Lesson_34 - Lesson 34 Lesson 34 Challenge 33 Lesson 34 –...

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Unformatted text preview: Lesson 34 Lesson 34 Challenge 33 Lesson 34 – Discrete Fourier Transform (DFT) No Challenge Problem Practice Quiz #3 next meeting Lesson 34 Challenge 34 An AN-DSB superheterodyne receiver is shown in the figure and consists of an antenna, RF amplifier, mixer, local oscillator (LO) producing a variable frequency signal x(t)=cos( ϖ t), an intermediate frequency (F) amplifier having a fixed center-frequency of 455kHz and bandwidth of 10kHz. and finally an envelop detector. What must be the tuning range of the local oscillator in order to operate properly? ⊗ x(t) y(t) Local Oscillator (LO) RF Amp IF Amp Det. Envelope Detector z(t) Output Lesson 34 Lesson 33 Table 1: Commercial Radio Item AM FM Carrier frequency 540-1600 kHz 88.1-107.9 MHz Transmission Bandwidth 10kHz 200kHz Audio bandwidths 3-5kHz 15kHz Using the difference frequencies, the LO range must be: 2 πϖ c ={540-455 = 85 kHz to 1600-455=1145 kHz} Using the sum frequencies, the LO range must be: 2 πϖ c ={540+455 = 995 kHz to 1600+455=2055 kHz} Lesson 34 Lesson 34 Continuous-time Fourier transform (CTFT) ∫ ∞ ∞-- = dt e t x X t j ϖ ϖ ) ( ) (j ∫ ∞ ∞- = ϖ ϖ π ϖ d e X t x t j ) (j 2 1 ) ( Lesson 34 Lesson 34 Continuous-time Fourier series (CTFS) ∫- = T t...
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Lesson_34 - Lesson 34 Lesson 34 Challenge 33 Lesson 34 –...

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