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(a)Explain any twofactors whichjustifythe needof modulatinga lowfrequencysignal. (b)Writetwoadvantages offrequencymodulationoveramplitudemodulation. |
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Answer» Solution :(a)Size of theantenna or aerial: Fortransmtting a signalantennashouldhavea sizecomparableto thewavelength of the SIGNAL (at least `lambda//4` indimension ) . Foran ELECTROMAGNETIC WAVE of frequency 20kHz , thewavelength`lambda` is 15 KM. Actually sucha longantenna is notpossibletoconstruct andoperate. Hence direct transmissionofsuch basebandsignals is notpractical. (b)Effectivepowerradiated by anantenna :A theoreticalsignalsis notpractical . (length l)showsthat thepower radiated is proprtionalto `( l// lambda)^(2)` .Thisimpliesthat for the sameantenna lengththe powerradiated increases withdecreasing`lambda` i.e.,increasingfrequency. Hencethe effectivepower radiated byalongwavelenthbasebandsignalwouldbe small.For agoodtransmissionwe needhighpowersand hencethisalsopointsout to theneedof usinghighfrequencytransmission. (b)(i) THEREIS verylessnoisein frequencymodulation. (ii)Rangeof requencymodulationis larger . |
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