CWNA

Components of RFcommunications

TransmitterAntennaReceiverisotropic radiatorIntentional Radiator (IR)�Equivalent Isotropically Radiated Power (EIRP)�

Transmitter

�Initial component in the creation of awireless signal�Receives data from the system and begins RF communication�Encodes the data�Modulates the AC signal�Sends modulated signal to the antenna

Antenna

Collects the Modulated signal�Radiates the waves into the air�Captures RF waves�Passes the AC signal to the receiver�Acts as a bi-directional passive amplifier�Shapes the coverage cell based on antennatype and design

Receiver

Final component in wireless signaling�Converts carrier signal into 1�s and 0�s �Receive amplitude (receive strength) isweaker than transmit amplitude

Isotropic Radiator

�Radiates in all directions, like the Sun�Omni-directional antennae are not IsotropicRadiators�There is not an isotropic antenna type,although Omni-directional antennae seem to provide such coverage

Intentional Radiator

A device that intentionally emits RF energyby radiation or induction�Regulatory bodies (governments) regulate themaximum IR power�IR power is measured from the transmitter tothe base of the antenna including all components except the antenna it�s self (basically the amount of power being sentinto the antenna for transmission onto the medium)

Equivalent IsotropicallyRadiated Power (EIRP)

The highest RF signal strength that isradiated by a specific antenna�Regulatory bodies (governments) regulate themaximum EIRP just like the IR�Measured after the antenna (the amount of power the total system placeson the medium)

Units of Power andComparison

Watt�Milliwatt�Decibel (dB)�dBi�dBd�dBm�Inverse Square Law

Watt

�An absolute measure of power�Named after James Watt 18th century Scottish inventor�A Watt (W) is the basic unit of power1W=1000mW�1W=1 ampere (amp) of power flowing at 1 volt.

Milliwatt (mW)

�An absolute measure of power�1mW=1/1000W�Most 802.11 devices transmit between 1wW and100mW�Bridge devices may often exceed 1000mW or 1Win transmissions(In comparison, microwaves (which use RF energy to cook) usethousands of Watts. It is no wonder thatthey often cause layer one interference for 802.11 devices)

Decibel (dB)

�Not an absolute unit of measure�Used as a comparison�Derived from the term bel fromBell Labs.�Normally used to measure change in signalstrength with either gain or loss�Bel�s canbe examined using logarithmsdB= 10xlog10(P1/P2)

Decibels Isotropic (dBi)

�Notan absolute unit of measure�DecibelsIsotropic is a value compared to what an isotropic radiator would generate�dBi is usually found in discussions aboutantenna gain�Alsophrased as change in power relative to an antenna�Alwayspositive or 0 (no gain)

Decibels Dipole (dBd)

�Not an absolute unit of measure�An additional reference used by antennamakers to describe change related to antenna gain�Denotes change relative to a dipole antenna(the proper name for an Omni-directional antenna)�Most antennae are labeled in dBi�1 dBd=2.14 dBi

dBm

Notan absolute unit of measure�Comparesa given signal against 1mW� 0 dBm = 1mW�10dBm = 10mW�20dBm = 100mW�30dBm = 1000mW = 1 W�36dBm = 4000mW = 4 W�See formula on page 74

Inverse Square Law

�Developed by Isaac Newton �States that the change in power is equal to 1 divided by the square of the change in distance. Page 76 �This can be used to accurately calculate expected Free Space Path Loss