Sea Tel ST88-21 C/Ku-Band TVRO Installation And Operation Manual Download Page 65

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ST88-21 C/Ku-Band TVRO

Setup – Home Flag Offset

7-1

Figure 7-1 Antenna stops In-line with Bow

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:

7.1.

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

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.

7.1.1.

You Found a Large AZ TRIM value:

If Targeting has been optimized by entering a large value of AZ TRIM: First, verify that you are able to

repeatedly accurately target a desired satellite (/- 1.0 degrees). Then you can use the AZ TRIM value
to calculate the value of HFO you should use (so you can set AZ TRIM to zero). AZ Trim is entered as the
number of

tenths

of degrees. You will have to convert the AZ TRIM value to the nearest

whole

degree

(round up or down as needed). Calculated HFO value is also rounded to the nearest whole number.