Antenna Components and Functions | Sensor box | Initialization | NMEA Heading Input to the ACU | SEARCH 3: Targeting and Searching with heading input. | SEARCH 1: Targeting and Searching without heading input. | Tracking |
Most of the intelligence controlling the antenna is located in the Main Control Unit MCU in the antenna, and not in the Antenna Control Unit ACU below deck. The MCU in the antenna houses a DVB-S2 tuner, and a Narrow Band Tuner and the stabilization and tracking is handled by the MCU. The DVB -S2 tuner allows positive identification of most modern satellite TV carriers.
The ACU below deck, serves as a human interface, and the connection to the gyro, the network and modem for control of the antenna. It also contains the satellite library and tracking information.
Feedback from the two level sensors inside the box to the motors, strive to keep the box level with the horizon, at all times, in elevation and cross level, by signalling the motors via the MCU..
Three rate sensors in the sensor box detect the slightest movement in the three axes and send commands via the MCU for the motors to counteract any movement of the antenna.
Then the cross level drives all the way to the right to its calibration end position which it detects by reading over current of the motor. It then drives back to the center to make to sensor box level in cross level.
If the antenna has not already been tracking on satellite, it will also drive the pol to it's limits to calibrate the pol axis. If it has previously been calibrated, it will skip this step.
The azimuth motor drives clockwise until it detects the home sensor which lights up as it passes the metal tab, to calibrate the relative azimuth (the angle from the bow).
The antenna will then target the satellite using one of two methods, depending if heading input is available to the antenna.
With a good heading input, the front panel of the ACU will show the Azimuth correctly, with the Relative Azimuth in brackets
eg. AZ 328.2 (162.5).
If there is no heading input, the front panel will show the Azimuth as dashes with the Relative Azimuth in brackets
eg. AZ: - - -.- (162.5)
Depending on the tracking parameters it may then try to verify if it is on the correct satellite. In the case of DVB tuner it will look for a specific frequency, symbol rate and NID from the satellite. In the case of a VSAT with narrow band tuning it will look for a carrier detect signal from the satellite modem.
Without heading, the antenna does not know which way the ship or the antenna is pointing, so it does not know where to point the azimuth toward the satellite. When targeting in SEARCH 1, the antenna will go to the correct elevation, and then begin a gradual sweep of Azimuth in a counter clockwise direction until it detects a signal above the DETECT level.
There are two threshold levels, the DETECT level and the TRACKING LEVEL. It seems that once the signal exceeds the DETECT level it will change from the sky search SEARCH 1 to the spiral search SEARCH 3 until it sees the signal above the TRACKING level.
If it does not see the TRACKING level it will continue on with SEARCH 1 in a counter clockwise direction until it finds and tracks a signal above the TRACKING level and verifies the correct satellite with Frequency, Symbol Rate and NID or carrier detect from the satellite modem.
If it does not find the satellte on the first 360 degree revolution, it will increment the elevation by half a degree and try again, then down half a degree below the target elevation, in plus or minus half degree steps until it has searched the whole area between plus 3 degrees and minus 3 degrees above and below target elevation.