Loran TD
Position Format
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Loran C Chart
Each Master Station transmits a pulsed radio frequency (RF)
signal at a set time interval. This time interval is referred to as the
Group Repetition Interval or GRI. The GRI is used to identify the
different Loran C transmitter chains. It is not important to under-
stand how this number is determined, just that it represents the
Master Station and chain.
After a Master Station transmits it’s pulsed RF signal, each
Secondary station after recieving the master station signal, trans-
mits a pulsed RF signal at a set time delay. As the signals are
processed by the Loran C receiver, the master signal is separated
and used to measure the difference in time with each secondary
signal. The time interval is very short, measured in millionths of a
second or micro seconds. This time difference is how the Loran C
determines a location.
To determine a location, a Loran C must receive signals from a
Master and two Secondary Stations of the same chain. From those
three signals, a set of two TD’s are constructed and using the TD’s a
location can be plotted.
Loran C.p65
12/21/99, 10:09 AM
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