11
Antennas
In this chapter:
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■
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Introduction
Measuring antenna heights
Antenna.ini file
11
1 1 Antennas
11.1
Introduction
This chapter describes the antennas that can be used during a GPS survey.
11.2
Measuring Antenna Heights
The antenna receives GPS signals at the antenna phase center (APC).
The APC is inside the plastic housing, so it is not possible to measure directly to it. Instead, measure the height from the survey mark on the ground to a specified part of the antenna housing. Enter the antenna height, then, in the Measured to field, specify the part on the housing where the measurement was taken.
For example, with a Zephyr or Micro-centered™ antenna, measure to the bottom of the plastic antenna housing. Enter this value in the
Antenna height field and, in the Measured to field select Bottom of antenna. With a GPS Total Station 4800 antenna, enter 1.800 m in the
Antenna height field.
The Trimble Survey Controller software corrects the antenna height value according to the antenna type selected and the setting in the
Measured to field. It calculates the APC based on the antenna type, the uncorrected height, and the value in the Measured to field. This APC height is used to calculate the ground height for points.
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11.2.1
Antennas 1 1
Measuring the Height of an Antenna on a Range Pole
Figure 11.1 shows how to measure the height of an antenna mounted
on a range pole when the Measured to field is set to Bottom of antenna or Bottom of antenna mount. With a fixed height range pole, the height is a constant value. rt
0.046 m Zephyr antenna
Uncorrected
height
Corrected height to APC
0.156 m
Uncorrected
height
of 1.80 m
0.0625 m
Uncorrected
height
GPS Total Station
4800 antenna
Corrected height to APC
Micro-centered antenna
Corrected height to APC
Figure 11.1
Measuring the height of a receiver mounted on a range pole
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1 1 Antennas
11.2.2
Measuring the Height of an Antenna on a Tripod
The way to measure this depends on the equipment used.
Zephyr antenna
If this antenna is mounted on a tripod, measure the height to the top of
the notch on the side of the antenna. See Figure 11.2.
Zephyr Geodetic antenna
If this antenna is mounted on a tripod, measure the height to the
bottom of the notch on the side of the antenna. See Figure 11.2.
GPS Total Station 4800 receiver
If this antenna is mounted on a tripod, measure the uncorrected height to one of the eight protruding notches on the edge of the plastic antenna housing. These are located inside the external shock resistant housing ring. Use the special measuring tape provided by Trimble.
Enter a value in the Antenna height field, and, in the Measured to field, select Hook using 4800 tape.
B
Tip – If you are using a fixed height tripod, you can measure the height to the bottom of the antenna housing and select Bottom of antenna mount in the Measured to field.
Micro-centered L1/L2 antenna
If this antenna is mounted on a tripod, measure the height to the bottom of the plastic housing. Enter this value in the Antenna height field and set the Measured to field to Bottom of antenna.
Ground plane
If you are using a ground plane, see the next section.
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11.2.3
Antennas 1 1
Measuring the Height of an Antenna When Using a Ground
Plane
A ground plane reduces the incidence of multipath. For more
information, see Multipath, page 265. It is generally used only at a
base receiver.
If you are using a ground plane, choose the w G/P option in the
Antenna type field (for example, Compact L1/L2 w G/P).
Figure 11.2 shows how to measure the uncorrected height of a Micro-
centered antenna (or a Compact L1/L2 antenna) that has a ground plane. Measure to the underside of the notch in the ground plane.
Top of notch
Micro-centered L1/L2 antenna
Ground plane
Bottom
of notch
1.520
1.515
1.510
1.505
Figure 11.2
Measuring the height of the antenna when using a ground plane
B
Tip – Measure the height to three different notches around the perimeter of the ground plane. Then record the average as the uncorrected antenna height.
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1 1 Antennas
11.3
Antenna.ini File
The Trimble Survey Controller software includes an integrated
Antenna.ini file that contains a list of antennas that you can choose from when creating a survey style. You cannot edit this list in the
Trimble Survey Controller software. However, if you want to shorten the list or add a new antenna type, you can edit and transfer a new
Antenna.ini file.
To edit the antenna.ini file, use a text editor such as Microsoft
Notepad. Edit the Survey Controller group, and transfer the new
Antenna.ini file to the Trimble Survey Controller software, using
Trimble’s Data Transfer utility.
Note – When you transfer an Antenna.ini file, it overwrites any existing file of that name. The information in this file is also used in preference to the antenna information built into the Trimble Survey
Controller software.
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