Mạch Phát FM

Mch pht FM in t 8-K53

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LI NI U

Trong nhng nm gn y, vic pht trin cc thit b khng dy l

hng pht trin mi v ang c ch trng u t vi nhiu thnh tu t c

khng nh. Xu hng ny khng ch cc nc pht trin m cc nc ang

pht trin cng hnh thnh rt r nt. Cng vi s pht trin ca cc mch tch

hp, u im ca cc thit b ny l nh gn v d dng trong lp t, s dng do

khng phi tnh ton vic i dy, b tr cc thit b. C th k ra y mt s ng

dng tin ch trong gia nh m s thay i ny em li s tin nghi, thoi mi

cho con ngi nh: in thoi ko di ,chung ca t xa, qut tng c iu khin

t xa

Mc Lc PHN I. C S L THUYT CA IU TN ............................................................. 3 1. iu ch tn s (FM) : ............................................................................................... 4


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a. Dng sng Udt(t). .................................................................................................... 4 b. Dng ph ca iu tn. ........................................................................................... 5

.Ch s iu bin FM:.................................................................................................... 6 PHN II. S NGUYN L ........................................................................................ 6 1. Ch tiu k thut........................................................................................................ 6 2. S khi: .................................................................................................................. 7 3. Chc nng cc khi: .................................................................................................... 7

a. Mch vo: ............................................................................................................... 7 b. Mch lc: ................................................................................................................ 8 c. Khi khuch i m tn: ......................................................................................... 8 d. Khi dao ng : ...................................................................................................... 8 f.cun cm ................................................................................................................... 9

4. S nguyn l: ....................................................................................................... 10 5. Nguyn tc hot ng ............................................................................................... 10

PHN III. TNH TON ................................................................................................... 11 1. Khi khuch i m tn ........................................................................................... 11 2. Khi dao ng (khi to sng) ................................................................................ 12 3. Cng sut pht ca mch .......................................................................................... 12 4. C li pht ti a. ........................................................................................................ 13 5. S mch in: .......................................................................................................... 14

PHN IV. Kt qu m phng trn phn mm workben ................................................... 14 PHN V. Kt lun ............................................................................................................ 15 1. V cc thng s k thut : ......................................................................................... 16 . V cc yu cu khc :................................................................................................ 16 3. u v nhc im ca sng FM: .............................................................................. 16 4. ng dng ca iu ch FM:...................................................................................... 16


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NI DUNG

PHN I. C S L THUYT CA IU TN

Thng tin m chng ta truyn t (m thanh..) phn ln nm khong tn

hiu thp, nu khng thng qua iu ch trc khi pht bng sng v tuyn , s

gp phi nhiu vn kh khn nh khong cch truyn, tn hao, nhiu, gii hn

bng thng, kh khn pha thu. ... khc phc nhng vn ny , ngi ta s

dng nhiu k thut khc nhau a tn s ca tn hiu mang tin ln khong tn

s cao ,ph hp vi hon cnh v thit b . Ngi ta gi l cc k thut iu

ch. iu ch l qu trnh ghi tin tc vo mt dao ng cao tn nh bin i mt

thng s no ( v d: bin , tn s, gc pha, rng xung, ) ca dao ng

cao tn theo tin tc.

Trong trng hp ny, tin tc c gi l tn hiu iu ch, dao ng cao tn

c gi l ti tin, cn dao ng cao tn mang tin tc c gi l dao ng cao tn

iu ch.

Ni chung cc phng php iu ch rt a dng , bao gm c iu ch cho

tn hiu tng t v cho tn hiu s , trong , mt trong nhng phng php n

gin cho tn hiu tng t l phng php iu tn frequency modulation (FM).

iu tn l qu trnh ghi tn hiu tin tc tn s thp vo mt dao ng tn s

cao lm bin i tn s theo tn hiu tin tc. Trong iu tn, tn hiu iu tn thay

i quanh tn hiu ti tin. Phng php ny khc vi phng php thay i bin

ca sng mang hay cn gi l iu ch bin - amplitude modulation (AM) .

Trong k thut truyn thng tng t , gi tr ca tn hiu mang tin s nh hng

trc tip ln tn s ca sng mang .

Mc ch ca iu ch l chn mt ph tn thch hp cho vic truyn thng

tin, vi cc tn s sng mang khc nhau ngi ta c th truyn nhiu tn hiu c

cng ph tn trn cc knh truyn khc nhau ca cng mt ng truyn. Xt tn

hiu ti tin : Ut(t) = Umt cos t t

Nu t thay i tng ng vi ngun thng tin, ta c tn hiu iu ch tn s

(FM). Mt k thut iu ch tng t l iu ch pha PM ((t) thay i). Trong

phm vi bi tp ny, ta ch xt k thut iu tn.


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1. iu ch tn s (FM) :

Xt tn hiu:

Tin tc Us(t) = Ums cos s t

Ti tin Ut(t) = Umt cos t t

Khi iu ch tn s, tn s ca dao ng cao tn bin thin t l vi tn hiu iu ch v c xc nh

dt = t + Kdt .Ums cos s t

Trong : t l tn s trung tm ca tn hiu iu tn.

fmax = Kdt .Ums gi lng di tn cc i

a. Dng sng Udt(t).

dt = t + Kdt .Ums cos s t

C dt = ddt(t)/ dt

ddt(t) = dt(t).dt

= (t + Kdt .Ums cos s t).dt

= t(t).dt + fmax cos s t .dt

= t.t + (fmax / s). Sin s t

Biu thc ca iu tn :

Udt = Umt cos (t.t + (fmax / s). Sin s t)

= Umt cos (t.t + mf Sin s t)

Hnh 1. S m t iu ch FM

Vi mch iu ch tn s th sng mang c bin khng i, nhng tn s

thay i theo bin ca tn hiu m tn, khi bin tn hiu m tn tng th tn


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s cao tn tng, khi bin m tn gim th tn s cao tn gim. Nh vy sng

mang FM c tn s tng gim theo tn hiu

Hnh : Tn hiu trc v sau iu tn

b. Dng ph ca iu tn.

Udt = Umt cos (t.t + mf Sin s t) c th biu din dng chui m h s l cc

hm Bessel loi 1 bc K.

Udt = Umt cos (t.t + mf Sin s t)

=Umt + J0(mf) cos tt + Umt J2k(mf)[sin(t + 2ks)t + sin (t- 2k s)t] +

Umt J2k+1(mf)[cos(t + (2k+1)s)t - cos (t- (2k+1) s)t] +...

Tn hiu iu tn c v s thnh phn tn s, trong diu tn di hp fmax


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Hnh 3: Ph tn hiu iu tn

2.Ch s iu in FM

Ging nh cc phng php iu ch khc , i vi FM ch s iu ch

cng ch ra mc thay i ca tn hiu iu ch so vi tn hiu cha qua iu

ch . trng hp ny , l mc bin thin ca tn s sng mang :

( )m

m m

f x tfh

f f

Trong mf l tn s iu bin cao nht .Nu h


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Mch pht tn hiu trn bng tn FM c thit k vi mc ch c tnh ng dng cao nn cn u tin mt s c im sau - Tn hiu pht i c cht lng tt, tm pht xa khong 20m. - Mch nh gn, tit kim chi ph ti mc ti a. - Ngun cung cp phi n gin v nh gn. Mch c cc thng s k thut nh sau - Ngun cung cp 9V - Tn s pht nm trong di FM t 64 108 Mhz. - Tm pht xa 20m.

2. S khi:

3. Chc nng cc khi:

a. Mch vo: bao gm khi ngun v micro-audio:

Khi ngun Micro


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Khi ngun: ch to t ngun tuyn tnh u ra c 9-10v

Micro: gm dy adio a tn hiu m thanh t my tnh hoc thit b m thanh (my tnh,i..)vo mch iu bin Fm b. Mch lc: Mch lc y ch n gin l t C1, ngn 1 chiu t mic vo Q1.V tr khng vo ca Transistor nh ln tn hiu m tn t b sp p trn C1 th dung khng ca chng phi nh hn nhiu so vi tr khng vo ca transistor,do C1 thng chn 3-10uF. Trong mch s dng t C1 l 10uF. c. Khi khuch i m tn: Gm Q1, R2, R3, R4, R5// C3. Q1 c mc theo kiu EC, R2, R3 lm nhim v phn p cho cc Base. To im lm vic tnh cho Q1.Chc nng ca khi lm nhim v khuch i tn hiu t mic a qua t C a ra tng sau:

Khi khuch i m tn

d. Khi dao ng :

Khung dao ng L1C5 to ra tn s dao ng ring chnh l tn s sng

mang .Khi tn hiu vo thay i, tn s ring ca mch cng hng ny thay i


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trong mt di tn theo s bin thin ca tn hiu. Gi tr trung tm ca di ny

chnh l tn s pht ca mch.

Cun cm L1 dng chn cao tn ( chn xoay chiu).

R7 ,R8 lm nhim v phn p to im lm vic cho Q

e. Anten:

Lm nhim v pht tn hiu c tc dng tng kh nng bc x sng in t ra mi trng xung quanh. C cu v tnh cht ca antena l mt trong nhng yu t quan trng quyt nh c ly pht ca mch. y em dng ngten l si dy dn nhiu si di khong 30cm

T C5 =5pf

f.cun cm

cng thc tnh cun cm cho hnh tr trn di

L = t dung o bng Henry (H)

0 = t thm ca chn khng = 4 10-7

H/m


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K = h s Nagaoka (ph thuc co gin cun dy c =1)

N = s vng

A = thit din cun dy o bng mt vung(m2)

l = chiu di cun dy (m)

y em cun cun cm c dy 0.4mm,cun 0 vng li khng kh

4. S nguyn l

5. Nguyn tc hot ng

Tn hiu c a vo mch thng qua mt rc micro. in tr 1 ni tip vi

micro vo ngun phn cc cho tn hiu vo. m thanh thay i khi qua dy ny

s c chuyn thnh tn hiu in a qua t C1 vo cc B (baz) ca transistor

Q1 mc Emiter chung (EC). in tr v 3 phi hp to im lm vic tnh Q

cho transistor Q1. ch xoay chiu, transistor lm vic xung quanh im lm

vic tnh Q ny. Tn hiu sau c khuch i v a vo cc Baz ca

transistor Q2 thng qua t C ( nhim v ngn 1 chiu v cho xoay chiu i qua).

Transistor Q c mc Emiter chung (EC), hi tip C-E bng t C6. Khi tn

hiu a ra t chn C ca transistor Q1 bin thin xoay quanh mt tr s tnh (do

im lm vic tnh Q ca Q1 quyt nh) t tn s ring ca mch dao ng


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bin i to nn s iu bin tn s (FM Frequence Modulation) cho mch ny.

Anten ni vi cc Colector ca transistor Q gip tng kh nng pht x ca

mch.

PHN III. TNH TON

1. Khi khuch i m tn

Q1 l transistor loi bnh thng (2N2222A), R2 v R3 l cc in tr nh

thin xc nh im lm vic cho transistor c chn trong mch vi gi tr

15K, 6,8K R4 l in tr ti, tr s thng dng trong khong 1K n 10K,

trong mch ta chn 10K.Nu in tr ti qu nh, h s khuch i s nh, nu


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in tr ti qu ln, in p mt chiu st trn ti s ln lm in p a vo

colector s qu nh lm hiu sut thp v tn hiu ra mo. R5 hi tip m dng

in mt chiu, C3 l t phn ng m tn dng n nh im lm vic

transistor,t thot thnh phn xoay chiu xung mt. Chn 5 4,7k, C6 47nF

(2A473).

2. Khi dao ng (khi to sng)

Khung dao ng to ra tn s dao ng ring chnh l tn s sng mang , ban u khi cha a tn hiu vo, tn s trung tm

Tn hiu sau khi qua transistor Q1 bin thin xoay quanh 1 gi tr c nh, lm thay i cm khng Lt lm cho tn s dao ng ca mch dao ng bin i theo tn hiu tin tc.

Cun cm c qun theo thng s : li khng kh, bn knh li r = 4mm. chiu di l=20cm. s vng dy N=20. dy ng ng knh d=0.4mm.

C6=33pF

Chn cc gi tr 7= 4,7K, R8=2,2K, R9=220.

3. Cng sut pht ca mch


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Cng sut ca Transistor: P=Uce.Ic

Uce = Vc Ve = 9 - Ve

Ub = R8Vc/R7+R8 = 2,2K.9 / 2,2K+4,7K

= 2,86V

Rb = R7R8/R7+R8 = 1,5K

Ub = Ib Rb + Ube + Ie R9 = Ib (Rb+ (1+) R9) + Ube

Vy Ib= Ub-Ube/ (Rb+ (1+) 9) ( =50)

= 2,87-0,7/1,5K+(1+ 50)220

= 1,7.10^-4 A = 0,17mA

Ie = (1+)Ib = 51. 0,17mA = 8,67mA

Suy ra Ve = Ie.R9 = 8,67mA. 220=2V

Uce = 9-Ve = 7V.

Cng sut pht ca mch l : Pt= Uce. Ic = 7. 8,67mA=60,7mW

4. C li pht ti a.

C li pht ca mch l khong cch ln nht tnh t mch m ti tn hiu thu c c cht lng nh khi pht i.

C li pht c tnh bng cn bc hai ca t s cng sut pht Pt vi cng sut my thu Pr

c trng ca sng radio l truyn v nhn trong mt di, cng sut thu ca my thu FM thng trong khong 0.1mW.

Vy khong cch ln nht m mch pht c l

Coi anten l l tng th khong cch pht thc t ca mch l d 24,6m


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5. S mch in

Do vic t mch in cn kh t vi mch c nh nn bn em lm mch in bng phng php th cng

PHN IV. Kt qu m phng trn phn mm workben

Do tnh cht mch tng t nn nhiu phn mm khng h tr m phng nh protues,..nn bn em chon phn mm wordkben m phng - phn mm ny d s dng v c th m phng c cc mch tng t tng i tt -Trong bi bo co ny em xin php khng trnh by cch s dng phn mm ny


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Di y l kt qu m phng cho mch trn

PHN V. Kt lun


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1. V cc thng s k thut :

Mch pht FM c thit k c cc thng s: tn s pht trong khong 64-

108MHz, ngun cung cp s dng l 9V, tm pht xa gn 20m hon ton m bo

cc yu cu k thut ra.

Cht lng tn hiu thu c s dng i thu FM thng thng cho tn hiu tt,

khng c ting n trong phm vi pht cho php ca thit b. .

2. V cc yu cu khc :

Mch c thit k c kch thc 4cm x 7cm, hn gn v chi ph thnh phm

thp, s dng linh kin truyn thng. Trn thc t, nu s dng cc linh kin dn

kch thc nh, ta c th thu hp kch thc mch xung m vn m bo cc yu

cu k thut vi gi thnh cao hn t 15% n 0%. Linh kin s dng ph bin,

quy trnh lp mch n gin v hiu chnh d dng . Nh vy, cc yu cu ny

m bo cho vic a vo thit b tai nghe khng dy m khng lm thay i

nhiu kch thc cng nh khi lng ca tai nghe, c tnh kh thi cao khi p

dng trong thc t.

3. u v nhc im ca sng FM:

Sng FM c nhiu u im v mt tn s, di tn m thanh sau khi tch sng

iu tn c cht lng rt tt, cho m thanh trung thc v c th truyn m thanh

Stereo , sng FM t b can nhiu hn so vi sng AM.

Nhc im ca sng FM l c ly truyn sng ngn, ch truyn c c ly t

vi chc n vi trm Km , do sng FM thng c s dng lm sng pht

thanh trn cc a phng.

4. ng dng ca iu ch FM

K thut iu ch FM c s dng ph bin trong khong tn s v tuyn VHF

dnh cho truyn pht m nhc v ging ni trung thc cao . H qu l FM gn

nh tr thnh mt loi chun iu ch truyn pht tng t tn s cao v

trung thc cao FM radio . iu ch FM s dng trong truyn pht tn hiu thng


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thng c gi l iu ch FM gii rng (W-FM) . Trong chuyn pht adio

chiu m FM gii hp (N-FM) c s dng tit kim bng thng .

Nhm sinh vin thc hin.

Ti liu tham kho: 1, K thut mch in t- Phm Minh H , Ngun internet: www.dientuvietnam.com,... 3, Electronic devices

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