Technical information

OM76_Rev J Page 14 of 28
Step 2 of 9: With the antenna positioned in Azimuth, with the transponder signal maximized, follow the same
procedure as in Step 1, only this time using the Elevation direction (scanning up-and-down). Once again, do
this until the transponder signal has been maximized.
Step 3 of 9: Repeat this procedure, alternating between the Azimuth and Elevation excursions of the antenna,
until you have peaked the antenna transponder amplitude.
 Transponder signal amplitude of 30 dB or greater from peak to average noise signal indicates that the
antenna is receiving the signal on the main beam.
 Transponder signal amplitude of less than 30 dB indicates the antenna is peaking on a side lobe of the main
beam.
Step 4 of 9: If the antenna is peaked on a side lobe in Az or El, move the antenna Azimuth while observing the
Spectrum Analyzer screen, as illustrated below in Figure 3-3.
Figure 3-3: Antenna Radiation Pattern Topographical Diagram w/ Plan View
Step 5 of 9: If the signal amplitude diminishes and does not increase (position B) to the level that was noted
when the antenna was peaked on a side lobe, then this means that the antenna is moving away from the main
beam. Reverse the direction of antenna movement.
 From the original side lobe position (Position A), the signal amplitude should now diminish to a null point at
Position C (minimum amplitude showing only signal noise) and then symmetrically increase again to the
same level at Position D as noted at Position A
 At the null point (Position C), the antenna is aligned with the alternate (El) axis. If antenna was peaked on a
side lobe in Azimuth, it was appropriately aligned with the El axis (go to Step 6).
 If the antenna was peaked on a side lobe in Elevation, it was appropriately aligned with the Az axis (go to
Step 6, moving the antenna in Azimuth rather than Elevation).
Step 6 of 9: Move the antenna in Elevation while observing the Spectrum Analyzer screen. If the signal
amplitude increases, then decreases, and then increases again (but to a lesser value than the first increase),
this means the antenna is moving in the wrong direction. Reverse direction of antenna movement.
 From the original null point, the signal level should increase and decrease alternately, but with increasing
amplitude until the transponder signal increases to a level of at least 30 dB, at which time it will be on the
main beam. Continue to manually peak the signal to a maximum level, using Azimuth and Elevation
adjustments.
Step 7 of 9: If antenna is aligned in Azimuth and Elevation (signal maximized) and a total of 24 transponder
signals of relatively equal amplitude are NOT noted (12 horizontal + 12 vertical = 24), the Polarization
adjustment is set incorrectly and must be modified. If 12 transponder signals are noted, they may or may not
be the properly polarized signals. Therefore, 24 transponder signals must be visually noted in order to
determine the proper Polarization setting.
Step 8 of 9: Rotate the feed assembly clockwise until 24 transponder signals are noted and of approximately
equal amplitude.
NOTE: it is more accurate and visually simple to minimize alternate set of transponder signals rather than maximizing the
transponder of interest.