Thursday, March 1, 2018

Big Station, Big Maintenance

For those of you prone to vertigo I apologize for the picture. It isn't gratuitous; I have a point to make. This picture was in the second last slide in a talk I gave on station building earlier this winter. The topic was maintenance.

The more towers and antennas you put up the more maintenance is required. Although also true for the quantity of equipment you have inside the shack there is an added component of danger, difficulty and expense with the former. Never forget that. There are substantial benefits to building your station with a eye on minimizing maintenance. It can never be eliminated so be prepared.

I was reminded of that this week when a problem occurred on top of my 150' tower. This was a potentially disastrous problem. On Monday I noticed that the top yagis were pointing towards an unexpected direction. As I gazed upward I noticed that the action of the wind was slowly turning them, first in one direction and then the other. Obviously something bad had happened.

Binoculars showed nothing amiss. I could not climb just then since it was immediately before sunset. The next day, with the wind howling but with unseasonably warm weather, I went up there to check it out. Before doing so I tried to arm myself with information by corresponding with another ham with extensive prop pitch motor experience and with the style of drive system I'm using.

Once up there I quickly saw what had gone wrong. The six sets of bolts, lock washers and nuts securing the motor flange to the drive platform had all unscrewed. The bolts fell out the bottom with the lock washers and nuts stranded up top. The loose motor allowed the mast to spin freely and yanked the motor wires out of the splices to the main cable run back to the shack.

The two bolts that landed on the drive shaft bearing were enough to temporarily secure the motor. The next day I climbed up with new hardware and electrical tools and fixed everything. Tower time was 2 hours, plus 90 minutes the previous day. The wind was howling which made the job unpleasant and difficult since I had to fight that wind to turn the mast and antennas to a better position for attaching the wiring. You can be sure that this time I made certain to properly torque the grade 5 galvanized fasteners.

This was also an opportunity to fix the coupling to the direction pot which will save me some grief. The fewer times I have to climb the tower the better.

This fiasco was, of course, entirely my fault. I am not ashamed to say it. We are all human and we make mistakes. How I made this mistake I don't know other than recalling the urgency to complete the project in December as the weather deteriorated day after day.

Mistakes at the top of 150' tower in winter are not like a mistake on a 50' tower or inside the shack. All mistakes and failures are aggravating but most do not involve dangerous repairs. On the bright side the weather was warm and the yagis -- TH6 and XM240 -- are pretty well torque balanced and so did not turn hard in the wind. All coaxial cables were undamaged.

The bigger your station the bigger your problems. If you seriously want a big station prepare yourself. There is lesson in this: build it to last. That was the message of the slide in my talk with the vertiginous picture. The picture shows me climbing the mast of the big tower to release the coiled up coax from the XM240 feed point. Although impressive in a way not even I want to do it often!

It is well worth the expense to buy or build the very best up front to reduce maintenance events. Use the best parts and methods and you can increase MTBF (mean time before failure). The initial expense will be recouped many times over the coming years. You do not want to be climbing towers and making repairs every week or two. It not only puts you at risk it is expensive and, perhaps most important, it can put you off the air just as a major DXpedition or contest occurs.

If, like most hams, you do not climb towers you must factor that into your calculations. Educate yourself about materials and engineering needed to build survivable antenna systems. Otherwise you are at the mercy of others and their opinions, and you will not know enough to distinguish good advice and workmanship from bad. What you don't know will hurt you. Money spent in no guarantee of quality. It helps a great deal if you are able to climb although it is not mandatory.

Do it right and be careful out there. Spring antenna season is nearly here.

1 comment:

  1. If you can, mount your rotator at ground leve or rotate whole tower. You will be getting to old one day to climb.....


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