1 0-200 . 5-5000 . ?
, .. 50 . 2×5 = 10 1 , .. 11 . : (200-50+5)/11 = 14 .
-:
Bu(t) = u(t) u(t-t) dt. (9.1.12)
C , , u(t)=U(t)cos wot :
cos wot cos wo(t-t) = 0.5 cos wot + 0.5 cos wo(2t-t).
Bu(t) = U(t) U(t-t) dt + 0.5 U(t) U(t-t) cos wo(2t-t) dt. (9.1.13)
- U(t)U(t-t) 2wo, . U(t). :
Bu(t) @ BU(t). (9.1.14)
:
Bu(0) @ (1/2) BU(0).
:
Bu(t) = . (9.1.15)
- .
( ) .
. 9.1.7 - ( ). : 30 , 3 , =1.
, , 2wo 5 . ( 4/5) . . =1 , =0 ( ) .
. 9.1.7.
2-, 3- (.. {117, 120, 123} , {177, 180, 183} ..), . 2%, . , .
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, .
. . :
y(t) = u(t) cos(wot) = U(t) cos(wot) cos(wot) = ½ U(t) + ½ U(t) cos(2wot). (9.1.16)
. 9.1.8.
, , , 2w. . 9.1.8 , . , , . , : 2w , wo , 2 . , .. 1.
-.
Dw :
y(t) = U(t) cos(wot) cos(wot-Dj) = ½ U(t) cos(-Dj) + ½ U(t) cos(2wot-Dj).
, Dw=p/2 .
:
y(t) = U(t) cos(wot) cos(wot-Dw) = ½ U(t) cos(-Dwt) + ½ U(t) cos((2wo-Dw)t),
(beat ) Dw.
.
. 9.1.9. . |
(-). , . , , , 100%. , ( ) U(t) = M×cos(Wt) :
u(t) = UmM×cos(Wt)×cos(wot) = (UmM/2){cos[(wo+W)t] + cos[(wo-W)t]}, (9.1.17)
.. . , . . 9.1.9. . 9.1.4 wo. , - wo :
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u(t) = (Um/2){ Mncos[(wo+Wn)t+Fn] + Mncos[(wo+Wn)t-Fn]}. (9.1.18)
. U(t) 1800, . ( ), wo, , , .
, . , , , - , . - , . "" (-), .
. . , . ( , single side band - SSB) 9.1.11. ( '+' ) ( '-') :
u(t) = Umcos(wot+jo) + (Um/2) Mncos[(woWn)t+jo Fn]. (9.1.19)
. 9.1.10. .
, . 9.1.10 , , , , U(t), = 1 ( ).
, , , . 2 .
( , -), .
, , , . .
s1(t) s2(t) ( ) . . . 9.1.11, s1 s2.
. 9.1.11. .
- . , :
smono(t) = s1(t) + s2(t), sdiff(t)= s1(t) - s2(t),
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:
s1(t) = (smono(t)+sdiff(t))/2, s1(t) = (smono(t) - sdiff(t))/2.
, . wo (subcarrier), ( ), ( ):
s(t) = smono(t) + (Ao + sdiff(t))cos(wot).
. , , . . 9.1.11, , . . 0, , .