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Caribou, Maine; (X) at Nantucket, Massachusetts; (Y) at
Carolina Beach, North Carolina, and (Z) at Dana, Indiana.
In order to keep chain operations precise, monitor
receivers are located at Cape Elizabeth, ME; Sandy Hook,
NJ; Dunbar Forest, MI, and Plumbrook, OH. Monitor
receivers continuously measure various aspects of the
quality (e.g., pulse shape) and accuracy (e.g., timing) of
LORAN signals and report system status to a control
station.
4. The line between the Master and each
secondary station is the “baseline” for a pair of
stations. Typical baselines are from 600 to
1,000 nautical miles in length. The continuation of
the baseline in either direction is a “baseline
extension.”
5. At the LORAN transmitter stations there are
cesium oscillators, transmitter time and control
equipment, a transmitter, primary power (e.g., commercial
or generator) and auxiliary power equipment
(e.g., uninterruptible power supplies and generators),
and a transmitting antenna (configurations may either
have 1 or 4 towers) with the tower heights ranging
from 700 to 1350 feet tall. Depending on the coverage
area requirements a LORAN station transmits from
400 to 1,600 kilowatts of peak signal power.
6. The USCG operates the LORAN transmitter
stations under a reduced staffing structure that is
made possible by the remote control and monitoring
of the critical station and signal parameters. The
actual control of the transmitting station is
accomplished remotely at Coast Guard Navigation
Center (NAVCEN) located in Alexandria, Virginia.
East Coast and Midwest stations are controlled by the
NAVCEN. Stations on the West Coast and in Alaska
are controlled by the NAVCEN Detachment (Det),
located in Petaluma, California. In the event of a
problem at one of these two 24 hour−a−day staffed
sites, monitoring and control of the entire LORAN
system can be done at either location. If both NACEN
and NAVCEN Det are down or if there is an
equipment problem at a specific station, local station
personnel are available to operate and perform repairs
at each LORAN station.
7. The transmitted signal is also monitored in
the service areas (i.e., area of published LORAN
coverage) and its status provided to NAVCEN and
NAVCEN Det. The System Area Monitor (SAM) is
a single site used to observe the transmitted signal
(signal strength, time difference, and pulse shape). If
an out−of−tolerance situation that could affect
navigation accuracy is detected, an alert signal called
“Blink” is activated. Blink is a distinctive change in
the group of eight pulses that can be recognized
automatically by a receiver so the user is notified
instantly that the LORAN system should not be used
for navigation. Out−of−tolerance situations which
only the local station can detect are also monitored.
These situations when detected cause signal
transmissions from a station to be halted.
8. Each individual LORAN chain provides
navigation-quality signal coverage over an identified
area as shown in FIG 1−1−15 for the West Coast
chain, GRI 9940. The chain Master station is at
Fallon, Nevada, and secondary stations are at George,
Washington; Middletown, California, and Searchlight,
Nevada. In a signal coverage area the signal
strength relative to the normal ambient radio noise
must be adequate to assure successful reception.
Similar coverage area charts are available for all
chains.
2/19/04 AIM
Air Navigation Aids 1−1−19
FIG 1−1−13
The LORAN Pulse and Pulse Group
AIM 2/19/04
1−1−20 Air Navigation Aids
FIG 1−1−14
Northeast U.S. LORAN Chain
2/19/04 AIM
Air Navigation Aids 1−1−21
FIG 1−1−15
West Coast U.S. LORAN Chain
AIM 2/19/04
1−1−22 Air Navigation Aids
c. The LORAN Receiver
1. For a currently certified LORAN aviation
receiver to provide navigation information for a pilot,
it must successfully receive, or “acquire,” signals
from three or more stations in a chain. Acquisition
involves the time synchronization of the receiver with
the chain GRI, identification of the Master station
signals from among those checked, identification of
secondary station signals, and the proper selection of
the tracking point on each signal at which
measurements are made. However, a new generation
of receivers has been developed that use pulses from
all stations that can be received at the pilot’s location.
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