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B. Jenis-Jenis Gelombang Elektromagnetik
1. Gelombang Radio
5<?=21>7 A149? =5AD@1;1> 75<?=21>7 5<5;CA?=17>5C9; 41> =5A1=21C
45>71> ;535@1C1> 3181G1 G19CD L = B 5<?=21>7 A149? =5=9<9;9
415A18 6A5;D5>B9 1>C1A1 H B1=@19 H 41> 497D>1;1> B521719 1<1C
;?=D>9;1B9 1C1D @5=21F1 9>6?A=1B9 41A9 BD1CD C5=@1C ;5 C5=@1C <19>
)961C 75<?=21>7 A149? =D418 49@1>CD<;1> ?<58 <1@9B1> 9?>?B65A D=9
B589>771 75<?=21>7 A149? 41@1C =5>31@19 C5=@1C C5=@1C 49 D=9 G1>7
:1A1;>G1 B1>71C :1D8 41A9 @5=1>31A A149?
5<?=21>7 A149? 497D>1;1> 41<1= B9BC5= @5=2931A11> :1A1; :1D8 G1>7
C941; =5>77D>1;1> ;1F1C @5>781>C1A 5<?=21>7 5<5;CA?=17>5C9;
25AC9>41; B521719 @5=21F1 75<?=21>7 1D49? BD1A1 41 4D1 =131=
31A1 D>CD; =5=21F1 75<?=21>7 2D>G9 ;5 @5>5A9=1>G1 G19CD 45>71> B9BC5=
1=@<9CD4? =?4D<1B9 41> B9BC5= 6A5;D5>B9 =?4D<1B9 # 41> #
Mari Mencari Tahu
>41 @1BC9 =5>75C18D9 A149? # 41> A149? # 2D;1> 5AB1=1 ;5<?=@?; 25<1:1A
>41 31A9<18 9>6?A=1B9 =5>75>19 1@1 G1>7 49=1;BD4 A149? # 41> A149? # @1
@5A25411> 49 1>C1A1 ;54D1>G1 41> 21719=1>1 :1>7;1D1> 6A5;D5>B9 ;54D1 :5>9B
A149? C5AB52DC 9;1 49@5A<D;1> 25A;D>:D>7<18 ;5 B1<18 B1CD BC1B9D> 49 415A18 >41
D1C<18 <1@?A1> 41A9 ;5791C1> 9>9 41> ;D=@D<;1> CD71B C5AB52DC ;5@141 7DAD >41
Gambar 9.2
Modulasi amplitudo pada
pancaran radio AM. a. Sistem AM (Amplitudo Modulasi)
5<?=21>7 2D>G9 25A6A5;D5>B9 A5>418 4921F1 ?<58 75<?=21>7 A149?
ionosfer G1>7 25A6A5;D5>B9 C9>779 &1;5C 75<?=21>7 C5AB52DC 49@1>31A;1> =5<1<D9
75<?=21>7 A149? B521719 @5AD2181> 1=@<9CD4? 5<?=21>7 A149? =5=9<9;9
gelombang
1=@<9CD4? G1>7 25A2541 2541 B5BD19 45>71> 75<?=21>7 2D>G9 G1>7
radio
4921F1>G1 45>71> 6A5;D5>B9 75<?=21>7 A149?>G1 C5C1@ #?4D<1B9
1=@<9CD4? @141 @1>31A1> A149? # 49<D;9B;1> @141 "-#"1
Bumi 5<?=21>7 BD1A1 G1>7 4921F1 ?<58 75<?=21>7 A149? B521719 1;921C
@5AD2181> 1=@<9CD4? 41@1C 45>71> =D418 49@1>CD<;1> ?<58 <1@9B1> 9?>?B65A
Gambar 9.3
Pantulan gelombang radio oleh G19CD <1@9B1> 1>7;1B1 G1>7 =5>71>4D>7 =D1C1> <9BCA9; &1>31A1> A149?
ionosfer. # 41@1C =5>:1>7;1D C5=@1C C5=@1C G1>7 :1D8 &1>CD<1> 75<?=21>7 A1
49? @141 <1@9B1> 9?>?B65A 49@5A<981C;1> @141 "-#"1
b. Sistem FM (Frekuensi Modulasi)
5<?=21>7 2D>G9 4921F1 ?<58 75<?=21>7 5<5;CA?=17>5C9; 41<1=
25>CD; =?4D<1B9 6A5;D5>B9 49 =1>1 6A5;D5>B9>G1 25AD218 D218 41>
1=@<9CD4?>G1 C5C1@ )9BC5= 9>9 =5=9<9;9 ;5<5=181> G1;>9 :1A1;
Gambar 9.4
Modulasi frekuensi pada radio :1>7;1D1>>G1 G1>7 C5A21C1B B5212 BD;1A 49@1>CD<;1> #?4D<1B9 6A5;D5>B9
pemancar FM. @141 @5=1>31A A149? # 49<D;9B;1> @141 "-#"1
)9BC5= # =5=9<9;9 ;D1<9C1B BD1A1 G1>7 219; 41> 2521B 41A9 9>C5A65A5>B9
G1>7 =5ADB1; B9>G1< B9>G1< 6A5;D5>B9 75<?=21>7 C5C1@9 =D418 =5>71<1=9 71>77D
1> ;5<9BCA9;1> 49 D41A1 41> C941; 41@1C 49@1>CD<;1> ?<58 <1@9B1> 9?>?B65A
%<58 ;1A5>1 75<?=21>7 # C941; 41@1C 49@1>CD<;1> ?<58 <1@9B1>
9?>?B65A 1;921C>G1 75<?=21>7 # 9>9 C941; 41@1C =5>31@19 C5=@1C
C5=@1C G1>7 :1D8 %<58 B5212 9CD 492DCD8;1> BC1B9D> BC1B9D> @5>78D2D>7
A5<19 G1>7 41@1C =5=1>31A;1> ;5=21<9 75<?=21>7 75<?=21>7 G1>7
Gambar 9.5
Untuk mengirimkan gelombang FM 49C5A9=1>G1 171A :1A1; :1>7;1D1>>G1 B5=1;9> =5<D1B )C1B9D> BC1B9D>
diperlukan antena pemancar. @5>78D2D>7 C5AB52DC 49<D;9B;1> @141 "-#"1
204 Mudah dan Aktif Belajar Fisika untuk Kelas X
