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Question 1. (25 points) In Figure 1, a block diagram is shown of a super-heterodyne receiver for the reception of VHF signals in the frequency band 156.0- 162.5 MHz for Maritime use. The intermediate frequency (IF) is chosen to be 10.7 MHz, and the frequency of the local oscillator is set higher than the frequency to which the receiver is tuned. Mixer IF Amplifier Detector Audio Amplifier K Oscillator Figure 1: Block diagram of a super heterodyne receiver. a) Calculate the frequency range over which the local oscillator of this receiver must be tunable. b) Explain in your own words the following: 1. What is an image frequency? 2. What is the mechanism that causes the presence of image frequencies? It turns out that the local oscillator signal is distorted and apart from the desired frequency component it also contains a 2nd harmonic component of this signal. c) Calculate for this situations the image frequencies when the receiver is tuned to the frequency f = 158.3 MHz? d) Derive a new intermediate frequency in order to make sure that the minimum distance between the tuning range of the receiver (156.0- 162.5 MHz) and the range of image frequencies is 35 MHz? Assume here a local oscillator without distortion. e) A USSB modulated signal is present at the input of the receiver. Motivate for each of the following four detectors = {USSB, LSSB, envelope detector, product detector} whether it can be used at the IF to retrieve the information signal. Also indicate which detector will perform best.