GPSPC 2/17/2003 1 Masterclock, Inc.
INTRODUCTION
The GPSPC is a PCI or ISA PC card that provides very stable accurate time and date information for a
Windows/NT PC. The card receives reference time information from Atomic Clocks in the GPS (Global
Positioning System) satellites.
GPS SATELLITES
The GPS satellites are operated and maintained by the US Department of Defense and allow for the precise
determination of local time and location at any point on (or above) the Earth. This is accomplished via the
transmission of very accurate timing information from a series of satellites that provide coverage of the entire
planet.
The GPSPC extracts timing reference from these signals and generates time information to the PC that is
synchronized to within less than 10 microseconds of UTC (Universal Coordinated or Greenwich Mean Time).
UTC/GREENWICH MEAN TIME
UTC is the local time at the prime reference meridian at Greenwich, England. At a given location on the planet,
local time can be displaced (referenced to UTC) by -11 to +12 hours. North and South America are from -3 to -
11 hours delayed; most of Europe and Africa and all of Asia and Australia are advanced by +1 to +12 hours.
TIME ZONES & DAYLIGHT SAVING TIME
The GPSPC provides UTC to the PC’s operating system. Time zone offsets and daylight savings time are
handled as a standard feature of the operating system.
INITIAL OPERATION
Each GPSPC is thoroughly tested with its external antenna prior to shipment. Physical installation is simply a
matter of installing the card into a PCI or ISA bus slot and connecting the antenna.
OPERATING THE GPSPC FOR THE FIRST TIME
When the GPSPC is initially powered up, after having been shipped to a new location, the time to first fix (time
the unit takes to acquire satellites and extract correct time) could be up to 25 minutes although it is typically 5
- 15 minutes. Factors such as atmospheric conditions, type of antenna, antenna location, and antenna cable
length will affect the time to first fix.
The GPSPC will provide time from an internal on-board clock whenever GPS time is not available. The
onboard clock runs from a backup battery in the absence of power from the PC.
The GPSPC’s GPS navigation module has its own backup battery that maintains startup data when the PC is
powered down. If, when starting up, the location, time and number of satellites that the GPSPC can receive
has not changed significantly since last power down, then the GPSPC time will be available much faster.
ANTENNA LOCATION
Depending on the type of building where the GPSPC is located and obstructions that may block reception of
signals from the GPS satellites, the antenna may have to be located where it has an unobstructed view of the
sky. In some cases this can be accomplished by placing the antenna adjacent to a window. In most cases it
will require mounting it outside of the building or on a roof. In the worse case, the basic requirement for
assured system operation is that the antenna module has a clear and unobstructed view of the sky for initial
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