Q $1$

What is meaning of detection? draw the envelope detection circuit and

define all parameter if the message signal is given by: $m(t)=5$

$cos(21000t)$ and the carrier signal is given by: $c(t)=5cos(2106t)$

assume the resistance is $8$

Q$2$

Figure $1.$ Shows the block diagram of a wideband frequency modulator using the indirect method. This modulator is used to transmit a voice signals containing frequencies in the range $300Hz-3KHz.$ The narrowband phase modulator is supplied with a carrier of frequency $f_1=0\mathrm{.}1MHz$ by crystal controlled oscillator, carrier frequency at the transmitter output, $f_c=200MHz,$ minimum frequency deviation, $f=120KHz.$ Maximum modulation index, $=0\mathrm{.}3$ radians, $($ consider $=0\mathrm{.}2$ radian which certainly satisfies the requirements$)$

$($a$)$ Calculate the frequency multiplication $n_1$

$($b$)$ Calculate the carrier frequency for the second control oscillator $f_2.$

$($c$)$ Specify the values of carrier frequency and frequency deviation at the various points in the modulator.

Q $3$

Given the data stream $1110010100,$ sketch the transmitted sequence of pulses for each of the following line codes:

$($a$)$ Unipolar nonreturn$-$to$-$zero

$($b$)$ Polar nonreturn$-$to$-$zero

$($c$)$ Unipolar retum$-$to$-$zero

$($d$)$ Bipolar return$-$to$-$zero

$($e$)$ Manchester code