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Part No. 96000001
during survey operations. If mounting the antenna on a vessel that has helicopter landing facilities,
coordinate the placement of the antenna with the personnel in charge of helicopter operations.
When the location for the antennae has been determined, the next step is determining how the
coaxial cable, connecting the antenna and the receiver, is to be run. The cables should be run in
such a manner to be protected from possible damage. Cables should not be run through hatches or
windows if it can be avoided; if such runs are necessary, then a block or other such obstruction
should be placed so that the hatch or window will not close on the cable. If the cables are to be
suspended between two points, a rope or other line should be strung to carry the weight of the
cables. Cables should never be kinked; all cables have a minimum bending radius, and if it is known,
adhere to it, if it is not known, use common sense. Do not run cables in a manner that they will
become safety hazards on the vessel, causing personnel to trip or be caught on them. Avoid running
cables along voltage carrying lines.
It is important to mark the cables at both ends to denote what they are and to where they go.
The connection to the antenna may be required to be completely waterproofed (depending on the
manufacturer’s recommendations) using electrical tape, with a secondary covering of self-
amalgamated tape. Ensure that there are no air gaps in the tape; they will become a channel for
water. If a cable is to be run upwards from the antenna, form a drip loop by leaving slack in the
cable that will hang below the antenna connector. This will allow any water that flows down the
cable to collect and drip from the slack loop instead of running into the connector.
The cables, connectors and antennae should be inspected regularly for signs of damage, corrosion
or abuse. Any abrasions on the cable should be securely taped; if possible, a waterproof coating
should also be applied.
8.2.2 GPS Calibration
Prior to commencing survey operations, the accuracy of the Differential GPS position and
transformation to local datum should be determined. There are two main methods to determine
the accuracy of the DGPS position and data transformation. For both methods, a local land survey
benchmark is required.
8.2.2.1 Position Accuracy Determination Method 1
The GPS antenna is physically placed over the survey benchmark. The surveyor will ensure that the
antenna has a clear view. This is particularly important if the benchmark being used is in a dock area.
The surveyor will also ensure that if a separate antenna is used to receive differential corrections,
that it is not blocked.
The GPS position data should be logged, in the data collection software, for not less than 15
minutes. The collected data can then be averaged, standard deviations determined and compared
to the published position of the survey benchmark.
The two main causes of error, in this area, are:
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