Technical information

OM56_Rev G Page 16 of 28
3.2 Subreflector Adjustment
After the satellite has been acquired and testing has taken place with the Spectrum Analyzer, 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.
Before proceeding, the Azimuth and Elevation patterns should be conducted to determine any 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 as shown in Figure 3-6.
NOTE: No adjustments should be made in the receive band.
If your pattern dictates a need to adjust the Azimuth angle (the left side lobe requires adjustment), the west
side of the subreflector should be adjusted outward by loosening the screws on the subreflector and adjusting
the left side 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 loosening 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 (Bold Out, Left Down).
Each of these adjustments should be repeated until each sidelobe is of equal distance from the peak of the
main lobe.
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 intersection of side lobes and top of main lobe) as
shown in Figure 3-6.
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 elevation 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.
C-Band feeds – Adjustment screws are 3/4 X 10. Move 1 turn per 1dB of imbalance.
Ku-Band feeds – Adjustment screws are 1/4 X 20. Move 1 turn per 1 dB of imbalance.
All adjustments should be continued until the desired pattern is achieved. Upon completion, the antenna
should be properly aligned with the satellite for maximum performance.