Subreflector Adjustment - Andrew 4.9-Meter ESA Operating And Maintenance

Subreflector
After the satellite has been acquired and testing has taken place with the spectrum ana-
Adjustment
lyzer, the subreflector may need to be adjusted to maximize optimum performance of
your antenna. The following procedures should be followed if a subreflector adjustment
is required to maximize optimum performance.
NOTE: All INTELSAT Type Approved antennas do not require subreflector adjustment
upon completion of mechanical adjustments referenced on pages 30 and 31.
Before proceeding, azimuth and elevation patterns should be conducted to determine
the adjustments that need to be made. The goal is to achieve a high peak on the main
lobe and even distances between the main lobe and sidelobes.
NOTE: No adjustments should be made in the receive band.
If your pattern dictates a need to adjust the azimuth angle(the left sidelobe requires
adjustment), the west side (northern hemisphere) of the subreflector should be adjusted
outward by loosening the screws on the subreflector and adjusting the left side (northern
hemisphere) outward. An easy way to remember this adjustment feature is through the
acronym WOLD (West Out Left Down).
If your pattern dictates a need to adjust the elevation angle(the right sidelobe requires
adjustment), the bottom side of the subreflector should be adjusted downward by loos-
ening the screws between the subreflector and the struts and adjusting the bottom side
of the subreflector downward. An easy way to remember this adjustment is through the
acronym BOLD (Bottom Out Left Down).
Each of these adjustments should be repeated until each sidelobe is of equal distance
from the peak of the mainlobe.
After the BOLD and WOLD adjustments have been made, it may be necessary to adjust
the main lobe. The goal is to achieve a high null depth (distance between lower inter-
section of sidelobes and top of main lobe) as shown in Figure 4-5.
In order to adjust the main lobe pattern characteristics ALL subreflector adjustment
screws should be adjusted at the same degree (Note: Because the azimuth and eleva-
tion adjustments have been set, it is very important that the null depth adjustment be
carefully conducted. Be careful not to alter any previous adjustments that have been
made to the subreflector. Follow the procedure listed below when adjusting the null
depth of the main lobe.
All adjustments should be continued until the desired pattern is achieved. Upon comple-
tion the antenna should be properly aligned with the satellite for maximum performance.
Operation
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