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RF Fundamentals

RF Fundamentals. Lecture 3. Objectives. Describe RF loss and gain, and how it can be measured List some of the characteristics of RF antenna transmissions Describe the different types of antennas. RF Components. Units. Free space path loss calculation. Units. RF Measurement: RF Math.

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RF Fundamentals

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  1. RF Fundamentals Lecture 3

  2. Objectives • Describe RF loss and gain, and how it can be measured • List some of the characteristics of RF antenna transmissions • Describe the different types of antennas

  3. RF Components

  4. Units

  5. Free space path loss calculation

  6. Units

  7. RF Measurement: RF Math • RF power measured by two units on two scales: • Linear scale: • Using milliwatts (mW) • Reference point is zero • Does not reveal gain or loss in relation to whole • Relative scale: • Reference point is the measurement itself • Often use logarithms • Measured in decibels (dB) • 10’s and 3’s Rules of RF Math: Basic rule of thumb in dealing with RF power gain and loss

  8. Understanding DBs

  9. RF Measurement: RF Math (continued) Table 3-3: The 10’s and 3’s Rules of RF Math

  10. RF Measurement: RF Math (continued) • dBm: Reference point that relates decibel scale to milliwatt scale • Equivalent Isotropically Radiated Power (EIRP): Power radiated out of antenna of a wireless system • Includes intended power output and antenna gain • Uses isotropic decibels (dBi) for units • Reference point is theoretical antenna with 100 percent efficiency

  11. Understanding Dbms

  12. RF Measurement: WLAN Measurements • In U.S., FCC defines power limitations for WLANs • Limit distance that WLAN can transmit • Transmitter Power Output (TPO): Measure of power being delivered to transmitting antenna • Receive Signal Strength Indicator (RSSI): Used to determine dBm, mW, signal strength percentage Table 3-4: IEEE 802.11b and 802.11g EIRP

  13. Understanding Dbs and mWs

  14. Dbms and mW

  15. RSSI and SNR

  16. EIR

  17. Rules 10 and 3s

  18. Rules 10s and 3s

  19. Rules of 10s and 3s

  20. Example

  21. Example

  22. Example

  23. Example

  24. Example 2

  25. Example 2

  26. Example 2

  27. Example 2

  28. Antenna Concepts • Radio waves transmitted/received using antennas Figure 3-24: Antennas are required for sending and receiving radio signals

  29. Characteristics of RF Antenna Transmissions • Polarization: Orientation of radio waves as they leave the antenna Figure 3-25: Vertical polarization

  30. Characteristics of RF Antenna Transmissions (continued) • Wave propagation: Pattern of wave dispersal Figure 3-26: Sky wave propagation

  31. Characteristics of RF Antenna Transmissions (continued) Figure 3-27: RF LOS propagation

  32. Characteristics of RF Antenna Transmissions (continued) • Because RF LOS propagation requires alignment of sending and receiving antennas, ground-level objects can obstruct signals • Can cause refraction or diffraction • Multipath distortion: Refracted or diffracted signals reach receiving antenna later than signals that do not encounter obstructions • Antenna diversity: Uses multiple antennas, inputs, and receivers to overcome multipath distortion

  33. RF line of sight

  34. RF Line of sight

  35. Line of sight

  36. Line of sight

  37. Line of sight

  38. Fresnel Zone

  39. Fresnel Zone

  40. Fresnel Zone

  41. Characteristics of RF Antenna Transmissions (continued) • Determining extent of “late” multipath signals can be done by calculating Fresnel zone Figure 3-28: Fresnel zone

  42. Fresnel zone

  43. Terrain effects on RF

  44. Weather effects on RF

  45. Rain effects in RF

  46. Characteristics of RF Antenna Transmissions (continued) • As RF signal propagates, it spreads out • Free space path loss: Greatest source of power loss in a wireless system • Antenna gain: Only way for an increase in amplification by antenna • Alter physical shape of antenna • Beamwidth: Measure of focusing of radiation emitted by antenna • Measured in horizontal and vertical degrees

  47. Characteristics of RF Antenna Transmissions (continued) Table 3-5: Free space path loss for IEEE 802.11b and 802.11g WLANs

  48. Antenna Types and Their Installations • Two fundamental characteristics of antennas: • As frequency gets higher, wavelength gets smaller • Size of antenna smaller • High-gain antennas offer larger coverage areas than low-gain antennas at same input power level • Omni-directional antenna: Radiates signal in all directions equally • Most common type of antenna

  49. Antenna Types and Their Installations (continued) • Semi-directional antenna: Focuses energy in one direction • Primarily used for short and medium range remote wireless bridge networks • Highly-directional antennas: Send narrowly focused signal beam • Generally concave dish-shaped devices • Used for long distance, point-to-point wireless links

  50. Antenna Types and Their Installations (continued) Figure 3-29: Omni-directional antenna

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