Sketchy – Prototype

 Ham Radio  No Responses »
Nov 112023
 

I thought “Ok, so let’s throw some parts at this thing and see if it works like the simulation…” and so I did:

As it turns out, I had a few different parts laying around the bench and using those would be easier than hunting down the specific values I had in my original simulation… those values aren’t critical really, so I just used what was already lying on the bench and updated the schematic in EveryCircuit to match:

Built up on the breadboard it looked like this:

I find that with a little effort and creative thought it’s not difficult to get breadboard layouts to closely resemble schematic diagrams… and from there it’s not too much of a leap to get to what the prototype(s) and final build(s) will resemble.

A clockwise tour of the circuit on the breadboard…

Here you can see from top to bottom on the breadboard matching roughly from left to right on the schematic: There is a 47K input resistor that I’ve connected to a white wire that will act as the switch.

I describe that as a “wire” so that I can reserve the word “jumper” for the short color coded jumpers I use to make patches between segments of the breadboard. These are fantastic, by the way, because they are color coded for the number of points they span. This saves a lot of time when building up more complex circuitry or trying to trace where one or more of these jumpers go…

See the red jumper connecting 2 points away, and the orange 3, and so forth… very nice. I bought a bunch of boxes of these and I use them all the time. They’re so cheerful and perky. Full of potential – like a fresh box of colored pens and a new graph pad. I love that… but I digress.

You can see the input resistor go directly to the base of the PNP transistor, and on the back side of that transistor you can see the filter capacitor between base and emitter; an orange jumper connecting that to the positive rail 3 points away.

Moving down from there we come to the MOSFET acting as a switch. A red jumper connecting the collector of the input transistor to the gate of the switching MOSTFET and then from there you can see another 47K resistor pulling that down to the negative rail on the right.

In parallel with that a yellow jumper connects the source of the MOSFET to the negative rail (which will be common ground)… so that the other side of the switch is a typical “open drain” version of the “open collector” type of switch. The key idea being that it’s either open, or connected to ground.

Speaking of the “open drain” you can find an orange jumper crossing the centerline gap to the left and acting as the “output” of the circuit. Over on the left side you see couple of header pins stuck in the breadboard as a test point connector of sorts and then a panel mount LED connected on it’s other side to the positive rail through a 470 ohm resistor. (It was laying right there, and I didn’t care about the LED being a little bit dimmer, so I just went with it!)

You may have a little trouble spotting the header pins because there is a white alligator clip chomping on them… and if you look over to the right you’ll see a black alligator clip chomping on another set of pins plugged into the negative rail. These two clip leads make it easy to keep the DVM in circuit to measure the voltage across the output of the circuit… that way we can see just a bit more detail than whether the LED is on or off.

Testing Sketchy with a floating input

The guess is that the tuner controls the status line as an open-collector type of output. This means that the long wire running from the shack out to the tuner would see a very high impedance and would be essentially “floating” whenever the open collector is “off” at the tuner.

In this test you can see that the white input wire is hanging in the air on the left. The voltage at the output of our circuit is about an LED drop down from the positive rail… I guess because the DVM pulls just enough current to see that drop. 1.256v = 5 – 3.743

The LED is off… so all is well.

Testing Sketchy with a “human antenna” input

A long “floating” wire seems a lot like an antenna that might pick up all kinds of noise or even some stray RF (this is going to an antenna tuner after all). We want to make sure the circuit isn’t sensitive to that so we put in a filter capacitor across the BE junction of the input transistor. The idea is that the input resistor and the capacitor make a low pass filter that will reject almost anything that isn’t close to DC.

Connecting myself to the input wire to give it some “extra length” we can see that I do inject some noise; but not enough to cause the circuit to really switch. The LED stays off, and the voltage across the output only goes down by a couple hundred millivolts. That’s enough to see on a DVM, but not enough to matter when switching LEDs on and off. (Nor even enough for any logic circuit that might come later to care about it either.) 201mv = 3.743 – 3.542

Testing Sketchy with the input pulled high

Another design spec is that the circuit should be happy with a TTL input. So, connecting the input to the positive rail (+5V) we get the same result as the floating input: The output is off as expected!!

Testing Sketchy with the input pulled low

Testing the other side of the TTL input spec as well as the open collector input spec, we pull the input low by connecting it to the negative (ground / common) rail. As expected, the output goes to ground and the LED comes on!! Not only on, but VERY on… 11mv measured across the output.

This is a benefit of using a good switching MOSFET vs a bipolar transistor for this kind of output (open drain/collector). The “closed circuit” or “on” condition of the output with the MOSFET will have a much lower voltage than you can get from a bipolar transistor. Definitely closer to ground.

Testing Sketchy with the input pulled low weakly

Finally, since our theory about the status line problem is that it may be oxidized at the connector near the tuner, we tested again with a high resistance in place. In this case, a 220K resistor to simulate whatever that unwelcome resistance might be out there. Again success! The LED is fully on just as if the input had been pulled hard to ground.

Qapla’ !!

Sketchy Long-Run “open collector” cleanup

 Ham Radio  No Responses »
Oct 102023
 

A while back we replaced the SGC-237 at the feed point of the big loop. Since then, the controller has been a bit sketchy. The indicator for a good tuning solution is intended to light either the yellow panel LED or the green panel LED; but since the upgrade the best it seems to manage is a bright or dim yellow.

I’m not sure what’s going on there, but I have a few theories. One is that the junction for the control indicator line in the box under the tree might be a bit oxidised causing extra resistance in the line. Another is that the design of the SGC-237 might have changed with the unit I have now, or that perhaps it never really was an open collector on the tuner end (that was a guess afterall). Another is that I just got lucky with the first design and that the long lead length might have something to do with my indicator not-quite getting the clear signal it needs.

I did measure the voltage across the input while the system was up doing it’s WSPR thing (where it must tune with each band change)… and I observed that the voltage from the indicator to ground seemed to get no higher than about 4V and no lower than about 3.2V… that’s weird, and suspiciously close to a silicon junction drop (about 0.8V)… almost as suspicious as frog’s breath… but of course, nothing is as suspicious as frog’s breath. Whatever is going on there has to do with how the indicator circuitry in my controller is interacting with the tuner through the controller cable and the junction box in the middle.

Anyway– at some point I will go out there and lie on the ground and “improve” the connections in the box. In the meantime, since the tuner seems to otherwise work just fine, I’m looking for a quick fix to get my indicator working properly again and generally make it more robust.

So, based on the idea that it’s probably some thing that looks reasonably like an open collector at the tuner end, or that even if it’s a TTL signal I might be able to interpret it like an open collector… I designed a circuit to clean up the indicator signal and make it FIRMLY on or off in an open collector manner.

Here is a snapshot of the schematic from Every Circuit (which was handier and a bit cleaner than my usual graph pad + phone camera… even if the N-Channel Mosfet symbol is a bit odd):

The diagram presumes I’ll be using the 5V supply from my existing controller. There is an SPST switch representing the input of the circuit which is the indicator line from the tuner. The output is the drain of the N Channel MOSFET that I’ve shown here connected to an LED via a 330 ohm resistor… but essentially that output will either be open if the input is “open” or “high”, or closed (shorted to ground) if the input is drawing current down from the 5V supply … as if it were “closed” (or trying to be) or “low” if it’s acting like a TTL signal.

Either way, the circuit should clean up the input by slamming the output fully open or closed. Here is the theory:

The input is tied to the base of a PNP transistor through a 47K resistor to limit the base current. The emitter of that transistor is tied to +5V (the positive rail).

If the input represents a high impedance between the positive rail and ground then effectively no current will flow through the base of the PNP transistor and it will be off. This will happen if either the input is something close to +5V like a TTL signal, or if the input is high impedance in general like an open collector would be.

The collector of the PNP transistor drives the gate of an N Channel MOSFET which is otherwise pulled to ground through another 47K resistor. So, if there is no current on the input then there is no current through the PNP transistor and the gate of the MOSFET will be at 0V. This will turn the MOSFET off and so it’s output will be “open” to ground.

On the other hand, if any current (even a fairly small one) flows to ground on the input, then the PNP transistor will switch on and pull up the gate on the MOSFET thus turning it on. The voltage gain of the PNP transistor given a 47K load (the MOSFET gate being essentially invisible to it) will be very high so that even a tiny current through the input will be enough to pull the MOSFET gate well above it’s “ON” voltage.

The choice of a 47K resistor on the input and also on the collector/gate is the same in both cases… it’s a high impedance (but not too high) and a handy value (I have a pretty good inventory of standard values like this). On the collector side of the PNP transistor this means a lot of gain. On the base side of the PNP transistor it means that not much current can flow through the transistor no matter what the input voltage is (within reason). That said, the beta of the PNP transistor is likely on the order of 100 so whatever the input current is at the base the output current will try to be about 100 times that amount.

I measured a 0.8v change between on and off in the existing circuit. The new circuit will amplify that by about the beta of the PNP transistor since the same resistance is on the base and on the collector, so any gain as big as 6 or so will be enough to swing the collector side between the 5V rails. With a beta of 100 I’ll be more concerned about instability than missing a weak signal. (I’ll address that if it shows up; but for now, simpler is better.)

Since I have these parts around I chose a 2N2907 (the complement of the 2N2222) as the PNP transistor; and a 2N7000 (a very common switching part) for the MOSFET.

Terrible Tiny Antenna Idea

 Ham Radio  No Responses »
Oct 052023
 

It was a dark and dismal November, a few years back; and there had been a lot of sudden, unwelcome changes that year. The house was empty, it didn’t feel very festive at all; but I had decided to treat myself to a new IC-705 and some other toys to try and break the gloom.

I sat in my living room pondering all the things, and wondering what to do for an antenna so I could light up the new rig and lighten the mood. I’d had a few discussions with folks who were trapped in apartments or even in tall buildings where there were essentially no good antenna options… so that was fresh in my mind.

I could have used the big loop outside — but it was busy with the robots, and not where I was. I looked out the window into the damp, cold, darkness… sinking slowly into madness.

Then, I thought, I could maybe string some wire around that window and make an antenna… surely I could at least receive with such a thing… and there’s nobody here to stop me or complain about it… My mood got a little brighter… but I knew the math and it wasn’t promising… and strictly receiving didn’t sound like quite as much fun as I hoped for.

I pondered some more, and the outside got darker; but eventually I dragged a few random bits of wire and odds and ends up from the lab along with a few other new toys I had… the random wire and bits and pieces reminded me of what the Grinch had left on the walls when he stole Christmas… it seemed fitting enough.

I figured if I was going to have “staring into the abyss” on my schedule I might as well tinker while I was at it… so I also grabbed my new Nano-VNA and my new LCR meter… additional toys I would be acquiring from Santa soon (or well, I could pretend anyway).

I’m normally the sort that draws a zillion pictures and diagrams and does all the math to figure out my designs before I set about building anything. This time, that seemed like a lot of work, and I wasn’t up for it… and since I had new toys that gave me the ability to “see” what the various parts and circuits “looked like” electrically, I decided to go the other route and just try stuff and see what happened. I figured I’d eventually end up with “something”, or I’d keep playing with it to see what I could learn. Besides, I’ve got plenty of theory in my head to give me some direction… it would keep me busy anyway.

The first idea I had was to take some shielded, multi-core cable I had and cross wire it so that it would be a 7 turn loop the size of my front window. I figured that with a large diameter and 7 turns it would be a pretty good inductor. I also thought that with the shielding in place it would be purely magnetic and so probably less noisy. But, in my temporary excitement I forgot about the inter-electrode capacitance. Each of those wires were all right next to each other inside the loop shield so that would defeat the multiple turns. I figured this out after trying it and being disappointed with the results.

The multi-turn loop idea had a few fairly narrow resonant points, but it didn’t really act like I wanted it to and was going to be really fiddly with the tuning. In fact, I had a devil of a time getting it to be sufficient at any of the frequencies I wanted to use.

Once I realized that the multi-core idea wasn’t going to work I grabbed some electrical ground wire I had laying around and decided to try a single loop with a loading coil to make up the difference in electrical length. That was less chaotic, but also didn’t quite work.

I knew I didn’t want to use a coupling loop because that would be impossible to hide as an inside antenna around a window… and well, also because I just didn’t like the idea! But that did make me think about the fact that that’s really a kind of transformer… So, I wrapped a couple of turns around the loading coil I’d made and that seemed to work much better.

I tried a handful of variations on that theme and got similar but varying results. I could see what was happening using the Nano-Vna, and I could measure the inductance and capacitance of the parts I was using with my LCR meter. This gave me a few ways to turn the wheels in my head… and so I kept tinkering… and it became morning, and then evening again…

2 turns on the primary of the transformer and 14 on the secondary with the tuning capacitor in series seemed to get an interesting result; so I played with that for a while… but I realized that the capacitor wasn’t really helping that much, and I also couldn’t get that second resonant point to be where I could really make use of it.

I started experimenting again… and essentially replaced the capacitor with an inductor… a loading coil, just to see how that would change things…

Tiger was supervising all of this work… Truth be told, it was Tiger who suggested replacing the cap with a coil and I told him it was a crazy idea and that it would never work because that’s not how you tune loops and … well, he’s a cat and … just … oh FINE, FINE! I’ll put in a coil and show you how it doesn’t work like that … you’ll see right!?

Nope, the crazy idea actually worked… the second resonant peek disappeared and the first one expanded… not quite as much as I had wanted, but quite a bit. Tiger, just looked at me as if to say “I told you so…”, but being a very cool cat, he refrained and just let me soak in the moment… then went back to doing cat things and occasionally supervising my continued tinkering.

After stumbling upon this solution I thought about it and realized I’d created a match that draws on several techniques.

The loading coil is borrowed from short whip antennas where it makes them electrically longer and therefore (typically) a higher impedance that’s easier to match to the feed line.

The high ratio transformer is borrowed from end-fed dipoles and similar kinds of antennas where it converts the high impedance at the end of the wire into a lower impedance that matches the feed line.

The loop antenna fed this way is completely balanced so it doesn’t need any kind of counterpoise nor does it have any free ends of it’s own which might expose high voltages.

I decided to take this to an extreme of sorts and scale it up. I basically doubled the number of turns on the loading coil and ramped up both sides of the transformer as well. The primary now had 3 turns, and the secondary had 30. The loading coil has 16 turns symmetrically split and bound to the secondary of the transformer so that there are no cuts in those wires… that is, the secondary of the transformer becomes the loading coil on a second core.

I have since called this contraption a Swamped Impedance Match because conceptually, the antenna and loading coil virtually guarantee a high impedance that “swamps out” the vagaries of the radiating element; and then that high impedance is divided by 100 using the high ratio transformer so that any of those “vagaries” are also divided by 100 thus making a reasonable match to the feed line across a wide range of frequencies.

The results were pretty good as far as matching goes. The antenna with the match manages to have a very wide frequency response covering most of the HF bands I wanted to play with and offering a usable SWR from about 4 MHz up to about 20 MHz. The antenna wire itself is a square about 80 inches on a side… but the actual loop isn’t critical. I picked that just because it would perfectly fit my window all the way down to the floor… the idea being that with any kind of drapes on the window the antenna could be completely hidden from view!

BUT, I hear you say; and I said it too; just because the thing has a reasonable 50 ohm match doesn’t mean it makes a good antenna… even if you can receive with it that doesn’t mean it’s actually a “good” antenna. It could be just a mediocre, and somewhat frequency specific, dummy load!

Tiger scoffed, and gave me a look, and an up-nod, and said (via kitty mind control) “You’re the Mad Scientist … do some science and prove it to yourself.”

So, I turned off the big rig temporarily and fired up WSPR on my Spectre laptop running Linux, and my new IC-705; connected it to the Terrible Tiny Antenna; and let it run for a couple of days to see what the rest of the world could tell me about the antenna’s performance.

It worked! No, really!! WSPR data from this setup shows fairly respectable results even when compared to my big loop in the back yard!

Here you can download the raw data (a text file) from that experiment. The top part of the data is for the Terrible Tiny Loop with the Swamped Impedance Match; and the bottom of the file is data from the big loop (with an SG-237 tuner at it’s feed point) for comparison. Both were running 5 watts. The small rig in my living room with the IC-705, and (at separate times) the big loop running from my lab with the Flex 6300.

Stealth-Antenna-WSPRDownload

Just to be extra sure about the results I asked some friends of mine in AMRAD to build the antenna themselves … and they also found it worked pretty well (though, their build quality was a bit better than my initial experiments.)

Here are some pictures of one of those builds:

Here is a schematic I hastily drew up for my friends to use as a guide… it’s simple enough as is the construction of the antenna and match.

The toroids are typical of what you might use for an HF balun (FT-240-43). Begin with about 4 meters of wire folded in half and wind the secondary on the first core from that mid-point. Half of the windings on each side of the core spaced so that they finish just opposite of the starting point.

Then, use a zip tie to attach the second core where the secondary wires are free and wind each of those wires through the second core about 8 turns on each side as if they are one winding split in the middle at the transformer.

This completes the secondary of the transformer and the loading coil with a single piece of wire. There should be just a bit left so that you can make some kind of connections for your antenna loop. Banana jacks are a good choice here.

Then complete the primary of the transformer by winding 3 interleaved turns of wire at the point where you began the secondary. Attach the free ends of the primary to some kind of coax connector of your choice. (it might be helpful to put a small value capacitor across the primary, but it’s not strictly necessary.)

The Swamped Impedance Match can be left loose like this for experiments, or it can be put in a box if you want it to look better and hide under your window behind your curtains 😉

The antenna loop itself as originally designed is approximately 80 inches on a side, but given the nature of the antenna the length is not critical and as long as you don’t have a lot of metal in your walls you can probably mount the antenna anywhere that works for your needs. I have taken this antenna out for demonstrations and simply stood it up in the air on a pair of lighting tripods with good results… it’s appears to be very tolerant of variations on installation and environment.

While the large toroids I used might imply that you can use some significant power with this — I don’t recommend it… certainly not if you’re using it inside where radiation and interference with other devices might be a concern. I simply used those toroids because they were what I had on hand. I suspect you could easily reduce the size and cost of your toroids and still get good results. Let me know if you try this and how it goes with any of your experiments.

Document

 Poems  No Responses »
Jun 292022
 

dot the I’s and cross the T’s
make the final strokes
and once more glimpse
with critical eyes
a masterpiece
a hard won craftwork
laced with ancient words
and flowery prose
a story carefully not told
in black and white
a monument to the dashing of hopes
and the slow tortuous death of dreams

SG-237 Controller for the Big Loop

 Ham Radio  No Responses »
Jan 042022
 

At the heart of the “big loop” antenna is the SG-237. Click here to see the manual for that.

The tuner can be run without a controller, but it offers a few features with a controller that are useful (and sometimes important) in practice. I took a look at the controller suggested in the manual and re-designed it a bit to better suit my purposes. First, because I wanted to use parts that I had laying around the lab, and second because I wanted a better “light-show.”

The important features are:

  • You can tell the tuner when NOT to tune. I find in practice that this can be particularly important when running digital modes as switching things around at the antenna can inject unwanted noise to your transmitted signal.
  • The tuner can tell you when it’s found a good tuning solution. Sure, it seems like this would be obvious enough once the SWR stops bouncing around… but it is awfully handy to have a nice green light tell you when the tuner has stopped looking.
  • I found this out AFTER I built my controller – The tuner can tell you when it didn’t find a solution but has given up trying! On my tuner controller there is an amber light for when the tuner doesn’t yet have a solution and a green one for when it has found a solution. One day I saw these flashing back and forth like it was shaking its’ head. I figured out that’s what it does when it gives up trying. This doesn’t seem to be documented anywhere, but it’s also a nice feature.

The first step was to draw up a schematic for the circuit and do a little math to make sure everything would work.

In the controller recommended in the manual they roll their own ~9 v regulator using a zener diode and an NPN transistor. They only use this to drive their LEDs, so I did something similar but instead used an actual 5V regulator.

The next thing I changed was the “tuned” indicator logic. Their controller pulls one side of their tuned indicator to ground when the tuner is happy. I presume this is done through something like an open collector in the tuner.

I wanted two lights instead of one so I added a 2N2222 transistor and a resistor to turn on an amber “not-tuned” LED when the green “tuned” LED is not on. Basically, the green LED and its’ current limiting resistor act like a pull-up resistor to bias the transistor on whenever the “tuned” LED is not pulled to ground by the tuner. The 47K resistor in series with the base ensures that any current that flows is tiny enough that the green LED won’t light (at least not in a way you can see it). The gain of the transistor is high enough that it will still effectively saturate in this condition thus turning on the amber “not-tuned” LED.

The rest of the circuit is essentially the same as their controller – so the tuner sees almost precisely the same signals. This consists of a DPDT switch, a momentary SPST push-button, and a handful of decoupling caps. All of this, a handy box, and some LEDs with built-in current limiting resistors were all handy in my lab… courtesy of the recently (at the time) defunct local Radio Shack – and my irresistible urge to grab everything I could from them in their last days.

Once the design was done it was time to put the mechanical components into the box and see how they all fit. Here is where some on-the-fly creativity was required because one cannot always be sure what parts they have nor how they can be used to solve a particular problem… I mean, I wasn’t building this from a BOM where I could order up precisely what I wanted right?! I had to see what I had around and improvise with that.

As it turns out all of the parts I had handy fit perfectly including some PCB mounted screw terminals that I was able to adapt to the back of the box with a little bit of drilling, sanding, and some small pieces of protoboard.

Next up I designed the layout of the electronics on another piece of proto-board. It’s always a good idea to take this extra step rather than going directly to soldering parts in place – even on something simple like this. The end result almost always turns out better and cleaner for the extra effort.

Then, once I’d put all of the parts in place I made a few measurements (idiot test) to make sure I got it right. A quick look at the box also informed me that I was going to need to make a notch somewhere on the board so that the wires from red LED could get to the other side. The simplest solution to that was to knock off a corner of the board.

Finally I connected everything together and “stuffed” it into the box. I say “stuffed” because, well, it’s a sloppy jumble of wires going everywhere all kind-of crammed into that space. I thought about making it neater, or maybe doing a more sophisticated PCB that would eliminate much of the wiring, but in the end this was a quick-and-dirty job. As such, the extra length of the wires was needed in order to be able to assemble and disassemble the device for testing and/or changes.

If you make the wires too short then there’s no room for getting the circuit board into and out of the box without having to desolder something. The lead length also doesn’t matter too much in this case since it’s all low-voltage DC, and the heat dissipation requirements are vanishingly small – so “stuff” it is.

Make one connection at a time until everything is wired up, make a final test, then it’s stuff-in-a-box. 🙂

Once the lid is on and it’s up and running it’s a pretty solid and fairly professional presentation. The LEDs all work as expected, and the orientation of the toggle switch and the red “do-not-tune” light make the user interface intuitive. With the switch to the left (away from the controls) the red LED is on and the controls are locked. With the switch to the right (toward the controls) the tuner is free to tune and can be reset with the push-button.

I’ve thought about doing something more sophisticated with this… and maybe putting it in a heavier box; but ultimately it does the job, has been reliable, and there really isn’t more to do!

In future, maybe, if I built a feed-point tuner I might like to have it provide information about its’ tuning solution and even provide an analysis of the antenna… or perhaps also take commands to fine-tune the solution or act as a pre-selector … but that’s just me dreaming and NOT what this tuner does. This one is designed to be simple and reliable and it hits those marks very well.

This controller seems to hit those marks too — with just one extra blinkenlight 🙂

Building the Big Loop

 Ham Radio  No Responses »
Jan 032022
 

I wanted an antenna that would be good for all HF bands; that would have reasonably good performance characteristics; and would be reasonably stealthy. Clearly, a wire antenna of some type… but what type?

There are dipoles that would work, and I’ve used them in the past, but they pose a couple of problems– mostly stemming from the heavy feed line and balun hanging in the middle, and the limited options for hanging a multi-band dipole on my property.

Then I looked at an inverted L… but that would need a counterpoise, and probably a complex one at that. Then it occured to me that if I connected the counterpoise to the far end of the inverted L I would actually have a large vertical loop – and that might even perform better! So that’s what I built.

I had a few other constraints to deal with though. For one thing, kids play in my yard (often without my knowledge or permission), so I would have to make sure that the antenna stayed safe for anyone around it and that all of the low, reachable elements were covered. I also wanted to have the tuner at the feed point in order to have minimal losses in the feed line.

The final design would have the vertical sides of the loop going up some trees about 65 feet apart; the bottom of the antenna buried a few inches under ground; and the tuner up about 10 feet in a box to protect it from the weather as well as any uninvited fingers. The wire itself would be insulated, and parts of it would be in conduit to protect it from the weather, squirrels, and other hazards.

The tuner itself is designed to be out in the weather, but by putting it in a box the termination points are hidden away, the tuner is further protected from the elements, and I have the option to eventually put additional equipment in the box.

The first step was to call Miss Utility and get the yard plotted so I could avoid my fiber and other possible hazards. Then we could begin burying the conduit. I say conduit, but really, it’s cheaper than that! I opted to use lawn sprinkler tubing which comes in various diameters, is designed to survive under ground, and is easy to work with.

The smaller diameter tube would go between the trees and be just big enough to carry the bottom part of the antenna. A larger diameter tube would go between my lab (in the basement) and the closest tree in order to carry the feed line and various other cables.

The next step was to assemble the loop and get it ready for installation. I would hire a “tree guy” to climb the two trees and install the hardware… but before that could happen I would have to have all of the ground work complete and ready to go.

Now, as a side note, my usual methodology is to do all of the math and drawings in meticulous detail and then execute that plan. This was no different. I had spent hours figuring out precisely what size loop would be required to have the least conflict on multiple bands and give the best performance overall. Everything would be precisely measured ahead of time so the installation would go off without a hitch and the end result would be perfection. You can probably tell by now that’s not how things worked out right?!! Indeed this experience broke me out of my shell and started me down a path of engineering both by intuition and by design somewhat abandoning my tight grasp of all things mathematical in favor of a more holistic approach— more on that later.

With the conduits in place the antenna wire, made from common electrical wiring, would need to be pushed through the conduit and various hardware installed. This included pulleys for each end to allow the antenna wire to move freely in the wind; and some insulators as strain reliefs in strategic locations to keep the wire from moving “too freely.”

The first excursion away from my usual engineering practice was how I treated the installation of the insulators. I had in mind to avoid joints and to keep the original insulation in place as much as possible. So, instead of a complicated arrangement at insulator locations I decided to simply push the wire through and tie a simple knot. In theory this tiny additional inductance would be invisible — and if that turned out not to be the case then I could always strip the insulation later and solder the joints at the insulators. As it turns out, my assumption about the inductance was correct and I never needed to rework the insulators.

The physical installation on the trees would be done using eye-bolts. These are much easier for a tree to handle than anything tied around a branch or trunk because they create only a tiny hole which the tree can usually heal. In contrast, loop tied around the tree could eventually strangle it or a the very least impose a much larger wound that might be too much for the tree to handle.

On installation day the arborist made a mistake – or more practically, uncovered one of mine. I had measured the antenna wire to precise specifications and had expected both ends of the loop to be up 30 feet. On the taller tree he installed the top pulley about as high as he could get it. My wire was too short for that — so either I would have to have him climb up again and fix it or I would have to adapt. I decided that in the end height would be more useful than precision… thus my second excursion from my usual “design first” paradigm.

I spliced in some extra wire to make up the difference. I used a Western-Union splice, soldered it, and wrapped it in heat-shrink tubing. As it stands now the “short” side of the loop goes up about 30 feet as originally planned and the “tall” side of the loop goes up about 45 feet. The loop runs roughly east to west (120° – 300°) between the two trees – though this orientation turns out not to be very important based on the propagation data I get from WSPR results.

The wire is hung with sufficient slack to allow the trees to sway in the wind without ever creating a high tension on the wire. This is much easier in this case than trying to configure some kind of weight or spring mechanism. As it turns out the extra slack doesn’t seem to affect antenna performance very much, and since this installation has now survived several years (initially built in 2014 and it is now 2022) the physical installation seems quite sound.

It’s probably also worth pointing out that the vertical portions of the antenna are running up the trees, and yes the bottom is technically under-ground. Shouldn’t that be a problem? Trees are conductive (sort of)! and the bottom of your loop is in the ground!! Are you mad!!??.

Yes, yes I am, and, it doesn’t matter 😉 This was never going to be a perfect antenna, just a good one. The tuner does a fantastic job of figuring out the various vagaries of the adjacent conductance of the ground and trees; and in the end the performance of the antenna turns out to be quite good in all weather.

Ultimately, though it might be fun to have an antenna farm where I could perfectly build all of my crazy ideas, I must bend to practical circumstances. What is kewl about this design is that almost anybody could build it almost anywhere and expect reasonably good performance. I’ve even considered using something like this on field day by just laying the bottom half of the loop on the ground stretched between a couple of cinder blocks. If I ever get to try that I’ll let you know how it goes– but it should work, and basically just requires a couple of reasonably high vertical points, a tuner, and a spool of wire.

The tuner box and various electrical conduit and outdoor boxes come from home depot. The goal is to keep the weather out and keep the electronics happy. That turns out to be pretty hard to do as the weather is relentless – so I decided not to skimp very much on these parts.

The tuner is an SGC SG-237. Currently I’m running the second of these devices on the antenna. The first one “went deaf” a couple of years ago for unknown reasons. I recently replaced it with an identical model. Testing that and being reminded of the antennas’ performance is what prompted me to finally publish this article.

The tuner goes in a weather proof box that’s large enough to house any additional equipment I might want to post outside on the tree. In addition to the feed line and control wiring I also pushed a cat-5 cable out to the box in case I want to run some POE driven computing gear and other devices. So far, I’ve not done that, but I do have ideas.

A second insulator acting as a strain relief is mounted on the antenna above the tuner box so that the wire doesn’t pull on the box nor the tuner.

In order to keep things serviceable and to provide some safety I installed a couple of boxes at ground level between the sprinkler tubing that goes to the lab and the outdoor electrical conduit that runs up to the tuner box.

One of these boxes acts as a connection point between the control cable from the lab and the control cable coming from the tuner. The other box connects the feed line from the tuner with the feed line from the lab via a lighting arrester: Alpha Delta model TT3G50.

All of these are grounded via an 8 ft ground rod driven at the base of the tree right next to the boxes.

Lately I’m re-thinking the screw terminal strip for the control wires and considering replacing those connections with heat-shrink soldered connections. It turns out that the time between servicing these connections is fairly long and I’d like to have better long-term connectivity than I can expect from screw-down terminals.

When I’m not otherwise using the HF rig I generally run WSPR continuously. Since the tuner refit I’ve been running WSPR at 2 watts on all HF bands with some pretty spectacular results. I can expect to see contact to Australia, Hawaii, Europe, Africa, the Arctic and Antarctic on a daily basis – usually on multiple bands.

The sweet spot for the antenna seems to be 17M but all bands 160 – 10 are usable, and 20-15 are quite good (sun spots permitting). The worst SWR I get is on 80M at about 2:1.

Here is a tweet I posted showing good DX WSPR contacts on 3 bands simultaneously. If you build something like this please do let me know how it works for you.

Complexity

 Poems  No Responses »
May 182021
 

The mathematics of complexity dictate that
the flapping of a butterflys’ wings might lead to
a hurricane on the other side of the world,…
or, they might not. It’s not up to the butterfly
and even if there is a hurricane the butterfly
probably won’t notice; and even for a god
there may be no better way to know the outcome
than letting the computations pay out.

This does not mean that the butterfly is powerless
nor inconsequential.

The Pauli exclusion principle states that
no two particles can occupy the same quantum state.
So, just by its’ very presence the butterfly has forced
countless other particles to be elsewhere; and
by the flapping of its’ wings it has rippled out
countless changes into the universe that
continue to drive change forever forward in
subtle ways.

Even the photons, traveling at the speed of light,
experiencing their beginning and end simultaniously
in the absence of time, don’t know where
they will end up… but every one of them matters.

The universe is a question pondering itself
and we are each a part of the answer.

Flap your wings!

on edge

 Poems  No Responses »
Apr 112020
 

So, this is the edge?
Or, is it the edge?
It’s hard to know.
Like the event horizon of a massive black hole,
it bends a little more steeply at every step;
but never so you would notice.
It’s as if I know I’m being swept away,
but as anything caught in the current,
I feel no movement…
just a persistent screaming in the back of my mind –
an itchy thought –
a superposition of sheer panic, and dead calm.
Like camping on the boundary
between the immovable object
and the irresistible force –
carefully balanced so that time stands still;
with unimaginable energy, poised
just a twitch away from cataclysm.
I stare into the abyss, and perhapse, later,
if not otherwise occupied,
I will sit in the dark and sink slowly into madness.

Magic Words

 Poems  No Responses »
Apr 102020
 

I wish I had the magic words
to bring you safely back (to me)
to feel your touch
to hear your voice
and hold you by my side

I watch your likeness on machines
hear your vibrations in my ears
you’re far away
but oh so close
a sparkle in my mind

I wish I had the magic words
but somehow they won’t come (to me)
still I can feel
your memory
stirring deep inside

Impulses and waves, electricity,
invisible forces, flow in between
I don’t recall imagining
a world unreal as this

Reach out to me from where you are
as I reach out from here (to you)
imagine it’s
my warm embrace
and don’t let it subside

I wish I had the magic words
to bring you safely back (to me)
to feel your touch
to hear your voice
and hold you by my side

Build intellectual equity in your enterprise with SOPs

 Ad-Hoc, Code Dweller  No Responses »
Dec 202019
 

It seemed obvious enough. I mean, I’ve been using these for as long as I can remember, but the other day I used the term SOP and somebody said “what’s that?”

An SOP, or “Standard Operating Procedure” is a collaborative tool I use in my organizations to build intellectual equity. Intellectual equity is what you get when you capture domain knowledge from wetware and make it persistent.

In order to better explain this, and make it more obvious and shareable, I offer you this SOP on SOPs. Enjoy!

This is an SOP about making SOPs.
It describes what an SOP looks like by example.
SOPs are files describing Standard Operating Procedures.
In general, the first thing in an SOP is a description of the SOP
including some text to make it easy to find - kind of like this one.

[ ] Create an SOP

  An SOP is a kind of check list. It should be just detailed enough so 
  that a reasonably competent individual for a given task can use the
  SOP to do the task most efficiently without missing any important
  steps.

  [ ] Store an SOP as a plain text file for use on any platform.
  [ ] Be mindful of security concerns.
    [ ] Try to make SOPs generic without making them obscure.
    [ ] Be sure they are stored and accessed appropriately.
      [ ] Some SOPs may not be appropriate for some groups.
      [ ] Some SOPs might necessarily contain sensitive information.

  [ ] Use square brackets to describe each step.
    [ ] Indent to describe more specific (sub) steps such as below...
      [ ] View thefile from the command line
        [ ] cat theFile

        Note: Sometimes you might want to make a note.
        And, sometimes a step might be an example of what to type or
        some other instruction to manipulate an interface. As long as
        it's clear to the intended reader it's good but keep in mind
        that this is a check list so each instruction should be
        a single step or should be broken down into smaller pieces.

      [ ] When leaving an indented step, skip a line for clarity.
      < > If a step is conditional.
        [ ] use angle brackets and list the condition.

  [ ] Use parentheses (round brackets) to indicate exclusive options.
    Note: Parentheses are reminiscent of radio buttons.

    ( ) You can do this thing or
    ( ) You can do this other thing or
    ( ) You can choose this third thing but only one at this level.

[ ] Use an SOP (best practice)
  [ ] Make a copy of the SOP.
    [ ] Save the copy with a unique name that fits with your workflow
      [ ] Be consistent

  [ ] Mark up the copy as you go through the process.
    [ ] Check off each step as you proceed.
      Note: This helps you (or someone) to know where you are in the
        process if you get interrupted. That never happens right?!

      [ ] Brackets with a space are not done yet.
      [ ] Use a * to mark an unfinished step you are working on.
      [ ] Use an x to mark a step that is completed.
      [ ] Use a - to indicate a step you are intentionaly skipping.
      [ ] Add notes when you do something unexpected.
        < > If skipping a step - why did you skip it.
        < > If doing steps out of order.
        < > If you run into a problem and have to work around it.
        < > If you think the SOP should be changed, why?
        < > If you use different marks explain them at the top.
          [ ] Make a legend for your marks.
          [ ] Collaborate with the team so everybody will understand.

    [ ] Add notes to include any important specific data.
      [ ] User accounts or equipment references.
      [ ] Parameters about this specific case.
      [ ] Basically, any variable that "plugs in" to the process.
      [ ] BE CAUTIOUS of anything that might be secure data.
        [ ] Avoid putting passwords into SOPs.
        [ ] Be sure they are stored and shared appropriately.
          [ ] Some SOPs may require more security than others.
          [ ] Some SOPs may be relevant only to special groups.

[ ] Use SOPs to capture intellectual equity!
  [ ] Use SOPs for onboarding and other training.
  [ ] Update your collection of SOPs over time as you learn.
    [ ] Template/Master SOPs describe how things should be done.
      [ ] Add SOPs when you learn something new.
      [ ] Modify SOPs when you find a better process.
      [ ] Delete SOPs when redundant, useless, or otherwise replaced.

    [ ] Completed SOPs are a great resource.
      [ ] Use them for after action reports.
      [ ] Use them for research.
      [ ] Use them for auditing.
      [ ] Use them to track performance.
      [ ] Use them as training examples.

  [ ] Collaborate with team mates on any changes. M2B!
    [ ] Referring to SOPs is a great way to discuss changes.
    [ ] Referring SOPs keeps teams "on the same page."
    [ ] Referring SOPs helps to develop a common language.
    [ ] Create SOPs as a planning tool - then work the plan.

  [ ] Keep SOPs accessible in some central place.
    [ ] GIT is a great way to keep, share, and maintain SOPs.
    [ ] An easily searchable repository is great (like GitTea?!)
      [ ] Be mindful of security concerns.

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