System information

9497B-20 Ku-Band TVRO Maintenance and Troubleshooting
7-3
small 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 within +/-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. Series 97B-20 Quad Ku-Band TVRO RF Flow
Refer to the System Block Diagram in the Drawings section of this manual. The feed has a 24VDC motor to
rotate 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. The 24VDC motor is remotely controlled by the ACU (Manual
OR Auto-Polarization) through the PCU and Shielded Polang Relay Assy.
One Quad Ku-Band LNB is installed. All four Ku-Band polarizations (High and Low Band H&V) are routed
through the four channels of the rotary joint.
7.3.2.1. Channel 1 (White)
HORIZ Ku low-band coax has +18 VDC Voltage supplied by Matrix Switch plus Ku-Band IF (950-
1950MHz) output from the Ku low-band horizontal LNB output. The Ku low-band IF output passes
through this channel of the 75 ohm coaxial rotary joint, to the base of the radome, down the ADE-
BDE coax to the Ku low-band HORIZ input of the four port Matrix Switch. The ACUs’ Tracking
Receiver and each of the Ku-Band Satellite Receivers is connected by coax cable to one of the
available IF outputs of the Matrix Switch. Total signal loss of this path is the accumulation of the
coax cable losses from antenna to receiver, plus the loss in the Matrix Switch.
7.3.2.2. Channel 2 (Blue)
VERT Ku low-band coax has +13 VDC Voltage supplied by Matrix Switch plus Ku-Band IF (950-
1950MHz) output from the Ku low-band vertical LNB output AND Antenna Control RF (Pedestal
TX at 1.1 & Base TX at 1.5 MHz) which is added onto this coax by the Pedestal FSK Modem
(connected to the PCU). The Ku low-band IF output passes through this channel of the 75 ohm
coaxial rotary joint, to the base of the radome, down the ADE-BDE coax to the Base FSK Modem
(connected to the ACU) and then to the Ku low-band VERT input of the four port Matrix Switch.
Total signal loss of this path is the accumulation of the coax cable losses from antenna to receiver,
plus the loss in the Pedestal & Base Modems (1 dB max loss each) and the Matrix Switch.
7.3.2.3. Channel 3 (Red)
HORIZ Ku high-band coax has +18 VDC Voltage supplied by Matrix Switch plus Ku-Band IF (1100-
2150MHz) output from the Ku high-band horizontal LNB output. The Ku high-band IF output passes
through this channel of the 75 ohm coaxial rotary joint, to the base of the radome, down the ADE-
BDE coax to the Ku high-band HORIZ input of the four port Matrix Switch. The ACUs’ Tracking
Receiver and each of the Ku-Band Satellite Receivers is connected by coax cable to one of the
available IF outputs of the Matrix Switch. Total signal loss of this path is the accumulation of the
coax cable losses from antenna to receiver, plus the loss in the Matrix Switch.
7.3.2.4. Channel 4 (Green)
VERT Ku high-band coax has +13 VDC Voltage supplied by Matrix Switch plus Ku-Band IF (1100-
2150MHz) output from the Ku high-band vertical LNB output. The Ku high-band IF output passes
through this channel of the 75 ohm coaxial rotary joint, to the base of the radome, down the ADE-
BDE coax to the Ku high-band VERT input of the four port Matrix Switch. The ACUs’ Tracking