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.

looking for trouble

part last: how to look

de Bill, K7WXW

Generally, when something in my shack stops working, I start with the basics: are the cables right? Have I turned on the power? Operator error is always the first hypothesis. When I’ve worked through the obvious stuff and don’t have a clue, I turn to the interwebs. Whatever I am trying to fix has probably been used, torn apart, repaired or modified by someone somewhere who subsequently wrote an email or blog post about it. A thorough search usually results in a pile of helpful files, bookmarks and contacts.lookingfortrouble2

Today, unfortunately, my first search didn’t reveal much so I went to plan b: asking for a little help from my friends.

Email lists and forums – what we used to call bulletin board systems and newsgroups – are my connection to hacker/maker/ham communities that always know more than I do about whatever piece of gear, technology, or software I am trying to make work, repair or hack. There’s a vast store of tribal knowledge in such places and on most lists, people are happy to help you if you do your homework and ask specific questions. In this case, I distilled what I needed to know into two questions, wrote a paragraph describing the symptoms and what I’d done so far, and sent it to a QRP list where I hang out. I write an email like this once or twice a month and the result is almost always helpful.

My email netted me a schematic of the base unit, good troubleshooting advice, and references to several articles about SWR meters. The articles helped me understand the theory and gave me pointers to other articles, along with the callsigns of hams interested in SWR meters and directional couplers. I used this info to do another web search and soon had a stack of articles, schematics, and photographs, more than enough to figure out how the WM-1 works and how to fix it.

It took a couple of hours to go through all the material. Along the way I learned a lot about directional couplers and RF measurement.  I was able to make some good guesses about nature of the problem, and come up with probable fixes. This is one of the benefits of I-have-to-fix-it-myself gear: figuring out what’s wrong with something is a great way to learn how it works.

I made a repair list and a plan for home brewing a new RF detector. I should be able to fix the old meter but building a new one will give me a backup and help me convert all the theory I’ve been digesting into a real piece of gear. Another perk of fixing-it-myself: the satisfaction that comes from using gear that I’ve repaired, modified or built myself.

I am glad I lost the habit of immediately replacing stuff that doesn’t work. My unusual meter spike has turned into a file of interesting articles, a repair project, a cool home brew project and a must-to-read list of RF design tutorials. I know a little more about SWR, RF power measurement, and directional couplers and I have had interesting conversations with three long time hams. If, three days ago, I was wondering about the wisdom of buying a flaky third-hand meter, today it appears to be a pretty good deal.

looking for trouble

part two: all the things it is not

de Bill, K7WXW

The sun is almost up when I let the dog out, make coffee for Amy, and sit down to check my email. I have three replies to my query. Someone sent me a schematic of the main board, someone else, three or four references to directional coupler designs along with technical data and photographs from three or four watt meters he built. The last email is a reminder not to rush through troubleshooting. I get my notebook.

My friend’s reminder is timely. Like most fools, I tend to rush in. Making a plan attenuates this tendency. My curiosity helps, too. Why doesn’t this work? is such a great question. I don’t just want to get this meter back on line, I want to know what makes it go. Troubleshooting is one way of figuring that out; maybe the best. Besides, I don’t have a spare meter. Until this one is fixed, I am without. Using the emails, schematic, and a little common sense, I make a list of things to do, then head downstairs.

After disconnecting the power and undoing the wing nut that holds the ground strap, I pull the desk away from the wall and start working through my list. I remove and test the coax cables and feedline. I examine the ground connections. Everything checks out. I make a note to look at the cables and connections at the outside panel, too. So far, though, no obvious problems.

I have two antennas, each going to a matchbox tuner. Between the rig and the tuners is a coax switch. The configuration is a bit complicated, so I take the switch out and test each antenna path separately. A basic troubleshooting rule I learned as an engineer: keep it simple. Complexity is hard to understand, let alone test. The corollary: change one thing at a time. Two variables changed means four possible outcomes, three means nine, and so on. Don’t make things harder than they already are!

I check the coax switch with an ohmmeter. It is good, too. I put the switch in line with the two tuners and test again. The antennas load on all bands. I make more notes. I’ve eliminated almost everything but the meter. I make sure I have cabled the radio correctly, push the desk back, and head upstairs. I haven’t completely nailed the problem down but I have eliminated a lot of possibilities. That is a good morning’s work; time for breakfast.

looking for trouble

part one: when stuff breaks


de Bill, K7WXW

While tuning through the 40 meter band, I notice the SWR meter spike and return to zero. Ten minutes later, it happens while I am not touching the rig. That’s weird, I think, but the net starts in twenty minutes. I don’t want to start taking things apart. I decide look into it later.

I drop to 80 meters, lower the RF power to five watts, and switch to AM. When I key up, the SWR meter goes to max and stays there. Adjusting the matchbox makes no difference. I move back to 40 meters. The same thing happens. Weirder. It worked ten minutes ago. Looks like I am taking things apart. With the meter out of line, I match the dipole on both bands. Putting it back in, I don’t.

Bad cable? I swap in a new one and check the old one with a ohmmeter. The new cable doesn’t make a difference and the old one is good, at least at DC. While I am switching the cables, I bump the meter and the receive audio gets a lot louder. I try to match the antenna again. Success. Could my third hand meter, an Autek WM-1, be the source of my woes?  I take it out of line and get ready for the net. For now, I can use the rig’s SWR meter.

I am embarrassed to admit this, but in an earlier life, I would have chucked the WM-1 and ordered something shiny and new. I was a busy guy.  Who had time to figure out why something didn’t work, right? In this life, I finish the net, put the meter on the bench and start taking the case apart.

I look for obvious problems: loose wires, cracked components, bad solder joints. The solder work is questionable and the sensing toroid isn’t glued down but there are no glaring (that is, easy to see) faults. I make a note to reflow the solder on all the connections and glue the toroid into place.

The instruction manual notes that unexplained SWR spikes aren’t anything to worry about. I speculate for a moment about career path of whoever approved the manual. There’s a schematic for the detection circuit but none for the main board and no explanation as to how it works. Not helpful.

I do a quick web search and turn up a few posts about the odd behavior I am seeing. Unfortunately, none include a fix or schematics of the base unit. I can’t call customer support; Autek disappeared years ago. I am not sure what to try other than cleaning up the bad soldering, so I go to plan usual: asking for help from people who know a lot more than me.  I send an email to the QRP list and set the meter aside for the night.

Grounding Bars and Bolts

Fine Tuning My Amateur Radio Station

de Bill, K7WXW

The ground bar is bolted to the shelf. The grounding straps of tinned copper braid between the bar and my rig, power supply and tuner, are in place. I am holding the last one, which will connect the case of the AC line filter to the bar, in my hand. The filter is on the floor near the wall outlet. But I can see there is a problem with the strap. Being four feet long, it will make a good antenna for any stray RF lurking around. Last thing I need is another entry point for noise, so I put it down and look for my notebook.

Other design decisions aren’t working out either. To get behind my rig, I have to move the desk. To move the desk I have to get out a quarter-inch socket wrench and unhook the copper strap that ties the ground bar to the rod outside.  Inevitably I need to crawl under the desk to retrieve the bolt after dropping it.  When I am done, I have to reverse the procedure, hopefully without the dropping-the-bolt step. This is not, as they say, an optimized process.

Sidenote: My friend Scott, N7NET, offers a tip for starting nuts in hard-to-reach places: dab a little Vasoline in the back of the socket to hold the nut in place until it catches the threads.

Apparently good paper designs often fail when they encounter real world voltages, screws, and transistors.  Spectacularly sometimes, too, as in what could you have possibly been thinking when you designed it that way? Mostly though, designs fail in small ways: a hard to reach screw or an oscillating amplifier.  Even good designers – and I am not in the category – have these problems. It is really impossible to know beforehand exactly how the thing we are designing is going to be used until someone is actually using it.

A piece of gear can’t get much simpler than a copper bar with holes drilled in it, a couple of standoffs, and a fistful of 4-20 nuts, lockwashers, and bolts.  Bolt the bar to the desk, secure each ground strap with a bolt, lockwasher, and nut, done. What could be easier? Something other than a ground bar, apparently.  The way I designed my system, undocking the main ground to get behind the desk is a giant hassle. The ground strap to the AC line filter is too long. And with a single bolt, nut, and washer per strap it takes two hands and two tools to make or break a connection. It all adds up to a list of changes that I didn’t know needed to be made until I actually put the ground bar together and tried to use it. And it also reflects a simple fact: paper designs, however carefully done, almost always need a tweak or three.

My first inclination is fix it now! Giving into this impulse almost always turns out, even in the simplest cases, to be a bad idea. My first unvarnished solution to a problem is usually (never) my best one. Sometimes it is not even my second or third best one. I don’t trash the first thing that comes to mind, but I don’t stop with it, either. I just see it as the start to a list of potential fixes to particular problems.

Even well-designed commercial gear doesn’t get through the design-build-use cycle without lists like this being written. When I was an engineer, we called them engineering change orders, ECOs for short. ECOs are another version of my lab notebook: what is the problem, what is the fix, what does it affect, how much does it cost? In the commercial world, an engineer has to write an ECO and get it approved by the people who live with the product and modifications made to it: manufacturing, marketing, testing and so on. Here’s a truth: those folks don’t like change. It mucks up their day. To get an ECO approved that engineer has to think through the problem he or she is trying to solve in a way that makes sense. Improvisation rarely wins the day.  Whether I was the designer or the design team manager, ECOs were my antidote for the spontaneous fix.

I don’t have a marketing department and I manage all the manufacturing and testing around here. The only person who has a bad day due to a poorly thought-out fix is me. That said, I don’t enjoy re-fixing a fix that didn’t work, so I address problems by following my homebrew version of the engineering change order process.

I start by looking at my original design. What was I trying to do? Did I miss something? I make a list of the problems and ask if any of them arise out of the original requirements. For the ground bar, ground straps should be as short as possible and in a star configuration. That requirement limits, among other things, where I can place the ground bar. If a requirement causes a problem and I can’t come up with a fix, I either live with it or I change the goal. Other problems come up because how I thought things would work is different from how they actually work. And, finally, there are the things I just get wrong. Now I have a to-be-fixed list, based on actual use, that reflects my original design goals.

Next, figuring out possible solutions. There are rarely more than three or four to consider. I just don’t have that many good ideas. As always, I write all this stuff down. Why? Mostly I don’t like having the same bad idea more than once.  The end product of this process is my homebrew ECO: a detailed lab notebook record of the what, why and how of whatever it is I am fixing, without all the check boxes and signature blocks one finds in the commercial version.

When I actually don’t know what might work, I go off to do some research. Maybe (almost always) someone has had this problem before. Or maybe a data sheet or application note will give me ideas. And sometimes simply setting the list aside for a bit does the trick. The list that comes out of this process will always be better than randomly trying something and hoping everything will turn out okay.

Now I have fixes I like. I start working through the list. The bolts are installed from the bottom of the bar with a lock washer and nut on the top side so they don’t have to be removed when I disconnect a ground strap. The  strap that runs outside is held with a wing nut instead of a nut now, so I don’t need a wrench or nut driver to take it off. The AC line filter is mounted to the underside of the desk with a six-inch, rather than four foot, ground strap. I can’t do much about needing to disconnect the outside ground every time I need to get behind the desk; no changes on that front.

After the fact, the fixes seem pretty simple and might hardly worth all the record keeping. Bill, that sure seems like a lot of work for a small problem. Couldn’t you just try something and see how it worked? Perhaps. Maybe though, simple fixes are simple because they are thoughtful and thoughtfulness is the result of writing down what one is doing and why.  It took me longer to write this post about the process than it did to actually do it.  That isn’t always the case. The chance of getting something wrong in a design goes up as the square (or worse) of the complexity. More parts, more chances for error. If that’s true, a process that includes time for making, testing and documenting changes seems prudent, even for a ham building gear in the basement.

I disconnect one of the ground connections to re-route it so it won’t block access to one of the antenna feeds. After checking everything against my wiring diagram, I plug gear into the new AC filter and the filter to the mains, then push the desk back against the wall. Getting behind the rig is a lot easier than it was two hours ago. Fix accomplished and later, when I am trying to remember why I did what I did on this project, I have my notes. It works.

Writing It Down

The Power of Lab Books

de Bill, K7WXW

I need an entrance panel for my antenna feeds. Snaking them through a partially open basement window isn’t working out so well. I look over the ready-made options and decide to design and build my own. What I come up with will work electrically but I have a problem: I have no idea how to bolt it all together.

Figuring that out involves a notebook, one 6×12 inch sheet of aluminum and a pile of lightning suppressors, all of which are on my desk, next to the keyboard. I’ve been doing this for a while; it’s a hard problem. A bigger piece of aluminum would be better but won’t fit in the space I have, the components are oddly shaped and the whole thing has to go together in a way that allows me to easily attach and route cables. Every once in a while, I re-arrange the pile, make a quick sketch and write another note.

The notebook is a product of Mr. Sivak, my junior high school science teacher. To get a passing grade, our notebooks had to formatted in a certain way and include certain stuff: the hypothesis, lab setup, initial conditions, experiment protocol, and results. There was, being high school, a lot of grumbling in the ranks. More writing? More rules? More stuff that I will never use again? Me? My resistance faded when I figured out that keeping records of my experiments enabled me to understand why things worked the way they did.

In science class, the notebook trained me to capture information in a way that made it useful. It also taught me cause-and-effect: I did this and that happened. As a vo-tech student, it cut down on the number of times I made the same mistake.

Later when I was learning electronics on a tube trainer rack made up of a pre-built plug-ins – power supplies, amplifiers, oscillators and such – I used a lab notebook to keep track of my choices. Recording what I did mattered because passing the class involved (a) developing a  design by the deadline and (b) not letting the smoke out of the same type of plug-in twice while doing so.

In the years that followed I filled a lot more notebooks. I stopped doing engineering bench work, but I kept using lab notebooks. Whatever name I used for them, the essential components – initial conditions, hypothesis, setup, protocol and results – that made up my high school lab notebook didn’t change. Whether I was building or managing or monitoring, whether it was a new product or a new company, using this format to guide my decisions simply made whatever I was doing turn out better. The notebooks of my professional career helped me develop, test and, most importantly, assess and tune good solutions to complex problems, which is what I got paid to do.

Today, I am on the eleventh arrangement of the panel. I have solved a couple of problems that I didn’t know I had when I started. I notice that the difference between the tenth and eleventh versions is pretty small, so I probably have a design that meets my goals. But if I build it and find a new problem, the next version can skip past all the designs I have already tried and rejected. The sketching and note taking added about an hour to the process. From past experience, I am certain that hour will save me from having a, “wish I had thought of that before I started drilling” moment, and rework or starting over, later.

I decide to try one more arrangement of the panel. It looks familiar. Reviewing my notes, I see it’s a repeat. But flipping one of the components around solves a spacing problem that’s stumped me until now.

Finished! I make one last sketch. Later I will use some LMR400 coax I have (my worst case scenario) to make sure my cabling assumptions are okay. Finally, I will dimension the components and make a drawing that will serve as the panel’s drilling template.

After measuring each of the components and making the drill template, I make a final parts list so I know what I need from the hardware store. It will take just an hour or two to drill the aluminum and assemble the panel. With all the arranging and sketching, I am confident that my cabling problem is solved, I’ve addressed the lightning and static charge problems, and I have a way to review my design choices if I want to make changes. Not a bad day’s work.

Why should hams bother with lab notebooks? It’s a hobby. Diplomas, promotions and stock certificates do not hang in the balance. An hour writing is an hour not devoted to making contacts. But anyone who has invested days in building an improvised piece of gear that doesn’t work or fit or last knows my answer: I suck at making things up on the fly. Every hour of designing, paper testing and documenting saves me two or four or more hours of rework later. And six months later, when I don’t remember why I made the choices I made – whether it is an antenna setup or homebrew balun or the way I configured my radio – my notebook has me covered.