Sony HKDW-704, Operation Manual

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1
Chapter 1 Using GPS Data
1-4
1-2-2 Transmitting GPS Initial Data (Almanac
Data)
When a GPS receiver performs a geodetic survey for the first time, since
it does not know which satellite signals are available in a particular area,
a GPS receiver searches all of satellites. Thus, it take some time to
perform an initial calculation of a location.
If a GPS receiver has almanac data (orbit information of satellites), it
starts searches for satellites that are within range by referring to this data
based on the current location and time. This is helpful to shorten the time
needed to finish calculating a location.
Almanac data is transmitted in a twelve and half minute cycle from all of
the GPS satellites. Thus, given sufficient time, a GPS receiver can obtain
data from satellites.
When you use the camcorder with this board for the first time, or after
you replace an old lithium battery with a new one, it takes a certain
amount of time to perform calculating a location. If almanac data has
been obtained already, a receiver can find satellites required for
calculation and calculate an exact location in shorter period of time.
Satellites that can be located
If a receiver has correct
almanac data, it can locate
receivable satellites easily.
Satellites that cannot be
located
If a receiver don’t have
correct almanac data, it will
look for satellites that are
located where a receiver
cannot find them.