Topic 1 Communications 1 Modulation, Slides of Communications Engineering

Download Topic 1 Communications 1 Modulation and more Slides Communications Engineering in PDF only on Docsity! Principles of Communications AMPLITUDE MODULATION BSECE 2nd year Engr. Christopher V. Maglaque, MEM Assistant Professor IV Amplitude Modulation Modulation It is the process of impressing or imparting a low frequency source information (voice, audio, video, or data) onto a high- frequency bandpass signal with a carrier frequency fc by the introduction of amplitude, frequency or phase perturbation. Demodulation It is the reverse process where the received signals are transformed back to their original form. Amplitude Modulation It is an analog modulation scheme in which the amplitude of a relatively high-frequency carrier signal is varied in accordance with the instantaneous amplitude of an information signal. Amplitude Modulation AM Waveform - Instantaneous Amplitude of the Modulated Wave Instantaneous Amplitude of the Modulated Wave The modulating signal is more often an arbitrary waveform, such as audio signal. However, an analysis of sine wave modulation is very useful, since Fourier analysis often allows complex signals to be express as a series of sinusoids. Hence, Amplitude Modulation AM Waveform - Instantaneous Amplitude of the Modulated Wave By applying little trigonometry, Amplitude Modulation AM Waveform - Instantaneous Amplitude of the Modulated Wave Amplitude Modulation AM Waveform -Coefficient of Modulation (m) Sample Problems: 1. An AM signal has the following characteristics: carrier frequency = 150 MHz; modulating frequency = 3 MHz; peak carrier voltage = 40 volts; and peak modulating voltage is 30 volts. Calculate the peak voltage of the lower sideband frequency. Amplitude Modulation AM Waveform -Coefficient of Modulation (m) 2. Calculate the modulation index for a standard AM transmission, if the maximum peak voltage of the modulated wave is 150 V and the modulating signal voltage is 50 V peak. Amplitude Modulation AM Waveform -Coefficient of Modulation (m) Several Cases of m: a. Undermodulation (m<1, Vm<Vc) b. 100% Modulation (m=1, Vm=Vc) c. Overmodulation (m>1, Vm>Vc) Amplitude Modulation B. SIMULTANEOUS MODULATION where: mT= total modulation index m1,m2……mn = modulation indices due to several modulating signal Amplitude Modulation B. SIMULTANEOUS MODULATION Sample Problems: 1. An AM transmitter is modulated by two sine waves at 1.5 kHz and 2.5 kHz, with modulation of 20 percent and 80 percent respectively. Calculate the effective modulation index. Amplitude Modulation B. SIMULTANEOUS MODULATION 2. Calculate the modulating voltage of an audio signal necessary to provide 100% modulation of a 100-V carrier that is simultaneously modulated by 2 audio waves with m1 and m2 equal to 75% and 45% respectively. Amplitude Modulation D. CONVENTIONAL AM SYSTEM (DSBFC) CONVENTIONAL AM SYSTEM (DSBFC) Amplitude Modulation D. CONVENTIONAL AM SYSTEM (DSBFC) Sample Problems: 1. What will be the total sideband power of an AM transmitting station whose carrier power is 1200 W and a modulation of 95%? Amplitude Modulation D. CONVENTIONAL AM SYSTEM (DSBFC) 2. Calculate the power in one sideband of an AM signal whose carrier power is 50 watts. The unmodulated current is 2 A while the modulated current is 2.4 A. Amplitude Modulation E. SUPPRESSED-CARRIER AM SYSTEM. Sample Problem: 1. A DSB-SC system must suppress the carrier by 50 dB from its original value of 10 W. To what value must the carrier be reduced? Amplitude Modulation E. SUPPRESSED-CARRIER AM SYSTEM. E. SUPPRESSED-CARRIER AM SYSTEM 2. Single-Sideband Full-Carrier (SSB-FC) Amplitude Modulation E. SUPPRESSED-CARRIER AM SYSTEM. Sample Problem: Assuming 100% modulation H3E system, what would be the transmitted power in the remaining sideband of an AM signal if the carrier power is 1000 watts? Amplitude Modulation F. PERCENTAGE POWER SAVING F. PERCENTAGE POWER SAVING Amplitude Modulation F. PERCENTAGE POWER SAVING Sample Problems: 1. Determine the power saving in percent when the carrier is suppressed in an AM signal modulated to 80%. Amplitude Modulation F. PERCENTAGE POWER SAVING 2. Calculate the percentage power saving for J3E system at 90% modulation.