The Pylon…

I have been absent from the keyboard for a while, I know there are a few of you interested to see more about the recent antenna build…  I have tried to keep the dry stuff to a minimum, and put in lot of pictures…

This was apparently just Phase One of our major IT restructuring.  Near completion we found out we are moving our VSAT (satellite dish we use to connect to the internet) from TASOK (The American School Of Kinshasa) to the MAF house, and that requires a lot of work on the infrastructure side.  Phase Two is starting this week and involves building a small structure to house the VSAT server, back up power system, and create a small work space for servicing those items.

The IT guys asked for a 10M pylon that would mount to the roof of the house and replace the existing 8M stick.  The old one was just a welded up water pipe with concrete tie-wire for guys.  It was a pain to raise and lower and required walking all over the roof to detach guys for lowering.  Additionally, the lack of rigidity caused the pole to dance in the slightest breeze which affected the quality of the radio signals.

The old “tower” – kinda shabby and not too strong (and dropped in the last storm)

Working with David Francis, I came up with a design for the new tower that would allow us to pivot the entire tower down for servicing as well as running guy wires we could work from the base of the tower (no more ridge walking).  David added a sweet detail of having the upper portion of the pylon fully rotational from the base – so the antenna alignment could be tweaked with the tower fully raised and guys fixed.

We started out with a pile of rather bent pipe, several 10s of meters of looped 8mm rebar, and a stack of decade old welding rod – not exactly a recipe for perfection, but we were not shooting that high anyway.

David found an old tripod from a previous radio pylon, and we used that to set jigs for spacing the tower legs.

Jigged up and ready for welding

It was then a matter of spending hours welding on trussing – this was a major pain as the rod was old, and the cheap Chinese rebar melted as soon as you got it hot enough to weld.  Our one saving grace was a beautiful old Lincoln Generator/Welder that had a very good voltage regulator as well as AC/DC dual polarity ability.

After we tacked it all down, David spent a loooong time finishing and dressing all the welds – cheap metal and poor rod makes for a lot of work!

Once the trussing was on, David custom fit the tripod (to support the upper mast) and fabricated a bunch of the detail work – a rotating anchor point for the upper guy wires, a clamp plate for locking the rotation of the upper mast, earrings for attachment points, etc…  I knocked out the pivot base, and welded in supports for the counterweight plates.

Cut to length, file to fit, paint to match…

Not easy fitting…

Fabbing the pivot – 75% of welding is fitting…

Thanks to David for his massive arsenal of vise grips!

Test fit in the pivot base

Trebuchet, or radio tower?

Looking good on the ground…

As soon as everything was welded and dressed, Nestor got to work with the anti-rust paint – everything looked a whole lot more official with a coat of paint!

The top coat was airbrushed – this primer was nice and thick, but took way too long to apply!

No picture, but our counterweight (so far) is a matched pair of cracked heads from two Toyota diesel engines, they easily bolted on to the base plate, and I will be adding some concrete to make up for the additional weight of the full antenna package at the extreme end of the lever.

One of the most expensive components was the ground wire and rod – these, along with the guys and rigging hardware cost more than the steel for the tower.  But, with the highest number of lightening strikes in the world, and a 10M lightening catcher on top of David’s house, we had some motivation to do it right.

Why are we all looking up roof?

The final touch is a winch attached to the tower base, that tensions the only guy wires required to slacken for lowering the tower.  This means that you just have to loosen the wire, pull the tower lock bolts, and swing it down.  You only have to walk up and down a major valley – causing a little less wear and tear on the roof as well as reducing risk to the crew.

Flight control pulleys turned block and tackle

I eventually want to run a 12v winch on the base plate, that will allow easy raising and lowering of the tower.  Ideally, it would be a  one-man operation.

To plug the next project here is a teaser pic of me clearing the site for the IT shack… I will try to get back to you all soon!

Me Tarzan, you Lisa