bao cao thuc tap ky thuat vt

7/31/2019 Bao Cao Thuc Tap Ky Thuat Vt

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GVHD:

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MC LC

1. THI GIAN ....................................................................................................... 22. NI DUNG ........................................................................................................ 2

2.1Cc khi nim cn bn iu ch, cc kiu iu ch, tin tc ...................... 2

2.2Cc mch tng t....................................................................................... 3

2.2.1iu chbin ( AM ) ....................................................................... 3

2.1.1.1 iu ch c dng sng mang ................................................. 32.1.1.2 iu ch khng dng sng mang ........................................... 7

2.2.2 iu chtn s( FM ) .................................................................... 102.1.2.1 S hnh thnh ca iu ch tn s ........................................ 102.1.2.2 Gii iu ch tn hiu tn s ................................................ 132.1.2.3 B gii hn v nhng nh hng ca nhiu ln vic gii iu

ch FM ...................................................................................................................... 16

2.2.3 Ngun tn hiu2.2.3.1 B to giao ng cu wien c bn ....................................... 222.2.3.2 Bgiao ng LC .............................................................. 22

2.2.3.3 Bgiao ng thch anh ........................................................ 252.2.3.4 Ba hi .............................................................................. 26

3.2 Cc mch s................................................................................................ 273.2.1 iu ch dch bin ( ASK ) ......................................................... 293.2.2 Kha dch tn s ( FSK ) .................................................................. 30


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1.THI GIANThi gian thc tp tngy 03/01/2012 n ngy 14/01/2012

2. NI DUNG2.1Cc khi nim cn bn viu ch, tin tc, cc kiu iu ch.

-iu chl qu trnh bin i dng tn hiu sng mang (carrier) tun theomt c trng no ca tn hiu iu ch ( tin tc) cn truyn i nhm to ra mt tncha mt s ni dung tin tc nhng c dng thc ph hp, c th lan truyn trong mitrng.

- Tin tc gi l tn hiu iu ch, dao ng cao tn gi l ti tin, dao ng caotn mang tin tc gi l dao ng cao tn iu ch.

-iu chtn hiu phi c hai thnh phn:

+ Tn hiu em iu ch: cha tin tc, thng c k hiu l s(t) hayx(t), m(t),, ty hon cnh.

s(t) = UScos(st)

+ Sng mang ( carrier): cn gi l giao ng ti tin, k hiu l Uc(t) hayXC(t), l dao ng tn scao, thng di dng in thhay dng in, nh sau:

Uc(t) = U0 cos(ct)

- Cc kiu iu ch:

+ Nu ghi tn hiu vo bin ca dao ng sng mang, lm cho binthay i theo quy lut ca tin tc, ta c tn hiu iu chbin .

+ Nu ghi tn hiu vo tn s ca dao ng sng mang, th tn s dao

ng sng mang thay i theo quy lut tin tc, ta c tn hiu iu ch tn s.+ Nu ghi tn hiu vo pha tc thi ca dao ng sng mang, th pha tcthi bn cnh sthay i u n theo thi gian, sthay i theo quy lut tin tc, ta ctn hiu iu ch pha.

+ Nu ghi tn hiu ng thi vo hai tham strn ( bin v pha) cadao ng mang, chng ta c tn hiu iu ch hn hp.

2.2 Cc mch tng t.2.2.1iu chbin ( AM).

2.2.1.1iu chc dng sng mang.

1.Mc tiuTm hiu v:

Nhng kin thc c bn viu chbin v gii iu ch.c im ca AM trong min thi gian.B pht hin ng baoD tc sng.

2. C sl thuyt- Phng trnh dng sng in p hnh sin c dng sau

v = Vmaxsin(t + )

v in p tc thi ti thi im t.


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Vmax in p ci tn sgc dao ngpha dao ng .

- Dng in p n nh da theo phng trnh trn th hu nh khng

mang thng tin, mang c thng tin dng sng phi c bin i sao cho nhngthay i ca n biu hin c thng tin v tin trnh ny c gi l iu ch.

- iu chbin AM:+ iu chbin s dng s bin i ca Vmax mang thng

tin, sng c bin b bin i gi l sng mang, tn hiu gy ra s bin i gi l tnhiu iu ch.

Xt phng trnh sng mang sau: vc = Vcsin(ct ) v phngtrnh tn hiu iu ch: vm = Vmsin(mt), th phng trnh sng sau iu ch c dng

sau: vc = Vcsin(ct ) + (

)[cos(c + m).t] - (

) [cos(c + m).t]

Trong m =

gi l ch siu ch nu nhn cho 100% ta c cng

thc v phn trm iu ch: m =

100%

Nu m =100% gi l 100% iu ch hay cn gi iu ch ton b, m 100% iu ch qu mc.

- Phn trm iu ch ch ra phn trm bin tn hiu ra bthay i khi tnhiu sng mang biu ch bi tn hiu tin.

- Dng biu din ny ca vc gm 3 phn:

+ Phn dng nguyn thy ca sng mang, ti tn sc, khng cha ngbin no, do khng mang bt k thng tin no.+ Thnh phn ti tn s (c - m) c bin ca n t l vi ch siu

ch, thnh phn ny gi l tn s ca di bin di.+ Thnh phn ti tn s(c + m) c bin ca n t l vi ch s s

diu ch, thnh phn ny gi l tn s ca di bin trn.- C hai di tn sny u mang thng tin v trong biu din ca mi thnh

phn trn u c ch siu chm do bin ca mi i tn su bin i theotn hiu iu ch.

- Nhng di bin trn v di ny ngi ta gi l nhng di bin mang thng

tin v c iu ch.3.Bi thc hnh.a. Bi 1: Biu chbin n gin

- Dng tn hiu cn truyn i l cc m morse, tn s truyn dn cchn cn cvo mi trng truyn dn v khng nh hng ti thng tin n mangtheo, gi l tn s sng mang.

- mang thng tin vi c tnh sng mang c thay i hay c iuch vi thng tin . y l dng n gin ca iu chbin (AM) bi v ch c haitrng thi: trng thi bin 0, trng thi bin ln nht.

- R rng vi bin sng mang cho trc c nhng gii hn v tn hiu

iu ch,mc ti thiu l 0, mc ti a cho php l 2 ln bin sng mang cha iuchnh. Khi vt gii hn ny, tn hiu iu ch s khng thc phc hi m khng


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mo m, ngi ta gi hin tng ny l qu iu ch- Khi tn hiu iu ch lm bin i sng mang t0 n 2 ln bin

sng mang th sng mang c gi l sng y hay l 100% iu ch.- Quan st thc nghim:

Cc bc tin hnh iu chnh thc nghim v phn tch thc nghim:+ t carrier level mc cao nht, t modulation level mc 0, ghi ch

tn hiu ti cc im quan st ? . Vy ti im s 4, tn hiu iu ch bng 0 lc nytrn mn hnh b to dao ng chl ng thng mu vng c dng y = 0, cn quanst ti im s 5 th nhn thy bin sng mang khi cha iu ch l cc i v nnh, cc dao ng c tn skhng i, khi quan st ti im 6 c ngha l sng mang qua iu ch, lc ny bin ch cn li 0.8 n nh, tn skhng i, chng t

c s hao ht nng lng qua biu ch khi m modulation level vn mc 0.+ Tng modulation level quan st ti im 6, lc ny ta thy sng mang

c iu ch, bin bin i theo tin hiu c iu ch, v khi tng modulationlevel cho ti khi sng mang chm ti nh 0 trn phn iu bin m lc ny l 100%iu ch. Quan st tn hiu ti cc im dao ng

-Ban u sng mang mc n nh. Tn s ca sng mang khng bin i mchc bin ca sng mang thay i theo tn hiu

- Ti im 5: iu ch sng mang mc ln nht: Vc = 1 VTa c tn hiu iu ch l nh nht Vs = min

- Gi nguyn trng thi v t quan st ti im 6: Tn s ca sng mangvn gi nguyn nhng bin thay i, Vs c phn gim i so vi tiim 5

+ im 5: Vc= 1 V -> T = 2 s+ im 6: Vc = 0,6 V -> T = 2,141 s

Trong qu trnh iu ch, mch lm cho tn hiu suy hao 40% so vi lc cha iu chNhn xt:

+ ng bin ca sng mang bao gm ng bin dng, v ng binm, nhng ng bin ny cha tn hiu qua iu ch. Nu nh xy ra siu chqu mc th tn hiu s b bp mo, lc ny hnh nh chng ta quan st thy l nh cang bin dng v y ca ng bin m vn tun theo siu chnhng phn

ng bin gn ng 0 ca bin sng mang trnn bt hn.


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b. Bi 2: B pht hin ng bao- Bi thc hnh ny nghin cu vic gii iu ch tn hiu AM s dng

b pht hin ng bao.- Mc ch chnh ca bt k b pht hin hay b gii iu ch no l khi

phc tn hiu ban u vi mc suy hao v mo m l nh nht. Phng php n ginnht i vi tn hiu AM l s dng mch chnh lu sng.

- Nu tn hiu iu ch ddng i qua diode ti in trthun mt cchd dng th u ra l mt chui na chu k xung tn s sng mang. B lc ny baogm mt tin v mt in trmc song song , tc np bi diode ti gi trnhchu ksng mang v u ra i theo ng bao ca tn hiu iu ch t ta c thutng pht hin ng bao.

- Hng s thi gian ca mch RC l yu t quan trng v nu qu ngn thu ra cha phn ln tn s sng mang lc ny tn hiu thu c c th khc xa vi tnhiu ngun, con ngc li nu qu di th lc bi nhng gi tru ra cn thit lmcho tn hiu c th b mt phn thng tin quan trng.

- Quan st thc nghim:

- Cc bc tin hnh quan st thc nghim, phn tch thc nghim:

+ t quan st ti im 16, iu chnh hng s thi gian, ghi ch li cctham s?. Nhn vo hnh quan st trn ta thy ng bao ca tn hiu iu ch chm

pha hn tn hiu ngun v khi iu chnh hng s thi gian tng n gi tr cc i thing bao ca tn hiu iu ch ny m t khng cn chnh xc so vi tn hiu ngun.

+ Quan st bng my phn tch ph?.

+ Khi iu chnh hng s thi gian mc Min th: As > Ac

Ac = 0,2 ; As = 0,8

+ im 6 thy c sng sau iu chng mu xanh l tn hiu nhn c ( b mo)

- Nhn xt:


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+ Tn hiu sau iu ch trpha hn so vi tn hiu ngun do b lc sauiu ch l mt h thng in dung nn lm qu mi dn n hin tng nh vy.

+ Trong trng hp t s gia tn siu ch v tn s sng mang nhth b lc i hi phi phc tp hn loi bsng mang nhng vn cho iu ch,iu ny c ngha l mi b lc c gii hn nht nh nu tin hiu sau iu ch qu nhth vic iu ch skhng em li hiu qu.

c. Bi 3: B pht hin sai khc- Trong phn thc hnh ny chng ta s lm quen vi thit b gii iu

ch c tn l b pht hin sai khc, c phc tp hn so vi b pht hin ng bao.L thit bc s dng gii iu chqu trnh iu chbin trit sng mang.

- Cn hiu b pht hin sai khc l g?.+ Nu tn hiu AM c ghp vo mt sng mang c cng tn s th 2 di tn

bin s b ko xung tn siu ch ngun v sng mang c dng tn hiu mt chiu.+ Cc biu thc ton hc cho thy iu ny ch xy ra khi m tn s ca sng

c ghp c cng tn s vi sng mang, m cn phi c sng b vpha. iu nygii thch ti sao b pht hin sai khc con gi l b pht hin ng b.

+ Tuy nhin tn hiu u ra cn phi i qua b lc sau iu ch loi b ccgn sng vi lc ny gn sng gp 2 ln tn s sng mang v khc xa so vi tn hiungun.Trong iu kin bnh thng th b pht hin sai li gy mo t hn hay ch cmt phn v n s dng c phn dng v phn m ca sng mang. iu ny cthc hin bi thit b c tn bdao ng tn s phch ( BFO), n c gi nh vy vkhi tn s ca n khng ging tn ssng mang th u ra ca b pht hin sai khc sc tn s bng s khc bit gia chng, bn thy c iu khi iu chnh BFOng b.


- Cc bc tin hnh quan st thc nghim, phn tch thc nghim:+ Quan st tn hiu ti im 6.+ Quan st u ra ca BFO.+ Xoay lt BFO frequency iu chnh BFO kha sng mang

li.+ Quan st tn hiu ti im 15 v ghi ch li tn s ca gn sng

vi sng mang.


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+ S dng my phn tch ph quan st hin tng trn.+ Quan st tn hiu ti im 14 v so snh vi tn hiu ngun.+ Quan st u ra ca b pht hin bng my nghim sng, sau

iu chnh BFO frequency v xem xt s bin i. lm tng t vi u ra ca b lc.+ Tng dn BFO -> Vc n nh mc 0,4 V v 0,6 V+ Tng tip BFO ln : sng tn hiu khng n nh+ Ti im 13: Vc (thu c) = Vc (ti im 5)

t quan st ti im 15: iu chnh khng c tn hiu.+ Khi i qua im 14: tn hiu thu c vn khng xc nh c dng sng

- Nhn xt:+ Trong b pht hin ng bao th b lc s loi b hon ton tn

s sng mang cn trong b pht hin sai khc th b lc loi b gn sng gp 2 ln tnssng mang. V iu khc bit quan trng nht l b pht sai khc c mc phctp hn, khnnga ra tn hiu sau gii iu ch tt hn, gy mo t hoc ch mtphn v n s dng phn dng, phn m ca sng mang.

+ Quan st mn hnh phn tch ph ta thy c ba im cao hn ccv tr khc, chng hin th tn s ca sng iu ch, tn s gp 2 ln tn s sng mang.

2.1.1.2. iu chkhng dng sng mang1.Mc ch

- Sinh vin nghin cu v nm c vn sau.+ iu bin trit sng mang+ iu bin trit sng mang hai di bin DSB.+ iu bin trit sng mang mt di bin SSB.+ B lc iu ch cn bng.+ To ra SSB vi cc b lc.+ Cch thc gii iu ch.

2. Bi thc hnha. Bi 1:Di bin kp trit sng mang

- Bi thc hnh ny gii thiu cho chng ta v tn hiu AM b trittiu sng mang qua hiu c cc vn sau:

+ Biu ch cn bng v s trit tiu sng mang.+ BFO s dng nh mt bdao ng chn sng mang

- Sng mang c hng sn nh v ch c hai di bin c s thayi c vbin ln tn s, iu ny chng t hai di bin mi tht s mang thng tintrong khi sng mang ko tc dng g ngoi vic gip ch cho gii iu ch.

-Nhng vy vic truyn dn song mang tiu tn nhiu nng lngdo nu chng ta trit tiu c sng mang v ch truyn 2 di bin ca chng thvn c tht c vic truyn dn thng tin.

- Nu tn hiu u vo cho qua biu ch cn bng th u ra sthu c mt tn hiu khng c sng mang v b loi b bi thit b ny. Tn hiuu ra gi l tn hiu 2 di bin trit sng mang hay DSB.

- S mt cn bng sng mang: nu thit biu ch cn bng l ltng th u ra hon ton b trit tiu sng mang, tuy nhin trong thc t khng xy rahin tng ny vn tn ti sng mang u ra. Ngi ta gi ci t l ny l t l trittiu sng mang, l mt thng squan trong. tnh c t l trit tiu sng mang ta


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cn bit c bin ca sng mang cha trit tiu. y l sng mang cho php 100%iu ch bi mc tn hiu ti a m h thng c thit k.


- Cc bc tin hnh thc nghip, phn tch thc nghim.+ Quan st thc nghim ti im 4 v 5 bng c hai my

phn tch.

+ Chnh carrier balance v mc gia t quan st ti im 6ghi li hnh dng sng, dng my phn tch ph quan st tn hiu.

+ iu chnh carrier balance v ghi li nhng nh hngca n n bin sng mang. Lm tng tnh trn vi vic iu chnh modulationlevel v carrier level ghi li tn hiu quan st c.

+ t que ti im 13 v iu chnh BFO frequency cmt sng n nh sao cho cng pha vi sng mang gc. Quan st u ra ca b phthin sai khc sao cho tng t vi tn hiu iu ch.

+ Mkha BFO v quan st kt qu.+ Ti im 6: Sng mang b trit

+ Ti im 16: Gii iu ch => pht hin sai khc gia fBFO vfc

+ o tn s: T= 2,148 s (ca BFO)+ T = 2 s (ca sng mang)+ Quan sat ti im 5: sng bnh thng+ Dng my phn tch ph quan st tn hiu: fs vo khong

401503 KHz+ Khi chnh carrier balance v mc gia => sng mang tri hn

so vi lc u.+ Khi tng ln vpha max, bin sng tri tng ln na.

+ Khi tng modulation level v carrier level th bin sng tiptc tng.

- Nhn xt:+ Nhn thy vic iu ch AM c hiu sut thp v phn

ln nng lng truyn dn i vo sng mang m khng mang tin tc, bi ch c hai dibin ca sng mang sau iu ch mi mang tin tc, sng mang ch gip ch cho viciu ch.

+ Trong thc t biu ch cn bng khng th trit tiuhon ton sng thu c tn hiu DSB, qua thc nghim cho thy iu ny.

+ Dng my phn tch ph th ddng quan st c tn sca DSB hn bng my nghim sng.


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+ Hiu sut truyn dn ca h thng DSB cao hn h thngAM n gin do trit tiu c sng mang sau iu ch, ch thu li di bin kp casng mang sau khi i qua biu ch cn bng.

+ T l trit sng mang ca h thng DSB khi t bin trit sng mang mc max tt hn nhiu khi t mc min. Khi bin sng mang mc min di bin kp cha tin hiu tin khng thxc nh c.

b. Bi 2: Shnh thnh ca di n bin trit sng mang SSB- Trong bi thc hnh DSB ln trc c th thy vic trit tiu

sng mang ta thu c di bin kp cha thng tin ging nhau. Do tit kimnng lng ln truyn dn mt di bin m vn m bo lng thng tin gc, ngoi ran s gip tit kim c bng thng s dng trong AM v DSB.

- Thit bc s dng trong bi thc hnh ny l biu chcn bng to ra DSB ni vi mt b lc ca di tn bin yu cu.

- Mi b lc di tn bin yu cu, dng lc di bin trn, dibin di theo yu cu.


- Cc bc tin hnh thc nghim v phn tch thc nghim.+ Dng my phn tch ph v my nghim sng quan

st tn hiu ti im 6. Ghi ch li tn hiu DSB. Chnh carrier balance v mc gia vquan st tn hiu ti im 8 v 9.

+ Dng my nghim sng quan st u ra SSB, iu chnhmy phn tch ph sao cho tn s ca di bin trn l tng ca tn s sng mang v tnsiu ch vi tn s ca di bn di l khc nhau.

+Ti im 6: iu chnh f cn bng, khi hng s cn bng

Max => thu c tn hiu tt+Ti im 9: Ts = 2,343 s, Ti im 8: Ts = 2,148 s

->Khng nhn r ph, tn s tn hiu thu c ti 2 im l gn nh nhauQuan st trn mn hnh, qua b lc di tn bin trn v bin di thu c2 tn hiu sng ngc pha nhau.

- Nhn xt:+ Nu nh khng c biu ch cn bng to ra DSB

th vic s dung biu ch SSB skhng em lai hiu qu, t hnh trn c th thy tu thng qua biu ch cn bng trit tiu c sng mang v thu c 2 di bin


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kp mang thng tin,v truyn 2 di bin ny tn nng lng ln mi dng n b SSBnhm em li hiu qu ti u nht trong truyn dn.

+ lc c di bin trn hoc di th bng thng cab lc SSB phi bng gii hn tn siu ch ci.

2.1.1.3 Nhn xt- iu chkhng dng sng mang v iu ch c dng song mang ca

AM th vic iu ch khng dng sng mang c hiu quhn tit kim c nnglng trong truyn dn, tit kim c bng thng sdung AM v DSB, chng ul dng tn hiu tng tsau iu ch.

- Xt v mc phc tp th thit biu ch khng dng sng mang cmc hot ng phc tp hn, i hi chnh xc cao hn v tc nhin l mc thng tin thu c sau gii iu ch tt hn so vi iu ch c dng sng mang.

2.2.2 iu chtn s( FM )

Bi thc hnh 1:Khi nim viu ch tn s

y l bi thc hnh gii thiu viu ch tn s.Trong iu tn th tn sthay i cn bin c gi nguyn.

Quan st:

Cc bc tin hnh: t carrier level mc gia. S dng my nghim song quan st khi iu chnh thue cng l vic thay

i tn s.

Quan st tn hiu u vo ti im s 16 v tn hiu u ra ti im s 4. Quan st ti im s 4 s dng chc nng phng to ca my nghim sng

o gi tr tn s.

S dng my phn tch ph so snh vi gi tro c ca my nghimsng.

M t quan st:


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Ti im 16: o g trin p: o c in p Max Vmax= 0,6 V khng c ph Quan st ti im 4:t carrier level gia,manual frequency min ta o c chu k ca sngl:

T=2,734 , vi Vmin = -0,592 V

Sau t level gia,manual frequency max o c chu k ca sng l:

T = 1.756 . vi Vmax = 0,6 V

Nhn xt: My phn tch ph dxc nh phm vi hn my nghim sng, my phn

tch ph cho ta nhn thy kt qur hn, xc nh c tn s f.

S bin i ca bin trong di tn s: Trong di tn sbin ch thayi mt lng khng ng k.

Bi thc hnh 2: iu ch tn hiu FM sdng VCO.

Trong bi thc hnh ny ta s s dng mt tn hiu dng hnh sin iutn do chng ta s nhn thy c s xt hin ca cc tn hiu cmin thi gian v min tn s.

Ta c thiu chnh lch v ch siu ch. Ch rng s xut hinca tn hiu FM trn my phn tch ph ging vi tn hiu AM khi ch siu ch nh.

Quan st:

Cc bc tin hnh:


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GVHD:

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t carrier level mc gia.Quan st im s 4 ca my nghimsng

iu chnh modulation level n im max v min sau quan stcc nh hng.

Ch rng tn sl thay i.Ch rng khi t ngoi im quan st s 4c tn s cao

hn. Thay i n im quan st 3 v quan st ga tr ca tn hiu iu ch.

Ch ghi li mc chnh no m modulation level c tn scao hn. Dng my phn tch phxem rng ca tn hiu iu ch iu chnh modulation level v quan st sthay i ca lch.

M t quan st: t carrier level gia, modulation level min ti im 4 o c : T=2,313 . t carrier level gia,modulation level max ti im 4 o cT=1.855539,083kHz

ti im 3 o c T=17,8 56,179kHz

t carrier level gia,modulation level gia ti im 4 o cT=1.953

510 kHz

Ti im 3 o c T=17.8755,96 kHz

Nhn xt: Nhn vo quang ph ca tn hiu iu ch, ta c thc lng c tn s

ca tn hiu iu ch v vi tn hiu n gin th thnh phn ca tn s lnhng khong u nhau v bng vi tn siu ch trn mn hnh quan stph.

Ta khng th c lng c bng thng ca tn hiu iu ch trn myphn tch phc kh nu tn hiu iu ch l phc tp v c nhiu tn sv n l 1 di


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Khi iu chnh modulation level th: Thnh phn tn s sng mang ca tn hiu iu chnh thay i v n

mang tin

Bin tn hiu iu chnh khng i (trc iu chv sau iu chl nh nhau)

Bi thc hnh 3: Ph ca tn hiu vi H siu ch ln

Ta c biu thc ca bng thng l:

B = 2 (Fd + Fm)

Nu Fd = Fm th h siu ch ln: B = 2 Fd

Vi: Fd - lch ca tn hiu iu ch

Fm - bng thng ca tn hiu iu ch

Bi thc hnh ny cho ta thy khi h s iu ch ln th bng thng c xc nhthng qua lch

Cc bc thc hin: Chnh carrier level v mc gia. Xoay nt 5 kHz v quan st sthay i ca bng thng M t quan st: Khi nt 5 kHz mc Min th f = 446,8 kHz Cng tng ln th ph cng khng thy r Khi nt 5 kHz mc Max th phkhng quan st c.

Nhn xt: Khi tnh ton bng thng tn hiu sdng thc Carson

B = 2 (Fd + Fm)

Vi BBng thng tn hiu

Fd- lch ca tn hiu iu ch

Fm - Tn s ln nht trong di tn s


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Nu thm b lc di u vo ca thit btch sng FM th bng thng can tng t vi bng thng ca tn hiu

2.1.2.2.Gii iu chtn hiu iu chtn s1.mc ch

- Sinh vin tn hiu: B tch sng cu phng l gi?, b tch sng sdng vng kha pha PLL, nhiu.

2.Bi thc hnha.Bi 1: B tch sng cu phng.

- Trong bi thc hnh ny ta s tm hiu nguyn tc hot ngca b tch sng cu phng.

- B tch sng cu phng chia tn hiu u vo lm 2 phn, mt phn cdn trc tip vo b pht hin pha v phn cn li c dn vo b dch pha, ti y tnhiu c dch pha 900. Do khi gii iu chta c tn hiu vung gc vi nhau l

do gi l b tch sng cu phng. u ra ca thit bny c gn vi b lc ch chodi tn gc i qua v chn sng mang lai.- Quan st thc nghim.

- Cc bc tin hnh thc nghim, phn tch thc nghim.+ Quan st tn hiu ti im 9 khi thay i modulation level, ghi ch tn hiu ti

2 u vo 9 v 11 ca thit b.+ Chnh modulation level v mc gia, quan st tn hiu ti im 12 v 14.


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- Nhn xt:+ Quan st ti im 9 v im 11 nhn thy tn hiu b lch pha nhau 900.+ Thit bny khi c gn vi b lc n s cho tn hiu iu chc i qua

cn sng mang b chn li.

+ Tht ra mi thit bu c mc tng i no vic ni c s hon hoch l th hin v mt l thuyt cn trong thc t th cc thit b b pht hin pha, bdch pha, b lc u c sai s nhno .

b. Bi 2:Sdng vng kha pha PLL tch sng FM

- Thit b ny c tc dng ng b pha gia tn hiu ngun bn ngoi vipha ca n thng qua vic s dng mt vng lun chuyn v khi xy sng b th tns ca chng s ging nhau.

- Mt vng kha pha gm ba phn: b to dao ng ngi ta thngdng VCO to nn dng in p lun chuyn trong mch PLL, b tch sng pha, blc c tc dng lm mt tn hiu u ra ca b tch sng pha nhm cung cp tn hiuiu khin VCO, tiu chnh tn s ca n nhm lm gim s khc bit pha.

- Nguyn tc hot ng ca PLL: Gi s c mt tn hiu u vo c a quabtch sng pha v c a qua b lc lm mt tn hiu, tn hiu ny c tn skhng i nm trong khong cho php ca VCO. Pha ca n c so snh vi pha caVCO, v th pha ca VCO bt u thay i di tc ng ca tn hiu u vo cho nchng cng pha vi nhau. Lc VCO ngng thay i pha v ta ni hai tn hiu c kha pha.

-Thit bny c gn vo mt b lc sau iu ch th n s loi b

mi thnh phn tn s trn tn s ci lc ta c mt b tch sng PLL.- Quan st thc nghim:

- Cc bc tin hnh thc nghim, phn tch thc nghim.


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+ t quan st ti im s 9 v quan st tn hiu FM khiiu chnh modulation level.

+ Quan st tn hiu ti im 9 v 11, tng carrier ln max,quan st tn hiu ti im 12 v 14. Nhn thy im 9 c bin 0,45, im 9 bin

0.7.+ t carrier level max,khi modulation min ti im s 9

ta o c T=1.953

+ t carrier level max,khi modulation gia ti im s9 ta o c T=2.148 = 470 kHz

+ t carrier level max,khi modulation maxti im s9 ta o c T=1.855

- Nhn xt:

+ Khi gim bin ca dng tn hiu iu ch cc i v th tn hiuu ra ca di iu ch d nguyn bn cht trong gii hn ca PLL.Nguyn nhn l dovic gim bin trn vn nm trong mc m gii hn PLL cn chp nhn c, cngha l dng tn hiu u vo vn ln PLL c th hot ng. Vic giam bin trn ng ngha vi vic gim mc iu ch tn hiu. Trc khi tn hiu iu chc a vo vng kha pha PLL.

+ Khi ta gim bin ca dng xung thp hn na th PLL khng thkha pha c.

+ Khi mc tn hiu v cng thp th dng vo PLL khng

cung cp cho VCO hot ng, do VCO khng th so snh pha cua mnh vi phaca tn hiu thc hin qu trnh ng b. gii quyt vn ny s gn b gii hntrc b gii iu ch.

2.1.2.3. B gii hn v nhng nh hng ca nhiu ln vic gii iu chFM

1.Mc ch- Gip sinh vin tm hiu v nhng vn sau: B gii hn, nhiu

pht hin trc, nhiu pht hin sau.2.Bi thc hnha.Bi 1: B tch sng cu phng sdng b gii hn- Trong bi thc hnh ny sinh vin tm hiu cch thc hot ng ca b

gi hn.- Trong mt h thng FM thng tin c truyn i bng cch thay i tn

s ca sng mang, sthay i ca bin khng lm thay i ni dung ca thng tindo chng ta hon ton c th loi bn trc khi n thit b tch sng v cng vicny c thc hin bi b gi hn.

- Mt b gii hn ch l thit b khuch i bin i sng mang hnh sin

thnh sng mang hnh vung c bin cnh, sng vung ny c cha tn s bini ca tn hiu ngun.


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- Vic thm vo b gii hn trong thit btch sng FM c bin cnh, c ngha l u ra ca n ch ph thuc vo s dch pha m khng ph thucvo bin . ng nhin l b gii hn khng th cho ra tn hiu m khng tiu tnnng lng, v thbin ca sng mang u vo s gim i qua b gii hn s gim

khi lng nhiu tng ln.- Quan st thc nghim.

- Cc bc tin hnh thc nghim, phn tch thc nghim.+ Gb b gii hn ra khi mch, chnh modulation ln

max, quan st tn hiu ti im 14 khi iu chnh carrier .+ Dng nt limier button gn b gii hn vo trong

mch, quan st sthay i ca tn hiu.Khi khng c b Limiter:

+ t carrier level min, modulation maxquan st ti im 14 :khng c sng

+ t carrier level gia,modulation max quan st ti im 14 ta oc :T=17.87 =55,96Hz

+ t carrier level max, modulation max quan st ti im 14 ta oc :T=17.87 =55959.71Hz

Khi c b Limiter:+ t carrier level min, modulation max quan st ti im 14 ta o

c :T=17.87 56 kHz

+ t carrier level gia, modulation max quan st ti im 14 tao c :T=17.87 = 56kHz

+ t carrier level max, modulation max quan st ti im 14 ta oc :T=17.87 56kHz

- Nhn xt:


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+ Vic khng c b gii hn trong mch th tn hiu cagii iu chu ra vn ph thuc vo bin ca sng mang. Tuy nhin vic phthuc vo bin sng mang hay khng ny cn ph thuc vo tn hiu ngun c phctp hay n gin.

+ Khi s dng b gii hn cho b tch sng cu phng tanhn thy ti im 9 sng mang c dng hnh vung, bin khng i, v tn hiu saugii iu ch tt hn nhiu vi vic khng s dng n.

+ Khi khng c b gii hn th sng mang ti im 9 cdng hnh sin, cn khi c thit b ny thi sng c dng hnh vung, bin khng iv u ra ca b tch sng ch ph thuc vo s dch pha m khng ph thuc bin .

b.Bi 2:nh hng nhiu ln b tch sng cu phng- Nhiu l g?. Nhiu l tn hiu khng mong mun c chn ln vi tn

hiu yu cu, trong nhiu trng hp n khng c mt tn s ring bit no v n tnghp ca rt nhiu tn s.

- T l tn hiu /nhiu(SNR)+ Mt phng php o cht lng tn hiu i vo btch sng l o

SNR. Khi ta o t lnng lng tn hiu trn nng lng nhiu tiu tn c thnh gic mc nhiu ca n.

+ C 2 t lSNR thng gi l nhiu trc iu ch SNRi v t l nhiusau iu ch SNR0.

- Khi c nhiu th cbin v tn su thay i, mc thay i ca

n cn ph thuc tng loi nhiu.- Quan st thc nghim.

- Cc bc tin hnh thc nghim, phn tch thc nghim.+ Chnh carrier level v modulation level ln max, chnh noise level v min,

gb b gii hn ra khi mch.Quan st tn hiu ti im 14 bng my nghim sngv tng t t noise level ln. Nhn thy ti im s14 khi cha c nhiu th tn hiusau gii iu chn nh, v khi tng noise ln dn nhn thy tn hiu bt u c xu

hng khng n nh, tn s, bin c sthay i, cht lng tn hiu khng tt.


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+ Gn b gi hn vo mch bng nt limiter button v lp li cc thao tc trn.Quan st ti tt ccc im thi hiu cch m h thng hot ng.Nh vy sau khign b gii hn tn hiu thu c ti im 14 n nh hn khicha c thit b ny, tuynhin khi iu chnh nhiu tng ln th tn hiu cng bt u khng n nh nhng

mc khng n nh nhhn khi khng s dng n.- Nhn xt:

+ T lSNR l thc o cht lng sng vin thng, SNR thng s dng nv tnh l dB v t ltng i ln.

+ Khi c nhiu th cbin v tn su thay i trong khi b gii hn cchc nng khuch i tn hiu dng hnh sin c bin thay i thnh tn hiu dnghnh vung c bin khng i do khi gn b gii hn ny th s gim c nhiu.

+ Khi chng ta gim mc sng mang th tn hiu sng mang iu chccng c xu hng gim m trong khi b gii hn khng th cho ra tn hiu m khngtiu tn nng lng, v thbin ca sng mang u vo s gim i qua b gii hns gim khi lng nhiu tng ln.Chnh v iu ny lm cho nhiu tng ln khi gimmc sng mang. Cho n khi tn hiu sng mang iu ch qu nhkhng khnng b gii hn c th nhn bit vi nhiu, th lc ny nhiu ln v tn hiu thu saugii iu chkhng xc nh c.

c.Bi 3: B tch sng sdng vng kha ph sdng vi b gii hn.- Trong bi ny chng ta s tm hiu cch m PLL hot ng cc tn hiu c

bin khc nhau. Nu tn hiu u vo ln th PLL skha pha giao ng ni ca

tn hiu v tn hiu c bin gp i khng lm thay i trng thi v th n khngnh hng n tn hiu u ra.- Sinh vin tm hiu xem khi s dng b gii hn vi vng kha pha PLL th

th tn hiu u ra sau gii iu ch snh th no?. N c tt hn khi s dng b tchsng cu phng hay khng ?. Mc ca nhiu sthay i nh th no khi c sdng b gii hn v khng s dng b gii hn, v khi tng nhiu th tn hiu u ra sc sthay i nh th no?.

- Nu tn hiu u vo nhv lch ln th b tch sng pha s khng th cho tn hiu u ra vn hnh VCO, do s khng th bt kp sthay i ca

lch. iu ny sc th hin khi ta thay i Carrier level v mc thp.- Quan st thc nghim.


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- Cc bc tin hnh thc nghim, phn tch thc nghim.+ Chnh carrier level v max quan st im 14 m khng c

b gii hn trong mch.+ Gim carrier level v quan st u ra?+ Gn b gii hn vo mch v quan st tn hiu ti u ra,

quan st tt cc im ca mch hiu cch m h thng hot ng.- Nhn xt.

+ Nu khng c b gii hn trong mch khi ta gim mc iu ch th mc sng mang cng gim theo trc khi xy ra s bin dng tn hiubi v PLL khuch i t hn, v trong tng hp ny s khng xy ra khi b gii hn

gn trong mch.+ Khi gn b gii hn th tn hiu u ra sau gii iu ch

sn nh hn nhng vn phi m bo iu kin l tn hiu sng mang iu chuvo phi ln b gii hn v vng kha pha PLL c th hot ng c, mi thitbu c gii hn nht nh hay c sai s gii hn no .

d.Bi 4:nh hng ca nhiu ln b tch sng sdng vng kha pha PLL- Nhiu lm cho cbin v pha ca tn hiu u vo bthay i, vic s

dng b gii hn gip cho vic loi bbin ny ra khi u vo PLL.- nh hng chnh ca nhiu lm cho bin ca nhiu c xu hng tr

v0, nhng vn cn bin ph hp ca tn hiu chy trong PLL. N tip tc bmtheo pha ca tn hiu u vo vi li nh nht gy ra bi sthay i bin nhiu.

- Quan st thc nghim.


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- Cc bc tin hnh thc nghim, phn tch thc nghim.+ Chnh carrier level v modulation level ln mc max,

chnh noise v min.+ Gb gii hn ra khi mch v quan st im 14, tng

noise level v quan st tn hiu u ra.+ Gim t l SNR bng cch gim carrier level cho n khi

tn hiu khng th nhn dng c.+ Gn b gii hn, quan st tn hiu u ra, quan st tn

hiu ti cc im hiu cch m h thng hot ng.- Nhn xt:

+ khi chnh carrier level v modulation level ln mc max,chnh noise v min, gb gii hn ra khi mch th ti im 14 tn hiu sau gii iuchtng i n nh. Cn khi bt u tng noise th tn hiu u ra bt u c s bt

n nh do tc ng ca nhiu ti u vo ca thit b tch sng.+ Khi gn b gii hn v tng noise t t ta nhn thy tn

hiu u ra bt u c s bt n nh v mc bt n nh stng ln khi vn noiselevel tin dn ti max.

+ Vic gn b gii hn lm tng t lSNR v bin canhiu b loi b.

+ Vic s dng biu ch bng PLL tt hn so vi vics dng b gii iu ch bng thit b so pha.Nguyn nhn PLL tt hn chnh nh

vo s dng vng kha pha PLL.2.2.3 Ngun tn hiu2.2.3.1 B to dao ng cu wien c bn

1.Mc chTm hiu vcc iu kin cho sdao ng ca bdao ng cu

wien, s cn thit phi kim sot bin ca bgiao ng cu wien.2.Thc hnh

a. Bi 1: Mch dao ng cu wien n gin


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- Trong bi thc hnh ny b khch i hot ng c cungcp vi mt mng hi tip m n gin, mng ny cho php iu chnh khuch ica n trong mt gii hn hp. Tip theo cc dng mang hi tip gn vo na cuwien bao gm R v C mc ni tip v song song.

- Bn cn lu rng khuch i qu mc lm cho thit b todao ng tin gn n gi tr gii hn bng vi dao ng u ra ca b khuch i, khivt qua ngng ny th sng u ra s b ct thnh dng hnh vung.


- Cc bc tin hnh thc nghim, phn tch thc nghim.+ R5 c thiu chnh c iu khin khuch i

bin . + t gain control mc cao nht, nhn vo dng sng ti2 im trn mn hnh. Quan st thy s dao dng ca chng.

Khi gain control max: f= 1.05 Hz

+ quan st ti im 2: sng c dng hnh sin,in p ca tn hiu= 4V+ quan st ti im 3: sng b gt, in p ca tn hiu= 11.2V

Khi gain control mc : f= 1.05Hz+ quan st ti im 2: sng khng n nh, in p ca tn hiu= 0.8V+ quan st ti im 3: khng n nh, in p ca tn hiu=2.4V

Khi gain control min

+ quan st ti im 2 v 3: khng c sng- Nhn xt:

+ Bin ca sng hnh sin ti im 2 nu vt qu mccho php s b ct gt khi n im 3 trn mn hnh.

+ Khi iu khin gain control th nhn thy bin ca tnhiu khng n nh, stng gim bin khng t l vi mc iu khin gain control.

b.Bi 2: Sn nh bin - Nu khuch i l rt nhbn di gi tr yu cu ca

bin th my to dao ng li ngng lm vic. Mt khc vi mt khuch i rt


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nh, sdao ng s gim dn cho ti khi bin b bin dng. Lm cch no chng tam bo tn hiu hnh sin n nh?.

- Biu trn cho thy hng hi tip m c iu chnh bihng khc c cha mt i i-t u lng. Chng dn in khng ng kcho nkhi in th qua chng khong 0.6 - 0.7v.

- Khi cc diot khng dn in hi tip m t khuch i

cao hn mt cht so vi cn thit cho sdao ng. Khi bin t ti 0.7v diot btu dn in tng hi tip m, hi tip m nhiu hn s lm gim khuch i. ys l mt bin ng cho khuch i duy tr sdao ng, bt k s bin thin noca bin cng lm thay i khuch i dn n vic phi dcho bin nnh.

- Quan st:

- Cc bc tin hnh thc nghim phn tch thc nghim.+ Bt u vi gain control ti gi tr ln nht, nhn cc dng

sng ti cc im kim tra trong khi thay i khuch i.+ Quan st cn thn bt k s khc bit no gia nh hng

ca vic iu khin khuch i trong bi thc hnh ny so vi bi thc hnh tosng wien c bn.

- Nhn xt: Bin tn hiu n nh hn khi trong mch c bnnh, n tng gim t t v t l vi mc gain control. l do c bdiot u lng mtn hiu khuch i n nh hn nhiu. So snh vi my tao sng wien n gin th tnhiu sau khuch i n nh hn, bin hu nh khng thay i. Bin ca sng

hnh sin ti im 2 nu vt qu mc cho php, diot bt u dn in tng hi tip m,


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hi tip m nhiu hn s lm gim khuch i, do ta quan st thy mc ctgt khi n im 3 trn mn hnh ca sng l nhkhng ng k.

c.Bi 3: Nhng thay i ttiu chun- Bi thc hnh nhm ch ra mt thit bdao ng cu wien c

th c s khc bit gia gia tr R, C.- Trong phn ny, phn cng c cung cp ging bi thc

hnh n nh bin , ngoi tr cc gi tr ca R2, R4.- Quan st thc nghim.

- Cc bc tin hnh thc nghim, phn tch thc nhim.iu chnh gain control to ra mt dao ng hnh sin n

nh, s dng my to dao ng ln xc nh khuch i ca my khuch i tim u vo dng cho n im u ra.

- Nhn xt:Ta stm c ra kt qu khc t gi tr ca im 3c a ra trong l thuyt Wien bridge oscilltaro. khng phi bi l thuyt nykhng ng m l vi mch khng di hn tng ng vi cc ginh ca l thuytWien bridge oscilltaro.

2.2.3.2. Bdao ng LC1.Mc ch

Sinh vin tm hiu v bgiao ng mch cng hng bao gmcuc cm v tin to tn sdao ng: Qu trnh hot ng ca bgiao ng iuchnh pha, Nhn t quyt nh n tn s ca n, Sn nh tn s ca bdao ng

i vi s bin i yu t khc.2.Bi thc hnh

a.Bi 1: Bgiao ng iu chnh thu.- Bi thc hnh ny gii thiu thit bdao ng cng hng

sau phn ny sinh vin s hiu: hi tip thno to ra dao ng, lm th no xuthin cc mch cng hng iu chnh tn sv m bo rng dao ng s xp x hnhsin, lm thno in dung r nh hng n s cng hng.

- Lu rng hu ht cc cuc tho lun cp v nhng gang xy ra tn s cng hng . tn s khc khng ch gim c vng lp m pha

ca n cn thay i kh nhanh vi tn s.


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- Cc bc tin hnh thc nghim, phn tch thc nghim.+ Quan st dao ng bin ,tn s khi dng mt t hay hai tu

mc song song ?.- Nhn xt: Khi mkha trong mch ch c mt t hot ng

th tn s tn hiu ln hn so vi khi kha ng vi 2 t mc song song. V khi 2 tmc song song th in dung trong mch tng th tn sdao ng s gim xung.

b.Bi 2:nh hng ca sbin i cc yu tkhc- Mt thit bdao ng thng phi c cung cp mt b

khuch i vng cao hn bt u dao ng, thay i thng xuyn in p cung cpsnh hng n bin dao ng. Bi thc hnh ny cho php bn nghin cu trngthi ca dao ng qua rng ca in p cung cp gia khong 5V n 10V.


- Cc bc tin hnh thc nghim, phn tch thc nghim.+ Phn cng c cu hnh nh tuned collector Oscillator

cc bi thc hnh trc ngoi trin p dng cung cp c ththay i gi tr giakhong 5V v 10V. Quan st nh hng ca sthay i in p cung cp n bin v tn s ca u ra.

+ im 6 o ngun in mt chiu, im 5 kim tra tnhiu sau khi qua trasistor to dao ng.


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-Nhn xt: Khi ngun in mt chiu tng th tn skhng inhng bin th gim xung, ngc li khi ngun in mt chiu trong mch gimtn skhng i nhng bin li tng.

2.2.3.3. Bdao ng thch

1.Mc tiuGip sinh vin c th hiu thm v: tnh nng ca bdao ng

thch anh, vic s tinh th thch anh n nh tn s ca bdao ng, dng sng cbn v sng hi bc cao ca dao ng gy ra bi bgiao ng thch anh.

2.Bi thc hnha.Bi 1: Dng sng c sv sng hi bc cao- Thit bdao ng thch anh c s dng khi mong mun mt

tn s rt n nh ca dao ng.- Cc tinh th thch anh ch c hiu qu tt nht ti mt tn s

nht nh. Vy bng cc t tinh th thch anh trong mt mch dao ng, thit b daong c th ch hot ng ti mt tn s.

- Bi thc hnh ny s cho chng ta bit lm cch no m vic akhong cht thch anh vo bdao ng c th lm n nh tn s.

- Thch anh l thnh phn ca my to dao ng in p, to rahiu ng in v ngc li hp th cc hiu ng in.

- Thch anh l mt hn hp nhiu vt liu, n c th to nhiukiu dao ng khc nhau ti cc tn s khc nhau.


- Cc bc tin hnh thc nghim, phn tch thc nghim.+ u tin vn nt iu chnh v ht ngc chiu kim ng h

ti gi tr tn s nh nht.+ Vn tuning control t ti mc ln nht sau iu chnh

dn dn v quan st hin tng.

- Nhn xt: Khi thay i tuning control t gi tr ln nht n gitr nh nht th bin v tn s ca tn hiu bin thin lin tc. Do cc tinh th thch


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anh cung cp c thit k s dng trong kiu dao ng chun ti 2MHz v nkhng tht tt lc dao ng bt u ti tn s hi bc cao. V hiu sut ca tinh ththch anh ti tn s bc cao khng thxc nh c v thit bdao ng c thit kcng bc nhng giao ng vi hiu sut tinh th thch anh thp. Scng bc ny

c th to ra cc dao ng ti nhng tn s khc nhau.2.2.3.4.Ba hi.

1.Mc ch: Lm quen vi ba hi n gin, y l loi bdao ngs dng transitor nh l cng tc, n to ra dng sng khc xa dng sng hnh sin.

2. Bi thc hnha.Bi 1: Mch c bn.

- Mi tng khuch i trong ba hi n gin l mt khuchi in p xoay chiu.

-Quan st thc nghim.

- Cc bc tin hnh thc nghim, phn tch thc nghim:Thit bdao ng c s dng kim tra sng mang ti 4 im trn mn hnh,myo tn sc ni n collector ca transitor tng th 2 ti im kim tra 11.

- Nhn xt: Do t C1,C2 ging nhau, dng tn hiu kim tra tiim 9 v im 12 ging nhau v cng mang gi tr m. Dng tn hiu ti im 10 v11 u l cc xung vung dng ngc pha so vi im 9 v 12 do n bo pha khii qua transitor.

b. Bi 2:nh hng tsthay i ca cc yu tkhc- Bi thc hnh ny gii thiu 2 c im mi: Ngun cung

cp in c ththay i c bi nt iu khin trn board mch, gii thiu diot c thc cho vo hoc ngt trong mch.

- Mc ch ca diot l ngn cn bo chiu dng in tdng chy, bo v2 transistor v on c tnh ca ba hi.



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- Cc bc tin hnh thc nghim, phn tch thc nghim.t ngun quan st mc max, s dng nt switch t

diot hoc ngt diot trong mch. Quan st sthay i ca tn s.- Nhn xt: khi khng t diot trong mch th dng tn hiu

tng tnh bi thc hnh trn. Khi s dng nt switch t diot vo trong mch thtn hiu ti cc im quan st thay i nh sau: Ti im 9 v 12 trn mn hnh quanst tn hiu n nh hn so vi khi khng dng n, ti im 10 v 11 xung c rnghn khi khi t diot trong mch.

c.Bi 3: iu khin tl mark/space.

- bi thc hnh ny c mt tnh nng mi l iu khin binthin t l mark/space. Thng qua mt bb p c thit lp vi 2 in trmc ni

tip vi nhau vi in trnh thi R1,R2.- Theo l thuyt vic thay i t l mark/space theo cch ny skhng lm bin i chu k ca u ra.


- Cc bc tin hnh thc nghim, phn tch thc nghim.+ T s mark/space c thiu chnh bi cc nt iu khin

cung cp trn bng in, iu chnh nt ny trong khi quan st tng im t, c bit

ch n dc ca hnh sng ti base transistor


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- Nhn xt: khi t smark/space thay i nhng tn s khngi v n thay i stng ti vi vic np nng lng ca cc t. Nu 2 tindung khc nhau tn s s bin i theo s bin i ca mark/space.

3.2 Cc mch s.

3.2.1. iu chdch bin ASK.1.Mc Tiu.

- ii iu ch nh phn ASK- S hnh thnh ca dng trit sng mang ASK (SC ASK)- ii iu ch trit ASK sng mang

2. C sl thuyt.a.Phng trnh ng bi hin di dng :

V(t) = Vcos(t + )Trong :

- V(t) l in p tc thi ca hnh dng sng.- V l bin ca hnh dng sng. - l tn s gc ca hnh dng sng.- l lch pha so vi pha chun. Biu thc tng qut cho 1 bin sng mang hnh Sin c iuu ch

bi sng iu ch hnh sin l:V(t) = (Vc + Vmcos m t).cos c tTong :- C biu th sng mang-

M sng iu ch- (Vc + Vmcos m t) l bin c iu ch ca sng mang. - cos c t l phn biu th tn s hnh sin sng mang.Sau khi phn tch, ta c phng trnh ca sng

V(t) = Vc cos c t + Vmcos(c - m).t + Vmcost(c + m).t

b. iu ch dch bin Trong h thng truyn thong s, tn hiu truyn i thng c dng sng

vung hay l mt chui xung.Ask l 1 dng iu ch bin , sng c iu ch bi cc sng vung v ccchui xung

S iu ch ny da trn s thay i bin ca sng mang gia 2 trng thi bt vtt. N c gi l on off AK hay kha on off.c. ii iu ch

Ti im n tn hiu ASK phi c iu ch. y l tin trnh ngc livi tin trnh iu ch v c thc hin bi my tch sng, lm nhim v loi bsng mang v ti to tn hiu u ra theo m nh phn ban u.

Nhng tn hiu ny s c a vo mch ti to xung duy tr tn hiu ngun v tnhiu uc khi phc.

3.Bi thc hnh.a.Bi 1: To tn hiu ASK

- Trong bi thc hnh ny ta s tm hiu vic ng ngt to ASK onoffiu ch nh bin cung cp dng tn hiu iu ch trc tip ca tn hiu s


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yu t c bn nht ca sng l kha. l s ng ngt theo chu k ng vi dng nhphn ca tn hiu.

- ASK c 3 thnh phn: sng mang, di bin trn v di bin di mimt di bin chim 1 tn s lin k vi tn s sng mangTrong Ask tn s sng mangkhng thay i, thnh phn ca sng mang c bin khng tong chu k ng.


- Cc bc tin hnh quan st thc nghim: Trong bi thc tp ny, ta c2 nt iu chnh pha gia, bn phi mch iu khin.Chnh nt iu khin in p vchnh gia.t MS bits switch (7) gi tr 0 v LS bits swich (8) gi tr 1. Ko qued ti mi im t v quan st tn hiu trn my dao ng.

- Nhn xt. Dng sng im s 1 l in p 1 chiu 2 nt data swith (7) v (8) MS bits (7) LS bits (8)iu chnh ngun tn hiu u vol cc s trong h thp lc phn, sau chuyn tn hiu nh phn iu ch tn hiuKhi ta thay i gi tr ti 2 nt ny, hnh dng tn hiu tu im 1 cng thay i titrng thy on hon ton khi thit 2 nt gi tr FF.

b. Bi 2: Di iu chdng diot- Bi thc hnh ny ta tm hiu khi nim gii iu ch tn hiu ASK s

dng b diode tch sng- Qu trnh ny c th xem l ngc ca qu trnh iu ch thc hin bi

mch tch sng loi b sng cao tn v to 1 tn hiu u ra tng ng vi tn hiu nhphn u vo.

- Tn hiu nhn c s qua mch c chp nhn khong gii hn nhngtn s gn vi tn s sng mang trnh nhng nh hng t nhng tn hiu bn ngoikhc

- V c bn b tch sng diode l 1 chnh lu v b lc thong thp - Cc bc tin hnh thc nghim, phn tch thc nghim. Quan st hnh

dng sng khi qua b tch sng diode cc mc khc nhau- Nhn xtnh dng sng c dng tng t nh ng bao quanh ti im s 2 tng t

nh im quan st s 1. Khi thay i gi tr u vo dng sng u ra cng thay iSng u ra cng c lm trn do tc dng ca b lc trong b tch sng diode.

c. Bi3: ASK trit sng mang


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- Cc bc tin hnh thc nghim, phn tch thc nghim: H thng nycng tng tnh h thng to thnh ASK m ta thc hin bi trc, ngoi trdng sng d liu u vo l dng lng cc, ta cng lm tng tnh bi thc hnhs mt v tin hnh quan st.

- Nhn xt: ti im mt dng s d liu nhn c l dng lng cc,ti im s 8 dng ca sng mang cng tng tnh dng sng bi trc. iuchnh balance control n10 nhn c sng u ra c bin ng nht, khi dliu iu chthay i trng thi tn hiu u ra s dch pha mt gc 180 . t MSbits witch s 7 v LS bits s 8 ti gi tr bng 0 dng sng mang ti im 2 khng i.

c. Bi 4: Gii iu chca ASK trit sng mang:- Cc bc tin hnh thc nghim, phn tch thc nghim: Ngoi

b tch sng diode h thng ny cn c thm pht hiu ng b. t cc ntiu khin v chnh gia. t MS bits swich v 0 v LS bits swich v 1, quanst tn hiu t vi my giao ng.

-Nhn xt.Ti cc im 1,2,v 8 dng sng ti ycng tng tnh dng sng ti bi thc hnh th 3 vi ASK trit sng mang. Quan st tiim s 2 v iu chnh balance control cho n khi nhn c bin ngnht, ta thy tn hiu ca b tch sng diedo khng going vi dng sng d liuiu ch.t MS swich 7 ti gi tr 0 va LS bits swich 8 gi tr ti 1iu chnh levelcontrol trn mc thp nht m ti sng u ra xut hin khng b gii hnnhng nh ca n khi :

o u ra ca b pht hin ng b khng tng ng vi d liu u vohay u nghch ca n

o C nhiu cao tng u ra b pht hin ng b 3.2.2. iu chtn sFSK

1.Mc tiu:Chng ta tm hiu v:- Qu trnh hot ng v c tnh ca b giao ng c iu khin bi

in p- S hnh thnh kha dch tn- ii iu ch FSK s dng vng lp pha.

2.Thc hnh:a.Bi 1: Qu trnh hot ng ca VCO

- cc bc tin hnh thc nghim, phn tch thc nghim: B daong c iu khin bi in p VCO trm c 3 bin tr iu khin Tn s, lch pha, pham vi. Cc nt iu khin ny chnh gia, phi trn caiu khin. Chnh tt c nt ny v v tr nh nht.

- Nhn xt: t Frequency, offset range control ti cc gi tr nhnht. Chnh requency control ln gi tr ln nht thay i in p ti im quanst v tn s ca b giao ng cng thay i theo. a frequency control v gitr min va range control ti gi tr ln nht. Chnh frequency control ln gi trmax ta thy range control khng nh hng ti n min bin thin di tn sVCO hot ng.

Frequency ctrl v range ctrl min value . t offset ctrl max value iu chnhfrequency ctrl ti gi tr ln nht ta thy:


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- Khng c s thay i no ng k- Tn s giao ng ng vi mi in p iu khin khng i vi tn s

thit lp nh nht ca offset ctrl- Offset ctrl c tc dng lm dch chuyn tn s

Nu in p VCO thay i gia 2 mc th dng sng u ra ti dao ng c ura di chuyn gia 2 gi tr.

b. Bi 2: Sto thnh ca FSK- Cc bc tin hnh thc nghim, phn tch thc nghim:

thng tng t trong bi iu ch theo bin tn hiu ASK, ngoi tr b iuch tn s c thay bng b iu ch bin . t tt c nhng nt iu khin gia. t MS bits Swich tai v tr 0 v LS bits swich ti 1 quan st cc imtrn mch my in ng.

- Nhn xt: Khi quan st im s 2 vi kch thc rng ca mydao ng ta thy iu ch tn s ca tn hiu

Khi t MS bits swich va LS bits Switch tai 0 th in p xut hin tiim quan st s 1

Khi t MS bits switch va LS bits tai gi tr F th in xut hin ti imquan st s 1Thay i c 2 gi tr data word switch thnh C v quan st quang ph ca dngsng tn hiu FSK trn kch thc ca quang ph my ta thy;

c. Bi 3: Gii iu chFSK sdng vng kha pha PLL- Cc bc tin hnh thc nghim, phn tch thc nghim:

thng sau s dng b tch sng vng kha pha gii iu ch FSk. t cc ntiu khin v v tr gia .t MS bit ti gi tr 7 v LS bit tai gi tr 0, LS bits

swich 8 ti gi tr bng 0. Quan st tn hiu cc im t vi my hin dao ng. - Nhn xt: Quan st trn kch thc din rng ca my giaoo dinti im s 1, ta nhn thy dng sng tai im ny dng in p 1 chiu, in pca dng sng l 0 V.Khi ta thy i MS bit 7 v LS 8 sang gi tr F.

- Dng sng vn l 1 chiu- in p ca sng dng ny l 5v

Quan st im s 2 vi kch thc rng ca my quang ph. Thay i c MS bits 7 vLS bits 8 sang gi tr 0, tn s ca dng sng ny l xp x 500kz. Thay i c MS

bits 7 v LS bits 8 sang gi tr F, tn s ca dng sng ny l xp x 160kz.B gii

iu ch vng kha pha to ra tn s ra khc vi tn s u v o v nhng tn s VCO.Quan st 12 vi my to dao ng . t range ctrl ti gi tr ln nht v iu chnhfrequency ctrl c gi tr nh nht. Khi , tn s VCO o c l 570 khz. t gi tr MS bits 7 v LS bits 8 sang gi tr 0 iu chnh frequency ctrl c gi

tr nh nht. Khi , tn s VCO o c l 470khz.Chn automatic VCO ctrl. Chnh PLL filter ctrl kha, ngha l, khi tn s VCOtng ng vi gi tr cho phch 0 ch iu khin bng tay. Khi tat hay i MS bitsang F, tn s VCO cng thay i sang trng thi tng ng 576khzThay i c MS bits 7 v LS bits 8 sang gi tr A , dng tn hiu ra b iu ch PLL ralung tn hiu.Thay i thit lp chuyn mch ca MS bits 7 v LS bits 8 ta nhn thy

tn hiu gii iu ch PLL u ra cng thay i theo lung d liu u vo.


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