BAND FREKWENSI RADIO VLF < 30kHz > 10 km LF 30 – 300 kHz

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1 BAND FREKWENSI RADIO VLF < 30kHz > 10 km LF 30 – 300 kHz
Glb. Myriametrik LF 30 – 300 kHz 1 – 10 km Glb. Kilometer MF 300 – 3000 kHz 100 – 1000 m Glb. Hektometer HF 3 – 30 MHz 10 – 100 m Glb. Dekameter VHF 30 – 300 MHz 1 – 10 m Glb. Meter UHF 300 – 3000 MHz 10 – 100 cm Glb. Decimeter SHF 3 – 30 GHz 1 – 10 cm Glb. Sentimeter EHF 30 – 300 GHz 1 – 10 mm Glb. milimeter

2 Gelombang Radio pada ruang bebas
Untuk sumber isotropis, glb. TEM dipancarkan dengan Densitas Power:

3 Model Propagasi Gelombang
Ground-Wave or Surface Propagation Baik digunakan untuk f<2 MHz Space-Wave or Direct wave Propagation (Line of Sight) Digunakan untuk VHF dan di atasnya Sky-Wave Propagation Digunakan untuk HF signal

4 Propagasi Ground-wave
Ground-wave dimulai dengan E tegak lurus terhadap bumi Direction of wave travel Wavefront Increasing Tilt Earth

5 Ground-wave (ljt) Glb. EM Yang berjalan sepanjang permukaan disebut sebagai gelombang permukaan (surface wave) Ground-wave terpolarisasi vertikal Digunakan untuk maritime mobile communication, radio navigation

6 Ground-wave (ljt) Keuntungan:
Power yang diberikan secukupnya dapat berjalan mengikuti curva bumi Relatif tidak terpengaruh dengan kondisi atmosferik Kerugian: Membutuhkan power transmisi yang tinggi Membutuhkan antena yang panjang/besar karena frekwensinya rendah Ground losses bervariasi terhadap terrain

7 Space-wave Energi yang diradiasikan berjalan dibawah beberapa km dari atmosfer bumi Terdiri dari glb. Langsung, glb. Pantul, dan glb. Refraksi Dibatasi oleh curva bumi (lengkung bumi) Intensitas medan pada Rx bergantung pada: Jarak Tx dan Rx Pergeseran fasa antara glb. Langsung glb. Refleksi Curvature bumi menggambarkan suatu radio horison

8 Space-wave Propagation
Tx dan Rx harus berada pada LOS Komunikasi Satelit (signal diatas 30 MHz tidak dipantulkan oleh ionosfer) Komunikasi Ground (antena dalam LOS yang efektif) Jarak maksimum komunikasi :

9 Kerugian Transmisi Wireless LOS
Adanya atenuasi dan distorsi Free Space Loss Noise Absorpsi atmosfer Multipath Refraksi Termal noise

10 Atenuasi Kekuatan sinyal akan berkurang jauh (merosot) sebanding dengan jarak medium transmisi Faktor atenuasi untuk unguided media: Signal yang diterima harus kuat agar receiver dapat menginterpretasikan signal Signal dijaga pada level lebih tinggi dari noise Atenuasi lebih besar pada frekuensi tinggi, ini penyebab distorsi

11 Free Space Loss Propagation in straight line without absorbtion or reflection : L p = (4  D/)2 = (4  f D/c)2 Lp = free-space pathloss in km f = frequency in Hz  = wave length in m c = 3 x 10 8 m/s D=jarak propagasi antara antena

12 Applications of Line-of-Sight Propagation
FM and TV broadcast Cellular radio Short-range marine and aircraft communication Microwave communications Utilities (police, fire etc) Wireless data

13 Ionospheric Propagation
Useful mainly in HF range (3-30 MHz) Signals are refracted in ionosphere and returned to earth Worldwide communication is possible using multiple “hops”

14 Ionospheric Layers D layer: height approx. 60-90 km
E layer: height approx km F1 layer: height approx km F2 layer: height approx km D, E layers disappear at night F layers combine into one at night

15 D Layer It disappears at night Reflects VLF, LF
Lowest, located between 50 to 100 km, little ionization Absorbs MF and HF

16 E Layer 100 – 140 km: Kennelly-Heaviside layer Disappear at night
Aids MF-surface wave Reflects HF waves somewhat during day time

17 F Layer F1 and F2 layers location changes from day to night and summer to winter F1: 140 to 250 km F2: 140 km-350 Most HF waves pass through to F2 where they are refracted back to Earth

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20 Daytime Propagation D and E layers absorb lower frequencies, below about 8-10 MHz F layers return signals from about MHz

21 Nighttime Propagation
D, E layers disappear F layer returns signals from about 2-10 MHz Higher frequencies pass through ionosphere into space

22 Important Frequencies in HF Propagation
Critical frequency Highest frequency that is returned to transmitter Maximum Usable Frequency (MUF) Highest frequency that is returned at a given point Optimum Working Frequency (OWF) 85% of MUF for more reliable communication

23 Skip Zone Region between maximum ground-wave distance and closest point where sky waves are returned from the ionosphere

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25 Applications of Ionospheric Propagation
Shortwave broadcasting Military Aircraft (long distance communication) Marine radio (long distances) Time and frequency standards

26 The Ionosphere

27 The Critical Frequency (fc)
When radio waves are transmitted straight up towards the ionosphere (vertical incidence), the radio wave will be returned to earth at all frequencies below the critical frequency, (fc) . The critical frequency depends on the degree of ionization of the ionosphere, as shown in the following equation: