WiFoo..The.Secrets.of.Wireless.Hacking [Electronic resources] نسخه متنی

F

fade margin

Additional signal level required to prevent the loss in signal along a signal path caused by environmental factors such as terrain, atmospheric conditions, and so on.

fading

Occurs when the power level of the signal drops because of various environmental factors.

Fast Ethernet

Extension of the Ethernet standard, IEEE 802.3u; defines the transmission of data over copper wire or fiber-optic cable at a rate of 100 Mbps.

fast roaming

Roaming between or changing connections from one AP to another in a timeframe suitable for time-sensitive applications. Typically this is under 150 ms.

FCC

Federal Communications Commission. The government agency responsible for regulating telecommunications in the United States.

feedhorn

The part of a parabolic or grid reflector antenna that contains the driven element.

filter

A device used to block or reduce signals at certain frequencies while allowing others to pass through.

frequency

The rate at which an electrical current alternates, expressed as the number of cycles per unit of time (from crest to crest in a sine wave pattern); frequency is typically measured in hertz (Hz) or cycles per second (cps). For example, a 1-MHz frequency would have a full cycle (a complete sine wave) pass a given point in space at the rate of one million cycles per second. A 1-GHz frequency would have sine waves pass a given point in space at the rate of one billion times per second, and so forth.

frequency hopping (FH)

A spread-spectrum modulation technique where the transmitter frequency hops from channel to channel in a predetermined but pseudo-random manner. The signal is tracked at the receiver by a frequency synthesizer controlled by a pseudo-random sequence generator synchronized to the transmitter's pseudo-random generator.

frequency modulation (FM)

An analog modulation technique whereby the frequency of a carrier is varied to encode information.

Fresnel effect

A phenomenon related to line of sight, whereby an object that does not obstruct the visual line of sight obstructs the line of transmission for radio frequencies.

Fresnel zone

The area around the line of site between two points caused by the Fresnel effect. In WLANs, the critical area is 60 percent of the overall Fresnel area.

full-duplex transmission

A channel that allows transmission in two directions.