2. a) Consider a single tone message with frequency fm (double-sideband) modulated carrier of frequency fe A = 2, i.e. g(t) = 2 cos(2nfet) cos(2nfmt). b) = 90 Hz and an AM-DSB 100 MHz and amplitude i) Find the total signal power. See the formula sheet for a decomposition of the product of two cosines. ii) The communication channel allows this signal to pass through as it is, but adds noise onto it. If the noise power Pn 0.5, what is the signal-to-noise = ratio of the received signal? TIMOL -10 kHz 0 10 kHz Figure Q2b. The amplitude spectrum |M(f) of the message signal. A message signal has the above amplitude spectrum. i) What is the message bandwidth? ii) What is the minimum channel bandwidth required for an AM double side- band (DSB) modulated carrier for this message signal? c) List the essential elements of any communication system and describe their functionality.

The baseband signal modulates a 98 kHz carrier sine wave. Using frequency and amplitude labelling similar to that in Figure 2, sketch the spectrum of the modulated signal using a template, similar to that in Figure 3, for the following modulations: AM with the amplitude of the carrier wave being 20 V   DSBSC   SSB – the lower sideband   SSB – the upper sideband

Q2: A modulating signal is used to modulate a carrier signal(AM modulation). Let Pr , Pc, Psa. PusB, PLSB and u are the total power, carrier power, side band power, upper side band power, lower side band power and modulation index respectively. Prove the following: a. Pc = Pr () c. Pusp = Pasa =) P, 2+m2. b. PsB = Pr %3D 2+m2 2 (2+m2

A carrier signal is amplitude modulated by a sinewave. The resulting AM waveform is shown below. 3.5V- 1V- a) What is the amplitude of the carrier signal? b) c) To achieve 75 percent modulation, what amplitude of the modulating signal is needed? d) Calculate the effective voltage of the AM signal What is the modulation index?

1. The Voltage spectrum of FM signal is shown in Figure 1. The maximum amplitude of modulating signal is 5V. Calculate the bandwidth , modulation index ,Carrier frequency, modulating frequency and specify the type of Modulator(narrow band or wide band). 1.54 4.06 4.06 2.45 2.45 0.91 0.91 0.21 0.21 192 194 196 198 200 202 204 206 208 KHz

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Question 2 (a) Briefly explain the advantage of the following Amplitude Modulation (AM) type and state ONE (1) application for each AM type: i. Double Sideband Full Carrier (DSBFC) ii. Double Sideband Suppressed Carrier (DSBSC) iii. Single Sideband (SSB). (b) The AM waveform for the modulated signal is illustrated in Figure 1. i. Calculate the percentage of modulation index, m. ii. State the type of the modulated signal. Justify the answer. iii. Write the equation for the modulated signal. iv. Calculate the percentage of power efficiency. 3V -1IV Figure 1

An FM signal has a maximum frequency deviation of 1500h and a modulating frequency of 500h, its total power is 6500w, applied to a resistive load of 1ohm, the carrier frequency is 400Mhz. Determine the voltage of the modulated signal and the modulation voltage.

An AM transmitter at 27 MHz develops 10W of carrier power into a 50-ohm load. It is modulated by 2-kHz sine wave between 20% and 90% modulation. Determine maximum and minimum waveform  voltage of the AM signal at 20%. Ans: Vmax=37.94V and Vmin=25.3V

2-Most of the power in an AM signal is in the a. Carrier b. Upper sideband c. Lower sideband d. Modulating signal