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# lecture_3 - LECTURE#3 NOISE IN COMMUNICATIONS NOISE IN...

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LECTURE #3 NOISE IN COMMUNICATIONS NOISE IN COMMUNICATIONS PART I 1. Read the handout named Noise in Communication Part I in the Modulation Handouts folder. NOISE IN COMMUNICATIONS PART II NOISE EQUATIONS 1. P N = kTB P N = noise power in Watts K = Boltzmann’s Constant, 1.38 × 10-23 Joules/Kelvin (J/K) T = absolute temperature in Kelvin (K) B = noise power bandwidth in Hertz (Hz) T˚ (K) = 273 + T˚(C) For maximum power transfer the same power is across both resistors. V N = Noise Voltage

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R N = resistance generating the noise R L = load (the amplifier or other device that receives the noise) 2. 4kTBR V N = Example 1 A 300 Ω resistor is connected across the 300 Ω antenna input of a television receiver. The bandwidth of the receiver is 6 MHz, and the resistor is at room temperature (293 K or 20˚C or 68˚F). Find the noise power and noise voltage applied to the receiver input. PN = kTB = (1.38 × 10-23 J/K)(293 K) (6 × 10 6 Hz) = 24.2 × 10 -15 W = 24.2 fW 4kTBR V N = = ) 300 ( ) Hz 10 (6 K) (293 J/K) 10 4(1.38 6 -23 × × × × × = 5.4 × 10 -6 V = 5.4 μV Of course, only one-half this voltage appears across the antenna terminals; the other half appears across the source resistance. Therefore the actual noise voltage at the input is 2.7 μV. 3. B 2qI I 0 N = R V I N N = I N = RMS noise current in amperes (A) q = magnitude of the charge on an electron, equal to 1.6 × 10 -19 C I 0 = dc bias current in the device in amperes (A) B = bandwidth over which the noise is observed in Hertz (Hz)
Example 2 A diode noise generator is required to produce 10 μV of noise in a receiver with an input impedance of 75 Ω, resistive, and a noise power bandwidth of 200 kHz. (These values are

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lecture_3 - LECTURE#3 NOISE IN COMMUNICATIONS NOISE IN...

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