1.

(a)Explain any twofactors whichjustifythe needof modulatinga lowfrequencysignal. (b)Writetwoadvantages offrequencymodulationoveramplitudemodulation.

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 .


Discussion

No Comment Found

Related InterviewSolutions