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Unformatted text preview: ECE 146A: Communications I Lab 5: Angle Modulation and Demodulation Hardware Lab Report Due: Thursday March 10 (by 5 pm in course homework box) 1 Objective The goal of this lab is to investigate the properties and characteristics of a frequency modulated (FM) signal and its spectrum. You will implement the FM modulator and demodulator using the MC14046 phase-locked loop (PLL) integrated circuit (IC). 2 Laboratory Room Engineering I, Room 5160. Note that you will work in groups of two students, but each student must submit a separate lab report. Due to the time crunch towards the end of the quarter, your report will be relatively brief compared to those of previous labs. 3 Equipment Along with an oscilloscope, a digital multimeter (DMM), a function generator, and a power supply, you will need the following equipment: 1. MC14046 PLL. 2. Various resistors, capacitors, and diodes. 3. Breadboard. 4. Cables: BNC to IC clips (3 each), banana cable for DC power supply (3 each), DMM test leads (1 each). 5. Needle nose pliers and wire cutters. 6. Wire. 7. Card key for room 5160. Most of these items can be purchased as a lab kit from the Electronics Shop on the first floor of Engineering I. 1 PHASE COMPARATOR LOWPASS FILTER VCO V (t) e V (t) c INPUT SIGNAL ERROR SIGNAL V (t) o Figure 1: Block diagram of the PLL components. V high F V low F( ) V low V high F( ) V c V c Figure 2: Voltage/frequency characteristic of a VCO. 4 Background 4.1 Phase-Locked Loop A phase-locked loop (PLL) is basically an electronic feedback system that provides frequency selec- tive tuning and filtering without the need for coils or inductors. It consists of three basic functional blocks: Phase comparator. Lowpass filter. Voltage-controlled oscillator. Figure 1 shows a block diagram of a PLL. Observe that the phase comparator output signal is computed as the phase difference between the input signal V c ( t ) and the output of the voltage- controlled oscillator (VCO) V o ( t ). This signal is then filtered by a lowpass filter (LPF) to produce the error signal V e ( t ), which is needed by the VCO to generate the output frequency. As the error), which is needed by the VCO to generate the output frequency....
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