Monday, June 16, 2014

Rebuilding: First Steps Upward

Since describing the tear down of my antennas and towers I have made progress towards the next phase of my suburban mini-antenna farm. But first a word about just how "deep" I went with my tear down.

The bases for both the guyed Golden Nugget tower (supported the multi-band dipole and 40 meters delta loop) and the house-bracketed mast (supported the multi-band inverted vee) were constructed from preserved wood. There are two layers of 4x4's nailed together, with just a bit of the top layer -- the platform -- projecting above grade. My reasons for using floating bases of this type were discussed in an article last year, so I don't need to go into details here.

Although the lumber is rated for ground contact there are many grades of pressure-treated wood preservation. Not all do well when you ground-contact rated lumber is buried. I have some experience with this since I have a 22 year old retaining wall built from 6x6x16' burial-rated lumber which I repaired earlier this spring. It's amazing how well it can endure, typically surviving better when fully buried than when exposed to sun and air.

With this in mind I dug up both preserved wood bases for inspection. My intention was to replace them if necessary or, if in good shape, to modify them to accommodate the new towers.

You can see the imprint of the Golden Nugget tower base in the exhumed platform. Although quite dirty the base is in excellent condition after being planted in the ground for one year. The other base (not pictured) was also in excellent condition.

Both bases are reusable and expandable with additional logs on the top layer. I doubled the number of logs in the top layer of the larger Golden Nugget and put it back in the ground in the same location. This will serve as the base for the guyed DMX-52. The position is important since I will make use of the same opportunistic guying for this tower as the last one.

To erect the Golden Nugget tower I attached it to the house using the same brackets I installed for the pipe mast. This too required adding logs to the base previously used to support the house-bracketed pipe mast. What took some time was manouevering the tower so that the improvised bracket arms could be properly attached and to place the tower close to the eaves (for roof access). The position of the arms has little room for adjustment since they are bonded to the house. This is not something I wanted to redo.

As the picture shows I was able to accomplish the job. It's not particularly pretty at present although I plan to clean it up somewhat. U-bolts attach two of the tower legs to the arms labelled A and B. These are the original ones used to support the pipe and mast for the inverted vee. The arms are commonly-available galvanized, large gauge angle steel that comes pre-drilled.

That third section of angle steel (C) might look redundant but it plays an important role. Without it there is insufficient resistance to lateral motion (parallel to the house wall). That is, the arms bend. While not initially dangerous there is a risk that over time fatigue weaken arms A and B or their attachments into the wood frame of the house. Wade's purpose-built bracket is a single V-shaped steel arm that achieves both objectives. The 3 improvised arms in combination achieve the same result. When installed the tower became rigid.

I will modify the bracket later to improve its appearance and to tie the third tower leg to the bracket. As currently built the rigidly is solely due to the strength of the bolts (and lock washers) tying C to A and B.

Although this tower in its present state is able to support an antenna I am not going to put one up just yet. That would only distract me from the important task of completing both towers.

The enlarged base for the DMX tower, with tower attached, is shown in the picture below. You can get an idea of how the tower will be secured to the base from looking at it.

The heavy-duty corner braces support the full weight of the tower, and those braces are bolted into the platform. The bolts hold the tower's position but do not actually hold the tower up. That is done with guy wires. There will be two set of guys wires.

However this is far from the full story. If you think about it you should be able to come up with several shortcomings with what I seem to be doing here. I deal with these in a future article.

Rope is used for the present in preparation for raising of the third section. The bottom two sections (16' and 100 lb) were walked up to a vertical orientation atop the base. This was easy to do myself since, although I can only reach up to ~7' (less than half way up) a tapered tower is bottom heavy.

Once the third section is lifted into place the first set of guys wires will be installed at the 23' level, which is just below the top of the section. I'll have more to say about guying in a later article. I am using a conventional guy station at the top of the fifth section and an improvised guy station at the top of the third section.

Further progress in the raising of towers and antennas will have to wait. For the next two weeks I have other responsibilities to attend to. I expect to get back to the towers and the blog at the end of June.

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