Sea Tel 9797B-70 C-Band TX/RX, Installation And Operation Manual

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9797B-70 C-Band TXRX Setup
5-3
Figure 5-1 Antenna stops In-line with
Bow
7. Press the RIGHT key again, make the next change as directed and hit ENTER to carry out the adjustment.
8. Repeat this process of making small adjustments until the technician confirms that cross-pol isolation is
optimized.
9. Save your new SAT SKEW value.
5.4. Calibrating Relative Antenna Position (Home Flag Offset)
During initialization, azimuth drives the CW antenna until the Home Switch is contacted, which “presets” the relative
position counter to the value stored in the Home Flag Offset. This assures that the encoder input
increments/decrements from this initialization value so that the encoder does not have to be precision aligned.
The Home Switch is a micro switch with a roller arm which is
actuated by cam mounted on the azimuth driven sprocket, or
it is a hall sensor which is actuated by a magnet mounted on
the azimuth driven sprocket, which produces the “Home Flag”
signal.
The Home Flag Offset is a value saved in NVRam (Non-
Volatile RAM) in the PCU. This value is the relative position
of the antenna when the home switch is engaged. Presetting
the counter to this value assures that when the antenna is
pointed in-line with the bow of the ship the counter will read
000.0
Relative
(360.0 = 000.0).
In most cases when the antenna stops at the home flag, it
will be pointed in-line with the Bow of the ship. In these
cases Home Flag Offset (HFO) should be set to zero. When
“Optimizing Targeting” small variations (up to +/- 5.0 degrees)
in Azimuth can be corrected using If it AZ TRIM as described
in the Optimizing Targeting procedure above.
Large variations in Azimuth position indicate that the Relative
position is incorrect and should be “calibrated” using the
correct HFO value instead of an Azimuth Trim offset. This is especially true if sector blockage mapping is used.
If the antenna stops at the home flag, but it is NOT pointed in-line with the Bow of the ship, it is important to assure
that the antennas
actual position (relative to the bow of the ship) is the value that gets “preset” into the Relative
position counter. By saving the antennas actual Relative position when at the home flag into HFO, you have
calibrated the antenna to the ship.
5.4.1. To Calculate HFO:
If Targeting has been optimized by entering a large value of AZ TRIM; First, verify that you are able to
repeatably 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.
If AZ TRIM was a
plus
value: HFO = (TRIM / 360) x 255 Example: AZ TRIM was 0200 (plus 20
degrees). HFO = (20/360) x 255 = (0.0556) x 255 = 14.16 round off to 14.
If AZ TRIM was a negative value: HFO = ((360-TRIM) / 360)) x 255 Example: AZ TRIM = -0450
(minus 45 degrees). HFO = ((360 – 45) / 360)) x 255 = (315 / 360) x 255 = 0.875 x 255 = 223.125
round of to 223.
If Targeting has NOT been optimized, allow the antenna to initialize to its home flag position. Visually
compare the antennas pointing to the bow-line of the ship (parallel to the Bow). Note the antennas position
relative to the Bow. If it appears to be very close to being parallel to the bow, HFO will probably not be
needed and you can proceed with Optimizing Targeting. If it is NOT close, initialization was driving the
azimuth CW, note if the antenna appears to have stopped before it got to the Bow or if it went past the Bow.
You may be able to guess an approximate amount of how many degrees the antenna is from the bow. This is
only intended to help you initially find the satellite (which direction you will have to drive and approximately
how far you will have to drive). Refer, in general terms, to the Optimizing Targeting procedure.