Monday, June 10, 2013

Preparing The Site-C Tower

As time has allowed I have been making decisions on siting, constructing and erecting the tower at (what I am calling) Site C. I think I now have everything I need in regard to hardware. The tower is, as earlier mentioned, a secondhand (actually third-hand) Golden Nugget 30' TV tower.

What antennas the tower will sport I will discuss later, once the tower is in the air. For the most part those will be low band antennas. However that will be delayed while I experiment with other, temporary antennas. That's part of the fun of doing all this: just playing around with stuff and see how it does.

Shopping for tower hardware isn't easy unless you patronize actual tower supply firms, of which there is little in the way of retail in this area. Part of the fun of building towers and antennas is to gather up what's needed from what's available. You just have to be careful that you are indeed picking the right hardware, for which experience is a handy guide.

My partial list of purchases:
  • Various U-bolts, for the tower and for anchoring guys -- Ottawa Fastener Supply
  • Class 5 hardware for the tower -- Ottawa Fastener Supply
  • Pipe clamps -- Canadian Tire (automotive section)
  • Guying hardware -- Ottawa Fastener Supply
  • UV-resistant rope -- Home Depot
  • Tower base -- Home Depot
There's more I have to buy once I get to erecting antennas, including wire and supports. These are easy purchases once I reach that point. Some specialized hardware such as antenna insulators I purchased from amateur radio outlets.

The first thing I needed to do with the tower was to remove old hardware. As is all too typical the hardware on the tower is terribly rusted. There are any number of ways to remove this hardware. My choice is the one of greatest expediency -- an example is in the adjacent picture -- in keeping with the legend of Alexander the Great cutting the Gordian Knot.

Those bolt cutters have been put to good use over the years. Many times I have walked down the length of every element of an old yagi with cutters in hand rapidly dispatching the rusted clamps holding together the tapered aluminum tubes. Hardware is cheap while my time and patience are in short supply.

Next, I came to the need for a conduit suitable for routing transmission lines and other cables through the wall of the house into the basement, which is where the shack is to be located. In most cases this is not a difficult decision, there is only the need to decide on the inside diameter of the plastic pipe to support the quantity and size of cables, with enough room for future expansion.

In my case the choice was more involved. The conduit will serve a purpose above and beyond that of merely routing cables. Because of its planned location I am able to kill two birds with one stone by employing the conduit to secure the tower. How this will be done I will come to in a future article. For now I will say that it needs to be very strong and able to be coupled to the house's frame.

Any plumbing supply outlet has suitable pipe. That trip wasn't necessary since my garage is stacked with lengths of aluminum and steel from my previous station. I settled on a old mast, a standard 22-foot length of 1.5" Schedule-40 galvanized pipe. I no longer need it to support stacked yagis so I lopped off less than a meter of it to serve as the conduit.

With an inner diameter of ~4 cm it can hold perhaps a half-dozen runs of RG-213. It is also strong enough to serve as an anchor. The prepared pipe is seen in the adjacent photo, hack-sawed, filed and leaning against the rough doorway to the as-yet unpainted shack.

One final aspect of the structure I'll mention here is the tower base. The standard (manufacture's) method of securing the base of a Golden Nugget tower to the ground is with three 3-foot long steel posts that are driven through the base plate into the soil beneath. This provides good lateral strength, sufficient resistance to uplift forces and plants the base below the frost line (some protection against motion due to freeze-thaw cycles). This option is not permissible at Site C since it is directly over the tile bed of my septic system.

The base I have come up with is a "floating" design, where the base does not reach below the frost line.The lumber you see in the picture is suitably rated for this application, and should provide many years of service. My objectives are to distribute the tower weight over an area larger than the base itself (to protect the tile bed), maximize the coupling to ground (for lateral stability) and to get it down far enough for a reasonable amount of protection against uplift forces and human tampering.

Now all I need is time enough to put it all together and have a tower raising. I also need to put a couple of finish paint coats on the shack walls and do related finishing work. I don't relish doing this in summer, but I may be persuaded by the several days of rain that are forecast this week.

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