NBS Antennas Mast

The old antenna tower had terminal rust ingress and had to be taken down many years ago.  Since then a Hills telescopic mast was sort of making do for smaller antennas.

Have been looking at an NBS hydraulic tilt over mast for a while now and finally got around to doing something about it.

The bits as they were delivered, foundation (right), mast base (left), tilt section (front).  Winch and hydraulic jack in the box.  Sliding carriage with rotator  between box and tilt section.

The hole is augered using a mini loader (Dingo).  As it is a small job, the trick is to wait until a contractor is close by doing some work.

The foundation ready for concrete, but the weather has turned now (of course) and rain is delaying things.

The rain has stopped and the ground dried out a little.  Its amazing that a small hole in the ground can affect the weather to such a degree.

We had 35mm of rain in a couple of hours after our driest October on record not long after the hole was dug.

The mast foundation was bolted to some wooden rails to keep it steady and perfectly level.

When the concrete was going in the hole, the force pushed the foundation slightly despite it’s weight and being fixed down.  It took a long pole and some heaving to get it back to level again.  25Mpa concrete was used as per the specification for the mast.

Well, concrete has cured, so the mast base and tilt section have been added.  Everything bolted together nicely.  The vertical mast base is perfectly vertical which is a relief as the foundation part did move when the concrete was poured.

Now waiting for the mast section to arrive.  It costs nearly as much for delivery as the mast section itself as they have to use a crane to get it off the truck.

The carriage part houses the rotator slides up the mast so it the antennas can be lowered and worked on a few metres above the ground.  I had a rotator in very good condition, which was hardly used that fits the bolt holes in the carriage.
For the antenna top bearing, I decided to go with a simple arrangement as the antenna will be lightweight.  The bearing is there to provide support against side forces on the rotating mast.

A 12mm thick section of PE material from a chopping board is clamped to the top of the rotator carriage.  Not too sure on the UV stability of the material though.   If the antennas become larger, then the bearing will be upgraded.

The next challenge is getting the mast section into the mast base socket.  The angle of the socket does not go to horizontal, limited by the fully contracted hydraulic ram.  This means that the high end of the mast must be lifted up to about 2.7 metres so that it is in line with the socket.

It turned out that with the top cap of the mast base removed and the hydraulic ram removed, the mast socket could be tilted downward to the point where the far end only needed to be a metre off the ground for the mast to line up with the mast socket.

 

 

 

Kevin pushed the mast section into the mast socket and then lifted the far end of the mast so I could put the hydraulic ram in place.  From there on it it was pretty easy, the carriage was slid over the mast, the top pulley installed and the winch rigged.

The six metre yagi was mounted with relative ease at the height of the ladder.