Figure 20.13:1pps accuracyThe GPS system consists of more than 20 satellites rotating in orbit above the earth. The satellites are not in geo-stationary orbit, and so the constellation that can be 'seen' is constantly changing. In general, up to 7 satellites can be 'seen' at any time. When GPS time synchronising receivers are energised, they need to initialise their timing algorithms. Generally, this requires that at least 4 satellites are in view for a short while.In order to receive the signals from the GPS satellites, an antenna is required. This needs to be mounted externally. A mounting pole is generally used as shown Figure 20.14.Figure 20.14: Antenna connection detailsIt is vital that the receiving antenna has the best possible mounting location to maintain reception with as many satellites as possible, thus the ideal mounting is shown in Figure 20.15.
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