Rf fundamentals
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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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Rf fundamentals

RF Fundamentals

Lecture 3


Objectives

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

RF Components


Units

Units


Free space path loss calculation

Free space path loss calculation


Units1

Units


Rf measurement rf math

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


Understanding dbs

Understanding DBs


Rf measurement rf math continued

RF Measurement: RF Math (continued)

Table 3-3: The 10’s and 3’s Rules of RF Math


Rf measurement rf math continued1

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


Understanding dbms

Understanding Dbms


Rf measurement wlan measurements

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


Understanding dbs and mws

Understanding Dbs and mWs


Dbms and mw

Dbms and mW


Rssi and snr

RSSI and SNR


Rf fundamentals

EIR


Rules 10 and 3s

Rules 10 and 3s


Rules 10s and 3s

Rules 10s and 3s


Rules of 10s and 3s

Rules of 10s and 3s


Example

Example


Example1

Example


Example2

Example


Example3

Example


Example 2

Example 2


Example 21

Example 2


Example 22

Example 2


Example 23

Example 2


Antenna concepts

Antenna Concepts

  • Radio waves transmitted/received using antennas

Figure 3-24: Antennas are required for sending and receiving radio signals


Characteristics of rf antenna transmissions

Characteristics of RF Antenna Transmissions

  • Polarization: Orientation of radio waves as they leave the antenna

Figure 3-25: Vertical polarization


Characteristics of rf antenna transmissions continued

Characteristics of RF Antenna Transmissions (continued)

  • Wave propagation: Pattern of wave dispersal

Figure 3-26: Sky wave propagation


Characteristics of rf antenna transmissions continued1

Characteristics of RF Antenna Transmissions (continued)

Figure 3-27: RF LOS propagation


Characteristics of rf antenna transmissions continued2

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


Rf line of sight

RF line of sight


Rf line of sight1

RF Line of sight


Line of sight

Line of sight


Line of sight1

Line of sight


Line of sight2

Line of sight


Fresnel zone

Fresnel Zone


Fresnel zone1

Fresnel Zone


Fresnel zone2

Fresnel Zone


Characteristics of rf antenna transmissions continued3

Characteristics of RF Antenna Transmissions (continued)

  • Determining extent of “late” multipath signals can be done by calculating Fresnel zone

Figure 3-28: Fresnel zone


Fresnel zone3

Fresnel zone


Terrain effects on rf

Terrain effects on RF


Weather effects on rf

Weather effects on RF


Rain effects in rf

Rain effects in RF


Characteristics of rf antenna transmissions continued4

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


Characteristics of rf antenna transmissions continued5

Characteristics of RF Antenna Transmissions (continued)

Table 3-5: Free space path loss for IEEE 802.11b and 802.11g WLANs


Antenna types and their installations

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


Antenna types and their installations continued

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


Antenna types and their installations continued1

Antenna Types and Their Installations (continued)

Figure 3-29: Omni-directional antenna


Antenna types and their installations continued2

Antenna Types and Their Installations (continued)

Figure 3-30: Semi-directional antenna


Wlan antenna locations and installation

WLAN Antenna Locations and Installation

  • Because WLAN systems use omni-directional antennas to provide broadest area of coverage, APs should be located near middle of coverage area

  • Antenna should be positioned as high as possible

  • If high-gain omni-directional antenna used, must determine that users located below antenna area still have reception


Summary

Summary

  • A type of electromagnetic wave that travels through space is called a radiotelephony wave or radio wave

  • An analog signal is a continuous signal with no breaks in it

  • A digital signal consists of data that is discrete or separate, as opposed to continuous

  • The carrier signal sent by radio transmissions is simply a continuous electrical signal and the signal itself carries no information


Summary continued

Summary (continued)

  • Three types of modulations or changes to the signal can be made to enable it to carry information: signal height, signal frequency, or the relative starting point

  • Gain is defined as a positive difference in amplitude between two signals

  • Loss, or attenuation, is a negative difference in amplitude between signals

  • RF power can be measured by two different units on two different scales


Summary continued1

Summary (continued)

  • An antenna is a copper wire or similar device that has one end in the air and the other end connected to the ground or a grounded device

  • There are a variety of characteristics of RF antenna transmissions that play a role in properly designing and setting up a WLAN


Lab 2

Lab 2

  • LAB A


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