A
Absolute Accuracy (in navigation)
The difference between the Loran-C determined position and the actual location as defined by the geographic coordinates
AC
Alternating Current
Analog
The traditional method of transmitting voice signals where the radio
wave is based on electrical impulses, which occur when speaking
into the phone.
Analog-to-Digital Converter
A device that converts an analog input voltage to a digital output
word. These are also known as ADCs, and have varying degrees of
input range and output resolution.
Antenna
An array of metal rods or wires used to intercept radio waves and
convert them into electrical currents. In microwave applications,
often a parabolic reflector with associated feed mechanism.
ASF (Additional Secondary Factor)
In Loran-C, a correction in addition to the secondary phase factor correction for the additional time (or phase delay) for transmission of a low-frequency signal over a composite land-seawater path, when the signal transmit time is based on the free-space velocity.
Attenuator
A device or network that absorbs part of a signal and transmits
the remainder with a minimum of distortion.
B
Bandwidth
The size of a network "pipe" or channel for communications
in wired networks. In wireless, it refers to the range of available
frequencies that can carry a signal.
BIPM (Bureau International des Poids et Measures)
An organization that calculates TAI (International Atomic Time).
C
C-band
The portion of the microwave spectrum (4,000-8,000 MHz) used most
widely for distribution of video programs by satellite to cable
systems.
CDPD
Cellular Digital Packet Data is a specification for supporting wireless
access to the Internet and other public packet-switched networks.
Cellular telephone and modem providers that offer CDPD support make
it possible for mobile users to get access to the Internet at up
to 19.2 Kbps.
Cellular Modem
A device that allows wireless data access by dialing a computer
network via the cellular network.
Channel
The width of the spectrum band taken up by a radio signal, usually
measured in kilohertz (kHz).
Coaxial Cable
A cable consisting of one center conductor to carry a signal, surrounded
concentrically (coaxial) by an insulating dielectric and a separate
outer conductor (braid or metal jacket) which acts as a shield.
CPU
Central processing unit of a computer.
CRC (cyclic redundancy check)
A final safety check of Eurofix message integrity.
D
Data Rate
Data rates are usually dictated by the system - how much data must
be transferred and how often does the transfer need to take place.
Lower data rates allow the radio module to have better receive sensitivity
and thus more range. Higher data rates allow the communication to
take place in less time, potentially using less power to transmit.
dB (decibel)
A logarithmic expression of ratios. Can be found by taking 10 times
the common logarithm of the ratio of 2 power levels, or 20 times
the common logarithm of the ratio of 2 voltage levels. The unit
generally used to express signal-to-noise ratio (SNR).
DC
Direct current
DGNSS (differential global navigation satellite system)
Differential GNSS, the use of GNSS measurements, some or all of
which are differentially corrected.
DGPS (differential global positioning system)
Differential GPS, the use of GPS measurements that are differentially
corrected
DSP
Digital signal processing
DTE
Data terminal equipment
E
ECD (envelope to cycle distortion)
The time relationship between the phase of the Loran-C carrier and
the time origin of the envelope waveform.
EIRP
Effective Isotropically Radiated Power. EIRP represents the total
effective transmit power of the radio, including gains that the
antenna provides and losses from the antenna cable.
eLoran
Enhanced Loran - the system that incorporates the latest
receiver, antenna and transmission system technology.
Encryption
The process of encoding information in such a way that only the
person (or computer) with the key can decode it.
ESD
Electrostatic discharge
F
FAA
Federal Aviation Administration
Fade Margin
A design allowance that provides for sufficient system gain or sensitivity
to accommodate expected fading, for the purpose of ensuring that
the required quality of service is maintained. Also, the amount
by which a received signal level may be reduced without causing
system performance to fall below a specified threshold value.
FCC
Federal Communications Commission. The U.S. government agency responsible
for allocating radio spectrum for communication services.
FEC (Forward error correction)
A means of correcting occasional errors and validating data in a
broadcast communication system.
FERNS (Far East radionavigation system)
A Loran-C consortium that includes Japan, China, Korea, and Russia
Frequency
The number of cycles per second of an electromagnetic transmission.
1 hertz (Hz) = 1 cycle per second; 1 kilohertz (kHz) = 1,000; 1
megahertz (MHz) = 1,000,000; 1 Gigahertz (GHz) 1 billion.
Frequency Modulation
A method of transmission in which the desired information is represented
by modulating (varying) the frequency of a "carrier" signal.
Fresnel Zone
The Fresnel (pronounced fray-nell) zone is the area around the visual
line-of-sight that radio waves spread out into after they leave
the antenna. This area must be clear or else radio signal strength
will weaken.
Full Duplex
The capability to both transmit and receive simultaneously on a
communication channel.
G
Gain
The ratio of the power required at the input of a loss-free reference
antenna to the power supplied to the input of the given antenna
to produce, in a given direction, the same field strength at the
same distance. Antenna gain is usually expressed in dB.
GDOP (geometric dilution of precision)
A value representing all geometric factors that degrade the accuracy
of a position fix derived from a navigation system.
GNSS (global navigation satellite system)
Any single or combined satellite navigation system. Currently the
options are: GPS, GLONASS, and combined GPS/GLONASS.
GHz
Gigahertz (billions of hertz).
GLONASS
An all-weather, continuous satellite navigation system maintained
by the Russian Space Forces. It is normally composed of 24 satellites
in three orbital planes, with eight satellites in each plane. The
spacing of satellites in orbit is arranged so that a minimum of
four satellites will be in view to users worldwide, providing position
dilution of precision (PDOP) of 6 or less.
GPS (global positioning system or global positioning satellite)
The full name is NAVSTAR Global Positioning System. GPS is an all-weather,
continuous satellite navigation system developed by the Department
of Defense under Air Force management. The fully deployed operational
system is intended to provide highly accurate position and velocity
information in three dimensions and precise time and time interval
on a global basis, to an unlimited number of authorized users.
GRI (group repetition interval)
For a particular Loran-C chain, the specified time interval for
all stations of the chain to transmit their pulse groups. For each
chain a minimum GRI is selected of sufficient duration to provide
time for each station to transmit its pulse group, and additional
time between each pulse group, so that signals from two or more
stations cannot overlap in time anywhere within the coverage area
H
HDOP (horizontal dilution of precision)
Similar to GDOP, except that elevation factors are ignored.
Hz or Hertz
The unit of measuring frequency signals (one cycle per second).
I
Insertion Loss
The loss measured in dB of any device that might be connected in
series with the antenna cable.
IRQ
Interrupt request
ISM
Industrial, Scientific, and Medical. It is the unlicensed radio
band in North America and some European countries. It is also referred
to as part 15.247, the FCC regulation that defines the parameters
for use of the ISM bands in the United States, including power output,
spread-spectrum, and non-interference. ISM frequencies include 902-928
MHz, 2.4 GHz and 5.8 GHz.
ISO
International Standards Organization
J
K
Kbps (kilobits per second)
A measurement of bandwidth in the United States.
KHz or Kilohertz
Thousands of hertz
kV
Kilovolt
L
LAD
Linear Averaging Digital
Latency
In a network, latency, a synonym for delay, is an expression of
how much time it takes for a packet of data to get from one designated
point to another.
LED (light emitting diode)
Solid state devices that glow when electric current is applied.
Type of display commonly used with electronic equipment.
Line-of-Sight
Line-of-sight means more than being able to see the receiving antenna
from the transmitting antenna. In order to have true line-of-sight,
no objects (including trees, houses or the ground) can be in the
Fresnel zone.
Locus
A "locus" is a set of points that satisfies certain requirements (e.g. a position). Locus, Incorporated took its company name from this definition.
LOPs (lines of position)
In Loran-C navigation systems, vectors obtained by measurement of
the time difference between the receipt of the master and slave
signals, which is then used to select a corresponding LOP from a
chart or table. Two or more intersecting LOPs are required to obtain
a position fix.
Loran
Long Range
Aid to Navigation
- a ground-based transmitter system that was implemented in the
late 1950s by the US government for navigational purposes. Loran
is the general designation of a group of radionavigation systems
by which a hyperbolic line of position is determined through measuring
the difference in the times of reception of synchronized pulse signals
from two fixed transmitters.
Loran-A
The predecessor technology to Loran-C.
Loran-C
Loran-C is a system of transmitters that generate electromagnetic pulses riding on a 100 KHz carrier. Transmitters are grouped into chains, of which at least three stations share the same frequency of transmitted pulses. The predecessor technology to eLoran.
M
MHz or Megahertz
Millions of hertz
Microwaves
High frequency radio waves lying roughly between infrared waves
and radio waves (above 1 GHz = 1 billion cycles per second). Microwaves
are generated by electron tubes, such as the klystron and the magnetron,
or solid state devices with built-in resonators to control the frequency
or by oscillators. Microwaves have many applications for radio,
television, radar, test and measurement communications, distance
and location measuring, and more.
MTBF
Mean Time Between Failure - A calculated figure representing the
estimated average lifetime of a device before it fails.
Multipath
Reception of one or more reflected signals along with a direct broadcast
signal, producing distortion.
N
NELS (Northwest European Loran-C System)
A Loran-C consortium that includes the countries of France, the Netherlands,
Norway, Denmark, Germany, and Ireland.
NIST
National Institute of Standards and Technology
NMEA (National Marine Electronics Association)
This organization’s standard allows marine electronics to
send information to computers and other marine equipment. The standard
also defines GPS receiver communication.
O
Output Power
The minimum and/or maximum output power at the output frequency
under all specified conditions. Usually the specified conditions
are temperature, load, VSWR and supply voltage variations. It is
typically expressed in dBm or milliwatts (mW).
P
PC
Personal computer
PCI (phase code interval)
Within a Loran-C pulse, the duration of an entire phase-coded pattern.
One
PCI is equal to two GRIs.
Power Amplifier
The final stage of amplification in a radio, the purpose of which
is to raise the signal to the level required by the antenna system.
Packet
A chunk of data that is sent over a network, whether it's the Internet
or wireless network. Packet data is the basis for packet-switched
networks, which are under development in the United States as a
faster, more reliable method of transferring wireless data than
a circuit-switched network. Packet-switched networks eliminate the
need to dial in to send or receive information because they are
"always on," transferring data without the need to dial.
The packets that hold data depend on the size of the data involved;
"chunks" are broken down into an efficient size for routing.
Each of these packets has a separate number and carries the Internet
address for which it is destined.
R
RAM
Random access memory, in a computer.
RASIM (Receiver Autonomous Signal Integrity Monitoring)
The lowest level of Eurofix message integrity is provided by the
signal demodulator using RASIM.
Relative Accuracy (in navigation)
The accuracy with which a user can determine position in relation to another user of the same navigation system at the same time.
Repeatable Accuracy (in navigation)
The accuracy of how closely a user can return to a position using coordinates that have been measured at a previous time using the same navigation system.
RF (radio frequency)
Generally referring to any frequencies at which the radiation of
electromagnetic energy is possible. Also used as designation for
frequencies below approximately 50 to 100 MHz (100-300 MHz is very
high frequency, 300 MHz – 1000 MHz is ultra-high frequency,
100 MHz and up is microwave).
ROM
Read-only memory, in a computer.
S
SAM
System area monitor
Selectivity
A measure of a radio receiver’s ability to isolate a specific
frequency at closely spaced frequencies without mutual interference.
Sensitivity
The minimum signal level that can be successfully captured and decoded
by a receiver, specified in dBm.
SNR (signal-to-noise ratio)
The ratio of the magnitude of a signal to that of the noise
(interference), often expressed in decibels.
Spectrum
The complete range of electromagnetic waves that can be transmitted
by natural sources such as the sun, and man-made radio devices.
Electromagnetic waves vary in length and therefore have different
characteristics. Longer waves in the low-frequency range can be
used for communications, while shorter waves of high frequency show
up as light. Spectrum with even shorter wavelengths and higher frequencies
are used in X rays.
Spread Spectrum
Originally developed by the military, spread spectrum radio transmission
essentially "spreads" a radio signal over a very wide
frequency band to make it difficult to intercept and difficult to
jam. Most spread-spectrum signals use a digital scheme called frequency
hopping. The transmitter frequency changes abruptly, many times
each second. Between "hops," the transmitter frequency
is stable. The length of time that the transmitter remains on a
given frequency between "hops" is known as the dwell time.
T
TAI (International Atomic Time)
A statistical time scale calculated by the Bureau International
des Poids et Measures (BIPM) from the readings of more than 200
atomic clocks in more than 30 countries.
TD (time difference)
In Loran-C, the time difference measured from the time of reception
of the master station signal to the time of reception of the slave
station signal.
TOA
Time of arrival
TOD
Time of day
TTFF
Time to First Fix
U
USCG
United States Coast Guard
USNO
United States Naval Observatory
UTC (Coordinated Universal Time)
A time scale based on the rotation of the earth that is disseminated
by most broadcast time services.
V
W
WAAS (wide-area augmentation system)
An augmentation to GNSS that uses geostationary satellites
to broadcast GNSS integrity and correction data, and additional
ranging signals.
Watt
A unit of electrical or acoustical power. Electrical power is the
product of voltage and current. Acoustical power is proportional
to sound-pressure intensity.
WAN
Wide Area Network
WGS (World Geodetic System)
A consistent set of parameters describing the size and shape of
the earth, the positions of a network of points with respect to
the center of mass of the earth, transformations from major geodetic
datums, and the potential of the earth (usually in terms of harmonic
coefficients).
X
Y
Z
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Glossary
of Terms and Acronyms