hwset4solution - ECE 453 Homework Assignment 4 Solution...

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ECE 453: Homework Assignment 4 Solution 2-14 Solution a. Down-conversion with high-side LO: f LO = f c + f IF = (1930 to 1975) + 70 = 2000 to 2045 MHz. low-side LO: f LO = f c f IF = (1930 to 1975) 70 = 1860 to 1905 MHz. b. high-side LO: f IM = f c + 2 f IF = 1940 + 140 = 2080 MHz. low-side LO: f IM = f c 2 f IF = 1940 140 = 1800 MHz. c. An unwanted signal at frequency f i can cause interference when the second harmonic of the signal ( 2 f i ) mixes with the second harmonic of the LO ( 2 f LO ) to give an output at the IF. One of the interference frequencies that results from this mechanism will be separated from the desired carrier frequency by 1/2 of the IF, hence the name “1/2-IF”. The other interference frequency will be farther from the carrier frequency, and hence easier to remove with the pre-selector filter. d. | 2 f LO 2 f i | = f IF 2 f LO 2 f i = ± f IF f i = f LO f IF / 2 . Since the receiver uses high LO, the desired carrier frequency is f c = f LO f IF , so the frequencies of the interferers become f i = ( f c + f IF ) f IF / 2 = f c + 3 / 2 f IF or f c +1 / 2 f IF . The 1/2-IF interference frequency refers to the interference frequency
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