Terrestrial Nav Systems Flashcards
Accurate too? & max operating range?
Accurate to 0.25NM & operating range of 650NM from its transmitter station.
Transmitters are in chains
In chains of 3-5 stations with one Master and 2-4 Slave stations
Transmission?
100kHz and uses time difference between pulses to fix a position.
Master = 9 pulses
Slave = 8 pulses
Advantages of (LORAN)
Advantages:
- High power
- Land based
- Transmissions are not as susceptible to jamming
Disadvantages to (LORAN)
Disadvantages:
- It’s not as accurate as GNSS
- Another system to maintain
- Largely discontinued at present
Fixed errors:
- Land error, as the oceans are a better conductor of radio waves than the land
- Diamond error and basline extension
Dynamic errors:
- Sky wave interference creates a distortion of the signal from the inosphere.
- Clock error, any inaccuracies will affect precision
More on description of errors of LORAN
What is eLoran?
Enhanced long-range navigation.
A hyperbolic radio system to calculate a position from a time difference
What is a G.R.I?
Group repetition interval: is unique to each group of stations.
- Time difference between individual slave stations from the master station
Master = 9 pulses
Slave = 8 pulses
Principle of a hyperbolic navigation system
Describe, with the aid of a sketch, the principle used by Loran C to
provide position information. (15 marks)
Hyperbolic position line diagram.
At least Master and 2 slaves.
What is understood by the term ‘Base line extension area’ and what is
its effect on the accuracy of the position? (5 marks)
The area beyond the ends of the line joining master and slave.
Large gradient therefore inaccurate positions.
Explain how a LORAN C receiver is able to distinguish between the
different chains within range?
Each chain operates using a different Group Repetition Frequency (4)
What is the approximate groundwave range of the LORAN C
system?
800 to 1200 Nm (2)
Explain the cause of the fixed errors in the Loran C system
Fixed errors caused when Loran signal passes over land AND sea causing
an effective change in the speed of propagation. (4)
Describe how these fixed errors are applied to the Loran position in
a modern receiver
ASF values incorporated into software so that they can be automatically
applied by the receiver.
Or by manually inputting the values from the tables into the appropriate
page and the receiver will then apply those values to the loran position. (4)
a). Construct a labelled diagram of a Loran C hyperbolic pattern generated by
a master and slave transmitters. On your diagram label the following:
i. Baseline
ii. Base line extension
iii. Centre line
iv. Master station
v. Slave station (10)
b). On your diagram clearly indicate an area where positional accuracy is
good and one where positional accuracy is poor. Give reasons for your
choice. (6)
