User Manual Dual C or Quad Ku Band TVRO Antenna (9497B-21)

9497B-21 C/Ku-Band TVRO Setup5.4. Calibrating Relative Antenna Position (Home Flag Offset)During initialization, azimuth drives the CW antenna until the Home Switch is contacted, which “presets” the relativeposition counter to the value stored in the Home Flag Offset. This assures that the encoder inputincrements/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 drivensprocket, or it is a hall sensor which is actuated by a magnet mounted on the azimuth driven sprocket, which producesthe “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 ofthe antenna when the home switch is engaged. Presetting the counter to this value assures that when the antenna ispointed 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 homeflag, it will be pointed in-line with the Bow of the ship.In these cases Home Flag Offset (HFO) should be setto zero. When “Optimizing Targeting” small variations(up to +/- 5.0 degrees) in Azimuth can be correctedusing If it AZ TRIM as described in the OptimizingTargeting procedure above.Large variations in Azimuth position indicate that theRelative position is incorrect and should be“calibrated” using the correct HFO value instead of anAzimuth Trim offset. This is especially true if sectorblockage mapping is used.If the antenna stops at the home flag, but it is NOTpointed in-line with the Bow of the ship, it isimportant to assure that the antennas actualposition (relative to the bow of the ship) is the valuethat gets “preset” into the Relative position counter.By saving the antennas actual Relative position whenat the home flag into HFO, you have calibrated theantenna to the ship.Figure 5-1 Antenna stops In-line with Bow5.4.1. To Calculate HFO:If Targeting has been optimized by entering a large value of AZ TRIM; First, verify that you are able torepeatably accurately target a desired satellite (within +/- 1.0 degrees). Then you can use the AZ TRIM valueto calculate the value of HFO you should use (so you can set AZ TRIM to zero). AZ Trim is entered as thenumber 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 20degrees). 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 = 223.125round of to 223.If Targeting has NOT been optimized, allow the antenna to initialize to its home flag position. Visuallycompare the antennas pointing to the bow-line of the ship (parallel to the Bow). Note the antennas positionrelative to the Bow. If it appears to be very close to being parallel to the bow, HFO will probably not beneeded and you can proceed with Optimizing Targeting. If it is NOT close, initialization was driving theazimuth 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 isonly intended to help you initially find the satellite (which direction you will have to drive and approximatelyhow far you will have to drive). Refer, in general terms, to the Optimizing Targeting procedure.5-3