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LI M U

Vo u th k 20 Marconi thnh cng trong vic lin lc v tuyn quai Ty Dng, Kenelly v Heaviside pht hin mt yu t l tng in ly hindin tng pha trn ca kh quyn c th dng lm vt phn x sng in t.

Nhng yu t m ra mt k nguyn thng tin v tyun cao tn i quy m.Chin tranh th gii ln th hai l mt bc ngot trong thng tin v

tuyn. Thng tin tm nhn thng - lnh vc thng tin s dng bng tn s cc cao(VHF) c nghin cu lin tc sau chin tranh th gii - tr thnh hinthc nh s pht trin cc linh kin in t dng cho VHF v UHF, ch yu l

pht trin ngnh raa.Vi s gia tng khng ngng ca lu lng truyn thng,tn s ca thng tin v tuyn vn ti cc bng tn siu cao (SHF) v cc cao(EHF). Vo nhng nm 1960, phng php chuyn tip qua v tinh c thchin v phng php chuyn tip bng tn x qua tng i lu ca kh quyn xut hin. Do nhng c tnh u vit ca mnh nh dung lng ln, phm vi thurng, hiu qu kinh t cao, thng tin v tuyn c s dng rt rng ri trong

pht thanh truyn hnh qung b, v tuyn o hng, hng khng, qun s, quanst kh tng, lin lc sng ngn, thng tin v tinh - v tr v.v... Tuy nhin, cannhiu vi lnh vc thng tin khc l iu khng trnh khi, bi v thng tin vtuyn s dng chung phn khng gian lm mi trng truyn dn.

Chnh v th iu ch tn hiu l mt phn khng th thiu c trongtruyn dn ca thng tin v tuyn. iu ch gip chng ta c th truyn i thngtin hoc tn hiu mong mun v nhn c nhng tn hiu m mnh mun c.

n c chia lm ba phn :Chng I: Tng quan v iu ch

Chng II: iu ch tn hiu sChng III: iu ch tn hiu tng tDo thi gian c hn, trong khi tm hiu chng em cn nhiu thiu st

mong thy c v cc bn thng cm v gp bi lm hon chnh hn.Xin cm n !

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MC LC

DANH MC T VIT TT

T vit tt Ngha ca cc t Chc nngBER Bt Error Rate S bt b li

FSK Frequency Shift Keying iu ch tn s s

AM Amplitude Modulationiu ch bin tng

t

ASKAmplitude Shift Keying

iu ch bin s

QAMQuature Amplitude

Modulationiu bin cu phng

PSK Phase Shift Keying iu ch pha s

BASK

Binary Amplitude Shift

Keying

iu ch kha dch bin

nh phnOOK On off keying iu ch khoa on-off STR Symbol Timing Recovery B khi phc ng b

BPSK Binary Phase Shift Keyingiu ch kha dch pha

nh phn

BFSKBinary Frequency Shift

Keyingiu ch kha dch tn

nh phn

QPSKQuadrature Phase Shift

Keyingiu ch kha pha cu

phng

FM Frequency Modulation iu ch tn s tng tDFM

Differential FrequencyModulation

Ph ca tn hiu iu tns

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Chng 1Tng quan v iu ch tn hiu

1.1 Khi nim iu chiu ch (modulation) ni chung l lm bin i cc c tnh ca mt tn

hiu theo mt tn hiu khc. Trong h thng thng tin tn hiu b bin i theosng mang (carrier). C th nh ngha iu ch l s bin i cc thng s catn hiu mang tin theo sng mang.

Mc ch chnh ca iu ch l gn tn hiu mang tin (thng l bng gc)vo tn hiu song mang c ph thch hp hn, to thnh tn hiu thng di :

+ Lm cho tn hiu mang tin tng xng vi cc c im ca knhtruyn.

+ Kt hp cc tn hiu li vi nhau (s dng ghp knh phn tn s) ritruyn i qua mt mi trng vt l chung.

+ Bc x tn hiu dng cc anten c kch thc ph hp thc t.

+ nh v ph v tuyn nhm gi cho giao thoa gia cc h thng dimc cho php.

bn thu qu trnh din ra ngc li so vi bn pht: tch li tn hiumang tin bng gc t tn hiu thng di.

so snh cc s iu ch khc nhau ta da vo hiu sut ph v hiusut cng sut. Hiu sut ph l s o tc truyn tin trn bng thng s dng,n v l bit/Hz. Mt yu cu t ra i vi k thut thng tin l truyn tin vitc ti a trn mt bng thng ti thiu. iu ny c bit ng vi thng tinv tuyn v ph tn v tuyn rt hp v do n l mt ti nguyn thng tin vgi.

Hiu sut cng sut lin quan n t s i vi mt xc sut li bt chotrc. Trong thc t iu ny c ngha l so vi cng sut tn hiu yu cu bicc s iu ch khc nhau gi c BER xc nh ng vi mt tc truyn tin qu gi.

1.2 S cn thit ca iu ch tn hiuThng tin v tuyn do cc tn hiu tin tc (tn hiu tng t v tn hiu s)

thng c tn s thp nn kh trc tip bc x thnh sng in t truyn i xa,nu c th bc x c th nng lng bc x cng rt yu v i hi phn t

bc x (anten) c kch thc ln. d dng truyn thng tin i xa bng sng

in t, ngi ta phi tin hnh iu ch tn hiu thng tin vo sng mang cao tnngha l gi tin tc cn truyn vo sng mang sau mi cho sng mang iuch bc x thnh sng in t truyn i xa. V sng mang c tn s cao nn

phn t bc x khng cn phi c kch thc qu ln.Trong ghp knh theo tn s: v cc tn hiu thng tin cng loi u c

chung mt bng tn truyn dn (V d nh tn hiu thoi c bng tn t 0,3 -3,4KHz) nn khi truyn nhiu tn hiu trn mt ng truyn dn th chng s bln vo nhau lm cho pha thu khng thu c tn hiu. truyn c nhiu tnhiu trn cng mt ng truyn th ngi ta phi iu ch cc tn hiu cntruyn vo cc sng mang khc nhau, mc ch l chuyn ph ca thng tin cn

truyn ln cc vng khc nhau sau mi truyn chung mt ng truyn dn.

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Nh s khc nhau v vng ph ca cc tn hiu truyn i m pha thu d

dng thu c tn hiu.1.3 Phn loi1.3.1 Phn loi theo tn hiu a vo iu ch- iu ch tng t : tn hiu iu ch l tn hiu tng t.- iu ch s : tn hiu iu ch l tn hiu s.

1.3.2 Phn loi theo s thay i ca cc tham s sng mang- iu ch bin : l tc ng tn hiu iu ch vo sng mang lm cho

bin ca sng mang thay i theo quy lut ca tn hiu iu ch. iu chbin tng t c gi l AM (Amplitude Modulation). iu ch bin sc gi l ASK (Amplitude Shift Keying).

- iu ch tn s: l tc ng tn hiu iu ch vo sng mang lm cho tns ca sng mang thay i theo quy lut ca tn hiu iu ch. iu ch tn stng t c gi l FM (Frequency Modulation). iu ch tn s s c gi lFSK (Frequency Shift Keying).

- iu ch pha: l tc ng tn hiu iu ch vo sng mang lm cho phaca sng mang thay i theo quy lut ca tn hiu iu ch. iu ch pha tngt c gi l PM (Phase Modulation). iu ch pha s c gi l PSK (PhaseShift Keying).

- iu ch QAM (Quature Amplitude Modulation): l phng php iuch kt hp c iu ch bin ASK v iu ch pha PSK. Vi iu ch ny thkhi tn hiu iu ch tc ng vo sng mang th c bin v pha ca sngmang u thay i theo quy lut ca tn hiu iu ch.

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Chng 2iu ch tn hiu s

2.1 iu ch nh phn

iu ch nh phn l kiu iu ch n gin nht v ph bin trong thct. y l trng hp tn hiu mang tin bng gc l tn hiu nh phn.

2.1.1 iu ch kha dch bin nh phn (BASK)Trong h thng BASK, bin ca sng mang tn s fc c chuyn i

gia hai gi tr ty thuc vo tn hiu bng gc, bin ca sng mang bao gmhai mc A0 v A1 biu din cho hai k t 0 v 1 tng ng. Trong thc t, dngsng BASK gm cc xung mark biu din k t 1 v space biu din k t0. Lc ny BASK cn c gi l biu din kha on-off OOK v k hiu BASKc biu din nh sau :

+

=

tfT

tA

tfTtA

tf

00

00

2cos

2cos

)(

B iu ch OOK c th c thc hin nh l mt kha chuyn mchn gin, kha sng mang on hay off ty tn hiu mang tin l 1 hay 0 hoc lmt b iu ch cn bng, nhn sng mang vi tn hiu OOK n cc bng gc.B tch sng OOK c th l kt hp hay khng kt hp. Trng hp ny tchsng kt hp c th dng mt b lc phi hp, u ra ca b lc phi hp t cc

i khi u vo c tn hiu v bng 0 khi u vo khng c tn hiu. Hoc dngb tch sng tng quan, yu cu l phi c b khi phc sng mang CR. Tnhiu sau c ly mu v quyt nh ngng vi ng h ly ra t b khi

phc ng h STR.Kiu tch sng khng kt hp c s dng ph bin hn, c cu thnh

hai knh tng quan tch thnh phn ng pha v vung pha ca tn hiu, sau bnh phng thnh phn ng pha v vung pha ri sau cng li. S spxp ny khc phc c yu cu v ng b pha sng mang. Kiu ny phc tpnhng vi s pht trin ca cng ngh VLSI, chng tr nn nh, nh v r hn sovi b lc v tch ng bao trong cc thit k truyn thng.

5

Cho s 1

Cho s 0

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Hnh 2.1 iu ch on-off: dng sng, b iu ch, ph

a Tn hiu bng gcb Ph in p ca tn hiu bng gcc B iu ch OOKd Tn hiu OOK thng die Ph in p ca tn hiu OOK thng di

Thi im quyt nh b quyt nh bn thu l f(nT0) v in p quytnh l:

=0

)( 10kE

nTf

Trong E l nng lng chun ha cha trong k t 1 v k l hng s,c th t bng 1.

Trng hp s dng b lc phi hp, xc xut li c tnh nh sau:

=

2

1

1

1

2

11

2

1

N

EerfPe

Trong N l PSD ca nhiu, erf(x) l hm li

t ( )2121

EEE += l nng lng trung bnh theo thi gian trn mt k

t, vi OOK th E0=0, ta c:

=

2

1

02

11

2

1

N

EerfPe

Hnh 2.2 a B thu dng b lc phi hp;b B thu tng quan6

Chn s 1Chn s 0

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c B thu tch sng ng bao; d B thu 2 knh

S dng cc quan h:

NBCT

NE

VBNN

VT

EC

0

0

20

2

0

)(

)(

=

=

=

y C l cng sut sng mang thu ly trung bnh trn tt c cc k t vN l cng sut nhiu chun ha trong mt bng thng B(Hz).2.1.2 iu ch kha dch pha nh phn (BPSK)Trong h thng BPSK, tn hiu bng gc c gn vo sng mang bng cchthay i pha ca sng mang ty thuc vo tn hiu bng gc:

+

=

tfT

tA

tfT

tA

tf

00

00

2cos

2cos

)(

V nguyn tc, c th chn bt k nhng thng chn trng thi ngcpha, tc l =1800. Kiu iu ch ny gi l iu ch kha o pha PRK.

Hnh 2.3 iu ch PRK: dng sng, b iu ch, pha Tn hiu bng gc

b Ph in p ca tn hiu bng gc

c B iu ch PRKd Tn hiu PRK thng die Ph in p ca tn hiu PRK thng di

Tch sng PRK l kiu tch sng kt hp, c th thc hin bng b lcphi hp hoc tng quan. V k t 1 v 0 ngc pha nn ch cn b thu mtknh.

Mc in p quyt nh sau khi lc:

=

kE

kEnTf )( 0

7

Chn s 1

Chn s 0

Chn s 1Chn s 0

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Hnh 2.4 B thu tng quan PRK

2.1.3 iu ch kha dch tn nh phn (BFSK)BFSK biu din s 1 v s 0 bng cc xung sng mang vi hai tn s l f1v f2:

=

tfT

tA

tfT

tA

tf

20

10

2cos

2cos

)(

B iu ch BFSK thng l mt b dao ng iu khin s. C th thytn hiu BFSK l xp chng ca hai tn hiu OOK, do vy ph in p ca tn

hiu BFSK l xp chng ca hai ph in p OOK, mt biu din tn hiu cho f1v mt OOK biu din cho f2. Ph tn hiu b chng ln, nu khong cch gia f1v f2 ln th s chng ln coi nh khng ng k.

B tch sng BFSK c th kt hp hay khng kt hp. Tch sng khngkt hp c t s CNR khng tt bng tch sng kt hp ging nh trong h thngOOK.

Nu cc k t nh phn trong h thng BFSK trc giao c ngha l :

=0

0

21 0)2cos()2cos(T

dttftf

Khi u ra ca mt knh trong b thu kt hp l ti a th u ra ca knhkia s ti thiu.

8

Chn s 1

Chn s 0

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Hnh 2.5 iu ch BFSK: dng sng, b iu ch, ph

a Tn hiu bng gcb Ph in p ca tn hiu bng gcc B iu ch BFSKd Tn hiu BFSKe Ph in p ca tn hiu BFSK

2.1.4 Khi phc sng mangTch sng kt hp trong cc b thu va xt yu cu phi c mt tham

chiu trng pha vi pha ca sng mang trong tn hiu.Trc tin ta bnh phng tn hiu PRK, s thu c tn s sng mang m

khng b dch chuyn pha. Tip n dng vng kha pha nh l mt b chia itn s to ra tn hiu tham chiu. Vng kha pha to ra tn hiu tham chiuvt 900 so vi tn hiu vo, do vy cn mt mch dch pha 900 trong vng vgia vng vi b gii iu ch, tn hiu tham chiu c pha chnh xc nhmgii iu ch chnh xc.

Hnh 2.6 Bnh phng khi phc sng mangMch khi phc ny c th cho ra sng mang trng pha hoc ngc pha

so vi sng mang pht. iu ny s lm cho k t trong d liu gii iu ch bo ngc.

khc phc, c th s dng phng php m ha vi sai trc khi iuch PRK v c gi l iu pha vi sai DPSK. S 1 c biu din bng mt sdch pha cn s 0 th khng dch pha.

2.2 iu ch tng hiu sut ph2.2.1 iu ch kha dch pha M mc

rng bng yu cu thng t l vi 1/Tb. Nu s dng iu ch hngM=2n th rng bng ch cn 1/nTb. y chnh l k thut iu ch c hiusut s dng bng tn cao. Song gi phi tr y l t l li bt cao hn PSKhng M:

T

nf

MiiM

tfT

ES

cc

ci

=

=+= ...2,1),1(2

2cos((2

Cc tn hiu trn l t hp ca 2 hm c bn:

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TttfT

t

TttfT

t

=

=

0),2sin(2

)(

0),2cos(2

)(

02

01

S vi M=8

8sin21812Edd ==

Hnh 2.7 Gin pha ca PSK 16 mc

2.2.2 iu bin cu phng QAMi vi b pht, ta c th kt hp iu bin vi iu pha ci thin s

phn b trng thi pha trong chm sao. Phng php ny c gii thiu ln utin vo nm 1960 vi 2 mc bin (tng ng 2 vng) v 8 mc pha trn

mi vng. V y l s kt hp gia iu bin v iu pha nn n c gi liu ch kha bin /pha APK. Sau ngi ta nhn thy rng nu s im vng trong gim cn 4, s im vng ngoi tng ln 12 th cc im trn chmsao cch u nhau hn. n nm 1962, ngi ta a ra mt cch chn bin v

pha khc. Ngi ta nhn thy kiu ny d thc hin hn v Pe c c ci thini cht. V tn hiu APK ny c th xem l cp ASK nhiu mc c iu chtrn cc sng mang vung gc nn n thng c gi l iu bin cu phngQAM. Nh vy QAM l mt trng hp ring ca APK.

Hnh 2.8 Chm sao ca cc tn hiu iu cha APK 16(8,8)

b APK 16(4,12),

c QAM 16( 4x4)

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Cng nh PSK nhiu mc, tt c cc k hiu trong APK hoc QAM u

chim cng mt di tn s nh nhau, do vy hiu sut ph ca tn hiu iu chAPK/QAM (danh nh v ti a) cng ging PSK nhiu mc.

2.2.3 iu ch pha cu phng QPSKKhi thit k h truyn thng ngoi mc tiu quan trng l xc sut li bit

phi thp cn c mc tiu l s dng c hiu sut rng bng. Kha dch vungpha l trng hp ring ca hp knh sng mang vung gc, mi dng sngmang thng tin 2 bit nn cn tt c 4 dng sng ng vi 4 pha c hiu sut bngtn cao. Dng sng ca k hiu l:

( )TtifT

ESi

+= 0

4

1)12(2cos

20

Khai trin ta c:

( ) ( ) ( )tfitftfiT

ESi 000 2sin4

122sin2cos4

12cos2

=

Vi 4 dng sng trn, 2 hm c s c xc nh l:

TttfT

t

TttfT

t

=

=

0),2sin(2

)(

0),2cos(2

)(

02

01

Dng sng ng vi tn hiu 01 10 10 00 s c to nn nh sau:Dy c chia thnh 2 dy con: Nhng bit c nh s chn gp vo

mt dy v nhng bit nh s l vo mt dy. ng vi 2 dy ny l cc dngsng ng vi tn hiu PSK t trn sng cosin v sin ring r. Khi cng li chng

s cho QPSK

Hnh 2.9 a Dy nh phn vo; b Bt l li vo v dng sng BPSK lin ktc Bt chn li vo v dng sng BPSK lin kt; d Dng sng QPSK

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2.3 iu ch khng ng b2.3.1 iu ch trc giao khng ng bTi bn thu nu khng bit pha ca sng mang khi truyn ti ni, c th

s dng k thut ch khng ng b. iu ny thng gp phi khi ng truynkhng xc nh .V nguyn tc iu ch nh phn khi dng 2 tn hiu trc giaos1(t) v s2(t) c nng lng bng nhau. Gi s tn hiu qua knh nhn c l

g1(t) v g2(t) vn gi tnh trc giao v nng lng bng nhau. B thu s gm 2 blc ph hp vi cc hm c s 1 t v 2 t l cc phin bn ca s1(t) v s2(t).V pha ca sng mang l khng bit, b thu ch da trn s phn bit bin nnli ra b lc c tch ng bao, ly mu v so snh vi nhau. Nu l 1>l2 thquyt nh l s1(t), ngc li th l s2(t). Khi mi b lc ph hp khng ng

b tng ng nh b thu vung gc 2 nhnh: nhnh trn l ng pha x(t)c tng quan vi )(ti l phin bn ca s1(t) hoc s2(t) vi pha sng mang

bng 0, nhnh di l knh vung gc, x(t) c tng quan vi )(ti l phin

bn ca ( )ti dch pha i -900, vi ( )ti v )(ti l trc giao vi nhau.

2.3.2 Kha dich tn nh phn khng ng bTrong trng hp FSK nh phn:

( )( )

==

0

0

0

0 ,0,2cos2

,0

T

nfTttf

T

EtS iii

i

12

Cn li

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Chng 3iu ch tn hiu tng t

3.1 iu ch tn s

Hnh 3.1 Mch iu ch tn s tng t FMTrong :+ CD l mt diode bin dung+ R1, R2: to thnh mt mch phn p nh im lm vic cho CD.+ Co: t dn tn hiu iu ch vo mch+ C2: mt t dn tn hiu c tr khng gn nh bng 0 i vi bng tn

cng tc nhm m bo cho CD dng nh c mc song song vi khung LC1.Nh vy 3 phn t CD, L v C1 to thnh mt khung cng hng vi tns cng hng ring:

( )12

1

CCLf

D +=

Khi cha c tn hiu iu ch a vo mch th trn diode bin dung cmt in p tnh c xc nh bi mch phn p R1 v R2 do diode ny cmt gi tr in dung CD khng i. Lc ny mch dao ng s hot ng vitn s khng i:

( )12

1

CCLf D +=

Khi c tn hiu iu ch a vo mch, nu bin ca tn hiu iu chtng th in p trn diode bin dung tng, lm cho tr s in dung CD ca diodegim, dn n tn s dao ng ca mch dao ng tng. Nu bin ca tn hiuiu ch gim th in p trn diode bin dung gim lm cho in dung CD tngdn n tn s cng tc ca mch dao ng gim.

Nh vy, tn s dao ng ca mch dao ng b khng ch bi tn hiuiu ch u vo v bin thin ng theo quy lut ca tn hiu iu ch. ngra ca mch dao ng ta thu c mt tn hiu c iu ch tn s.

Trong iu ch tn s, nu tn hiu iu ch l V(t) vi tVtV = cos)( , tnhiu sng mang l V vi tVV 00 cos= th sau iu ch ta thu c mt tnhiu iu ch VFM:

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)sincos( 00 ttVVFM

+=

Trong : l di tn cc i.H s iu ch mf ca mch iu ch tn s c tnh nh sau:

=

=

V

kmf

k: h s t l ph thuc vo c im ca tng mch iu ch.T biu thc trn ta c: = kV . Nh vy, ta thy rng khi constV =

th const= , nhng khi thay i th mf cng thay i.

Hnh 3.2 Dng sng ca mch iu ch tn s.a Tn hiu iu ch; b Sng mang; c Tn hiu sau khi iu ch

Khi iu ch n tn, ph ca tn hiu iu tn cha thnh phn v nhiu

thnh phn tn s bin n

0 vi n = 1, 2, 3... Bin ca cc thnh phn tn sbin bin i khng ng u.Mt cch gn ng, rng ph ca tn hiu iu tn sau iu ch c th

tnh nh sau:++= )1(2 ffFM mmD

DFM: rng ca ph sau iu ch tn s.Khi tn hiu iu ch l mt bng tn th ph ca tn hiu iu tn DFM s

l:

max)1(2 ++= ffFM mmD

max: tn s ln nht trong tn hiu iu ch+ Khi mf > 1 th ph ca tn hiu iu tn c th tnh gn ng:= 22 maxfmDFM

+ Khi mf 1 th ph ca tn hiu iu tn c th tnh gn ng:max2DFM

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3.2 iu ch bin (AM)

Hnh 3.3 iu ch AM bng mt diode

Tn hiu iu ch c a n u vo R1, tn hiu sng mang c an u vo R2. Mng in tr R1, R2 v R3 thc hin trn tuyn tnh hai tnhiu vi nhau theo nguyn tc cng s hc. Nu tn hiu iu ch l tn hiu hnhsin th tn hiu sau khi trn (ly trn in tr R3) .Ta thy rng sng mang binthin trn nn ca tn hiu iu ch, nhng y cha phi l tn hiu iu ch

bin . y hai tn hiu mi c cng vi nhau, trong khi iu ch lnhn hai tn hiu vi nhau. Tn hiu sau khi cng c nn qua diode D. Sau khinn ta thu c mt dy xung dng l tp hp ca cc na chu k dng catn hiu tng, bin ca cc xung thay i theo quy lut ca tn hiu iu ch.Cc xung ny c a n kch thch cho mt mch cng hng song song LC.

Khung cng hng LC ny c tn s cng hng ring f LC=1

2 ng

bng tn s ca sng mang. Khi c kch thch th khung LC s dao ng vitn s ng bng tn s sng mang, cn bin th ph thuc vo bin ca tnhiu kch thch. Khi xung kch thch c bin ln th dao ng ly ra trn khungc bin ln, khi bin ca xung kch thch nh th dao ng ly ra trnkhung c bin nh.

Nh ni trn, bin ca cc xung kch thch thay i theo quy lutca tn hiu iu ch nn dao ng ly ra trn khung LC cng c bin binthin ng theo quy lut ca tn hiu iu ch. y chnh l tn hiu iu ch

bin (hnh 3.3 e). Trong iu ch bin , nu gi tin tc cn truyn c tn s l V(t) vi tVtV = cos)( ( V l bin cc i ca tn hiu iu ch), sngmang cao tn l tVV 00 cos= th sau khi iu ch ta thu c mt tn hiumi :

tVVtVAM += cos)( 0

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Hnh 3.4 a Tn hiu iu chb Sng mang

c Tn hiu trn in tr R3d Dng tn hiu qua diodee Tn hiu trn khung cng hng

Hnh 3.5 a Ph ca tn hiu iu ch n tnb Ph ca tn hiu AM iu ch n tn

c Ph ca tn hiu iu ch a tnd Ph ca tn hiu AM iu ch a tn

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TI LIU THAM KHO

[1] Bi ging : L thuyt tn hiu ca Th.S L Xun K[2] Tm tt bi ging in t thng tin ca Th.S Nguyn Trng Hi[3] Cc h thng thng tin hin nay ca Proakis J.G v Salehi M

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