COBHAM Sea Tel 9711-56 IMA C Band, Installation Manual

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Site Survey Sea Tel 9711-56 IMA
3-2
EAR Controlled - ECCN EAR99
3.2. Antenna Shadowing (Blockage) and RF Interference
At the transmission frequencies of this satellite antenna system, any substantial structures in the way of the
beam path will cause significant degradation of the signal. Care should be taken to locate the ADE so that it
has direct line-of-sight with the satellite without any structures in the beam path through the full 360 degree
ships turn. Wire rope stays, lifelines, small diameter handrails and other accessories may pass through the
beam path in limited numbers; however, even these relatively insignificant shadows can produce measurable
signal loss at these frequencies.
3.3. Mounting Foundation
3.3.1. Mounting on Deck or Deckhouse
While mounting the ADE on a mast is a common solution to elevate the ADE far enough above the
various obstructions, sometimes the best mounting position is on a deck or deckhouse top. These
installations are inherently stiffer than a mast installation as the design of the deck/deckhouse
structure is prescribed by the ship’s classification society. In the deck/deckhouse design rules, the
minimum plating and stiffener guidelines are chosen to preclude high local vibration amplitudes.
Most installations will have a base frame with multiple attachment points around the perimeter of
the base frame to mount the ADE onto a deck or deckhouse structure of the ship. The base frame
may be mounted using the supplied legs & braces to raise the ADE above the deck for radome hatch
access. The base frame may be directly attached to the deck, in which case the access panel in the
floor of the base frame cannot be utilized. In this case, the installation must allow acces through a
door in one of the side panels or an access opening directly under the hacth. Some care must be
taken to ensure the mounting pedestal is properly aligned with the stiffeners under the deck plating.
Alternately, a specifically designed and stiffened mast may be used to mount the base frame above
the deck; although, this should only be attempted if sufficient deck space high on the ship is not
available.
3.3.2. ADE Mounting Considerations
Mounting the radome directly on the deck, or platform prevents access to the hatch in the base of
the radome unless an opening is designed into the mounting surface to allow such entry. If there is
no access to the hatch the only way to service the antenna is to remove the radome top.
Ladder rungs must be provided on all mounting stanchions greater than 3-4 feet tall to allow footing
for personnel safety when entering the hatch of the radome.
The recommended cable passage is through the bottom (near center) of the radome base, down
through the ADE support pedestal (if used), through the deck and into the interior of the ship.
3.3.3. Sizing of the support pedestal
The following should be taken into account when choosing the height of a mounting support stand:
1. The height of the pedestal should be kept as short as possible, taking into account
recommendations given in other Sea Tel Guidelines.
2. The minimum height of the pedestal above a flat deck or platform to allow access into the
radome for maintenance should be 0.6 meters (24 inches).
3. The connection of the ADE mounting plate to the stanchion and the connection of the
pedestal to the ship should be properly braced with triangular gussets (see graphic above).
Care should be taken to align the pedestal gussets to the ship’s stiffeners as much as
possible. Doublers or other reinforcing plates should be considered to distribute the forces
when under-deck stiffeners are inadequate.
4. The diameter of the pedestal stanchion shall not be smaller than 100 millimeters (4 inches).
Where the ADE base diameter exceeds 1.5 meters (60 inches), additional stanchions
(quantity greater than 3) should be placed rather than a single large stanchion.
5. Shear and bending should be taken into account in sizing the ADE mounting plate and
associated gussets.
6. Shear and bending must be taken into account when sizing the pedestal to ship connection.