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7 months ago

Communication Systems Class 12th

An amplitude modulated wave is as shown in figure. Calculate
(i) The percentage modulation,
(ii) Peak carrier voltage and
(iii) Peak value of information voltage

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alok kumar singh

Contributor-Level 10

This is a Long Answer Type Questions as classified in NCERT Exemplar

Maximum voltage = 100/2 = 50V

And minimum voltage = 20/2 = 10V

Percentage modulation= max voltage -min voltage/ max voltage + min voltage $* 100$

= $\frac{50 - 10}{50 + 10} * 100$ = 66.67%

Peak career voltage= max voltage+ min voltage/2= 50+10/2=30V

Peak value of information voltage= 66.67/100 $*$ 30= 20V

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New answer posted

7 months ago

Communication Systems Class 12th

A 50 MHz sky wave takes 4.04 ms to reach a receiver via re-transmission from a satellite 600 km above Earth's surface. Assuming re-transmission time by satellite negligible, find the distance between source and receiver. If communication between the two was to be done by Line of Sight (LOS) method, what should size and placement of receiving and transmitting antenna be?

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alok kumar singh

Contributor-Level 10

This is a Long Answer Type Questions as classified in NCERT Exemplar

height of satellite hs= 600km
As we know velocity = distance/time

2x/4.0410^-3 = 3⁸

So x=606 km after solving
According to Pythagoras theorem d²=x²-h²= 606²-600²= 7236

So d= 85.06km so total distance will be double from receiver to transmitter = 170.1km
And d = √2Rh
h=7236/2*6400 = 565m

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New answer posted

7 months ago

Communication Systems Class 12th

The intensity of a light pulse travelling along a communication channel decreases exponentially with distance x according to the relation I = I₀e^-ax, where I₀is the intensity at x = 0 and α is the attenuation constant.
(a) Show that the intensity reduces by 75% after a distance of (In4/α).
(b) Attenuation of a signal can be expressed in decibel (dB) according to the relation dB=10 log₁₀(I/I₀).What is the attenuation in dB/km for an optical fibre in which the intensity falls by 50% over a distance of 50 km?

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alok kumar singh

Contributor-Level 10

This is a Long Answer Type Questions as classified in NCERT Exemplar

as we know that I= I_{0
$e^{- \propto x}$}

And I= 25%of I₀=

I=I₀/4

I₀/4= I_{0
$e^{- \propto x}$}

I₀cancel from both sides

¼= $e^{- \propto x}$

Taking log on both sides log1 -log4= - $\propto x$ loge

X= log4/ $\propto$

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