Meinberg IMS LANTIME M4000, Руководство пользователя

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5 Mounting the Antenna
5 Mounting the Antenna
5.1 GNSS Signal Reception
The satellites of most Global Navigation Satellite Systems (GNSS) like GPS , GLONASS , and Galileo are
not stationary but circle round the globe in periods of several hours. Only few GNSS systems like the Chinese
Beidou system work with stationary satellites. Such systems can only be received in certain regions of the Earth.
GNSS receivers need to track at least four satellites to determine their own position in space (x, y, z) as
well as their time offset from the GNSS system time (t). Only if the receiver can determine its own position
accurately the propagation delay of the satellite signals can also be compensated accurately, which is require-
ment to yield an accurate time. If the receiver position can only be determined less accurately then the accuracy
of the derived time is also degraded.
GNSS satellite signals can only be received directly if no building is in the line-of-sight from the antenna
to the satellite. The signals can eventually be reflected at buildings, etc., and the reflected signals can then be
received. However, in this case the true signal propagation path is longer than expected, which causes a small
error in the computed position, which in turn yields less accurate time.
Since most of the satellites are not stationary, the antenna has to be installed in a location with as much
clear view of the sky as possible (e.g. on a rooftop) to allow for continuous, reliable reception and operation.
Best reception is achieved when the antenna has a free view of 8
◦
angular elevation above the horizon. If
this is not possible then the antenna should be installed with the best free view to the sky in direction of the
equator. Since the satellite orbits are located between latitudes 55
◦
North and 55
◦
South, this allows for the
best possible reception.
Meinberg provides their own GPS receivers which operate with an antenna/converter unit and thus allow
for very long antenna cables, but some devices also include GNSS receivers which support other satellite sys-
tems like GLONASS, or Galileo in addition to GPS. These receivers usually require a different type of antenna
equipment which is described in chapter (4.1.2).
IMS - LANTIME M4000 Date: 2nd July 2020 15