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NETW-125/PW0-105 > Chapter 3 - Radio Frequency Components, Measurements, and Mathematics > Flashcards

Chapter 3 - Radio Frequency Components, Measurements, and Mathematics Flashcards

1
Q

The _____ is the initial component in the creation of the wireless medium. The computer hands the data off to the _____, and it is the _____’s job to begin the RF communication.

A

transmitter

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2
Q

When the transmitter receives the data, it begins generating an _____ _____ signal.

A

alternating current (AC)

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3
Q

The transmitter takes the data provided and modifies the AC signal by using a _____ technique to encode the data into the signal.

A

modulation

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4
Q

In addition to generating a signal at a specific frequency, the transmitter is responsible for determining the original transmission amplitude, or what is more commonly referred to as the _____ _____, of the transmitter.

A

power level

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5
Q

The power levels that the transmitter is allowed to generate are determined by the local regulatory domain authorities, such as the _____ _____ _____ in the United States.

A

Federal Communications Commission (FCC)

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6
Q

Although we are explaining the transmitter and receiver separately in this chapter, and although functionally they are different components, typically they are one device that is referred to as a _____ (transmitter/receiver).

A

transceiver

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7
Q

An _____ provides two functions in a communication system. When connected to the transmitter, it collects the AC signal that it receives from the transmitter and directs, or radiates, the RF waves away from the _____ in a pattern specific to the _____ type.

A

antenna

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8
Q

The receiver converts the AC signal to _____ and _____.

A

bits, bytes

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9
Q

The RF transmission of an antenna is usually compared or referenced to an _____ _____. An _____ _____ is a point source that radiates signal equally in all directions. The sun is probably one of the best examples of an _____ _____. It generates equal amounts of energy in all directions.

A

isotropic radiator

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10
Q

The _____ is the final component in the wireless medium. The _____ takes the carrier signal that is received from the antenna and translates the modulated signals into 1s and 0s.

A

receiver

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11
Q

The FCC Code of Federal Regulations (CFR) Part 15 defines an _____ _____ as “a device that intentionally generates and emits radio frequency energy by radiation or induction.”

A

intentional radiator (IR)

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12
Q

The IR consists of all the components from the transmitter to the antenna but not including the _____.

A

antenna

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13
Q

The power of the IR is measured at the _____ that provides the input to the antenna. Because this is the point where the IR is measured and regulated, we often refer to this point alone as the IR.

A

connector

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14
Q

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

A

Equivalent isotropically radiated power (EIRP)

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15
Q

_____ units are ones that represent a known or set value.

A

Actual

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16
Q

_____ units are comparative values comparing one item to a similar type of item.

A

Relative

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17
Q

Units of power are used to measure transmission amplitude and received amplitude. In other words, units of power measurements are _____ _____ measurements.

A

absolute power

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18
Q

Units of comparison are also used to represent a difference in power from point A to point B. In other words, units of comparison are measurements of _____ in power.

A

change

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19
Q

One _____ is equal to 1 ampere (amp) of current flowing at 1 volt.

A

watt

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20
Q

In wireless networking, _____ are often used either to compare the power of two transmitters or, more often, to compare the difference or loss between the EIRP output of a transmitter’s antenna and the amount of power received by the receiver’s antenna.

A

decibels (dB)

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21
Q

The gain, or increase, of power from an antenna when compared to what an isotropic radiator would generate is known as _____ _____.

A

decibels isotropic (dBi)

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22
Q

Antennas are measured in _____, not power

A

gain

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23
Q

The dBi value is measured at the strongest point, or the focus point, of the antenna _____.

A

signal

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24
Q

A 2.4 GHz half-wave dipole antenna has a dBi value of _____.

A

2.14

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25
Q

A _____ _____ value is the increase in gain of an antenna when it is compared to the signal of a dipole antenna.

A

decibels dipole (dBd)

26
Q

A standard dipole antenna has a dBi value of 2.14. If an antenna has a value of 3 dBd, this means that it is 3 dB _____ than a dipole antenna. So a 3 dBd antenna is equal to a _____ dBi antenna.

A

greater, 5.14

27
Q

_____ is an absolute assessment that measures change of power referenced to 1 milliwatt.

A

dBm

28
Q

During a site survey, WLAN engineers will always determine coverage zones by recording the received signal strength in –_____ values.

A

dBm

29
Q

If you double the distance between the transmitter and the receiver, the received signal will decrease by _____ dB. No matter what numbers are chosen, if the distance is doubled the decibel loss will be _____ dB. This rule also implies that if you increase the amplitude by _____ dB, the usable distance will double.

A

6

30
Q

The 6 dB rule is also useful for understanding antenna _____, because every 6 dB of extra antenna _____ will double the usable distance of an RF signal.

A

gain

31
Q

Using dBm also makes it easy to calculate the effects of antenna gain on a signal. If a transmitter generates a +20 dBm signal and the antenna adds 5 dBi of gain to the signal, then the power that is radiating from the antenna (EIRP) is equal to the ____ of the two numbers, which is _____ dBm.

A

sum, +25

32
Q

The _____ _____ law states that the change in power is equal to 1 divided by the square of the change in distance. In other words, as the distance from the source of a signal doubles, the energy is spread out over four times the area, resulting in one-fourth of the original intensity of the signal.

A

Inverse Square

33
Q

The main variable for the inverse square law is simply _____. The FSPL formula is also based on _____ but includes another variable: frequency.

A

distance

34
Q

The rule of 10s and 3s states that for every 3 dB of gain (relative), _____ the absolute power (mW).

A

double

35
Q

The rule of 10s and 3s states that for every 3 dB of loss (relative), _____ the absolute power (mW).

A

halve

36
Q

The rule of 10s and 3s states that for every 10 dB of gain (relative), _____ the absolute power (mW) by a factor of 10.

A

multiply

37
Q

The rule of 10s and 3s states that for every 10 dB of loss (relative), _____ the absolute power (mW) by a factor of 10.

A

divide

38
Q

The _____ _____ is the ambient or background level of radio energy on a specific channel. This background energy can include modulated or encoded bits from nearby 802.11 transmitting radios or from unmodulated energy coming from non-802.11 devices such as microwave ovens, Bluetooth devices, portable telephones, and so on. Anything electromagnetic has the potential of raising the amplitude of the _____ _____ on a specific channel.

A

noise floor

39
Q

The amplitude of the noise floor, which is sometimes simply referred to as “_____ _____,” varies in different environments.

A

background noise

40
Q

Many Wi-Fi vendors define signal quality as the _____-_____-_____.

A

signal-to-noise ratio (SNR)

41
Q

The SNR is the _____ _____ _____ between the received signal and the background noise level (noise floor), not actually a ratio.

A

difference in decibels

42
Q

Data transmissions can become corrupted with a very _____ SNR.

A

low

43
Q

If the amplitude of the noise floor is too close to the amplitude of the received signal, data corruption will occur and result in layer 2 _____.

A

retransmissions

44
Q

An SNR of _____ dB or greater is considered good signal quality, and an SNR of _____ dB or lower is considered very poor signal quality.

A

25, 10

45
Q

_____ _____ refers to the power level of an RF signal required to be successfully received by the receiver radio. The lower the power level that the receiver can successfully process, the better the _____ _____.

A

Receive sensitivity

46
Q

In WLAN equipment, receive sensitivity is usually defined as a function of network _____.

A

speed

47
Q

Wi-Fi vendors will usually specify their receive sensitivity thresholds at various _____ _____.

A

data rates

48
Q

Different speeds use different modulation techniques and encoding methods, and the higher data rates use encoding methods that are _____ susceptible to corruption. The lower data rates use modulation-encoding methods that are _____ susceptible to corruption.

A

more, less

49
Q

The 802.11-2007 standard defines the _____ _____ _____ _____ as a relative metric used by 802.11 radios to measure signal strength (amplitude).

A

received signal strength indicator (RSSI)

50
Q

The 802.11 RSSI measurement parameter can have a value from _____ to _____.

A

0, 255

51
Q

RSSI metrics are typically mapped to receive sensitivity thresholds expressed in absolute _____ values.

A

dBm

52
Q

The 802.11-2007 standard also defines another metric called _____ _____, which is a measure of _____ code correlation quality received by a radio.

A

signal quality (SQ), pseudonoise (PN)

53
Q

Although SQ metrics and RSSI metrics are technically separate measurements, most Wi-Fi vendors refer to both together as simply _____ metrics.

A

RSSI

54
Q

WLAN vendors can define _____ metrics in a proprietary manner.

A

RSSI

55
Q

During the _____ process, clients make the decision to move from one access point to the next. RSSI thresholds are key factors for clients when they initiate the _____ handoff.

A

roaming

56
Q

RSSI thresholds are also used by vendors to implement _____ _____ _____, which is a process used by 802.11 radios to shift between data rates.

A

dynamic rate switching (DRS)

57
Q

When deploying radio communications, a _____ _____ is the sum of all gains and losses from the transmitting radio, through the RF medium, to the receiver radio. The purpose of _____ _____ calculations is to guarantee that the final received signal amplitude is above the receiver sensitivity threshold of the receiver radio.

A

link budget

58
Q

Any hardware device installed in a radio system adds a certain amount of signal attenuation called _____ _____. Cabling is rated for dB loss per 100 feet, and connectors typically add about 0.5 dB of _____ _____.

A

insertion loss

59
Q

_____ _____ is a level of desired signal above what is required.

A

Fade margin

60
Q

A fade margin of _____ dB is an absolute minimum. This would only be acceptable for links less than 3 miles or so. Up to 5 miles should have at least a _____ dB fade margin, and links greater than that should be higher. A fade margin of _____ dB is recommended for links greater than 5 miles.

A

10, 15, 25

61
Q

By increasing the fade margin, you are essentially increasing the _____ of the link.

A

reliability

62
Q

The _____ is the difference between the actual received signal and the signal necessary for reliable communications.

A

system operating margin (SOM)

NETW-125/PW0-105 (4 decks)

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