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

Page: 20 / 234

Site Survey Sea Tel 9711-56 IMA
3-4
EAR Controlled - ECCN EAR99
3.5. Mast Configurations
Sea Tel recommends the ADE be mounted on the ship in a location which has both a clear line-of-sight to the
target satellites in all potential azimuth/elevation ranges and sufficient support against vibration excitement.
If possible, mounting the ADE pedestal directly to ship deckhouse structures or other box stiffened structures
is preferred. However, in many cases, this imposes limits on the clear line-of-sight the antenna system has.
Often the solution for providing the full azimuth/elevation range the antenna needs is to mount the ADE on
the ship’s mast. Unfortunately, masts do not consider equipment masses in design and often have harmonic
frequencies of their own.
For these large systems, the mast for the ADE should be designed specifically for the ADE. Other equipment
may be mounted alongside, but the mast should be configured to accept the mass, loads and resonance of
the ADE primarily. The following sections describe various mast configurations and some considerations for
mast design.
3.5.1. Vertical Masts
Vertical masts are a very ancient and common mast design. In essence, it is the mast derived from
the sailing mast and adapted for mounting the ever-increasing array of antennae which ships need to
communicate with the world. This drawing of a
vertical mast shows the preferred mounting of the
ADE center-line above the plane of the radar.
Alternatively the ADE is mounted below the plane of
the radar signal
Vertical masts are most commonly found on cargo
ships – they are simple, inelegant and functional.
They are also fairly stiff against torsional reaction and
lateral vibrations, as long as the ADE is mounted on a
stiff pedestal near the vertical centerline of the mast.
If centerline mounting is impractical or otherwise prohibited, the mast platform the ADE is mounted
on should be checked for torsional vibration about the centerline of the mast and the orthogonal
centerline of the platform.
If the estimated natural frequency of the mast or platform is less than 35 Hertz, the mast or platform
should be stiffened by the addition of deeper gussets under the platform or behind the mast.