Say Goodnight, Gracie…
Yep, that headline is what my intention was about 3 days ago. I was simply going to throw in the towel on the K5WLF Tech Blog. I'm sick and tired of dealing with a flood of crap comments written by complete idiots or by computer scripts written by complete idiots, every time I publish a new post. I was just going to quit trying to help out the newbies at all and give myself a break.
However, a fellow blogging friend of mine told me about a Captcha plug-in for WordPress, so if I can get it to work and it keeps out the spam bastards, I'll keep on trying to share what I know about the technical side of amateur radio.
I'm really hoping the Captcha (stupid name, aint' it?) thing works, because I really enjoy doing the research and writing the pieces about the various tech subjects that I discuss here. There's at least one more installment of the grounding topic left to do, but if the Captcha plug-in doesn't work, it'll never be written. Did I ever mention that I support the death penalty for spammers and all others of that ilk? It may seem a little harsh to some of you, but I don't really care.
Well, let's give it a shot and see if the plug-in actually works. If it doesn't, the idiots will have a week to mess up my inbox, because I'm headed out of town to direct a video. I'll clean it all up and either get started on the next grounding installment or take the thing down entirely when I get back.
73,
ldb
K5WLF
It’s been awhile…
For a blog that I was going to try and update every two weeks, it's been a really long time. Many things have conspired to keep me from posting and, as you've undoubtedly noticed, they've been successful. I was out of the country for about three weeks, but that doesn't account for the other five-and-a half months without a post.
I checked the stats for this Tech Blog and, while there were some visits, it didn't get as many hits as I'd expected or hoped. So, it's up to y'all. If you'd like to see this tech blog continue, let me know. If I get a pile of folks who want it, I'll keep doing it. If not, we'll just let it die by the side of a boreen somewhere in Co. Donegal.
73,
ldb
K5WLF
Antenna System Grounding — Part 2…
In our last post, we discussed what lightning is, how it forms, and the basic design requirements for a low-impedance grounding system. In this installment, we'll learn what to do and how to do it when it comes to the 'hands-on' stages of actually building the grounding system.
Each leg of a tower should be grounded to an 8' ground rod with a minimum of #2 AWG solid copper wire. There are some folks who specify #6 wire, but I prefer to use the larger conductor. We're dealing with the possibility of a lot of current and I want to give it the best path to ground that I can. If you can afford larger wire, go for it. I've seen installations with 2/0 welding cable. Now, that's a ground conductor!
Then connect the ground rods, which should be at least 3' or so from the tower base with a ground ring of at least #2 solid copper. Ideally, you'll want to take a radial field out from the ring. It's an absolute must if the tower is a radiating element. Some folks say that you should have ground rods connected the full length of each radial, two ground rod lengths apart. It certainly can't hurt, but I hope you've hit the Lotto before you head off to your local hardware store to get the rods.
You can also take advantage of the metal -- re-bar, brackets, plates, etc. -- inside your tower's concrete base and utilize a "Ufer" ground. Just connect all the internal metal together and tie it to the ground rod system as well.
Be sure to connect all the metallic guy lines together and ground them at the anchor points. This is very effective because it diverts the lightning away from the tower and therefore from your antenna feedlines. Although we love our self-supporting towers because they take up less real estate, guyed towers are really better when it comes to grounding against lightning.
If you're using a crank-up tower or a push-up pole, jumper the joints with copper strap or a wide braided conductor. The copper strap is better because the braid tends to break down where the little wires cross each other. Also, remember to use an anti-oxidant on bolted tower joints.
OK, now we have the tower grounded. In the next installment, we discuss how to get the feedlines into the shack without taking the lightning with it.
73,
ldb
K5WLF
Antenna System Grounding — Part 1…
Well, we got a bit off the two-week posting schedule I was hoping for, but I think you'll find some useful information in this somewhat tardy post. I gave a presentation on antenna system grounding for the monthly meeting of our local club, the Tarleton Area Amateur Radio Club, last Tuesday and decided to divide it into multiple sections and post it here on the Tech Blog.
Lightning is a vital force of Mother Nature. It's great to watch, has wonderful sound effects, helps to fertilize the ground, and makes for some very striking, if you'll pardon the expression, pictures. However, we certainly don't want it in our shack, running through our radios or, even worse, our bodies. This series of posts will discuss how to keep lightning out of the shack where it belongs. In this first post we'll talk about how lightning is formed, the design goals of a grounding system, and a few of the technical details of lightning protection.
Lightning is created when a warm air mass collides with a cold air mass with resultant upsurging convection air currents. Friction between these air masses creates static electricity in the cloud formations. These charges stratify with a negative charge at the bottom of the cloud and positive at the top. The low negative charge layer creates a positive charge in the ground below it -- like the opposing plates of a capacitor. When the charge between the cloud and the ground exceeds the dielectric resistance of the air, an arc flashes between the two to neutralize the charges. That arc is lightning. Lightning can also occur from cloud to cloud. This form of lightning is also dangerous and damaging since it results in a current being induced in the ground below the discharge. This charge can couple inductively into antenna feedlines, power lines, telephone lines, etc. The static charges in volcanic ash clouds and the smoke and dust from wildfires can also cause lightning.
Commercial broadcast and telecommunications sites, with their tall towers -- which in the case of AM broadcasting are also the radiating element -- take direct lightning hits regularly and never miss a second of on-air time. Of course, they sometimes spend as much on the grounding system as they do on the building and transmitter combined. As hams, we probably can't afford to spend that much money, but we can use the same engineering principles and achieve excellent protection for our shacks and equipment.
Lightning wants to go to ground. We are going to help it achieve its goal, by the shortest possible path that does not include our shack or our radio equipment. Our design goals for our grounding system are:
- No shock or over-voltage hazards
- No fires due to overheating from excessive current or arcing from voltage
- Reliable equipment operation
We accomplish these goals by creating a low impedance path to ground for the lightning. Why, you may be asking, do we need a low impedance path? That's a very good question and before we answer it, let's take a quick look at the difference between resistance and impedance.
Resistance is opposition to current flow in a DC (direct current) circuit. Alternating current (AC) circuits are also affected by reactive components that react to change over time -- inductors and capacitors. The opposition provided by these components is called "reactance" and its symbol is "X". Inductive reactance is denoted by "XsubL" and capacitive reactance by "XsubC". Impedance measures the combined effects of resistance and reactance. All three parameters are measured in ohms.
Although it's natural to think of lightning as a DC current, it is really a series of diminishing electrical pulses. A lightning strike has a typical rise time of 2 microseconds (2μs) and a fall, or decay, time of 10 to 40μs. These fast rise and fall times make lightning act like RF, so we must create a low impedance path for it to follow to ground. Otherwise, it will simply jump off our chosen conductor and go where it wants.
There is an average of three pulses per lighting strike with an average current of 18,000 amperes (18 kA) for the first pulse. Ten percent of strikes are 60 kA and one percent equal 120 kA. The largest lightning event ever recorded was greater than 400 kA. This is the energy that we're trying to keep out of our shack and our equipment. We'll begin learning some of the techniques to accomplish that in the next post.
73,
ldb
K5WLF
Electricity 101 — Ohm’s Law…
This article originally appeared in the February 2005 issue of Energy Self Sufficiency Newsletter. I’ve made a few changes from the original article to fit the target audience of this blog. When it first appeared in ESSN, it was intended for folks who are attempting to live off-grid, to be electrically self-sufficient. I’ve re-written portions of it to reflect the needs of my current amateur radio audience. My thanks to my co-author, Steve Spence, for his input on the original article. ldb
====================================================================
I’ve talked to quite a few new Technician class hams recently who have lamented the fact that their technical knowledge is not what they feel it should be. I believe that this is due, in large part, to the fact that the Technician class license test has been stripped of the majority of the technical content that it used to contain. There are opposing opinions on the wisdom of this fact, and I will not debate those issues in this blog. (I may, however, debate them in my other blog, The K5WLF Blog) Rather, we will deal with the result (a technically deficient group of Technician class licensees – ironic, eh?), and provide a sound footing in the technical subjects that formerly were included in the Technician class license test.
It’s possible to have an enjoyable career in amateur radio with minimal technical knowledge, but to fully enjoy your new avocation, a solid grounding (no pun intended) in the basics of electricity is essential. You don’t need to be an electrical engineer, but there are some things that you absolutely must know. In this post, and the ones to follow, we’ll teach you those things. By the way, even if you’re not a ham, you’re still welcome to join us and learn with us.
What is electricity? Very simply, it’s the flow of electrons (those little things that orbit the nucleus of an atom) from one place to another. Preferably under control. Lightning is electricity. But not in a form mere humans can control.
Conventional electrical theory says that electricity flows from “positive” to “negative.” That’s not strictly true. Electrons carry a negative charge and actually travel from an area or object with a surplus or excess of them (a negatively charged area), to an area or object that has fewer (a positively charged area). So, the actual flow is from negative to positive – but we’re going to stick with conventional ‘positive to negative’ theory for this series of articles. Ben Franklin started it, and that’s good enough for me.
Let’s talk for a few minutes about the minimal amount of math we’ll need to understand in order to plan and install our renewable energy system. It’s quite painless, really.
There are four essential parameters that we use to measure what’s happening in an electrical circuit or path. They are: voltage, which is measured in volts, and represents the pressure or intensity of the flow of electrons; current, measured in amperes or amps, is the amount or volume of the flow; power, measured in watts, is the product of the voltage and the current and is the total amount of energy flowing through the circuit at a given time and; resistance, which is measured in ohms and is exactly what its name implies, a restriction or resistance to the flow of electrons in the circuit.
We’ll also discuss a couple other terms which you’ll run across in your ham radio career, but once we cover the four essentials above, you’ll be able to see just how they fit in and why we need them. So, let’s get to the basics.
The behavior of voltage, current, resistance and power are described by, and calculated with, a series of formulae known as Ohm’s Law. It’s named in recognition of Georg Simon Ohm, who discovered the relationship between them.
In the formulae of Ohm’s Law, voltage is signified by “E”, current by “I”, resistance by “R” and power by “P”. Here’s how they work with each other. We’ll use “*” to denote multiplication, like the computer folks do and “/” to show division.
The basic formula is E = I * R, meaning that voltage (E) can be calculated by multiplying the current (I) flowing in a circuit by the resistance (R) that’s in the circuit path. As an example, if there are 2 amperes of current (I) measured in a circuit with a 6 ohm resistor (R), the circuit voltage is 12 volts (E).
We all learned how to transpose terms in first year algebra, so let’s have a short flashback to high school and derive the rest of the equations that we’ll need to completely understand Ohm’s Law. Transposition of terms in an equation isn’t difficult, so don’t shy away from it. In this case, it merely involves dividing both sides of the equation by the same term, to isolate the term we’re solving for. Didn’t think you were going to get an algebra refresher in this article, did you? Let’s get to it.
First, we’ll transpose the terms so that we can solve the equation for current. That’s “I”, remember?
Here’s how we do it. Starting with our original formula:
E = I * R
Dividing both sides by “R” yields:
E / R = (I * R) / R
which equates to:
E / R = I
and reversing the terms to fit the standard format leaves us with:
I = E / R
Let’s see if it works in our example circuit. We’ve already said that we have 12 volts flowing in a circuit which contains 6 ohms of resistance. So, it checks out. Twelve volts divided by six ohms equals two amperes of current flowing in the circuit. That didn’t hurt, so let’s solve for resistance. Again, starting with our original formula:
E = I * R
Dividing both sides by “I” yields:
E / I = (I * R) /I
equating to:
E / I = R
and, again, reversing the terms to put the unknown to the left, we have:
R = E / I
Testing once again, in our 12 volt circuit that’s flowing 2 amperes, we divide 12 by 2 and, sure enough, we verify that our resistor is, in fact, six ohms.
That’s about enough for our first lesson. In our next post, we’ll show you a useful application for all this knowledge. See you soon.
73,
ldb
K5WLF
Welcome to my new blog…
Welcome to the first post of the K5WLF Tech Blog. Unlike my other blog, The K5WLF Blog, wherein I ramble and discuss anything from computers to ham radio to film directing to ??, we're going to stay focused here and just discuss technical issues. In the course of those discussions, we'll talk about the tech stuff and we'll discuss some of the history of electricity and electronics. We'll also take a look at some of the pioneers who made it possible for us to have the technology we have today. Folks like Faraday, Ampere, Volta, Tesla, Edison, Westinghouse, DeForest, Marconi and so many more. I've created a special category called "The Great Ones" that you'll see whenever there's a post about one of them.
I decided to undertake this blog after having quite a few new Technician class licensees tell me that they felt did not have a solid understanding of the technical foundation of our hobby. I'm happy to say that none of those new hams were from a class that I taught.
There are, I believe, two main causes for this lack of technical understanding among newly licensed Technician class hams. One cause is that, over the years, the technical content of the exams has lessened and been replaced by more questions about rules and regulations. The technical questions that remain are simply not as rigorous as they used to be. The second cause is the recent proliferation of one-day classes for the Technician license that only teach the student to "pass the test". These classes are usually touted as a way to get folks involved in Emergency Communications, or EmComm. A very worthy endeavor and one that I am personally heavily involved in. Unfortunately, the student has not learned proper communications practice or any technical background, and will probably never get on the air until there's an emergency. At that time, with no idea of how to communicate properly and lacking the technical knowledge to keep their radio on the air under adverse conditions, they will be virtually useless to the EmComm effort. And, sadly, in spite of their best intentions.
It is not the new ham's fault. The responsibility lies with those who administered the test, but neglected to teach the new licensee what being a ham radio operator is all about. Not just the tech part, but the on-the-air part as well. It's difficult to teach proper on-air procedures over the Internet, but we might, at some time in the future discuss a few things about on-air ops. It's easy, however, to teach technical subjects on the Net and that's really what this blog is here for.
If you're a new licensee and want to improve your technical knowledge over what you were taught in a one-day class or what you learned from self-study, or if you've been licensed for a while and would like to get a bit more deeply involved in the tech aspects of our hobby, this blog is for you. If you're not a ham, but just interested in electricity and electronics, this blog is for you also -- and we can help you become a ham if you decide to join us.
Amateur radio is, by definition, a technical hobby and there's really no reason for a ham to be lacking a certain amount of technical knowledge. No one expects you to be able to design a transceiver from scratch, but all hams should be conversant in the basic technical aspects of our hobby.
And that is the purpose of this blog. We'll start with what I call Electricity 101, right at the beginning, and proceed from there. I don't know where we'll stop; a lot of that depends on you, the readers. I'm counting on y'all to let me know what you'd like to talk about. You'll need to register on the blog to post comments. If you're a ham, please register with your call sign as your user name, just to help me keep a count of how many hams we have on the list.
I'm planning on posting a new entry at a maximum of two-week intervals. We'll have an RSS feed set up before long, so that you'll be able to keep up to what's going on here automagically via your RSS reader. Thanks for being here and we'll see you soon with our first lesson.
73,
ldb
K5WLF