Certified Wireless Network Administrator (CWNA) Chapter Four

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Certified Wireless Network Administrator (CWNA)

• Chapter Four
• Radio Frequency Signal and Antenna Concepts

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Radio Frequency Signal and Antenna Concepts

• Active and Passive Gain
• Azimuth and Elevation Charts
• Interpreting Polar Charts
• Antenna Types
• Visual and RF Line of Sight
• Fresnel Zone
• Earth Bulge
• Antenna Polarization and Diversity
• Multiple-Input Multiple-Output (MIMO)

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Active and Passive Gain

• Active gain is created by a devices addition of
  electrical current to the signal (such as the
  transmitter or an amplifier)
• Passive gain is created by a devices shaping of
  the signal (such as an antenna)

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Azimuth and Elevation Charts
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Interpreting Polar Charts
An Omni-Directional antenna
A Directional antenna
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Beamwidth

• The measure of how broad or narrow the focus of
  an antenna is, measuring both horizontally and
  vertically

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Antenna Types

• Omni-Directional
• Semi-Directional
• Highly-Directional
• Sector
• Phased Array

The proper antenna use is not only important for
network coverage, but is also considered by many
to be important for network security.
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Visual and RF Line of Sight

• Both clear visual and RF line of sight are
  required for good RF communications

Any blockage in either line of sight can impede
RF signaling. A good site survey should be able
to identify potential blockage, allowing
accommodation prior to deployment.
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Fresnel Zone
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Earth Bulge

• The earth its self can cause blockage in the
  Fresnel Zone.
• At 7 miles/11.265408 kilometers Earth Bulge may
  be an issue.
• Buildings, trees and mountains may be of a more
  immediate concern than the curve of the earth

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Antenna Polarization

• A Vertically Polarized antenna has an Horizontal
  Beamwidth.
• An Horizontally Polarized Antenna has a Vertical
  Beamwidth.

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Antenna Diversity

• Helps to mitigate the effects of Multipath
• Antennae are not used concurrently

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Multiple-Input Multiple-Output (MIMO)

• Used to improve signal quality
• Uses multiple antennae concurrently.

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Additional Considerations

• Device Placement
• Mounting
• Orientation/Alignment
• Safety
• Maintenance
• Periodic Inventory

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Voltage Standing Wave Ratio (VSWR)

• Measurement of change to impedances to an AC
  signal.
• Compares maximum voltage (at the transmitter) to
  minimum voltage in the system.
• Mismatches in impedance will cause loss of signal
  strength

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Antenna Accessories

• Cables
• Connectors
• Splitters
• Amplifiers
• Attenuators
• Lightning Arrestors

Remember ANYTHING in the system other than the
transmitter or an amplifier (passive or active)
introduces loss into the RF communication.
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CH 4 Summary

• Understand Gain both Active and Passive
• Know the Antenna types and when to use them
• Understand the Fresnel Zone and what blockage in
  it will do to RF signaling
• Know the various antenna accessories
• Understand Polarization and the impact on
  coverage area

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