Tiltplate for beam antenna

Tiltplate for beam antenna

The problem

EDIT: Due to the construction and assembly of my UltraBeam, I realize that the tiltplate would not be needed anyway!

However, I'm sure the design is sound and that it actually would work in "real life" :)

Maybe one day I will find out when getting another antenna.

As nice as a tilt-over tower is, there is a problem using it with large beam antennas. When you lower the tower the elements (or the boom) of a large beam antenna will reach the ground level before the tower is at an comfortable position. Before I used to use a large step ladder to reach the tip of the tower/rotor etc, this would also mean that you will need to mount the beam antenna when it is upright, not exactly easy if the elements or the boom is 11 meter long and the antenna weighs 40 Kg or so!

The solution is to use a "tilt plate" for the antenna. A tilt plate will keep the beam antenna horisontal all the way from when the tower is standing upright to when it is laying down. This places the beam antenna at a horisontal level close to the ground, now it is suddenly a "one man job" to mount the antenna, doing maintenance etc.

There are a couple of commercially solutions for tilt plate systems, but I did not find one that I thought was perfect. 

So the only solution is to design and build one myself.

In my case, I have a 15 meter (50 foot) tilting tower and a UltraBeam VL 2.3 antenna. The UltraBeam has 3 elements (plus 2 extra for 6 meter), each element is 11 meter long. The boom (60 x 60 mm) is 4.5 meter long.

This page will be updated thru the process og design, building and installing, hopefully it will end up with a system that actually works :)

The antenna

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The tower

As can be seen on the pictures, it will not be easy to fit the antenna in that position.

The solution

I looked at various other solutions "out there", especially one from Bill, W5YAR. He makes a system that has a positive lock of the antenna once the tower is upright. This means that no matter if the winds blows or not, the antenna is kept solid at the mast. Some of the commercial systems has the antenna "hanging" loose, the antenna will move in the wind. One of the commercial solutions has a lock that is activated by gravity, I'm also not sure I like that method that much. Bill, W5YAR uses a piece of string to unlock the tilt system when lowering the tower, in my case I think it will be hard to get that string to play nice, it will naturally follow the antenna when turning and might end up tangled in some way.

I spent a couple of níghts with a CAD system and finally came up with something that might just work.

On the picture to the left, you see the top of the tower when in normal operating mode (upright). Imagine we are looking from the end of the boom of the antenna (the square tube, 60 x 60 mm). The "tilting plate" where the antenna is mounted is locked by the hook (near the bottom of the picture)

The next picture shows the hook is now in the unlocked position. The hook is held in the locked position by two stainless steel springs (not shown on the picture yet). When the hook is to be unlocked, a electrical (12VDC) driven small linear actuator moved the lock 20 mm away from the tilting plate. This will unlock the tilting plate so it can move freely. As long as the tower is upright, the antenna will just keept is horisontal (normal) position.

Once the tower starts to tilt over, the tilting plate with the antenna on will start to swivel, keeping the antenna (near) horisontal. This continues all the way to the ground

Once the tower is beginning to move and the tilting plate starts to move, the linear actuator is moved to the retracted position again. The hook will then move into the "lock" position again as the two stainless steel springs will pull it back. Once the tower is begging to move towards the upright position, the tilting plate will be touching the hook, and when sufficient pressure is put on the hook, it will move out (overcoming the tension of the springs) and the plate will be locked in place.

The picture below shows the tower tilted all the way down, the antenna is laying horisontally on the ground, making it easy to install, repair doing maintenance etc (at least that is the plan...)

The tilting mechanism

I have tried my best to use materials that could be acquired thru Amazon, I wanted to use stuff that would be easily accessible to others that might want to go the same route as me. The total cost (excluding bolts and nuts) are around €250,- on Amazon (that is all the aluminum, the bearings/blocks and the linear actuator. The box for the linear actuator is 3D printed (in ABS).

The hook mechanism is one of the more critical things in the design. It needs to hold the tilting plate firmly in postion when the tower is in its normal operating position. It also needs to be able to unlock in a predictable manner. The lock itself has a piece of rod thru it (at 90 deg), the two stainless stell springs will be attached to this rod. They must be selected/adjusted to give "the right amount" of force to the lock. At the same time, the linear actuator must also be able to unlock (working against the force of the springs). The two "L" profiles, the spacer at the top and the bottom will be covered with PTFE sheet to make the lock move more freely. The "L" brackets are 60 x 60 x 3 mm, the spacer and hook are made of 10 mm thick aluminium (the spacer is 20 x 10 x  120 mm, the hook is made out of a piece of 10 mm thick aluminum, 80 x 180 mm.

The horisontal rod is a 25 mm solid aluminum rod. It is held on the mast plate with 4 stainless steel "U" brackets. The mast plate itself is held with 3 "U" brackets to the mast (a 60 mm tube). The mast plate is 300 x 400 x 8 mm.

The box for the linear actuator is 3D printed in ABS. The design in not yet finalized, but it will be something like the picture to the left. The 4 slots in the bottom will allow the box to be moved on the mast plate a little, this is so that the movement (30 mm) of the acutator will unlock the lock mechanism once it moves.

The tilting plate where the antenna boom is mounted has two bearing blocks on it. These connects to the 25 mm aluminum rod that is attached to the mast plate. This is the hinge point for the antenna when the tower is lowered down to the ground.

The plate is 300 x 390 x 8 mm.

The wonders of CAD design :)

Did some checking of the maximum angle the tiltplate can swing to, 105 degrees. This is more than enough, the 15 meter tower folds over at 3 meter, this means that 12 meter is on the other side of the hinge point of the tower. Getting the top of the tower to touch the ground requires the tower to go -14 degree below horzontal (so 104 degree from the upright position of the tower). The 105 degree freedom of the tilplate hinge is 1 degree more than that, in practical use, the tower will not go down to -14 degree as the 1 meter tube (mast) at the top would need to go into the ground. I guess that I need a max of 10 degree below horisontal for the tower (the Ultrabem is 80 cm "high" when touching the gound, this would need the tower to be even higher up that the -14 degrees)

Stay tuned... more info to come