Chapter 3. Flashcards Preview

CWNA > Chapter 3. > Flashcards

Flashcards in Chapter 3. Deck (54):
1

Is a unit of transmit or receive power a absolute or a relative power?

Absolute

2

Most 802.11 AP can interpret a signal between what 2 values in dBm?

-30 dBm and and -100 dBm.

3

Name the 3 units of comparison

* Decibel
* Decibels relative to an isotropic radiator (dBi)
* Decibels relative to a half-wave dipole antenna (dBd)

4

Name the 3 units of power (absolute)

* Watt
* Milliwatt
* Decibels

5

Units of comparison are often used to measure what?

How much gain or loss occurs because of the introduction of cabling or an antenna.
Units of comparison are also used to represent a comparison of power between unit A and Unit B.

6

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

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

7

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

1. Generate more power at the transmitter, as stated in the previous section.
2. To direct, or focus, the RF signal that is radiating from the antenna.

8

What are the 3 units of comparison (relative)

decibel 9 (dB)
decibels relative to isotropic radiator (dBi)
decibels relative to a half-wave dipole antenna (dBd)

9

What are the 3 units of power (absolute)

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

10

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

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.

11

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

2.14

12

What does 1 mW equal to in dBm?

0 dBm

13

What does the 802.11 state should be a range between RSSI values?

0 - 255

14

What environment is mostly concerned with abiding my FCC max transmitting power regulations?

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

15

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

Turns into 200 mW

16

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

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

17

What is 23 dBi in mW?

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.

18

What is a decibel ?

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.

19

What is a fade buffer?

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.

20

What is a link budget?

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.

21

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

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

22

What is a relative measure or unit?

A measurement that is only possible when a comparison between 2 similar objects are made.

23

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

A watt is the basic unit of power. One watt is equal to 1 amp of current flowing at 2 volt. The amount of watts generated is equal to the volts times the amps.

24

What is a watt? What is the basic equation to get a watt?

A basic unit of power.

Watts = Volts times the Amps.

25

What is an Intentional Radiator ?

A device that intentionally generates and emits radio frequency energy by radiation or induction.

26

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

This is a point source that radiates signal equally in all directions. Omni antenna radiate RF energy this way.

27

What is an isotropic radiator?

A point source that radiates signal equally in all directions.

28

What is an MCS code?

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

29

What is best practice when planning wireless in a very high multipath environment?

In a high-multipath or noisy environment, a common best practice is to add a 5 dB fade margin when designing for coverage based on a vendor’s recommended received signal strength or the noise floor, whichever is louder.

30

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

A dBd value is a measurement of omnidirectional antenna gain and not unidirectional antenna gain. Relative term.

31

What is dBd? What is it used for?

Decibel gain relative to a dipole antenna. The dBd value is the increase in gain of an antenna when it is compared to the signal of a dipole antenna. Dipole antenna are also omni directional, therefore a dipole antenna is a measure of gain of an omni directional antenna. Relative measure.

32

What is dBi or decibels isotropic? What do you think of when you see dBi?

The gain, or increase, of power from an antenna when compared to what an isotropic radiator would generate. When you see dBi you think of antenna gain.

33

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

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

34

What is equivalent isotropic radiated power (EIRP)?

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.

35

What is Equivalent isotropically radiated power?

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

36

What is insertion loss extended?

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.

37

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

Is an ambient or background level of radio energy on a specific channel. blue-tooth, radios, unmodulated energy. Also, 2.4 Ghz is noisier because 2.4 is more crowded then 5.0

38

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

Refers to the power level of an RF signal required to be successfully received by the radio. The lower the power level that the receiver can successfully process, the better the received sensitivity. The weakest signal that the transceiver can decode under normal circumstances. The weaker the signal the lower the transmission is allowed.

39

What is RSSI? What are they typically mapped too?

A relative metric used by 802.11 radios to measure signal strength.

They are mapped too receive sensitivity thresholds express in absolute dBm values.

40

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

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

41

What is SQ or received signal strength?

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

42

What is the 6 dB rule regarding distance?

That +6 dB doubles the distance of the usable signal, and - 6dB half the signal strength affectedness.

43

What is the 802.11 - 2012 meaning of signal quality (SQ)?

A measure of pseudonoise (PN) code correlation quality received by a radio.

44

What is the exact term for dBi?

dBi is defined as “decibel gain referenced to an isotropic radiator” or “change in power relative to an antenna.” dBi is the most common measurement of antenna gain.

45

What is the intentional radiator? What components does IR encompass?

A device that intentionally generates and emits radio frequency energy by radiation or induction. Basically its something designed to intentionally generate and emit radio frequency energy.

All components that make up the transmitter, to the antenna, but not the antenna itself.

46

What is the inverse square law?

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

47

What is the noise floor?

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

48

What is the received signal strength indicator or RSSI? What is the value range? What is it designed to do?

This is a metric used in 802.11-2012 to measure signal strength or amplitude. Can be a value of 0 to 255. Designed to be used by the WLAN hardware manufacture as a relative measurement of the RF signal strength that is received by an 802.11 radio.

49

What is the recommended buffer zone to have between RSSI and signal strength?

Good idea to have at least 10 - 25 dB range.

50

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

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.

51

What is the term decibel derived from?

bel. From Bell Telephone Laboratories.

52

What is the usual measure of a dipole antenna?

2.14

53

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

54 Mbps.

54

Where is the power of the IR measured at?

The connector that provides input to the antenna.