30th April 2011 , 11:50 PM #1 Fuchcha FaaDoO Engineer
Gender: : Male
City : Surat
You have 10 telephone signals which you have to transmit over a distance of 100 km. You have a cable through which you can transmit signals in the band from 1MHz to 1.5MHz with a loss of 1 dB/km. Any signal which falls below 1 mw is lost. Design a system for achieving this. Give a block diagram of the system, showing all the major units required. Determine the power levels and frequencies,
Discus the parameters which influence your choice of the various blocks and parameters.
Draw the waveforms and spectra at different parts of the system. Give expressions for these as also the values.
1st May 2011 , 12:05 AM #2 Fuchcha FaaDoO Engineer
Gender: : Male
City : Durgapur
1 dB per km is a huge loss. Considering that every 3dB loss accounts for power dropping to half it's initial value. 100 km leads to halving of power 33 times and the final power limit has to at least 1 mW! Taking a margin of 1.5 the initial signal strength therefore has to be at least (1.5 * 2^(33-1)) = 6.5MW approx.
That's awesome... or am I going terribly wrong somewhere?
Well, no matter what be the modulation technique adopted this high loss won't work. Repeaters have to be used, no doubt.
Well Dipak. Read Kennedy. You don't have to be lazy. This sounds like a very complicated problem but there are many ways you can answer it in simple ways. Just get your basics right. There is no right or wrong answer to this problem as I understand it. It's just for academic purpose and is intended only to test your grasp of the subject. I second him.
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