Figure 5-6: Omnidirectional and dish Antennas Dish Antenna Om nidirectional Antenna Focuses signals in a narrow range spread signals in all directions Signals can be sent over long distances Rapid signal attenuation Must point at the sender No need to point at receiver Good for fixed subscribers Good for mobile subscribers 5-11
5-11 Figure 5-6: Omnidirectional and Dish Antennas Omnidirectional Antenna Spread signals in all directions Rapid signal attenuation ----- No need to point at receiver Good for mobile subscribers Dish Antenna Focuses signals in a narrow range Signals can be sent over long distances ----- Must point at the sender Good for fixed subscribers
Test Your understanding Page 239 5 b)c)d) 5-12
5-12 Test Your understanding • Page 239 • 5 b) c) d)
I Figure 5-7: Wireless Propagation Problems Electromagnetic Interference (EMI) from Other stations Microwave 2. ovens, etc Attenuation: signal gets weaker with distance Blockin Object shadow Zone (Dead Spot) 5-13
5-13 Figure 5-7: Wireless Propagation Problems 2. Attenuation: signal gets weaker with distance 3. Shadow Zone (Dead Spot) 1. Electromagnetic Interference (EMI) from Other stations, Microwave ovens, etc. Blocking Object
I Figure 5-7: Wireless Propagation Problems Blocking Direct Signal Object Laptop 4. Multipath Interference Reflected Signal Direct and reflected signals may interfere 5-14
5-14 Figure 5-7: Wireless Propagation Problems Reflected Signal Laptop Direct Signal 4. Multipath Interference Direct and reflected signals may interfere Blocking Object
Inverse Square Law Attenuation Inverse square law attenuation To compare relative power at two distances Divide the longer distance by the shorter distance Square the result; this is the relative power ratio Examples 100 mW(milliwatts)at 10 meters At20 meters,100/(20/10)2=100mW/4=25mW At30 meters,100/(30/10)2=100mW/9=11mW Much faster attenuation than utP or fiber 5-15
5-15 Inverse Square Law Attenuation • Inverse square law attenuation – To compare relative power at two distances • Divide the longer distance by the shorter distance • Square the result; this is the relative power ratio – Examples • 100 mW (milliwatts) at 10 meters • At 20 meters, 100 / (20/10)2 = 100 mW / 4 = 25 mW • At 30 meters, 100 / (30/10)2 = 100 mW / 9 = 11 mW – Much faster attenuation than UTP or fiber