COBHAM Sea Tel 9711-56 IMA C Band, Руководство по установке

Страница: 19 / 234

Sea Tel 9711-56 IMA Site Survey
3-3
EAR Controlled - ECCN EAR99
7. All welding should be full penetration welds –V-groove welds with additional fillet welds –
with throats equivalent to the thickness of the thinnest base material.
8. For an ADE mounted greater than 0.6 meters (24 inches) above the ship’s structure, at least
one (1) foot rung should be added. Additional rungs should be added for every 0.3 meter (12
inches) of pedestal height above the ship’s structure.
9. For an ADE mounted greater than 3 meters (9 feet) above the ship’s structure, a fully
enclosing cage should be included in way of the access ladder, starting 2.3 meters (7 feet)
above the ship’s structure.
3.4. Mounting Height and Fore-Aft Location
Installations with mast or deck vibrations at frequencies between 2 and 15 Hertz have been identified by Sea
Tel as causing problems with the isolation systems of the ADE. Preventing problems prior to installation due
to these vibrations is one of the primary considerations in choosing where to mount the antenna.
In some installations, though, the combination of mounting height, fore-aft location and ship motion can
impart significant accelerations on the entire ADE. Installations where the ADE is situated high on the ship –
usually at the top of a mast – places the ADE is a position where the low frequency ship motion in roll and/or
pitch creates two accelerations – tangential and radial. These accelerations vary in a periodic function, out-of-
phase from the ship response to the wave motions.
Radial acceleration is the acceleration acting on the mass of the ADE pulling away from the center of the axis
(roll or pitch). In this sense, it would be a force trying to ‘pull’ the ADE away from the ship. We normally are
not too concerned with radial acceleration, since it must become far greater than gravity to have a
detrimental effect on the ADE.
Tangential acceleration is the acceleration acting on the mass of the ADE pulling across the center of the axis
(roll or pitch). This acceleration becomes a force trying to pull the ADE to the side. The tangential
acceleration has an effect on both the strength of the ADE pedestal and the tracking accuracy of the control
algorithm.
The effect of tangential acceleration is felt by the structure of the ADE before it truly affects the tracking
accuracy. For instance, Sea Tel normally accepts that a tracking error of 0.1 degrees RMS at 0.5 G to be within
acceptable error margins. A 0.5 G tangential acceleration on the ADE means that ½ of the weight of the ADE
is acting sideways on the pedestal structure.
The higher up you mount the antenna above the pivot point of the ship the higher the tangential acceleration
(g-force) exerted on the antenna will be (see chart below). When the g-force exerted on the antenna is light,
antenna stabilization and overall performance will not be affected.
If the g-force exerted on the antenna is high enough (> 1 G), antenna stabilization and overall performance
will be affected.
If the g-force exerted on the antenna is excessive (1-2 Gs), the antenna will not maintain stabilization and may
even be physically damaged by the g-force.