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Published byIra Charles Modified over 9 years ago
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Chapter 1 : Part 3 Noise
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Noise, interference and distortion Noise unwanted signals that coincide with the desired signals. Two type of noise: internal and external noise. Internal noise Caused by internal devices/components in the circuits. External noise noise that is generated outside the circuit. E.g. atmospheric noise, solar noise, cosmic noise, man made noise. EKT343 –Principle of Communication Engineering 2
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Noise, interference and distortion (Cont’d) Interference Contamination by extraneous signals from human sources. E.g. from other transmitters, power lines and machineries. Occurs most often in radio systems whose receiving antennas usually intercept several signals at the same time One type of noise. Distortion Signals or waves perturbation caused by imperfect response of the system to the desired signal itself. May be corrected or reduced with the help of equalizers. EKT343 –Principle of Communication Engineering 3
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Noise Temperature & Equivalent noise Temperature Thermal noise directly proportional to temperature ~ can be expressed in degrees, watts or volts. EKT343 –Principle of Communication Engineering 4 Where P n @ N = noise power ( Watt ) k = Boltzman constant (1.38 x 10 -23 J / K ) T = environmental temperature ( K ) [Add 273 to C] B = Bandwidth of system ( Hz ) P n = k T B
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Cont’d… Equivalent noise temperature, (T e ) T e = T(F-1) Where T = environmental temperature (kelvin) F = Noise factor T e often used in low noise, sophisticated radio receivers rather than noise figure. EKT343 –Principle of Communication Engineering 5
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Example 1 A domestic television receives antenna delivers a sky noise power of -105 dBm to a matched coaxial feeder in a radio frequency bandwidth of 8 MHz. Find the antenna noise temperature. EKT343 –Principle of Communication Engineering 6
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Insertion loss IL is a parameter associated with the frequencies that fall within the passband of a filter. The ratio of the power transferred to a load with a filter in the circuit to the power transferred to a load without the filter. IL (dB) = 10 log (P out /P in ) EKT343 –Principle of Communication Engineering 7
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Signal to Noise Ratio EKT343 –Principle of Communication Engineering 8 SNR is ratio of signal power, S to noise power, N. Noise Factor, F Noise Figure, NF
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For a nonideal amplifier with the following parameters: Table 1 Determine the following: 1)Input Signal-to-Noise ratio (dB). 2)Output Signal-to-Noise ratio (dB). 3)Noise factor and noise figure. 4)Equivalent noise temperature. Exercise EKT343 –Principle of Communication Engineering 9
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