Sea Tel 9497B-1 Installation And Operation Manual Download

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9497B-1 C/Ku-Band TVRO

Maintenance and Troubleshooting

7-3

air currents within the radome. These motors are also used to re-position the antenna in azimuth and
elevation.
The Pedestal Control Unit (PCU) uses inputs from the level cage sensors to calculate the amount of torque
required in each axis to keep the antenna pointed /-0.2 degrees. The primary sensor input for each
loop is the rate sensor mounted in the Level Cage Assembly. This sensor reports all motion of the antenna to
the PCU. The PCU immediately responds by applying a torque in the opposite direction to the disturbance to
bring the antenna back to its desired position. Both the instantaneous output of the rate sensor (Velocity
Error) and the integrated output of the rate sensor (Position Error) are used to achieve the high pointing
accuracy specification.
The calculated torque commands are converted to a 5 volt differential analog signal by a Digital to Analog
converter (D/A) and sent to each of three Brush-Less Servo Amplifiers. These amplifiers provide the proper
drive polarities and commutation required to operate the Brush-Less DC Servo Motors in torque mode. The
Torque acting on the mass of the antenna cause it to move, restoring the rate sensors to their original
position, and closing the control loop.
Since the rate sensors only monitor motion and not absolute position, a second input is required in each axis
as a long term reference to keep the antenna from slowly drifting in position. The Level and Cross Level
reference is provided by a two axis tilt sensor in the level cage assembly. The Azimuth reference is provided
by combining the ships gyro compass input and the antenna relative position.

7.3.2.

Refer to the System Block Diagram in the Drawings section of this manual. This feed assembly has 5VDC
pulse servo motor to select the polarization MODE of the feed (LHCP, HORIZ, RHCP or VERT) and a 24 VDC
motor to optimize the linear polarity of the feed. One fixed frequency C-Band LNB and one fixed frequency
Ku-Band LNB are installed. C-Band can be operated in linear or circular mode. Ku-Band can only be operated
in linear mode.

Series 97B-1 1C(Linear/Circular)/1Ku (Linear only) TVRO RF Flow

The 5VDC pulse servo motor drives a small dipole in the inner throat (brass tubing) of the feed to
align with 4 pads in the larger throat. When the dipole is centered in-line with 2 of the pads, a linear
(HORIX or VERT) polarity mode is selected. When the dipole is centered diagonally between 2 of
the pads, a circular (LHCP or RHCP) polarity mode is selected. Rotation position of the dipole is
determined by square-wave duty cycle (On time vs OFF time).
24VDC motor rotates the body of the OMT to optimize the linear polarization angle of the LNBs to
the polarization angle of the signal coming from the targeted satellite. Both polarization motors are
remotely controlled by the ACU (Manual OR Auto-Polarization) through the PCU and Aux Polang
Relay Assy.

Ku-Band LNB gets DC Voltage from Ku-Band Splitter/Matrix Switch. The IF output from the LNB (950-
1450MHz or 950-1750MHz) routes directly through the Coax Rotary Joint (75 ohm) then connects to the
Ku-Band ADE-BDE cable to the Ku-Band Splitter/Matrix Switch then by coax to the IF input on the Ku-Band
Satellite Receiver(s). Total signal loss is the accumulation of the coax cable losses from antenna to
receiver(s), plus the loss in the Ku-Band splitter.
C-Band LNB get DC Voltage from Ped Modem (or passed from the C-Band Splitter/Matrix Switch). The IF
output from the LNB (950-1450MHz) and the 1.1 & 1.5MHz Ped M&C are combined in the Pedestal Modem
and is routed through the Coax Rotary Joint (75 ohm) to the C-Band ADE-BDE cable to the Base Modem
(where Pedestal M&C is picked off and routed to the ACU). IF output of the Base Modem is connected to the
C-Band Splitter/Matrix Switch and then to the IF input on the C-Band Satellite Receiver(s). Total signal loss is
the accumulation of the coax cable losses from antenna to receiver, plus the loss in the Modems (3 dB each)
AND the loss through the C-Band Splitter/Matrix Switch.
One coax connection from the C-Band Splitter/Matrix Switch and one from the Ku-Band Splitter/Matrix
Switch will have to be connected to a Coax Switch. A coax connection from the output of the switch will
provide the tracking input to the SatID Tracking Receiver in the Antenna Control Unit. The MODE –
TRACKING Band Selection will control the Coax Switch through a control wire connection to SW2 output on
the Terminal Mounting Strip.

7.3.3.

Turn the pedestal power supply ON. The brakes on the Elevation and Cross-Level motors will release.. Brake
release power supply control circuit supplies 24 VDC to the brakes initially (5-10 seconds) and then reduces
the voltage to 12VDC. The PCU will initialize the stabilized portion of the mass to be level with the horizon
and at a prescribed Azimuth and Elevation angles. The antenna will go through the specific sequence of steps

Antenna Initialization (Series 97B & Series 00 )