CWNA Chapter 3: Radio Frequency Components, Measurements, and Mathematics

The rules of 10s and 3s:

*For every 3 dB of gain (relative) double the absolute power (mW). *For every 3 dB of loss (relative), halve the absolute power (mW). *For every 10 dB of gain (relative) multiply the absolute power (mW) by a factor of 10. * For every 10 dB pf loss (relative), divide the absolute power (mW) by a factor of 10.

power coming out of the antenna:

EIRP

Power provided to the antenna:

IR

transmitter

The computer hands the data off to the transmitter, and it is the transmitter's job to begin the RF communication.

Components of RF communications:

Transmitter Receiver Antenna Isotropic radiator Intentional radiator (IR) Equivalent isotropically radiated power (EIRP)

Units of power and comparison:

Watt Milliwatt Decibel (dB) dBi dBm Inverse square law

6 dB rule

a +6 dB change in signal will double the usable distance of te signal, and e -6 dB change in signal will halve the usable distance of a signal.

Intentional Radiator (IR)

a device that intentionally generates and emits radio frequency energy by radiation or induction. Basically, it is designed to generate RF.

Fade margin

a level of desired signal above what is required.

An isotropic radiator is:

a point source that radiates signal equally in all directions. (like what the sun does)

Decibel (dB)

a unit of comparison, not a unit of power. A relative expression and a measurement of change in power.

milliwattt (mW)

also a unit of power. A milliwatt is 1/1000 of a watt.

Antenna provides two functions:

collects the AC signal that it receives from the transmitter and directs, or radiates, the RF waves away from the antenna in a pattern specific to the antenna type. When connected to a receiver, the antenna takes the RF waves that it receives through the air and directs the AB signal to the receiver.

Units of comparison (relative)

decibel (dB) decibels relative to an isotropic radiator (dBi) decibels relative to a half-wave dipole antenna (dBd)

decibels isotropic (dBi)

decibel gain referenced to an isotropic radiator or change in power relative to an antenna.

dBm

decibels relative to 1 milliwatt

FSPL

free space path loss

mW

milliwatts

receive sensitivity

refers to the power level of an RF signal required to be successfully received by the receiver radio.

receiver

takes the carrier signal that is received from the antenna and translates the modulated signals into 1s and 0s. Then passes it to the computer to e processed.

noise floor

the ambient or background level of radio energy on a specific channel.

Watt (W)

the basic unit of power. One watt is equal to 1 ampere (amp) of current flowing at 1 volt.

Inverse square law:

the change in power is equal to 1 divided by the square of teh change in distance.

signal-to-noise ratio (SNR)

the difference in decibels between the received signal and the background noise level.

Equivalent Isotropically Radiated Power (EIRP)

the highest RF signal strength that is transmitted from a particular antenna.

Link budget

the sum of all the planned and expected gains and lossis from the transmitting radio, through the RF medium, to the receiver radio.

The components of the IR include:

the transmitter, all cables and connectors, and any other equipment between the transmitter and the antenna, not including the antenna though.

absolute power measurements

units of transmit or received power measurments

Units of comparison

used to represent a difference in power from point A to point B.

Units of power (absolute)

watt (W) milliwatt (mW) decibels relative to 1 milliwatt (dBm)