[TowerTalk] Self-supporting Tower

[Tom Martin]

I have been following this thread with a vested interest.  I have a 72 foot Heights tower located in the only place on the city lot where the XYL would allow it to be erected.  It is in the back of the lot next to the garage and 25 yards from the utility lines that run parallel to the tower down the alley.  The tower is also 20 yards from my two story house.  There are no guys but I increased the size of the concrete base (4X7), added square tubing at each joint with 8 inch bolts running vertically to safe guard the "egging" problem with the bolt holes at each leg joint, and added extra horizontal struts where each section joined.  The original design didn't have any horizontal bars.  All of this extra welding was done by a professional aluminum welder.

Only 9 months after I erected the tower, we had a F2 tornado go through the area.  It thankfully veered east two blocks from my QTH and I didn't get hit with the major winds.  However, the top 30 feet of the tower did suffer a slight "twist" which is noticeable.  The southwest wind must have had enough sustained force to drive the 5 element 20 meter beam and 2 element 40 in clockwise motion causing the twist.  The TX2 brake was damaged but there wasn't any windmill effect.  I was out of town that evening and missed witnessing the damage.  I would have been a nervous wreck, if I had to watch the tower and beams in that storm.  At least there wasn't any buckling of the tower.  I had to replace the rotator and repair the 40 meter reflector.  

If the worst comes and the tower does ever buckle, I hope it occurs at the 48 foot level.  Otherwise, I have the choice of taking down the power lines, or having the antennas come crashing through the roof.  Since the most damaging winds come from the southwest, it looks like the former.

I have slopers on the tower but they would not be effective as safety lines.  I think I will consider the copperweld idea with decent insulators.  I think the XYL will go along with that scenario.

In conclusion, some of us do not have the luxury of acres of land for our antenna systems.  Also, we don't want to operate with a low dipole, or vertical with a few short radials.  We have to be diligent and design our towers with safety in mind...all within reason.  Excellent insurance coverage is also a plus!

Tom W8JWN/V31TR