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ALAN MAP 600
User’s Manual
Technical characteristics
13.4 The GPS receiver
The GPS receiver, (in this case, the PMR-GPS unit), uses NAVSTAR satellite signals
as a way of determining exact position on earth. Mathematically, you need four
satellite ranges to accomplish these coordinates. Although three ranges are enough,
an additional range is required for technical purposes.
So, our position is based on how long it takes for a signal sent from the satellite to
arrive at our receiver. Since timing is everything, the satellite signal is almost perfect
since it has an atomic clock on board. But, what about our GPS receiver timing? Our
receiver certainly contains no atomic clock; if it did, its cost would be prohibitive --
nobody could afford it. To get around this problem, our receiver must take an addi-
tional satellite measurement. Hence, it really needs four satellite signals to insure our
correct position. Since this fourth measurement, done as a cross check, does not
intersect with the first three, our receiver’s computer says, in effect, there is a dis-
crepancy in my measurements, and I must not be synchronized with universal time.
Since any offset from universal time will affect all of our measurements, the receiver
looks for a single correction factor that it can subtract from all its timing measure-
ments that would cause them all to intersect at a single point. That correction brings
the receiver’s clock back into sync with universal time and, in this way, atomic timing
accuracy is in the palm of your hand!
Once our receiver has that correction, it applies to all the rest of its measurements
and now we’ve got precise positioning.
14. Technical characteristics
Map
• Scale view: 50m – 200 Km with 9 levels of zoom (enlarge/reduce)
• Memory card: Compact Flash (CF) by Scandisk or another 100% compatible brand
• Map memory capacity: In combination with Mapshow CRD vector detailed
maps can be modified to .LST files and loaded on CF cards.
Navigation
• Waypoints: up to 1000 waypoints, including their names, comments, and display
• Routes: up to 50 routes, each with a maximum of 150 waypoints
• Tracking: up to 9 recordings of movement – 8 in memory and 1 in use, with a
maximum of 2500 points each. Movement recording mode modifiable.
Functions
• Receives and synchronizes up to 12 satellites
• Acquisition
time:
- First start-up: 300 seconds, on average
- Already turned on in the area: 40 seconds, on average
- Already warm: 15 seconds, on average
- Speed of satellite acquisition: every 0.1 second
- Speed of data update: every second
Precision
• Position: 5 – 25 meters
• Speed: within 0.1m/second
• Time: ± 1 µS
Measurement fields
• Altitude: from -1.000 to 18.000 m
• Speed: within 515 m per second
• Acceleration:
± 4
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