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ANALOG

COMMUNICATIONS

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1. What is the need f! "d#$atin%

Ans. Mainly to decrease the antenna size

to increase the bandwidth o the si!nalto multi"le# the si!nalsto reduce the intererence made when we transmit the si!nals with nearly same

re$uency in the audio re$uency ran!e %&'(&')*)+z.to a,our the com"le#ity o the transmission system

&. What is Cstas L'%

Ans. - Cstas $' is a "hase(loc)ed loo" used or carrier "hase reco,ery rom su""ressed(carrier modulation si!nals such as rom double(sideband su""ressed carrier si!nals. The "rimarya""lication o /ostas loo"s is in wireless recei,ers. 0ts ad,anta!e o,er the 1LL(based detectors is

that at small de,iations the /ostas loo" error ,olta!e is sin%&% i2 f** ,s sin% i2 f*. This translates

to double the sensiti,ity and also ma)es the /ostas loo" uni$uely suited or trac)in! Do""ler(shited carriers es". in O3DM and 415.

(. What is SS)%

Ans. Sin*$e+side,and "d#$atin %556* is a reinement o am"litude modulation that moreeiciently uses electrical "ower and bandwidth. 0t is closely related to ,esti!ial sidebandmodulation %756*

-m"litude modulation "roduces a modulated out"ut si!nal that has twice the bandwidth o the

ori!inal baseband si!nal. 5in!le(sideband modulation a,oids this bandwidth doublin! and the"ower wasted on a carrier at the cost o somewhat increased de,ice com"le#ity.

4. What is -M%

Ans. -!e#en/ "d#$atin %3M* con,eys inormation o,er a carrier wa,e by ,aryin! itsinstantaneous re$uency. This is in contrast with am"litude modulation in which the am"litude

o the carrier is ,aried while its re$uency remains constant. 0n analo! a""lications thedierence between the instantaneous and the base re$uency o the carrier is directly

"ro"ortional to the instantaneous ,alue o the in"ut si!nal am"litude. Di!ital data can be sent by

shitin! the carrier8s re$uency amon! a set o discrete ,alues a techni$ue )nown as re$uency(shit )eyin!.

3M is widely used or broadcastin! o music and s"eech and in two(way radio systems

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. Nise in Ana$* /""#ni/atin%

Ans. -nalo! systems are less tolerant to noise ma)e !ood use o bandwidth and are easy tomani"ulate mathematically. +owe,er analo! si!nals re$uire hardware recei,ers and transmittersthat are desi!ned to "erectly it the "articular transmission. 0 you are wor)in! on a new system

and you decide to chan!e your analo! si!nal you need to com"letely chan!e your transmitters

and recei,ers.

2. What is a Radi t!ans"itte!%

Ans. Radi t!ans"itte! is an electronic de,ice which with the aid o an antenna "roduces radiowa,es. The transmitter itsel !enerates a radio re$uency alternatin! current which is a""lied tothe antenna. When e#cited by this alternatin! current the antenna radiates radio wa,es. 0n

addition to their use in broadcastin! transmitters are necessary com"onent "arts o many

electronic de,ices that communicate by radio.

3. What is a Radi !e/eie!%

Ans. - !adi !e/eie! is an electronic circuit that recei,es its in"ut rom an antenna useselectronic ilters to se"arate a wanted radio si!nal rom all other si!nals "ic)ed u" by this

antenna am"liies it to a le,el suitable or urther "rocessin! and inally con,erts throu!h

demodulation and decodin! the si!nal into a orm usable or the consumer such as sound

"ictures di!ital data measurement ,alues na,i!ational "ositions etc

8. What is T5M%

Ans. Time(di,ision multi"le#in! %TDM* is a method o "uttin! multi"le data streams in a sin!lesi!nal by se"aratin! the si!nal into many se!ments each ha,in! a ,ery short duration. 9ach

indi,idual data stream is reassembled at the recei,in! end based on the timin!.

The circuit that combines si!nals at the source %transmittin!* end o a communications lin) is)nown as a multi"le#er. 0t acce"ts the in"ut rom each indi,idual end user brea)s each si!nal

into se!ments and assi!ns the se!ments to the com"osite si!nal in a rotatin! re"eatin!

se$uence.

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TRR ENGINEERING COLLEGE RAVEE0408@GMAIL.COM