# E sketch the signal in the time domain showing

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(e) Sketch the signal in the time domain, showing voltage and time scales.
30) An audio system requires a frequency response from 50Hz to 15kHz for high fidelity. If this signal were transmitted using AM, what bandwidth would it require?
33) An AM signal has the following characteristics: fc = 150 MHz fm = 3 kHz Ec = 50V Em = 40V For this signal, find: (a) The modulation index (m) = Em / Ec (m) = 40 / 50
(b) The bandwidth B = 2 fm B = 2 (3kHz)
(c) the peak voltage of the upper side frequency
48) An AM CB transmitter with a carrier frequency of 27.005 MHz is connected as shown in figure 3.22(a). The oscillo-scope display is shown in figure 3.22(b). Sketch the same signal as it would appear on the spectrum analyzer.
F(lsb) = fc – fm =27.005 MHz – 2.5 kHz =27.0025 MHz Peak Voltage: Vpk = 20V + 10V / 2 Vpk = 15V Vrms = Vpk / √2 Vrms = 15 / √2 Vrms = 10.6V Carrier Power: Pc = Vrms^2 / RL Pc = 10.6^2 / 50 Pc = 2.25 W Pc (dBm) = 10log(2.25 x 10^3) Pc = 33.5 dBm Pc = 33.5 dBm – 40 dBm Pc = -6.5 dBm Modulation Index: (m) = E-max – E-min / E-max + E-min (m) = 40 – 20 / 40 + 20 (m) = .33 P(usb) = (m^2/4) Pc P(usb) = (.33^2 / 4) 2.25 P(usb) = 62.4mW P(usb) = 10log(62.4) P(usb) = 18 dBm P(usb) = 18 dBm – 40 dB P(usb = -22 dBm
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