magnolias and antennas


bending with the wind

de bill, k7WXW

The magnolias, one in the open, the other behind the scotch pines, are a couple of days from full bloom. Like most of the flowering trees around here, they happen in a burst. When they do, Amy harvests a branch or two for flower arrangements but mostly we enjoy them where they are.

This morning, however, there are two buckets of branches in the dining room, and on the porch, a pan piled with not-quite-flowering buds. My phone beeps while we are filling the second bucket: high wind alert. Old news around here. The gusts are sweeping flowers from trees all over the neighborhood and both magnolias will, I think, be bare before noon.

My antenna masts are two scotch pines, a birch, and a cedar. At this moment, the top of the birch is sweeping eight foot arcs, the cedar and pines, three or four. The dipole and end fed are, so far, moving with them. I finish helping Amy and head out to take care of the antennas.

At the base of each tree is an eye hook and a cleat. The pulley lanyard is cleated and the line that runs through it is attached to one end of an antenna. I can take the antennas down (and put them back up) without climbing. My original design included a tensioning spring between the eye hook and the antenna rope. Then I decided I was over-engineering things and didn’t install them. I watch the treetops bend, untie the rope, add four feet of slack and retie it. I move to the cedar and repeat the process. The gusts come and go. In the calm moments, the antennas dip toward the yard, forming deep, graceful curves. I’ve probably dodged losing one or both of them. Good thing I was home.

I spend the morning apparently working, but mostly I am watching the trees. The magnolias are holding up better than I expected. Of course. Trees are built to bend. On the way to more coffee I take the long route, through the yard. The dipole lifts and drops eight or nine feet in the middle. Amy is in the living room, turning blooms and branches into flower arrangements.

My antenna wasn’t built for this. If I hadn’t been around this morning, I’d have a tangle of wire in the middle of the yard rather than an antenna above it.  I am reminded that an antenna on paper is one thing, spanning my house, it is something else entirely.

On my laptop, a dipole is a wire of particular length and height, fed with more wire, and connected to a radio. EZNEC tells me it will have a certain resonant frequency and radiation pattern. A couple of websites help me estimate the cost, and so on. Before I get an antenna into the air, my problems have names like efficiency, loss, and noise. It’s all straight lines and numbers, like this diagram from the ARRL. Later, when 18 gauge wire, three or four insulators and a couple of pulleys are involved, the problems become unrelentingly physical: wind, tangled ropebranches, house-in-the-way. After all this time, I should not be surprised by this but I am.

Pines and magnolias move with the wind. In good years, they weave their branches around one another, grow over the house, drop some buds in a storm. In bad years, not so much growth, maybe some lost branches. They are not impervious to the weather – witness the ragged stump that is the top of one of the antenna-free scotch pines – but their organic responsiveness helps them survive most sudden or severe environmental changes.

Good designers can’t work slow as trees but they can mimic their way of adapting by asking questions. Sometimes obvious, what if something that isn’t part of the system changes? and sometimes not: how to get the feedline away from the gutter? Questions can be in the form of calculating or simulating or breadboarding or just going outside and looking at the trees. Whatever works! The important thing is asking. Don’t get lulled into thinking, there’s never lightning around here or when was the last time the wind really blew?

Good design isn’t organic like a tree growing, it is methodical and pragmatic. But the designer who blends good design practice with the willingness to not-know ends up with a tree-sturdy design: it doesn’t fail whenever the world outside isn’t quite as neatly organized as one’s lab notebook.  Which, by the way, is pretty much always. How do you not-know? Simply questioning everything during the design process is a good start. Your assumptions, the boundary conditions of the problem, your taken-for-granted knowledge? Put it all up for grabs, at least for a little while.

I used to begrudge the time required for this kind of questioning. git ‘er done!  was my motto. The reward for such parsimony was often a tangle of wire, glowing transistors and the like. Or when I made time for questions, I would dismiss the answers, as I did with the springs. Oh, that will never happen!  By now I’ve let plenty smoke out of stuff; I allow lots of not-knowing time.  My “dump the springs” decision suggests that I still need work on the pay-attention-to-the-answers-you-get end of things.

Late afternoon. The wind is a slow steady breeze. I was wrong, the trees aren’t bare. The porch is covered with petals but the magnolia is still mostly flowers. The dipole is drifting up and down a foot or two. I decide to give the wind another hour or two of free rein before taking the slack out and head to the basement to find some springs.


One thought on “magnolias and antennas

  1. Scott says:

    Outstanding, Bill. I felt your grief as the wind began. My grief was for the anticipated wait for the blossoms. And now this? . Wait another year? Unreal. The antennas? Serious stuff, but worst case, back to the lab book.


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