Chapter 3.

Question 1

Most 802.11 AP can interpret a signal between what two values in dBm?

Answer 1

-30 dBm and and -100 dBm.

Question 2

Units of comparison are often used to measure what?

Answer 2

How much gain or loss occurs across a cable, as a result of increases in transmit power/antenna gain, or in attenuation across a distance
Units of comparison are also used to represent a comparison of power between unit A and Unit B.

Question 3

What are “actual units” in relation to relative? What is a good example?

Answer 3

They represent a known or set value. A measure of your height, 5 ‘ 6 is a known or actual value.

Question 4

What are the 2 ways to increase power output from an antenna?

Answer 4

1. Generate more power at the transmitter.

2. To direct, or focus, the RF signal that is radiating from the antenna.

Question 5

What are the 3 units of comparison (relative)

Answer 5

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

Question 6

What are the 3 units of power (absolute)

Answer 6

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

Question 7

What components make up the IR or intentional radiator? What component is specifically left out?

Answer 7

The IR consists of all components from the transmitter to the antenna but NOT including the antenna.
The IR is the sum of all components, transmitter, all cables and connectors, and any other equipment like amplifiers, attenuators, and so forth.

Question 8

What do you add to the dbd value to get dBI?

Answer 8

2.14

Question 9

What does 1 mW equal to in dBm?

Answer 9

0 dBm

Question 10

What environment is most concerned with abiding by FCC max transmitting power regulations?

Answer 10

Outdoor, as they are usually significantly more powerful than indoor access points.

Question 11

What happens to 100mW if you add +3 dB to it?

Answer 11

it doubles to 200 mW

Question 12

What happens to the RF waves when more power is applied to the AP?

Answer 12

The amplitude is increased. The higher the amplitude of the wave, the more powerful the wave is and the farther it can be received.

Question 13

What is 23 dBi in mW?

Answer 13

To convert to mW, first calculate how many 10s and 3s are needed to add up to 23, which is 0 + 10 + 10 + 3.
To calculate the mW, you must multiply 1 × 10 × 10 × 2, which calculates to 200 mW.

Question 14

What is a decibel ?

Answer 14

A decibel is a unit of comparison and a relative measure. For example, comparing the power of 2 transmitters or more often, to compare the difference or loss between the EIRP output of a transmitters antenna and the amount of power received by a receivers antenna.

Question 15

What is a fade buffer?

Answer 15

The dB buffer that is determined during the link budget calculations. Meaning this is the signal that the receiving unit sees subtracted from the lowest signal that the RX unit can get and hear.

Question 16

What is a link budget?

Answer 16

The sum of all planned and expected gains and loses from the transmitting radio, through the RF medium, to the receiver radio.
This is all links and cables as well. This all ALL THE WAY through the receiving unit as well and all cables and connectors.

Question 17

What is a milliwatt? How much of a watt is a milliwatt?

Answer 17

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

Question 18

What is a watt, how do we get the measure of the watt? What is the equation?

Answer 18

A watt is the basic unit of power.

One watt is equal to 1 amp of current flowing at 1 volt.

Watts = Volts times the Amps.

Question 19

What is an Intentional Radiator ?

Answer 19

A device that intentionally generates and emits radio frequency energy by radiation or induction, includes everything except the antenna

Question 20

What is an isotropic radiator and why are antenna usually referred to them that way?

Answer 20

This is a point source that radiates signal equally in all directions, and therefore has 0 gain.

Question 21

What is an MCS code?

Answer 21

Used to define the modulation a device will use when its QAM drops or increases.

Question 22

What is dBd and what type of antenna is it usually used with?

Answer 22

A dBd value is a measurement of omnidirectional antenna gain

dBd = dBi + 2.14

Question 23

What is dBi or decibels isotropic?

Answer 23

The gain of an antenna relative to an isotropic antenna, which transmits equally in all directions.

Question 24

What is dBm? What is it used for? Is it an absolute or a relative?

Answer 24

Used to compare a signal to 1 milliwatt of power. This is an absolute power.

Question 25

What is equivalent Isotropic Radiated Power (EIRP)?

Answer 25

This is the highest RF signal strength that is transmitted from a particular antenna. This is a combination of all components that make up the unit.

Question 26

What is insertion loss?

Answer 26

Any hardware device that is added to an RF system creates a level of attenuation against the RF signal. Cable is rated per 100 ft and connectors usually 0.5 dB loss.

Question 27

What is noise floor? What are some thing that can cause noise? What is noisier 2.4Ghz or 5.0Ghz and why?

Answer 27

The ambient or background level of radio energy on a specific channel. This can include RF transmissions or non 802.11 noise.

Created by blue-tooth, radios, engines, unmodulated energy, etc.

2.4 GHz tends to be noisier because 2.4 is more crowded then 5 GHz

Question 28

What is received sensitivity? What happens when the signal gets lower in strength?

Answer 28

Refers to the minimum power level of an RF signal that can be successfully received by the radio. If the received signal is below the receiver sensitivity, the signal cannot be understood.

Question 29

What is RSSI? What are they typically mapped too?

Answer 29

A relative metric used by 802.11 radios to measure signal strength. Ranges between 0 - 255

They are mapped to receive sensitivity thresholds express in absolute dBm values. but each RSSI scale is proprietary, so it can’t be compared between vendors, except as a percentage of each vendor’s RSSI_Max

Question 30

What is signal to noise ratio? Which ratio is considered good and which is considered bad?

Answer 30

The difference in decibels between the received signal and the background noise level. SNR or 25+ is considered voice grade, 15 is considered data grade, and a 10 dB or lower is considered bad.

Question 31

What is SQ or received signal strength?

Answer 31

A measure of signal quality measurement that might affect coding techniques and anything that might increase bit error rate.

Question 32

What is the 6 dB rule regarding distance?

Answer 32

That +/-6 dB doubles/halves the distance of the usable signal

A +6 dB increase at the transmitter will double the distance of a given signal’s cell boundary

Additionally, a -75 dBm cell will be roughly twice the radius of a -69 dBm cell

Question 33

What is the inverse square law?

Answer 33

The law states that the change in power is equal to 1 divided by the square of the change in distance.

Question 34

What is the roaming process? What is a key factor that client use?

Answer 34

Clients make the decision to move from one access point to the next. The RSSI thresholds are key factors for clients when they initiate the roaming hand off.

Question 35

What is the term decibel derived from?

Answer 35

bel. From Bell Telephone Laboratories.

Question 36

What is the usual measure of a dipole antenna?

Answer 36

2.14 dBi

Question 37

What is usually the data transfer speed that -67 dBm can transmit at?

Answer 37

54 Mbps.

Question 38

Where is the power of the IR measured at?

Answer 38

The connector that provides input to the antenna.