Codan Radio Radio Repeater Systems Training Guide - Manual (Page 83)

RADIO REPEATER SYSTEM | TRAINING GUIDE
Appendix J: Glossary of Terms Page 75
Forward Gain
See “gain”.
Four-Wire Line
Two separate two-wire lines, one for
receiving and the other for transmitting
in remote control operations.
Frequency
The number of complete cycles per
second of alternating current or radio
waves. Usually measured in Hertz
(Hz).
Frequency Band
A continuous range of frequencies
extending between two limiting
frequencies. Common frequency bands
in two-way radio are 29-50 MHz (low
band), 136-174 MHz (VHF or High
Band), 406-512 MHz, 806-824 MHz,
851-869 MHz , 869-901 MHz and 935-
940 MHz (UHF Bands).
Frequency Modulation (FM)
A method of modulating a carrier
frequency by causing the frequency
to vary above and below the carrier
in accordance with the sound being
transmitted. The amount of deviation
in frequency above and below the
carrier frequency is proportional to
the amplitude of the sound being
transmitted. The advantages of this
system are almost complete freedom
from atmospheric and man-made
interference.
Frequency Range
A frequency band including the
frequencies at which a system is able to
transmit, receive or amplify power.
Fresnel Zone
A measurement of path clearance in
terms of the effect at the frequency in
question. The First Fresnel Zone is the
surface containing every point for which
the sum of the distances from that point
to the two ends is one-half wavelength
longer than the direct end-to-end path.
Front-To-Back Ratio (F/B)
The ratio between the power radiated in
the forward direction from an antenna to
that radiated to the rear.
Gain
The increase in voltage, current or
power as measured (usually in dB)
against an established standard.
Gain Antenna
An antenna designed to increase its
normal fi eld range through a more
directional pattern.
Grounded
Connected to earth or some conducting
body that serves in place of the earth.
Harmonic
Frequencies which are a multiple of a
carrier frequency.
Hertz (Hz)
The unit of frequency measurement
equal to one cycle per second.
Hysteresis
The lag of an effect in respect to its
cause.
Interface
A method for interconnecting units or
systems which may not be compatible.
Interference
The effects that occur when undesired
signals interfere with the reception of a
desired signal.
Intermodulation
The product of two waves beating
together and producing other interfering
waves. Sometimes called “intermod” or
“IM”.
Kilohertz (kHz)
One thousand Hertz or one thousand
cycles per second.
Line-Of-Sight Distance (L/S)
The straight-line distance from station to
station or horizon. This represents the
approximate normal transmitting range
of stations in the VHF and UHF bands.