day 1

Question 1

wavelength

Answer 1

the length of one complete oscillation of a signal

Question 2

frequency

Answer 2

the number of cycles (or oscillations) of a wave per second

Question 3

frequency and wavelength

Answer 3

are inversely related to one another

Question 4

more on frequency

Answer 4

network providers compete with each other to use signals with higher frequencies because they typically have wider channels than lower-frequency signals; channel width determines how much bandwidth a signal carries.
a downside of higher frequencies is they attenuate faster than lower frequencies

Question 5

amplitude

Answer 5

the amount of power a wave contains and is measured in Watts (W)

Question 6

in phase

Answer 6

when two waves arrive at about the same time.

this results in increased signal power

Question 7

out of phase

Answer 7

when two waves arrive at the same time but with phase angle difference greater than 90 degrees, they are out of phase and decrease the received signal power.

Question 8

modulation

Answer 8

the process of encoding data onto a radio wave

Question 9

dynamic rate switching

Answer 9

when a mobile device is further away from its tower, the tower and mobile device must transmit at a slower rate in order to reduce errors when receiving the ones and zero’s
fewer errors lead to fewer retransmissions

Question 10

signal loss (attenuation)

Answer 10

a decrease of an RF wave’s amplitude

Question 11

diffusion

Answer 11

the natural spreading of an RF wave as it travels away from its emitter.
every signal transmitted suffers diffusion.

Question 12

absorption

Answer 12

occurs when an object absorbs a portion or all of an RF

how a wave can be completely attenuated….through absorption

Question 13

reflection

Answer 13

an RF wave experiences reflection when it bounces off an object with larger dimensions than the wave’s wavelength

Question 14

refraction

Answer 14

occurs when a wave bends and changes speed as it passes through a medium with a different density

Question 15

scattering

Answer 15

a wave experiences scattering (splitting into multiple waves) when it strikes an uneven surface- or multiple objects

Question 16

diffraction

Answer 16

diffracted waves bend around objects and move in a different direction

Question 17

multipath

Answer 17

the combination of reflection, refraction, scattering, and diffraction

Question 18

multipath is…

Answer 18

the phenomenon of the same radio signal reaching an antenna by two or more paths.
multipath ususally causes the waves to arrive out of phase.
reflection is the primary cause of multipath.

Question 19

antenna diversity

a single radio connected to more than one antenna

Answer 19

helps overcome the effects of multipath by allowing a radio to choose the best signal at any given time.

Question 20

2.4GHz

Answer 20

ISM band

Question 21

antennas

Answer 21

type examples uses
omnidirectional dipole many
whip laptop/access point

semidirectional patch collect on a target
(up to 3 miles) panel building to building
yagi
sector

highly directional parabolic dish building to building
(3-30 miles) point to point or point to multipoint

Question 22

gain

Answer 22

boosting either trasnmitted or received signals

Question 23

passive gain

Answer 23

focuses the emitted RF signal of an antenna in specific directions

Question 24

active gain

Answer 24

uses a power source to increase an RF wave’s amplitude.

Amplifiers boost both outgoing and incoming signals and noise

Question 25

intentional radiated power (IRP)

Answer 25

the amount of power leaving a transmitter

Question 26

effective radiated power (ERP)

Answer 26

the highest amount of RF energy transmitted by the antenna of a particular system

Question 27

decibel (dB)

Answer 27

the unit of measure for both loss and gain

Question 28

dBi

Answer 28

used to reference active gain and the overall power of an RF wave.
1mW equals 0 dBm
-40dBm is more power than -80 dBm

dB and dBi are relative.
dBm is an absolute value

Question 29

rules of 3’s and 10’s

Answer 29

add up all db values.
use the rules to get to that number.   if there is a mW, multiply the result by the mW.
\+10 = *10
-10 = /10
\+3 = *2
-3 = /2

Question 30

impedance mismatch

Answer 30

results when two adjacent devices on a circuit have different impedances
802.11 devices have an impedance of 50 ohms

Question 31

results of impedance mismatch

Answer 31

1. signal loss as heat
2. damage to transmitter
3. standing wave (VSWR)

Question 32

simplex

Answer 32

a systems allow communication in only one direction

(tv/radio and security alarm systems

Question 33

half-duplex

Answer 33

each participant can transit and receive, though only one station transmits at any given time
(walkie-talkies, tactical radios, intercom systems)
802.11 operates in half-duplex mode

Question 34

full-duplex

Answer 34

mode enables each transmitter to send and receive at the same time.
(telephones and cellphones)