Setup - Home Flag Offset; Electronic Calibration Of Relative Antenna Position (Home Flag Offset) - COBHAM Sea Tel 9711-50 Installation Manual

Setup – Home Flag Offset
9. Setup – Home Flag Offset
Home Flag Offset is used to calibrate the relative azimuth value of the antenna to the bow line of the ship. This
assures that the encoder input increments/decrements from this initialization value so that the encoder does not have
to be precision aligned. When the antenna is pointed in-line with the bow (parallel to the bow) the "Relative" display
value should be 000.0 Relative (360.0 = 000.0). Good calibration is especially important if blockage mapping is used,
because the values entered into the AZ LIMIT parameters are entered in Relative Azimuth. The default Home Flag
Offset value saved in the PCU is 000.
The Home Flag Sensor mounted on the pedestal is actuated
by a metal tab mounted on the azimuth spindle which causes
it to produce the "Home Flag" signal.
The default mounting of the radome is with its bow reference
in-line with the bow and the base hatch in-line with the stern
(aft reference of the radome). There are valid reasons for
mounting the ADE in a different orientation than the default.
One of these would be that the hatch of radome needs to be
oriented inboard of the ship for safe entry into the dome (ie
ADE is mounted on the port, or starboard, edge of the ship
and safe entry is only available from inboard deck or inboard
mast rungs).
Observe initialization of the antenna. When azimuth drives
CW and then stops at "Home" position, VISUALLY compare
the antennas pointing, while at Home position, to the bow-
line of the ship (parallel to the bow).
If it appears to be very close to being parallel to the bow,
you will not need to change the HFO and should proceed with
Optimizing Targeting. When "Optimizing Targeting" small variations (up to +/- 5.0 degrees) in azimuth can be easily
corrected using the AZ TRIM parameter.
If it is NOT close (stops before the bow or continues to drive past the bow) HFO needs to be adjusted.
If the antenna is pointing to the LEFT of the bow line: If the antenna stops driving before the bow line, when
targeting a satellite it will fall short of the desired satellite by exactly the same number of degrees that it fell
short of the bow line. You must calibrate HFO using either of the methods below.
If the antenna is pointing to the RIGHT of the bow line: If the antenna continues to drive past the bow line,
when targeting a satellite it will overshoot the desired satellite by exactly the same number of degrees that it
went past the bow line. You must calibrate HFO using either of the methods below.
If you find that a large value of AZ TRIM parameter has been used to calibrate the antenna. This indicates that the
Relative position is incorrect and should be "calibrated" using the correct HFO value instead of an Azimuth Trim offset.
If the radome was purposely rotated, has a large value of AZ TRIM or was inaccurately installed (greater than +/- 5
degrees), there are two ways of setting Home Flag to compensate for the mounting error. They are:
9.1.

Electronic Calibration of Relative Antenna Position (Home Flag Offset)

Above, you VISUALLY compared the antenna pointing, while at "Home" position, to the bow-line of the ship
and found that the antenna pointing was NOT close to being parallel to the bow-line. It stopped before the
bow or went past the bow OR you found AZ TRIM has been set to a large value, therefore, HFO needs to be
adjusted.
Ascertain the exact amount of error using the appropriate procedure below, enter the HFO to calibrate the
antenna to the ship, save the value and re-initialize the antenna to begin using the new value.
9-1
EAR Controlled - ECCN EAR99
Figure 8-1 Antenna stops In-line with Bow
Sea Tel 9711-50