, ( 1 0) - . 1 0 , , to ( ) . . - , , - . , "" , .. "1" - t, "" - , t , 3 t (.2.2). ( , - ) , , .
( )
1 1 0 1 1 1
"" "" ▬
t t 3t
.2.2
( , ) , . k . k
k = log2 N, N - , .
(1 0) , 1 (bit - bi nary digi T), /. to B = 1/to . , to = 20 = 50 /. (, 1 / 1 ).
, 1 0, .
, .
(-2)
, - (). - . , N 2 (-2 - ITA -2). 5-, .. 25=32 (.2.3). , ( - , ) . , . , 10011 , - , - ?. .
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-2 ( )
1 0 0 1 1
+U
t
to to to to to
- U
.2.3
ASCII
ASCII (American Standart
Code for Information Interchange) - . 7 . 7 () 27=128 , , , .
- (1 = 8 ), - , , , ( ASCII 128 255).
, (-2, ASCII), - . (, "" -2 ( 11000) - ( 1100 1) "". .. , . - - , . . . , , "1". - 1 0 - , . , 11000 - 110000. , , - 1100 1 0 . , , "" . . (check parity) . , - , . , , . , 3 5 - 11 1 0 1 0 "", 11101 -2.
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( ) . , 7- 3:4, 3 "" 4 "" (, 1001001, 1101000, 1100100). 27 35 . "" 3:4 , "". . (): , ). , .
. , .
¥ ¥
X(w) = ∫S(t)℮- jwtdt, S(t) = [1/(2p)]∫ X(w)℮ jwt dw[RV1]
-¥ -¥
w=2pf
X(f) S(t). , ( ), . , , , .. , . , . (, 1 ). . 2.4 .
, 3 1/to. to, ∆f = (1...3)/to. , (0...1/to) 90% , (0...2/to) - 95% , (0...3/to) - 97% .
.2.4
, , 20 20000 , , . , 300...3400 ( 300...3300 ).
( - 3000 ).
, (, , ) . "" , .. (. .2.3), . ( ), . (). , . , ( , ) () , . , .
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2.4.1.
() . , (Socos2pFot - .. , .2.5).
.2.5
- () :
U =( + Soos2pFo)os2pfot = Ao[cos2pfot + 0.5Mcos2p(fo+Fo)t + 0.5̷cos2p(fo+Fo)t]
,
0 ,
S0 - ,
f0 ,
F0 .
.2.6 c - Fo S (.), - fo (.) (.). , ( Fo) (fo). (fo) - (fo+Fo)
(fo-F0). = So/ , 0 ≤ ≤ 1.
> 1 , , , .
-
S0 A0 0
0.50 0.50
f f f
0 F0 0 f0 0 f0-F0 f0 fo+F0
) ) )
.2.6
, F - (.1) F (.2) (.2.7.), - , (fo-F) - (.3) (fo-F) (.4) , (fo+F) (.6) (fo+F) (.7) (.2.7,). fo .5.
-
f f
0 0
1 2 3 4 5 6 7
) )
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.2.7
, -, fo 2F. . , 2 .
2.4.2.
fo (.2.8).
. 2.8
- :
U = cos(2pfo+kScos2pFo).
fd = kS fo . = fd/Fo . , .
, . ( - , - ), - .
, , - - .
- F = 2∆F, ∆F - , .
> 1, - -. , , , .
. , , , , .. . - . - , , , , .
().
2.4.3. -
( ). , . , . , , ( ) , .
(Amplitude Shift Keying) , 0 1. , 1
S1 = A·Cos(2pft), 0 - , ..
S0 = 0. . , , . , , .. .
(Frequency Shift Keying) . , 1 , 0 - : S1 = A·Cos(2pf1t), S0 = A·Cos(2pf0t), "' "" (, +/- 85 , f0 - f1 = 170 , +/-400 ). . , - .
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(Phase Shift Keying) . S1 S0 , .. p.
S1 = A·Cos(2pft), S0 = A·Cos(2pft+p) = - S1. .
- .
2.4.4.
() - .. . .
( = + ). , "" , .. , 300 . 300...3400 (.2.9). , , 1 0
1270 (f1) 1070 (f2) . 2225 (f3) 2025 (f4). , . , .
.2.9
2.4.5.
- (.1.3) , . f ( ) . , = 1, - 25% , .. . . , , ( ). - (SSB). , 4...8 .
, .
2.4.6. , .
(). .
, . , , :
;
;
R - ;
J ;
.
, , :
F - ;
G - .
, , . :
1 - ;
2 ( );
3 .
, , ,
( );
( );
;
.
1 - Unmodulated Morse code -
f - -
A2A - Double-sideband (DSB) modulated Morse
H2A - Single-sideband (SSB) modulated Morse code
3 - DSB Telephony (Commercial broadcast)
H3E - SSB Full-carrier telephony (2182 kHz)
R3E - SSB Reduced-carrier telephony
"" ( 16...18 )
J3E - SSB Suppressed - carrier telephony
F1B Telex -
- ()
fo =f - 85 , f1 = f +85
J2B - Telex
- ()
( , , )
f -
f0=f-85 = f,+1615
f1=f+85 = f,+1785
F3E\G3E - Frequency\Phase modulated telephony
/
2.4.7.
, . , , . s(t) (.2.10,) : (.2.10,), (.2.10,) ( 2.10,).
.2.10
, s(t) s(t1), s(t2) t1, t2... c . ( ), , F, = 1/(2F). . , ( 0) N /(N+1). , . N , n = log2 N. . .
to to = 1/(2F n). , F = 4000 N =256 (n = 8), 64 /c.
2
1. .
2. .
3. .
4. ?
5.
6. ?
7. ?
8. , - , F.
9. .
10. .
11.
12. - - .
13.