Eion LibraPlus 5845, Руководство пользователя, Страница: 130 / 140

ESD Electrostatic Discharge. Caused by static electricity. ESD Protec-
tion should be used to protect electronic components from damage.
F
Fade Margin The amount by which the system gain plus the total antenna gain
exceed the path loss is called the fade margin. The fade margin is
the number of dB that the received signal strength exceeds the
minimum receiver sensitivity.
FEC Forward Error Correction. A method of correcting data errors
without retransmission.
Filtering Filtering in remote stations limits certain data packets.
Flash A type of electrically erasable non-volatile memory that can easily
be erased without removal from a unit. Using Flash, the Access
Point can be upgraded in the field.
Fresnel Zone The line of sight between two antennas. It consists of one of a
theoretically infinite number of a concentric ellipsoids of revolution
that define volumes in the radiation pattern of a usually circular
aperture. The cross glossdiv of the first Fresnel zone is circular.
Subsequent Fresnel zones are annular in cross-glossdiv, and con-
centric with the first. Odd-numbered Fresnel zones have relatively
intense field strengths and even-numbered Fresnel zones are nulls.
Fresnel zones result from diffraction by the circular aperture.
Front to Back Ratio (F/B) Directional antennas focus the signal in a forward path, reducing
the signal in the opposite direction. The proportion between the
two is called the front-to-back ratio. A higher gain antenna typic-
ally has a greater F/B ratio.
Frost Loading A concern of antenna operation affected by low temperatures.
FTP File Transfer Protocol. A method of copying files from one site
to another. An operator of EION equipment might use ftp to
download software upgrades.
G
Gain The ability of a device to amplify a signal. Gain is the ratio of
output power divided by input power, usually expressed in decibels
(dB). Gain can also be measured as an absolute value, referenced
to an input signal of one milliwatt (dBm). For antennas, gain
measures the ability of an antenna to focus a signal and is expressed
in dBd (half-wave dipole reference) or dBi (isotropic radiator ref-
erence).
GPS Global Positioning System. EION Broadband Wireless Access
Systems installers may use GPS devices instead of maps and
compasses to locate their unit and orient it toward another station.
I
Ice loading A problem of antenna operation in cold countries. Ice collects on
the antenna and degrades its performance.
120
Appendices