NTP Server
Static GPS Antenna Systems
This article provides an overview of GPS for
timing applications and describes the equipment used to install a GPS antenna in
a static location.
Overview - Using GPS for Accurate Time
The satellites continuously broadcast time and
position information. The time and position information can be obtained
worldwide with a GPS receiver and antenna.
Many computer timing systems and NTP Server
systems utilise GPS as an accurate external timing reference.
The Accuracy of GPS Timing Systems
GPS receivers provide highly accurate position
and timing information. NTP Server systems can obtain timing information from
GPS to a resolution of a few nanoseconds.
The GPS Signal
The transmitted GPS signal is very weak
low-power radio signal, designated L1 and L2.
GPS Timing Antenna Types
The GPS antenna acts as an amplifier to boost
the GPS signal for transmission along a cable, usually coax, to the GPS
receiver. GPS Timing antenna's provided with NTP server systems utilise a
pole-mounting system. This arrangement provides the GPS antenna with a rigid
mount easily able to withstand high winds without damage. Typically the GPS
antenna is fairly small in size, measuring less than 90cm in diameter.
GPS Antenna Cable Types and Cabling Distances
The cable distance that can be utilised by a
GPS antenna depends mainly on the amplification of the GPS antenna and the
quality of coax used in the installation. A typical GPS timing antenna may have
a gain of 35 db.
Extending Cabling Distance with In-Line GPS Amplifiers
In-line GPS amplifiers provide further
amplification of the GPS signal to increase the cable distance between the GPS
antenna and receiver. GPS amplifiers are fitted in-line with the antenna cable
and obtain power from the receiver via the coax cable. Typically, a GPS
amplifier may add a further 20 dB of gain, adding 30m of low-quality RG58 coax,
40m of LMR200 coax or 100m of high quality LMR400 coax.
Sharing a Single Antenna Between Multiple
Receivers - GPS Splitters
GPS splitters allow a single GPS antenna to be utilised by two or more NTP
server systems. The GPS splitter splits the signal received from the GPS antenna
into multiple outputs for synchronizing multiple NTP servers. GPS splitters are
generally available with 2, 4 or 8 outputs.
Protecting GPS Systems - GPS Surge Suppressors
Surge suppressors protect expensive NTP server
equipment from electro-static discharges, such as lightning, that may be picked
up by an externally mounted GPS antenna. Surge suppressors are installed in-line
on the coax cable between the antenna and receiver, ideally where the cable
enters the building.
by Andrew_Frain
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