Advent VISLINK Newswift 90 Technical Operation Handbook page 56

VISLINK
Special Notes:
All wind loads and moment calculations are based on a wind speed of eighty miles per hour.
The forces and moments given for F1, F2, M1 and M2 are maximum values for different
antenna orientations and do not necessarily occur simultaneously. All force values are either
tensile or compressive, and moments are either clockwise or anti-clockwise. Wind forces and
moments do not include static weights.
7.3 VEHICLE ROOF FRAME DESIGN
The transit frame that the antenna is supplied on is not stiff enough to be used as a mounting
frame and should not be used as part of the antenna support structure.
The antenna should be mounted facing the rear of the vehicle to avoid excessive wind loads
on the reflector while it is stowed and the vehicle is being driven at speed. Mounting the
antenna facing the rear will also protect the RF equipment located on the feedarm from being
damaged if the antenna is stowed and the vehicle is driven under any low branches
overhanging the road.
The antenna support structure should provide a load path from the antenna mounting points
to appropriate points on the vehicle that will then transfer the loads through the vehicle
structure to the jacks onto the ground. The support frame should be fixed to the internal
cross braces in the vehicle roof and to the main side rails running along the roof. If possible,
the support structure should also brace down from the roof mounting points to any
electronics racking that is used, to provide additional stiffness. The frame should be designed
so that it provides sufficient stiffness in all azimuth angles.
A typical mounting frame should be manufactured from at least four inch deep (100mm) by 2
inch wide (50mm) by 1/8 inch (3.175mm) thick aluminium alloy 6082. The mounting points of
the frame to the vehicle roof should ensure that the connection points are securely held in
place and will take rotational as well as in line loads. A set of bolts are to be used to fix the
antenna to the frame and access is needed from under the frame to fix these bolts in place.
The fixing bolt positions should be kept as close as possible to the vertical faces of the box
section to reduce the bending of the top face of the box section while leaving enough room
for the antenna bolts to be securely fastened in place. If a fixing plate is mounted on top of
the box section similar guidelines should be followed. Any fixing plate should be over 8mm in
thickness if the fixing holes are within 20mm of the box vertical wall. Threadlock, flat and
spring washers should be used with the main antenna bolts to stop the bolts coming loose
under vibration. The frame may be constructed inside the vehicle rather than on top of the
vehicle if height restricts the use of a frame on top of the vehicle although the same design
criteria still hold true.
Clearance should be left for any cabling and waveguide that passes through the bottom
centre of the azimuth axis. The cabling and waveguide may be routed through the side of the
main azimuth ring. Any cabling that passes between the antenna and vehicle roof should
have sufficient space so that the cabling is not stretched or kinked as the antenna moves
through its azimuth range. The hole in the centre of the azimuth axis at the base of the
antenna is not waterproof so if any waveguide or cables are to be routed through the vehicle
roof then they should be sealed. Cables can be run out away from the azimuth centre and a
Roxtec type box may be used to seal them through the vehicle roof.
The frame should deflect by less than 0.05 degrees when subjected to a load equivalent to
the operational wind speed of the antenna. If the frame deflects more than this then the
operational wind speed of the antenna will be reduced.
Newswift 90-180 Motorised Antenna 51