ViaSat 8116 Series, Инструкция по установке и эксплуатации

Страница: 138 / 188

OPERATION
____________________________________________________________________________________________
4. Rotate the feed clockwise until the meter has passed through the peak
and has decreased to the level recorded in step 3. Make a mark on
the hub in line with the mark of the feed mounting plate.
5. Measure the distance between the marks on the hub. Calculate the
mid-point between these marks. Rotate the feed until the mark on the
feed mounting plate is aligned with the mid-point.
The following procedure should be used in the event that the
antenna performance demonstrates that a subreflector adjustment is
necessary. (Subreflector alignment using the theodolite should be
performed prior to this final adjustment.) The purpose of the
physical measurement is to position the subreflector to its optimum
optical location along the adjustment axis. SUBREFLECTOR
ADJUSTMENT
1. Ensure all antenna hardware including mount parts are installed and
tightened properly prior to making any subreflector adjustment.
NOTE
A straight edge may be placed across the feed bezel and
measurement may then be made from the inside of the straight
edge to the subreflector.
The subreflector adjustment screws should not stress the
subreflector in any way.
2. Take a reference measurement from back of subreflector mounting
frame at each adjustment rod prior to subreflector adjustment.
3. The subreflector should be adjusted toward or away from the main
dish with the subreflector adjustment mechanism. By adjusting the
support studs equally, the subreflector alignment is maintained.
Signal level monitoring equipment is necessary to accurately set the
subreflector for the highest gain and the deepest radiation pattern
nulls. The following equipment or its equivalent is necessary:
• Spectrum Analyzer
• Power Meter
• X-Y Recorder
• Time Base
The radiation pattern (relative power versus off-axis angle) should be
recorded and evaluated for each adjustment of the subreflector.
Typical patterns at various subreflector positions which are identified
in Figure 5-1 show the changes which take place as the subreflector is
moved closer to the optimum focal position.
____________________________________________________________________________________________
5-2
SERIES 8116/8118 16-/18-METER EARTH STATION ANTENNA
42S183D