO WAVE PROPAGATION Common Propagation Problems Diversity System Selective / Switched System Outputs are monitored Switched to signal with greatest strength University of Southeastern Philippines COLLEGE OF ENGINEERING 52 Electronics Engineering Program  University of Southeastern Philippines COLLEGE OF ENGINEERING Electronics Engineering Program ECE 222 Principles of Communication Systems INTRODUCTION TO DIGITAL COMMUNICATIONS University of Southeastern Philippines COLLEGE OF ENGINEERING 1 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Types of Modulation Pulse Modulation A modulation technique where an analog signal is converted into a series of pulses. University of Southeastern Philippines COLLEGE OF ENGINEERING 2 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Types of Modulation PAM (Pulse Amplitude Modulation) Pulse amplitude represents the signal's amplitude at specific time intervals. University of Southeastern Philippines COLLEGE OF ENGINEERING 3 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Types of Modulation PPM (Pulse Position Modulation) Pulse position represents the signal’s value at a specific time. University of Southeastern Philippines COLLEGE OF ENGINEERING 4 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Types of Modulation PWM (Pulse Width Modulation) Pulse width represents the signal's value. University of Southeastern Philippines COLLEGE OF ENGINEERING 5 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Types of Modulation PCM (Pulse Code Modulation) Converts an analog signal into a digital form by sampling and quantizing the signal. University of Southeastern Philippines COLLEGE OF ENGINEERING 6 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing A technique that allows multiple signals to be transmitted simultaneously over a single communication channel. Efficient use of bandwidth and cost savings. University of Southeastern Philippines COLLEGE OF ENGINEERING 7 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing University of Southeastern Philippines COLLEGE OF ENGINEERING 8 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing Types: Frequency-Division Multiplexing (FDM) Time-Division Multiplexing (TDM) University of Southeastern Philippines COLLEGE OF ENGINEERING 9 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing Types: Frequency-Division Multiplexing (FDM) Signals are assigned different frequency bands within a common bandwidth. Example: FM Radio, Telemetry. University of Southeastern Philippines COLLEGE OF ENGINEERING 10 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing Types: Frequency-Division Multiplexing (FDM) University of Southeastern Philippines COLLEGE OF ENGINEERING 11 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing Types: Frequency-Division Multiplexing (FDM) University of Southeastern Philippines COLLEGE OF ENGINEERING 12 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing Types: Frequency-Division Multiplexing (FDM) University of Southeastern Philippines COLLEGE OF ENGINEERING 13 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing Types: Time-Division Multiplexing (TDM) Signals are transmitted in turn, each occupying the entire bandwidth for a short period of time. Example: Telephone systems, digital communications. University of Southeastern Philippines COLLEGE OF ENGINEERING 14 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing Types: Time-Division Multiplexing (TDM) University of Southeastern Philippines COLLEGE OF ENGINEERING 15 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing Types: Time-Division Multiplexing (TDM) University of Southeastern Philippines COLLEGE OF ENGINEERING 16 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing Types: Time-Division Multiplexing (TDM) Electronic Multiplexer University of Southeastern Philippines COLLEGE OF ENGINEERING 17 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Multiplexing Types: Time-Division Multiplexing (TDM) Electronic Multiplexer University of Southeastern Philippines COLLEGE OF ENGINEERING 18 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: FDMA (Frequency Division Multiple Access) TDMA (Time Division Multiple Access) CDMA (Code Division Multiple Access) University of Southeastern Philippines COLLEGE OF ENGINEERING 19 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: FDMA (Frequency Division Multiple Access) Multiple users share frequency bands. FDMA allocates a specific frequency and bandwidth for each channel. Each subscriber is assigned a unique pair of voice channels for the duration of a call, ensuring simultaneous transmissions from multiple users without interference University of Southeastern Philippines COLLEGE OF ENGINEERING 20 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: TDMA (Time Division Multiple Access) Multiple users share time slots. University of Southeastern Philippines COLLEGE OF ENGINEERING 21 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: CDMA (Code Division Multiple Access) Multiple signals are spread across the same bandwidth using unique codes. In CDMA, each user is assigned a unique code (called a spreading code or pseudo- random noise (PN) code). This code is used to modulate the signal, spreading it across a wider bandwidth than the original signal. University of Southeastern Philippines COLLEGE OF ENGINEERING 22 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: CDMA (Code Division Multiple Access) University of Southeastern Philippines COLLEGE OF ENGINEERING 23 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: Pulse Modulation in Multiplexing PAM in TDM: Sampling multiple analog signals (PAM) at high speeds and transmitting them in time slots. University of Southeastern Philippines COLLEGE OF ENGINEERING 24 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: Pulse Modulation in Multiplexing PAM in TDM: (4 Signals) University of Southeastern Philippines COLLEGE OF ENGINEERING 25 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: Pulse Modulation in Multiplexing PCM in Multiplexing: PCM converts analog signals into digital form, allowing more efficient and accurate multiplexing of data. University of Southeastern Philippines COLLEGE OF ENGINEERING 26 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: Pulse Modulation in Multiplexing PCM in Multiplexing: Example: T1 Lines: PCM used in telecommunications for transmitting multiple voice channels (24 voice channels over a 1.544 Mbps line) University of Southeastern Philippines COLLEGE OF ENGINEERING 27 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: Plain Old Telephone Service University of Southeastern Philippines COLLEGE OF ENGINEERING 28 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: Pulse Modulation in Multiplexing T1 Lines: University of Southeastern Philippines COLLEGE OF ENGINEERING 29 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Other Variations: Pulse Modulation in Multiplexing T1 Lines: University of Southeastern Philippines COLLEGE OF ENGINEERING 30 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Broadband Communication Definition: Communication systems that provide high-speed data transfer across wide bandwidths. Technologies: 1. Fiber Optics: Transmits data as light pulses, offering high bandwidth and low loss. 2. DSL (Digital Subscriber Line): High- speed internet over telephone lines. University of Southeastern Philippines COLLEGE OF ENGINEERING 31 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Broadband Communication Definition: Communication systems that provide high-speed data transfer across wide bandwidths. Technologies: 3. Cable Modems: High-speed internet over coaxial cable. 4. Wireless Broadband: Internet via wireless technology (e.g., Wi-Fi, LTE). University of Southeastern Philippines COLLEGE OF ENGINEERING 32 Electronics Engineering Program INTRODUCTION TO DIGITAL COMMUNICATIONS Broadband Communication Applications: Internet Access: High-speed internet connections. Video Streaming: Real-time video content delivery (e.g., Netflix, YouTube). VoIP (Voice over IP): Internet-based voice communication (e.g., Skype, Zoom). University of Southeastern Philippines COLLEGE OF ENGINEERING 33 Electronics Engineering Program