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[Articles Home]  [Add Article]  

SWR Meters Make You Stupid

Eric P. Nichols (KL7AJ) on March 10, 2010
View comments about this article!

SWR Meters Make You Stupid

Or

Ladder Line to Eternity

It may have already occurred to you that it might be desirable to locate your amateur radio antenna at some distance from your transmitter and/or receiver. In fact, unless you intend to operate your station from the top of a tree or a tower, it is very likely that you will be employing some form of transmission line. The purpose of a transmission line is to convey radio frequency energy from a radio set to an antenna, or vice versa, in as painless a fashion as possible. You can think of a transmission line as an extension cord for R.F. In fact, for the lower regions of the radio frequency spectrum, actual extension cord can serve reasonably well, for reasonable distances.

Like so many other facets of Amateur Radio, the transmission line seems to have taken on a life of its own, accumulating a vast, sticky, woolly hairball of misinformation along the way. This is all so unnecessary. A transmission line is a means to an end, never an end in itself. And don't let anyone tell you otherwise.

A Bit of History

In the early years of radio, there wasn't much of a line of demarcation between a transmission line and an antenna. In fact, let's look at a very typical amateur radio antenna of days past. It consisted of an array of parallel wires, or “flat-top” arranged much like a clothes line, and a SINGLE WIRE leading from the flat top to the transmitter. This single wire “transmission line” typically radiated as much signal as the flat-top antenna itself, which wasn't necessarily a bad thing. Anything you could hang out there in space that radiated a signal was a help.

Countless hundreds of thousands of long-distance radio contacts were made with such contraptions.

If it Ain't Broke, Fix it Anyway

Despite the unquestioned effectiveness of such an arrangement for much of amateur radio's history, for some mysterious reason, sometime around the end of the First War to End All Wars, it was decided that life shouldn't be so simple. This bizarre concept of “specialization” began to infiltrate life on Planet Earth. The specialization Nazis decided that an antenna should radiate and a transmission line should not. It was discovered that a single wire transmission line could be made to not radiate by placing another single wire transmission line next to it, and grounding it at the “bottom” end—the end nearest the transmitter. Add twice the copper to disable half the antenna...such a deal! Sounds like a government project, doesn't it?

Well, this is one concept that, alas, couldn't be blamed on the government. It was actual radio amateurs who came up with this “idea.” The end product of this was what was called the “Zepp” antenna, because it was used on Zeppelins.

Actually, we shouldn't be too harsh. The whole idea of a non-radiating transmission line was to somewhat remove one source of high voltage R.F. from the immediate vicinity of a gasbag the size of Milwaukee filled with hydrogen. For some peculiar reason, certain white-smocked hand-wringers were a bit nervous about sources of high voltage R.F. being right next to a gasbag the size of Milwaukee filled with hydrogen. Since the onboard radios at the time were spark gap transmitters, it probably wasn't too bad an idea to keep this fact under consideration, after all. We still ended up with the Hindenburg disaster, but at least it wasn't caused by the radio on board! (At least as far as we know).

After hams resumed their post-war operations, and had better things to do with their skills than preventing dirigibles from bursting into flames, they discovered that the Zepp antenna actually worked fairly well on the ground, as well. (Well, actually a few feet OFF the ground, but you see our point).

Now, in order to keep the two halves of the Zepp transmission line fairly parallel, under which condition they did the least amount of radiating, the two wires were held together (or apart) with uniformly spaced insulators, giving the transmission line a somewhat ladder-like appearance. Oddly enough, it came to be called ladder line. Of course, once again, they couldn't leave well enough alone. Some genius somewhere imagined that the TOP end of the second wire of the ladder line should actually go somewhere. In the conventional Zepp configuration, it didn't. It just ended. This bothered some people. The fact that it actually worked was immaterial. Some people just hate things like lopsided antennas and the number Pi, no matter how well they work. So, once again, they decided to try to fix something that wasn't all that broken.

After a lot of pondering about exactly WHAT the free end of the ladder line should go to, one of the aforementioned someones decided that if that went to an antenna wire as well, things might be more symmetrical.

And so was born the `Double Zepp” antenna, actually two Zepp antennas fed end to end with just one transmission line. The symmetry gods were pleased. And to be honest, the antenna actually worked slightly better than the single-sided Zepp...it had a slight amount of actual gain over the original incarnation. But, perhaps more significantly, the function of the antenna and the transmission line were now two entirely separate entities. Everything was wonderful.

Actually, not. Our troubles had just begun.

Don't Try This at Home

With a few very rare exceptions, the early impoverished radio amateur usually had little if anything that resembled actual test equipment. In fact, most of the diagnostic equipment that modern hams take for granted was not available at any price for much of amateur radio's existence. This was actually a good thing, for a few reasons:

  1. Amateur radio station performance was based strictly on...well...performance. The only indication that things were working as they should was the fact that one was making a lot of contacts. The lack of test equipment kept the end goal well in sight.

  2. Ham radio was cheaper. Why use an expensive plate current meter when you could check your transmitter's tuning by seeing how long an R.F. arc you could draw from the final tube's plate cap to the tip of a lead pencil held in your bare hand? YES! Hams actually DID this...and most lived to tell about it. Cabinet? What cabinet?

  3. You were likely to make a useful accidental discovery from time to time. Theory is great...up to a point. It helps explain what you already discovered by accident, but it doesn't often lead to new discoveries, at least on its own. You need to get knocked on your keister a few times and singe a few eyebrows to really understand radio. (Don't tell OSHA I said this, by the way).

The salient point is that having a lot of “tools” around usually gives you more information than you need to know, and unless you know how to USE that information, it can be worse than ignorance, as we shall shortly see.

Sometime between the two wars to end all wars, radio amateurs discovered that you could make a transmission line radiate almost NOTHING if you kept the currents in each leg of the ladder precisely equal in magnitude, and OUT OF PHASE. This allowed the antenna to behave more like a pure antenna, and the transmission line to behave like a pure transmission line. The original Zepp was a half-step in this direction, but the double Zepp really completed the task. Hams started worrying about transmission line current balance a lot...whether they could afford to or not. If you were really cheap and/or poor, the instrument of choice was a pair of incandescent lamps, one in each leg of the ladder line. If you were really high-falutin' you had an actual R.F. ammeter in each leg. (You can see these instruments in a lot of ancient ham station photos; they were about the size of modern watt-hour meters). If the currents were equal in each leg, it meant your antenna was doing most of the radiating, and the transmission line wasn't, which was generally a good thing. With but one small rub.

The antenna current meters, whether they were just a couple of light bulbs or high-falutin' R.F. ammeters, told you nothing about the relative phase between the two legs. However, it was generally assumed that if your double Zepp antenna was PHYSICALLY symmetrical, and your ladder line was relatively perpendicular to said double Zepp, the current phases WOULD be, indeed, equal and opposite. So, though not really scientifically rigorous, the R.F. ammeter pairs turned out to be quite useful. At the very least, tuning for MAXIMUM R.F. current always resulted in the strongest radiated signal. In the case of light bulbs, you just tuned for maximum brightness, and all was right in the world. For a while, at least.

However, hams being who they were, weren't content unless they had something new to worry about. At this point, we need to take a small departure, and introduce yet another Dead Ham, an obscure German electrical engineer by the name of Ernst Lecher. He lived at the turn of the century...the 20th century, that is. His work had already, for the most part, been learned and forgotten by much of the radio world by mid century. Alas, poor Ernst did much of his great work before anyone had a use for radio. He was well ahead of his time. Unfortunately, if you look up Ernst Lecher on the Internet, you will be inundated with all sorts of really bizarre “information” about things like psychic energy and even dousing rods, for Pete's sake!

Let me set the record straight on behalf of poor Ernst, who is undoubtedly spinning in his grave and unable to defend himself against his brainless “disciples” and various other tin-foil-hat groupies. Ernst Lecher had ABSOLUTELY NOTHING to do with metaphysics, dousing rods, psychic energy, or any other kind of New Age wacko pseudo-science. He was a REAL scientist, a REAL engineer, and achieved REAL results in a REAL laboratory. I pronounce a festering POX upon all those who desecrate his name with such unmitigated balderdash and buffalo snot.

Let's look, instead, at his REAL contribution to radio knowledge, the Lecher Line, (also known as the Lecher Wire).

A Lecher line is a fabulously simple and revealing instrument. It allows you to measure wavelength of a radio signal directly...the first instrument in existence to allow one to do so. It consists of nothing more than a pair of parallel wires or copper rods, a couple of wavelengths long or so, at the frequency of interest, with a yardstick or (or meter stick) placed along the line. You also have a moveable voltage detector so you can measure R.F. voltage at any location along the line. (I built a really snazzy Lecher Line for my electronics class that always generates lots of ooohs and ahhs from my rapt students).

You feed a small amount of R.F. into one end of the line, which sets up STANDING WAVES along the line. As you slide the R.F. voltage indicator along the line, the voltage will swing between some maximum voltage and zero each half wavelength. You simply measure the distance between the zero voltage points and voila, you have precisely half a wavelength. Well, almost precisely, since there's a small delay time of a wave propagating through a Lecher Line as compared to free space...that is, the VELOCITY FACTOR through a transmission line is slightly less than that of free space. Just a couple of percent additional delay for a typical set of lines with about 3” spacing between rods. (You can also measure the distance between MAXIMUM voltage points, but these are much less defined, whereas a ZERO or NULL is extremely sharp).

At any rate, it's a very sensitive and accurate instrument...in fact, until the 1950s the Lecher Wire was the most accurate means of measuring UHF signals known. Frequency counters didn't exist.

The Lecher Line also serves as an extremely high Q (selective) circuit in UHF amplifiers and filters. Variations of the Lecher Line (loaded Lecher Lines) have also been used that are a bit smaller than the full sized version. Most high power FM broadcast transmitters still use some variation of the loaded Lecher Line in the plate tuning circuit.

In addition, devices such as the shorted stub tuner, nearly universal in the microwave industry, are based on the Lecher Line. In fact, as any microwave engineer can tell you, ANY impedance can be matched to ANY OTHER impedance using just two stub tuners. All because of Ernst Lecher and his fabulous trained STANDING WAVES.

So simple, so educational, so elegant, and so incredibly useful. And yet, sadly, one more source of posthumous Ernst angst.

For, in recent years, STANDING WAVES have come to be viewed as something to be avoided like the Ebola virus. This, more than any other misconception, has resulted in the single greatest source of Amateur Radio Stupidity Exchange (ARSE). For some inexplicable reason that will probably never be known, presumably sentient, rational beings become the village idiots of the Petri dish when the term STANDING WAVE is uttered, wringing their collective hands, palpitating in unison and hyperventilating in horror.

The fact of the matter is that about 95% of what makes radio work at all is the application of STANDING WAVES of some sort. Standing Waves are like water. Just because some Cro-Magnon manages to drown himself in a bathtub is no reason the rest of us need to live on a diet of dry sand. Amateur Radio NEEDS standings waves to survive!

Now, there may be a few readers who have never encountered the term standing wave ratio, or SWR. If you happen to be one of these individuals, consider yourself most blessed, indeed. You will not have to “unlearn” anything. You are a blank slate, unencumbered by countless man-centuries of accumulated collective ignorance pertinent to the subject.

Are you ready?

Great! Let's get started.

One of the best habits you can get into as a new radio amateur is the habit of MEASURING everything. You NEVER want to take anyone's word for anything when it comes to amateur radio electronics, (or any other subject, for that matter), even from an infallible reliable source (or even me!) This one habit alone, if followed religiously, would eliminate 99% of ARSE, as defined above. The fact of the matter is that actually doing experiments takes a bit of work...repeating ignorance takes none whatsoever. Well, maybe flapping your gums uses a calorie or two, but that's about it.

Here's another great principle, right from the physics lab: If you want to know what's happening, follow the heat.

What's this mean? Quite simple, actually, but it does have some subtle implications. When you generate a certain amount of radio frequency energy, it can only go to two places. It can be radiated into space. Or it can make something hot. There are no other options.

We'll see why this is crucially important as we move along.

No End in Sight

Let's take a look at a transmission line that's infinitely long...our Ladder Line to Eternity. At the far end of the ladder line, let's put a 100 watt light bulb. (Granted, it may take you a while to stroll out there and attach the light bulb, and then stroll back to complete the experiment, but bear with us for a moment).

Now, let's connect a 100 watt radio transmitter to the input end of our infinite transmission line. Let's turn on the radio transmitter for precisely one second, and then turn it off. Now, let's go make some coffee, and while it's perking away, or dripping away, or reheating in the microwave, we'll rummage around in our closet and find an old pair of binoculars. We grab our coffee and sit down on the lawn and train our binoculars toward the end or our infinite length transmission line. (It might be advantageous to do this experiment at night, as you can imagine). Actually, it will take an infinite amount of time for the one-second R.F. burst to get to the light bulb, and ANOTHER infinite period of time to see the results of the light bulb.

Most likely, this experiment will fail, unless you live to a REALLY REALLY REALLY ripe old age. But that's okay; even failed experiments are educational.

Let's modify our experiment a little, so as to be a bit more likely to succeed. Let's use a transmission line that's only one light minute long. That will be a mere 11.16 million miles long, plus some spare change, a MUCH more manageable figure.

Again, let's turn our transmitter on for one second, and then turn it off. We'll now train our binoculars on the light bulb a mere 11.16 million miles away. After TWO minutes, we'll see the light bulb turn on, for exactly one second. (Again, keeping in mind it takes a minute for the light from the bulb to get back to your eyeball).

Now, isn't that amazing?

At the risk of unduly complicating matters, we'll add a few minor details. One should know that a conventional incandescent light bulb is horribly inefficient. If you're lucky, about 2-1/2% of the energy is actually converted into light; the remaining 97.5% is, you guessed it, HEAT. It also has a resistance that changes dramatically with the power applied, which becomes more relevant when we use light bulbs for actual R.F. indicators. But we have a long ways to go in our lesson before those factors become significant.

The important point to glean from this is that ALL the energy we sent down the transmission line, (100 watt-seconds in this case, to be precise) is dissipated, that is, never to be heard from again. It is LOST energy. Radio energy radiated from an antenna is also LOST energy. Of course, it might be a little philosophically weird to call the energy radiated from an antenna “lost” because that is the whole purpose of the thing in the first place. But we can never call that energy back, which is the important point.

Now, if you've been really paying attention, you may have thought to yourself, “What about that 59 second interval before the energy reaches the light bulb? How can we even define POWER or ENERGY? Don't you need some sort of LOAD? Until the burst gets to the light bulb, there IS no load! Aren't we violating Ohm's Law...or something?”

All excellent questions. And they are central to the discussion.

This is where we encounter a mysterious entity known as “Characteristic Impedance.” Characteristic impedance can be thought of as an EQUIVALENT RESISTANCE at the input end of an infinitely long transmission line. Its value is independent of the length of the line. It is a function of the spacing between the conductors, and the diameter of the conductors. There's a formula that's not too complicated, but you don't need to memorize it. You just need to know that the characteristic impedance is LOW for closely spaced, fat conductors, and HIGH for widely spaced, thin conductors. For typical commercial-grade ladder line, it's about 450 ohms. In days of yore, homebrew ladder line generally ran at around 600 ohms.

Now, this is where we get to the good stuff.

As far as your transmitter is concerned, characteristic impedance of an infinite line appears as a REAL resistance. You can calculate power generated just as if the input terminals of the transmission line were a REAL flesh-and-blood (or at least, CARBON) resistor.

And furthermore... until the transmitted signal REACHES the far end of the transmission line AND back (we'll talk about reflected waves shortly) the input impedance is also equal to the characteristic impedance of the transmission line. In other words, the impedance a transmitter sees for a BURST is always equal to the Characteristic Impedance, no matter WHAT happens to be dangling at the far end of the line. (We will see that for STEADY STATE radio signals the situation can be very different). We could also say that AT THE INSTANT of launch, we can use the characteristic impedance to calculate power and energy of any transmitted signal, using voltage and current, just as if it were an actual physical resistance.

So now, if we were to REMOVE the light bulb from the far end of the transmission line, and repeat the experiment, it wouldn't make a hill of beans worth of difference as far as our transmitter is concerned...at least for two minutes...after which time it wouldn't matter anyway, since by that time our transmitter has been long shut down! Our transmitter has no way of knowing (or caring) what's at the far end of the transmission line, under instantaneous (short burst) conditions.

I think you'll agree that the description of a burst's behavior in a transmission line is pretty trivial...hardly worth elaborating.

Where things get interesting (and more complicated) though, is when we have FORWARD and REFLECTED waves occurring simultaneously. But take heart...we don't have to deal with that quite yet.

Let's return to our missing light bulb configuration. What DOES happen to that 100 watt-second burst when it encounters a “bridge out” condition?

Interestingly enough, the R.F. energy doesn't just blorp out of the end of the transmission line into space. If it COULD do this, there wouldn't be much point in an antenna in the first place. In fact, if you could invent a transmission line that could efficiently blorp R.F. off into space, you'd be a very rich person.

Instead, what happens is that the R.F. burst gets TOTALLY REFLECTED back toward the source. That energy has to go somewhere, and if it's not converted into heat or radiated into space as a radio signal, it has to find someplace where it CAN do either one or the other.

Well, to be perfectly honest, it DOES have one other option. It can keep bouncing around forever. We'll talk about that option a bit later.

But first, let's modify our test setup once more. Let's leave the far end of the transmission line flapping in the breeze. (Hmmm...I guess at 11.16 million miles out in space, there probably isn't much of a breeze). Anyway...we have an UNTERMINATED transmission line out yonder.

At the NEAR end we'll connect a double throw switch, so we can conveniently connect either a transmitter or a light bulb to the transmission line.

Now, we'll throw the switch to the transmitter side and send a one second burst. Next, we'll shut off the transmitter and throw the switch to the light bulb side, and wait a couple of minutes. (Actually one minute and 59 seconds).

Voila! At the appointed time, the light bulb shines for one second. Aren't we amazed? What have we learned?

Well, a couple of things, at least. Number one is that REFLECTED energy is REAL energy. We were able to light our light bulb with the energy that was reflected from the far end of the un-terminated transmission line.

The second thing we learned is that that transmission line is 11.16 million miles long. Well, we already knew then when we strung the thing out there, didn't we? But, in case we didn't, we could have determined its length by carefully measuring the round trip time, knowing that electrical currents travel through a transmission line at about 186,000 miles a second, plus some loose change.

In fact, telecommunications people actually use this method in the real world for locating discontinuities in otherwise inaccessible transmission lines. This method is called TDR for “Time Domain Reflectivity” measurement. As you might suspect, in the real world, we don't usually have 11.16 million-mile-long transmission lines. Actual TDR tests use much shorter bursts...generally in the order of nanoseconds...which will allow you to measure transmission lines that are mere hundreds of feet long. As long as your outgoing burst quits before your reflected burst comes back, you can do TDR tests. (You also don't generally use light bulbs for TDR detectors, but rather oscilloscopes).

Now, let's talk a bit about the discontinuities mentioned in the previous paragraph. You don't need totally open (or shorted) transmission line to give you a reflected energy burst. It's just that under these two conditions you get TOTAL reflected energy. (You also get total reflected energy if the termination is a pure reactance...either a perfect capacitor or inductor...but we'll address that later).

At any rate, a discontinuity is any sudden change in the characteristic impedance of the transmission line, such as a point where the lines are squished closer together or stretched apart. (A sudden right-angle bend will also cause a small discontinuity). A burst of R.F. will be partially reflected from any discontinuity in a transmission line. Part of it will be returned to sender; part of it will be passed along to the termination. Very gradual changes in characteristic impedance will NOT cause a discontinuity. In fact, “tapered” transmission lines can be used as smooth impedance matching devices. Such things as the slant wire feed and the delta match, both variations of the tapered transmission line, were universally used in the broadcast industry and amateur radio for much of their early history. (There's an ancient local A.M. broadcast station in Fairbanks that until just a couple of years ago used a slant-wire-fed grounded tower! I had the dubious honor of working on the thing at one time.)

Anyway...where were we? Oh yes...discontinuities and partial reflections. We need to set the record straight right here and say that these are NOT inherently bad things! We can USE reflections on a transmission line to do all kinds of useful and wonderful things. We can't just IGNORE them, but we don't need to wring our hands over them, either! Things are generally SIMPLER when there no reflections to contend with; but this by no means suggests that a MATCHED transmission line system is necessarily any better than an unmatched one. We'll talk a bit about the CONJUGATE MATCH before too long. As a prelude to this, however, let's modify our experiment one more time.

Let's remove the light bulb from the double-throw switch, and connect a shorting bar to those terminals, instead. Switch the switch to the transmit side. Send a one-second burst, turn off the transmitter, and then throw the switch to the other side. What happens when the pulse returns from the distant land and encounters the shorting bar? Why, it gets TOTALLY REFLECTED back out to the far end again! In fact, it will keep bouncing back and forth between the two ends of the transmission line forever. Actually, we could REMOVE the shorting bar and get the same result...an OPEN transmission line is just as reflective as a SHORTED one. As long as there is NO RESISTANCE in the termination, the reflection is total.

Now, we hope you have understood that all the previous discussion assumes an IDEAL transmission line. We always have to study IDEAL components in order understand the real-world editions thereof. Actual, practical transmission lines have resistive losses in them, which complicates the matter a little bit. In reality, an R.F. burst would never even make it to the far end of an 11.16 million mile transmission line. (Well, actually, it WOULD, but it would be less than the cosmic noise in the wire by the time it got there!) In reality, H.F. radio signals start running into trouble after a couple of miles, even in the best transmission lines humanly makeable. (I understand someone was able to make Ethernet work over a mile of rusty barbed wire, but this is NOT recommended practice!)

Now for the FUN Part

Hopefully you've been able to follow, and actually ENJOY some of this transmission line stuff, because we're just about ready to get to the real meat.

We've intentionally separated our FORWARD and REFLECTED signals for all the previous discussion. This is easy to do with short bursts, for (hopefully) quite obvious reasons.

However, amateur radio transmissions do NOT consist of such short bursts of R.F. (relative to the length of the transmission line, that is. A CW “dit” is MUCH less than a second long...but typical ham radio transmission lines are MUCH less than 11.16 million miles long, as well!) In typical communications service (as opposed to RADAR), any reflected signal on a transmission line is almost assuredly going to coincide with, or overlap, the outgoing signal. This opens up ENTIRELY new phenomena...as well as potential for confusion.

Whenever two electrical signals overlap each other in a conductor, you have the potential for interference to occur. If you remember from our chapter on antenna fundamentals, interference can be either constructive or destructive. Interference can occur in wires, just as it can in free space, with much the same results.

Allow me to introduce one more term that will help tie all this together: the Superposition Theorem.

Now, the Superposition Theorem is one of those physical truisms that seem so obvious it shouldn't even need mentioning, but it has profound implications. Stated simply, it's this:

At any point in time, any given location on a wire must have one and only one voltage.

Seems pretty obvious, doesn't it? Or to state it even more stupidly: You can't have two voltages in one place at the same time.

How does this truth affect life on Earth as we know it?

If we have two waves traveling on a wire...one going East and one going West...at ANY point on the wire, the waves MUST add or MUST subtract. There are no other options.

Now, whether they ADD or SUBTRACT depends on their relative phasing. For the case of total reflection, we have a few options. An OPEN transmission line termination (no termination) will return a reflected radio signal IN PHASE with the forward signal. The two signals will SUPERIMPOSE, or ADD at the point of reflection. Since the forward and reflected signal amplitudes are equal, the VOLTAGE at the termination point will be twice what it would be if no reflection existed. You can actually see this with a Lecher Wire. Remember the Lecher Wire at the start of the chapter? You just KNEW we'd come back to that sooner or later, didn't you? Well, here we are!

What about the case of a dead short at the termination?

Again, we have total reflection, but the reflected wave is 180 degrees OUT OF PHASE with the forward wave. So the SUPERIMPOSED voltage will be the DIFFERENCE between the forward and reflected signals, which are, as mentioned above, EXACTLY equal (but opposite). The resulting voltage at that point will be zero, as the Superposition Theorem tells us it must be. But we already know that, because we ALWAYS have zero volts across a dead short! So, whether we're treating our transmission line as a “lumped constant” (Ohm's Law) device or as a “distributed” (wave) device, we come up with the same answer!

Which brings us to another DEEP truth about physics. Our Universe is staggeringly consistent. If we can't arrive at PRECISELY the same answer to a problem by approaching it from two different angles, we're doing something WRONG! You can ALWAYS double-check this stuff. Don't take my word for it. MEASURE it yourself!

Now this process of superimposing an East traveling wave and a West traveling wave on a single pair or wires generates what is known as a STANDING WAVE. It's fairly obvious why it's called this; the relative values of voltage (SUPERPOSED VOLTAGE, that is, remain stationary relative to position along the line. You can see mechanical standing waves on any vibrating object, a plucked guitar string, for example. Or you can wobble a curly telephone cord back and forth and generate nice standing waves (if you can still find a phone with an actual cord!) You can easily measure electrical standing waves with a Lecher Wire...in fact, that is its main function.

Now, here's something very interesting and important.

Remember how we demonstrated that a FORWARD moving wave (traveling wave) has real energy? We lit up a light bulb with it. Remember how we demonstrated that a REFLECTED traveling wave has real energy? We lit a bulb with that too.

But guess what? A Standing Wave has no energy! It is a pure mathematical construct! It is analogous to isobar lines on a weather map. They INDICATE where pressure air pressure variances occur but they are NOT air pressure in themselves.

Now a system that SUPPORTS standing waves does indeed store energy. But this energy is in the form of forward and reflected REAL energy waves. The STANDING wave is just the visible, but powerless (“Wattless”) MANIFESTATION of the two traveling wave components.

And this one point is where most of the Amateur Radio Stupidity Exchange concerning transmission lines comes from. A standing wave in itself can do NOTHING good or bad to any piece of amateur radio equipment. Blaming “standing waves” for transmitter damage or other ills is like blaming the number Pi for the truck tire that ran over your foot. Yes, Pi describes the diameter and circumference of the truck tire that ran over your foot, but Pi is NOT a truck tire!

Does this mean that we ignore standing waves? Not at all! But we need to know that Standing Waves are an INDICATION...not the THING ITSELF. With the PROPER INTERPRETATION, they can tell us a few things. Unfortunately, most hams have no clue how to properly interpret standing waves.

Fortunately, we don't HAVE to! There are other MUCH more meaningful indications than standing wave ratio that we can use to know what's really happening. REAL things with REAL effects.

Conjugal Rights

The Superposition Theorem allows us to do some really amazing things with transmission lines. But to understand this requires that you have ABSOLUTE FAITH in Ohm's Law. We already showed how consistent our physical universe is. You don't violate physical laws...they violate YOU. They apply EVERYWHERE, from all viewpoints.

We talked briefly about characteristic impedance of a transmission line...how it's built into the physical construction of the line...how it's totally independent of length...how it doesn't care what's at the far end.

However, despite this seeming rigidity, the Superposition Theorem allows us to ALTER the impedance of a transmission line at different locations, using the magic of wave interference. Let's look how this works.

Let's return to the case of a transmission line with a dead short at the termination. We know the forward and reflected power are the same, but the voltages are exactly out of phase. (Grudgingly deferring to the SWR-obsessed, we have infinite SWR on this transmission line). Now, moving BACK from the termination by wave, we see something interesting. We have added an extra 90 degrees of phase lag to our reflected signal, but that OVERLAPS the outbound signal 90 degrees BEFORE the latter reaches the termination. So, what happens is the two overlapping voltages are now 0 (or 360 degrees, depending on how you look at it) apart. In other words, wave back from the termination, the voltages are IN PHASE, and therefore add.

We now have a maximum voltage point. But when we look at the POWER, something doesn't add up. Or does it?

How much power is delivered to the load? Well, a dead short doesn't dissipate ANY power, so the answer is zero. How much power is reflected? All of it. At any point along the transmission line, the reflected power equals the forward power, so the TOTAL power has to equal zero. But we're measuring a HIGH voltage wave back from the termination. How do we reconcile a high voltage with no power? The answer is Ohm's law. What circuit condition, in combination with a very high voltage gives us zero power? Infinite resistance! That's right. One quarter wave back from the termination, we have an infinite resistance load. Physically, it's a chunk of transmission line; electrically it's a chunk of air. Pretty amazing, isn't it?

How about if we go back a half-wave from the termination? Well, we get an additional 180 degree phase change between forward and reflected voltages. The forward and reflected voltages cancel, and we get zero. Let's double check. Zero volts across zero ohms is how much power? Zero!

Transmission lines REPEAT the load impedance every half wave, and INVERT the impedance every quarter wave. And also every ODD multiple of a quarter wave. However, in every case, if we have either a dead short or an open termination, the total power is zero.

If we insert a transmitter at any point in the transmission line, how much power will the transmitter put out? ZERO!

What heresy is this??!! A transmitter's OUTPUT power is determined by the LOAD impedance? Are we nuts?

Well, do you believe Ohm's Law or not? How you answer the following two questions will reveal who the REAL heretic is!

How much power can a transmitter put into a dead short?

(Answer: Zero).

How much power can a transmitter put into an open circuit?

(Answer: Zero.

You CANNOT violate Ohms law. It violates you if you try.

Often I hear statements like “If you have a big mismatch, all that reflected power is going to come back and burn up your transmitter!”

Impossible. Absolutely impossible...at least in this world. And most likely in the next, as well. All that reflected power, as we've clearly demonstrated, prevents the transmitter from generating the power in the first place!

Engrave this on the inside of your eyelids:

WHERE A TRANSMISSION LINE EXISTS, THE POWER GENERATED BY ANY RADIO TRANSMITTER EQUALS THE FORWARD POWER MINUS THE REFLECTED POWER IN THE TRANSMISSION LINE. ALWAYS.

It's important to note the clause “where a transmission line exists,” because, as we mentioned very early in the article, this is far from always the case. Think of all those hand-held radios out there with a whip sticking right out of the radio.

Are we saying that it's impossible to damage any radio transmitter by having a “bad” load? No, not at all. You can torch almost any transmitter by putting a dead short on it. And you can fry most modern radios by having an open circuit on them, as well, mainly by over-voltage of the output transistors. But it is NOT the SWR that does the damage! NEVER NEVER NEVER. A transmitter always sees an IMPEDANCE; it never sees an SWR. And don't ever forget it.

We've talked about reflections. We've talked about MULTIPLE reflections. And it is with regard to multiple reflections that things get really useful and clever.

The conjugate matching theorem tells us that maximum power will be transferred between a generator (transmitter) and a load when the load impedance is the COMPLEX CONJUGATE of the source impedance. This is a good thing to know. Without going into a lot of esoteric math, what the conjugate match theorem tells us is that you can match ANYTHING to ANYTHING with just two components, one parallel and one series. And sometimes less, if you're lucky.

When it comes to transmission lines, it translates into this: Any reflection in a transmission line can be compensated for with an equal and opposite reflection elsewhere in the transmission line.

We should, in all fairness, add one small caveat to this: The load impedance must have a real value of resistance less than infinity but greater than zero. What this means is that you really CAN'T match into a dead short or an open circuit...but you can come really really really close to doing it, if you have large enough matching components. The real point is that you only need TWO of them.

Let's look at a practical example to demonstrate this. Let's say we have a dipole antenna that has a radiation resistance of 50 ohms. To keep things simple, let's assume our antenna is perfectly resonant. (Reactive terminations of transmission lines can be a bit trickier to analyze). We want to feed this with 450 ohm ladder line. We know that we will have a 9:1 impedance mismatch at the antenna. (Assuming our transmission line is very good, we'll have the same mismatch at the INPUT end as well). Once again, in deference to our SWR worrywarts, we have an SWR of 9:1. Now, this is one case where this SWR information is good to know. What this tells us is that we have a WIDE RANGE of impedances to choose from, depending on our transmission line length. We know that if we pick a multiple of a half-wavelength, our transmission line input impedance will REPEAT the load impedance. So, if we cut our line to be a full wavelength long, we will have 50 ohms impedance, which will make most transmitters happy all by itself. What if we choose a transmission line length of wave? We know the impedance of a wave line INVERTS itself. The quarter wave transmission line is a very useful special case. If the load is resistive (which in this case it is), the input impedance is equal to the characteristic impedance squared, divided by the load impedance. (This is called the “geometric mean”). So this gives us 450 squared divided by 50= 202,500/50=4050 ohms.

Well, not too many transmitters are going to be happy with a 4050 ohm load...even if it IS purely resistive! So, this might not be too smart a choice of transmission line length.

On the other hand, what if we replace our dipole with the venerable Double Zepp, mentioned in the beginning of this fascinating chapter? As it turns out, the impedance at the center of a double Zepp is on the order of 2500-3000 ohms at resonance. Let's use a value of 2500 ohms, just for jollies. If we were to connect a 450 ohm line to the center of that, wave long, what might we expect to see at the input end? Using our same geometric mean formula, we have 450 squared divided by 2500, which gives us an impedance of 81 ohms at the input end. Oh, joy joy! This is well within the “happy” range of any typical ham transmitter. With no further adjustments whatsoever, our transmitter will put out 96% of the power that it would put into a perfect 50 ohm load...assuming the transmitter is truly optimized for 50 ohms. (I have to admit I cheated to come up with the answer...the venerable ARRL Antenna Book has all kinds of handy graphs to show power loss vs impedance mismatching and such. It's okay to use cheat charts and computers as long as you don't use them as a substitute for thought processes).

What have we done with the impedance inversion of the wave transmission line? We've performed a conjugate match. The impedance looking back TOWARD the transmitter with the wave section in place is the COMPLEX CONJUGATE of the antenna impedance itself.

Now, sections of transmission lines are not the only means of performing conjugate matching. In fact, using “series sections” as described in the above has become a bit of a lost art in most modern ham shacks. Standard practice now is to use a “lumped constant” antenna tuner, using one or more coils and capacitors to perform the conjugate match. As mentioned earlier, there is NO fundamental difference between lumped constants and distributed components as far as the physics is concerned. Any combination of distributed and lumped components may be used to achieve a conjugate match. In the above example, it might be practical to use a lumped component tuner to move that 81 ohms down to 50 ohms for the truly obsessive. More commonly, a lumped tuner would be used to tune out REACTANCES where the antenna is operated somewhat removed from its resonant frequency.

It should be emphasized that NO amount of twiddling of an antenna tuner at the INPUT end of a transmission line has any effect whatsoever on the standing wave ratio on that transmission line. The SWR is determined ONLY by the load impedance at the line termination. The antenna tuner only adjusts the impedance the transmitter sees.

Now, this fact brings up another very interesting point. Let's say we have a 100 watt transmitter, designed for a 50 ohm load. We have a wide range antenna tuner immediately after the transmitter. Beyond that, we have a length of transmission line, finally terminated in a severely mismatched antenna. Let's use our very first example, with a 450 ohm transmission line and a 50 ohm antenna. We have a 9:1 SWR on the transmission line. Taking a gander at another ARRL Handbook chart, we see that we will have about 60 watts of reflected power on the transmission line.

Now, remember what I had you engrave on the inside of your eyelids a while back? Transmitted power is equal to forward power minus reflected power.

Now, if we twiddle the antenna tuner so that our transmitter sees 50 ohms, we know the transmitter is putting out 100 watts. On the far side of the antenna tuner (away from the transmitter) we see 60 watts of power reflected from the antenna toward the antenna tuner. Does something seem amiss? Is our transmitter only putting out 40 watts? No...it's seeing 50 ohms...so we know it's putting out 100 watts (assuming the transmitter is functioning properly). Let's look at the FORWARD power on the transmission line. 160 watts! Well, how about that? Now the math works out...but WHERE does that extra 60 watts come from? Our transmitter can only put out 100 watts. What have we overlooked?

It's simple. It's a DOUBLE reflection. The 60 watts of REFLECTED power is RE-REFLECTED from the antenna tuner...actually added IN PHASE with the original forward power. But WHY the double reflection?

Without KNOWING it...when we adjusted our antenna tuner to make our transmitter “happy” we created a conjugate match on the other side of the tuner. It's actually a gross mismatch looking toward the transmitter...but it's a gross mismatch in the exact Complex Conjugate of the impedance looking the other way!

Actually, in this example, we have TWO complex conjugate pairs...one at the junction of the input of the tuner and the transmitter...and another at the junction of the antenna tuner's output and everything after it!

Again, this is stuff you can CONSISTENTLY DEMONSTRATE on the work bench. I always love showing a room full of skeptical “SWR Gurus” how the forward power on the output of a tuner EXCEEDS the power capacity of the transmitter!

Well, I suppose I could go on and on about this absolutely intriguing subject, but instead I'll refer you to two pieces of required reading:

      1. “My Feedline Tunes My Antenna,” By Byron Goodman, W1DX (SK). Originally published in QST in 1956, it has been reprinted several times since. A genuine classic, and a fine example of clear analytical thinking...a rarity in ham radio today.

      2. “Reflections” by Walt Maxwell, W2DU. This is the most eloquent and detailed work on the subject ever written. Most of the material in this EPILOGUE chapter was stolen, not in prose, but in principle, from Walt's writings. This originally appeared in a series of QST articles in the 1970s, but has been consolidated in a couple of excellent books, Reflections and Reflections II. I understand there's a Reflections III coming out soon.

Member Comments:
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SWR Meters Make You Stupid  
by W4ZDI on March 10, 2010 Mail this to a friend!
Good reading!

Would like to see more articles like this.
 
SWR Meters Make You Stupid  
by K9ZF on March 10, 2010 Mail this to a friend!
Nice article.

Yes, I highly recommend "Reflections" by Maxwell. It dispels many of the common antenna myths out there.


73
Dan
--
Amateur Radio Emergency Service, Clark County Indiana. EM78el
K9ZF /R no budget Rover ***QRP-l #1269 Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla> List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!
 
VERY GOOD PIECE!  
by N8NSN on March 10, 2010 Mail this to a friend!
I am getting ready to leave for school... :-) BUT, as soon as I return I will be reading this article in its entirety. I am impressed with just a short sift through... WOW !

Ladder Line - Open Feeders - I use and learn more about them every day.

Thanks for a good article.

Jimmie N8NSN (Dayton, OH)

Got Morse?
 
RE: VERY GOOD PIECE!  
by WA7NCL on March 10, 2010 Mail this to a friend!
Wow, so many words... so little math. No wonder hams don't understand antenna matching and transmission lines.
 
RE: SWR Meters Make You Stupid  
by KG4RUL on March 10, 2010 Mail this to a friend!
A picture is worth a thousand words.
 
SWR Meters Make You Stupid  
by N3QE on March 10, 2010 Mail this to a friend!
I agree with the title of the article at least :-). For many decades the definition for many of a "good antenna" has been "the SWR is 1:1" and this is so far off base that it's "not even wrong".

At the same time antenna tuners have been moved away from something that everyone built and tweaked, to something that magically fixes your problem without any manual adjustment at all. This isn't really right either.

But a high SWR coming back into the transmitter being a problem is not some sort of fiction. We can pooh-pooh the SWR meter but a scope on your transmitter's output - or even better on the final output device before the matching network - is a powerful tool. Try driving a short or an open, or just a high unmatched SWR, and you will see really nasty spikes on the active devices in the final (be they tubes or transistors). See eg: http://www.w8ji.com/demonstation.htm
 
SWR Meters Make You Stupid  
by N5TGL on March 10, 2010 Mail this to a friend!
Excellent article. I agree, the Maxwell "Reflections" series should be required reading for every ham.
 
SWR Meters Make You Stupid  
by K9JCS on March 10, 2010 Mail this to a friend!
Thanks, Eric.

Facts, theories, analogies and humor. A winning combination for a very good and instructive article.

You didn't discuss velocity factor of the feedline. My guess is that VF probably makes no difference in the overall scheme of standing waves, it just changes the physical location of the voltage maxima and minima on the feedline. So, if my guess (conclusion?) is correct, I should adjust the physical length of my feedline by the VF, if I was trying to make a half wave feed to an antenna?

I enjoyed the article and look forward to others in the future.
73

Jim
K9JCS
 
RE: SWR Meters Make You Stupid  
by AA4HA on March 10, 2010 Mail this to a friend!
It is difficult to find a copy of Reflections I or Reflections II, they are out of print.

I agree that they should be standard fare for all amateur operators. A lack of understanding the fundamentals of antenna systems and their behavior is not just limited to ham radio. Even in the electrical engineering profession it is considered black art. If we are to advance the science of radio communications there needs to be more of us who experiment, build homebrew gear and antennas, and study new modes of communicating.

"Yesterday I couldn't spell enjuneer, today I are one".

Tisha Hayes
KJ4SHJ (AA4HA)
 
SWR Meters Make You Stupid  
by N8BHL on March 10, 2010 Mail this to a friend!
Wow. just...wow. Excellent reading. So my next question is, with effectively 160 watts of power, do we see that power actually radiated even though the antenna itself is non-resonant? What's the next lesson on antenna radiation of all this? I can hardly wait. Thanks for the article.
 
SWR Meters Make You Stupid  
by KJ4NBM on March 10, 2010 Mail this to a friend!
"The salient point is that having a lot of “tools” around usually gives you more information than you need to know, and unless you know how to USE that information, it can be worse than ignorance, as we shall shortly see."

Wow, a true statement for many areas of life, not just radio!

KJ4NBM
 
SWR Meters Make You Stupid  
by KY4TS on March 10, 2010 Mail this to a friend!
VERY entertaining and informative. Well done, OM!
73, de KY4TS
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
Hi Tish:

Last time I talked with Walt he was in very poor health. He has been unable to complete the full manuscript of REFLECTIONS III. I'm so saddened about this; Walt has such a great mind. It would be great if some of us fans of Walt could find someone interested in reprinting REFLECTIONS. I've heard rumots that ARRL is thinking about republishing, but I haven't seen that yet. Fortunately, the entire QST series REFLECTIONS can be downloaded from the ARRL archives, if you're a member.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
JCS:

I make a brief mention of velocity factor in my decription of the LECHER WIRE. However, this is not crucial for understanding the bulk of the article. I also intentionally avoided LOSSY transmission lines for the same reason. These are both fully covered in REFLECTIONS. There's also a very good rundown of the Smith Chart in REFLECTIONS. I will say this about that, however. Whenever people tell me how daunting the Smith Chart is, I always refer them to the underlying Telegraph Equations. If you want DAUNTING, try working out all those hyperbolic trig functions by hand! Phillip Smith made life SOOOOOOO much simpler!

73!

Eric
 
SWR Meters Make You Stupid  
by KE9PP on March 10, 2010 Mail this to a friend!
Let me start by saying that I have a very short attention span and generally do not read articles over a paragraph or so in length. Yet, I read this one from start to finish, primarily due to the style in which it was written. I found it to be easy reading, enjoyable and informative to boot. Keep articles like this coming and I just might develop a longer attention span. Tnx es 73.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
BHL:

No, the actual radiated power is 100 watts. We haven't violated conservation of energy. :)

Eric

p.s. I really really really recoomend actually DOING this experiment if you possibly can. It is SO revealing and enlightening.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
Tisha:

By the way, do you realize how absolutely hideous your callsign is on CW? HI! Good gravy, I hope you aren't a contester....I'd feel for you!

73!

Eric
 
SWR Meters Make You Stupid  
by PHILIP_EX_KC7FWB on March 10, 2010 Mail this to a friend!
I think there are some words missing in this section:

"So, if we cut our line to be a full wavelength long, we will have 50 ohms impedance, which will make most transmitters happy all by itself. What if we choose a transmission line length of wave? We know the impedance of a wave line INVERTS itself. The quarter wave transmission line is a very useful special case. If the load is resistive (which in this case it is), the input impedance is equal to the characteristic impedance squared, divided by the load impedance. (This is called the “geometric mean”). So this gives us 450 squared divided by 50= 202,500/50=4050 ohms. "

In particular, "What if we choose a transmission line length of wave?" doesn't make sense.

Again in the next sentence: "We know the impedance of a wave line INVERTS itself."

"A wave" line?

Is that like a clothes line?

:-)
 
SWR Meters Make You Stupid  
by KJ6BSO on March 10, 2010 Mail this to a friend!
Thanks for the excellent article, Eric--if for no other reason than that I can now blame my stupidity on my SWR meter instead of the 18-wheeler I drive.
 
SWR Meters Make You Stupid  
by AB4D on March 10, 2010 Mail this to a friend!
Geeesh. You could have broken this "novel" down into a series of articles. Once it got to Lecher, I got tired and disinterested. Let me know how it turns out in the end.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
UF...good catch. For some reason Word does weird things with fractional symbols...it makes some browsers IGNORE them. It should be 1/4 wave. I see that in some other places in that section too.


Eric
 
RE: SWR Meters Make You Stupid  
by KG4TKC on March 10, 2010 Mail this to a friend!
Thanks once again KL7AJ for a wonderful article. You have done it again! Keep up the good work. Your articles are always a bright spot on eham 73,KG4TKC
 
RE: SWR Meters Make You Stupid  
by K0FF on March 10, 2010 Mail this to a friend!
Thanks for the nice article. I enjoyed the section on G-Line microwave transmission line.

Hams used to use this simple method a lot but it has virtually been lost to history:

http://en.wikipedia.org/wiki/Goubou_line


http://coldwar-c4i.net/G-Line/EE0860/p638.html

I wonder if any other readers have use the G-Line?

Geo>K0FF
K0VHF club station.
 
RE: SWR Meters Make You Stupid  
by N9BH on March 10, 2010 Mail this to a friend!
"UF...good catch. For some reason Word does weird things with fractional symbols...it makes some browsers IGNORE them. It should be 1/4 wave. I see that in some other places in that section too.

Eric"

Eric, any chance you can make this available as a word or acrobat file so we can see the numbers?

Thanks,
Bruce
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
FF:

G-lines are really a special case, so I made only a very glancing reference to them. (So glancing, I think you're the only one who caught it! :) ) But they're a very INTERESTING case. And the way they function is actually closer to GROUND WAVE propagation along the surface of the Earth.

The G-line propagation is not a TE wave such as you'd have in a waveguide, since there is no "return" line. It is a true electromagnetic wave that stays in contact with the wire becaue of the difference in dielectric constant between the wire and the surrounding air. (Actully, most G-lines have a dielectric coating to assure this happening) The propagating wave, which is always VERTICALLY POLARIZED relative to the center (core) of the wire, always wants to BEND toward that center...thus stays confined to the region.

Eric
 
RE: SWR Meters Make You Stupid  
by W0FM on March 10, 2010 Mail this to a friend!
Wow! What an eye-opener. I love your writing style, Eric. I was captivated and read the whole thing start to finish in one sitting (I don't normally do that).

I wish I had had instructors like you when I was in school. I wouldn't have gotten as much sleep as I did! ;o)

Thanks Eric.

Terry, WØFM
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
FM:

Why thanks, Terry. Now you know why Eham pays me the big bucks. :)


Eric


I hear and I forget,
I see and I remember,
I do and I understand.

-----Confucius
 
RE: SWR Meters Make You Stupid  
by K0FF on March 10, 2010 Mail this to a friend!
Eric said:
I hear and I forget,
I see and I remember,
I do and I understand.

-----Confucius "

Veni Vidi Visa

I came,
I saw it
I bought it

--------------My wife

K0FF
 
SWR Meters Make You Stupid  
by KJ6ETL on March 10, 2010 Mail this to a friend!
Thanks for the excellent article!
One day I will have some space and instruments to do some practical experimentations. Still struggling with the academics behind all this.
 
SWR Meters Make You Stupid  
by OLLIEOXEN27 on March 10, 2010 Mail this to a friend!
Just aim for the lowest SWR. If that doesn't work change the length or orientation of the transmission line.

If you need to know everything the author just wrote you're on the wrong track - you need to find other hobbies.

oli
 
RE: SWR Meters Make You Stupid  
by KJ4AUR on March 10, 2010 Mail this to a friend!
Eric, this was well written, easy to comprehend, captive, and certainly brought about an epiphany over here. Thank you for sharing this I enjoyed reading all of it and have walked away with greater understanding regarding SWR and feedline.

I've printed it out and highlighted key sections for future reference.

73 - Nathan
 
RE: SWR Meters Make You Stupid  
by WI7B on March 10, 2010 Mail this to a friend!
One of the things that really get my goat is the plethora of SWR/Wattmeters available made to be placed at the transmitter, yet the relative lack of RF Ammeters meant to be remotely placed at the antenna.

Such a simple thing could be SO instructive.

73,

---* Ken
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
Ken:

I hope you saw my Feb, 2009 QST article, "Keeping Current with Antenna Performance." It's all about antenna ammeters. :)

Eric
 
SWR Meters Make You Stupid  
by WD9FUM on March 10, 2010 Mail this to a friend!
Eric, thanks for an informative and witty article - a very enjoyable read.
 
RE: SWR Meters Make You Stupid  
by NB3O on March 10, 2010 Mail this to a friend!
All of us became interested in our hobby for a variety of different reasons.
However comments such as:

"Once it got to Lecher, I got tired and disinterested."

and

"If you need to know everything the author just wrote you're on the wrong track"

are responsible for propagating the multitude of myths and old wives' tales.

If a couple pages of good and entertaining technical info can't hold our interest, maybe we need to find another hobby.

We can learn a lot from each other if we just give an honest look first and verify second.

Eric, I do not know how you could have improved on the article to address such a broad spectrum of individuals.

Please don't give up on us.

73
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
3O:

Not to worry. I've got thick skin...and I have enough positive feedback it doesn't matter anyway.

Just wait till my X and O propagation article shows up in QST next September. It took YEARS to get them to acknowledge that X and O modes even exist. I expect to get a lot of flack from that one.

I start out with the premise that ALL ionospherically reflected signals are circularly polarized.

And then I prove it.

Stay tuned!

Eric
 
SWR Meters Make You Stupid  
by KB2DHG on March 10, 2010 Mail this to a friend!
WO! I MEAN WOW!. Very nice informative article. Although I am going to have to read it over a couple of more times. This is good reading and learning! THANK YOU
 
RE: SWR Meters Make You Stupid  
by WD9FUM on March 10, 2010 Mail this to a friend!
Ken, WI7B, hit the nail on the head. Where do commercial stations measure their output - at the transmitter or the antenna? I've seen remote antenna ammeters for around $150 on commercial equipment websites.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
The FCC STILL requires A.M. broadcasters to measure current at the antenna feed point. The only thing they relaxed is that it no longer has to be a thermocouple ammeter, but can be an inductive current probe.

Sure makes it easier when you've got a long winded DJ. Since the readings have to be taken with DEAD air, with the old TC ammeters, you could be in for a looooong wait!

Eric
 
RE: SWR Meters Make You Stupid  
by KU5Q on March 10, 2010 Mail this to a friend!
Thanks for all your work here and other forums Eric. You enjoy your work and it shows. Keep it coming.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
5O

Well, thanks. Like they say: If you aren't having fun, you aren't doing it right. :)

Eric
 
SWR Meters Make You Stupid  
by NX8J on March 10, 2010 Mail this to a friend!
What an easy to understand explanation. Another engineer by the name of Robert Pease wrote using a similar, easy to understand style. He collected his wisdom into a very good book, Troubleshooting Analog Circuits. If you were to write a book about RF, it would find a place in my shack. Amazon has good reviews on your fictional work.
 
SWR Meters Make You Stupid  
by WR9H on March 10, 2010 Mail this to a friend!
Hello Eric,
Fantastic!
Your students are lucky fellows having you as their teacher.
We're blessed to have you teaching us!
TNXs 73
Herb/WR9H
 
RE: SWR Meters Make You Stupid  
by WD9FUM on March 10, 2010 Mail this to a friend!
Weren't there some problems with the thermocouple ammeters?
 
SWR Meters Make You Stupid  
by KA8OCN on March 10, 2010 Mail this to a friend!
I Think this is the best article I have ever read on eham.net Thank You for all the time and effort that must have went into creating this.

I read the entire thing at once, just could not stop!

I will have to come back when I have time and cut and paste it so I can save a copy on my computer because I am going to need to read it a few more times.

Thank You again for the article!

Delbert McCord
KA8OCN
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
Bob Pease is one of my heroes. I've read Pease Porridge for ages. :)

I still have a bottle of floobydust in his honor. HI!

Eric
 
SWR Meters Make You Stupid  
by K9ARM on March 10, 2010 Mail this to a friend!
Thank you Eric, good article.

I didn't see anyone mention that you could see and download parts of "Reflections" on W2DU.com.

It inspired me to buy a good manual tuner and put up a doublet fed with ladder line, works great. Next step, homebrew open-wire line.

Andy K9ARM
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
FUM:

If you didn't take thermocouple ammeters out of the circuit when you weren't using them, they'd slowly lose calibration. You always had a knife switch at the tower base so you could switch them out when you weren't taking a reading.
Also, they were only calibrated for the upper two-thirds of the scale. If you had a station with two very different power levels (As some Day/Night licenses required), you couldn't use the same meter...and they wouldn't let you just use a different meter multiplier. The certification was required to use the same meter and thermocouple together. So some stations had to have two or more ammeters at each tower...this could add up if you had a big DA array!




And they were SLOOOOOW...as mentioned above. :)

However, within their specs, they were very insensitive to frequency, and extremely accurate...which is why the FCC required them for so long.

ERic
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
Thanks for mentioning that, Andy. I knew I forgot something. :)
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
XU

"....Amazon has good reviews on your fictional work...."

I'm not sure if that's a good thing or not, on this forum, HI! Just means I'm a good story teller. :)

By the way, I see you're a REAL old timer! My hat's off to you. :)

Eric
 
SWR Meters Make You Stupid  
by W8JII on March 10, 2010 Mail this to a friend!
One of the best articles I've seen on E-Ham. Well written. EXCELLENT!!!!
 
SWR Meters Make You Stupid  
by K1DA on March 10, 2010 Mail this to a friend!
This interesting article caused me to wonder, once again, about a question which I have not been able to muddle through to an answer: What happens to signals, such as analog TV signals, with all the complex relationships contained therein,
when fed through a half wave or even multiple thereof,
of feedline which is not of the impedance of either the transmitter and antenna, (and assuming the transmitter and antenna have the SAME impedance). I suspect that a simple FM signal would not be degraded but am not so sure about a complex am signal with "timing" content. I'm thinking "multipath" but may be all wet.
 
RE: SWR Meters Make You Stupid  
by W7ETA on March 10, 2010 Mail this to a friend!
Wheeew!
Thanks for a fascinating, comprehensive and informative read woven by lattice of great prose.

Three pairs of two thumbs up from Tucson OM.
Bob

PS: math? I kept a trig book and have a Sci calc, but the calc has been gathering dust since my last Calc II class, more than two decades ago. Huuum. My calc will quality for QCW soon. HI Hi
 
RE: SWR Meters Make You Stupid  
by K3AN on March 10, 2010 Mail this to a friend!
7,925 words, according to my older version of Microsoft Word. I think the info could have been better conveyed in less than half that number. Even fewer if accompanied by some illustrations.

I do see one benefit however. I intend to print it out and place it on my nightstand for the next time I have a bout of insomnia.
 
RE: SWR Meters Make You Stupid  
by AJ4MJ on March 10, 2010 Mail this to a friend!
Great read!

Here's something I'm not able to get my head around: Since the Superposition Theorem tells us that a given point will only have one voltage, how are we able to produce meters that measure both forward and reflected power?

73 de AJ4MJ
 
SWR Meters Make You Stupid  
by WB2GBF on March 10, 2010 Mail this to a friend!
This is the best article I've ever seen on the topic. I tried explaining this to a ham the other day and found it difficult. The thought experiment is a great way to get the reader to think.

Great work.

Pat
 
RE: SWR Meters Make You Stupid  
by K1JHS on March 10, 2010 Mail this to a friend!
Eric, Without a doubt one of the very best technical articles I have ever read.

Mildly reminiscent of those Nasa films I saw as a youngster. Humorous and made you think.

A keeper for sure!
 
SWR Meters Make You Stupid  
by K9CTB on March 10, 2010 Mail this to a friend!
Great article!!! I appreciate your sense of humor, and your ability to use it in your writing!

Could I add however, to your comment about Lecher lines not being used since the 1950s?

Lecher lines are still in use today in modern microwave system calibration laboratories. Although they are not relied upon for frequency measurements, they still function for measuring reflected power in precision attenuator and load calibrating setups.

Hmmm ... I never associated Professor Lecher with tin-foil hats or divining rods ... perhaps I don't google stuff enough. :)

73 and thanks again for a great article!!!

de Neil
K9CTB / NNN0ZVU
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
BH:

Hi Bruce. Yeah, I can make a PDF from this. I'll try to tweak it this weekend. So far the only missing character seems to be "1/4" HI!

Eric
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
W8JI:

Tom, I can't tell you how much your comment means to me, since you are one of my mentors and elmers. Even when we disagree from time to time. Makes things more interesting, anyway. :)

73 es God bless!

Eric
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
CTB:

When I said the Lecher Wire was the ONLY means of measurement until the 1950s, I in no means meant it suddenly became obsolete after that time! I use one in my class every semester! Great teaching tool, as well as instrument. The microwave slotted line is, of course, still in common use.

Thansk for the comments!

Eric
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
K1DA:

Very perceptive question. TV broadcast antennas must have very broad and flat characteristics. A TV channel is 6 MHZ wide....on Channel 2, that's a HUGE percentage bandwidth. No mean feat to building an antenna that can handle that. (Hmmmm, I guess I should speak in the past tense about NTSC TV~!~!)

Anyway, the consequence of NOT having a flat TV antenna are many. FCC standards require an SWR of no more than 1.05:1 across the entire video bandpass. Since TV is largely pulse based, with similarities to radar, with a high SWR you can BUILD MULTIPATH right into the system! NOT GOOD! Wben a TV engineer gets reports of multipath that the viewer can't fix, he looks at his antenna system for multiple internal reflections.

more subtle defects happne, as well. DIfferential phase delay (smearing of color, or even DISPLACEMENT Of color information from the luminosity information) can happen.

So, to answer your question...."With great difficulty!"

Hope this helps.

Eric
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 10, 2010 Mail this to a friend!
AJ$MJ:

Great question with a simple answer.

They Don't!

EVen the cheapest Monimatch SWR meter measures a SECTION of transmission line, where a difference of phase and amplitude can be detected. Likewise, with the Lecher wire, you can't make this determination with one measurement...you have to SLIDE the voltage probe to get a meaningful reading.

The fact is that the SHORTER this sample line is relative to the wavelength, the trickier it is to get an accurate reading. The Sensitivity, as well, decreases with wavelength...or increases with frequency.

The pricey Bird Wattmeter uses essentially the same sampling method as your el cheapo CB swr bridge...it's just built a lot more precisely. :)

Eric
 
RE: SWR Meters Make You Stupid  
by W9PMZ on March 11, 2010 Mail this to a friend!
AJ4MJ - Here's something I'm not able to get my head around: Since the Superposition Theorem tells us that a given point will only have one voltage, how are we able to produce meters that measure both forward and reflected power?

Well you can use a dual directional coupler.

Oh by the way, we should now be able to answer this question,

if 3 10dB cascade amplifiers with non-zero reflection coefficients are connected in series, with matching networks, what is the total gain?

a) < 30dB
b) = 30dB
c) > 30dB

Great article!

73,

Carl - W9PMZ
 
SWR Meters Make You Stupid  
by K9CTB on March 11, 2010 Mail this to a friend!
Hiya again Eric...

Actually, I knew that you knew ... I just added that for your readers.

73 and thanks again for a great article!!!
 
RE: SWR Meters Make You Stupid  
by VK6NDT on March 11, 2010 Mail this to a friend!
"But it is NOT the SWR that does the damage! NEVER NEVER NEVER. A transmitter always sees an IMPEDANCE; it never sees an SWR. And don't ever forget it."

Just a quick question, why is it that say for instance your tuning an vhf antenna on a car and using a bird Power metre. you tune the antenna for max forward power and min reflected power. you say its the impedance miss match that does the damage, then why do we look at the forward and reflected power?
 
SWR Meters Make You Stupid  
by AI4WC on March 11, 2010 Mail this to a friend!
I'm not going going to read all the comments, just in case the "flamers" come out. What I would like, Eric, is for you to prepare a You Tube "physics lab" demo of these basic and important concepts. I don't know about the others, but I would watch it! I admit, I need it, because I learned long ago that I learn best in a "visual/physical" situation, such as lab demos! Thanks for the great article!
 
RE: SWR Meters Make You Stupid  
by NB3O on March 11, 2010 Mail this to a friend!
"a You Tube "physics lab" demo"

2nd the motion!

I'd purchase a DVD as well for the club.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 11, 2010 Mail this to a friend!
NDT:

I don't want to convey that SWR is not USEFUL...just that it can be misinterpreted. Likewise in the case of the Bird wattmeter, it is an impedance mismatch that CAUSES the reflected power in the first place. Reflected power is a perfectly good indicator of a mismatch...but it's not the CAUSE of a mismatch. You still have to FIX it by fixing the mismatch.

One shortcoming in common with either the cheapest SWR bridge or the best quality Bird wattmeter is this: It will tell you something is wrong...but it won't tell you how to fix it. You can make a change and see whether it gets better or worse, but that's about it. The IMPEDANCE bridge, however, will tell you exactly what change you need to make to FIX the mismatch.

Hope this helps,

Eric
 
RE: SWR Meters Make You Stupid  
by WB4JZY on March 11, 2010 Mail this to a friend!
"An OPEN transmission line termination (no termination) will return a reflected radio signal IN PHASE with the forward signal.

What about the case of a dead short at the termination?
Again, we have total reflection, but the reflected wave is 180 degrees OUT OF PHASE with the forward wave."


I would like to hear an easy to understand explanation of these two reflection conditions. Not just, "the line is shorted, so the voltage has to be zero". What happens at the end of the line with respect to fields and current.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 11, 2010 Mail this to a friend!
NB3O et al:

I do have a Lecher Wire video I plan on putting on YouTube, as well as the HARES club page. (It's currently in a weird video format I need to convert, but I think I'm going to reshoot it anyway :) )

This summer I'm going to be doing a lot of work with my 500KC antenna. I can also do a video of the operation of an impedamce bridge....very fun and "retro" as well.

Stay tuned!

Eric
 
RE: SWR Meters Make You Stupid  
by KJ6BSO on March 11, 2010 Mail this to a friend!
Eric--

I made a PDF file of this article for my own use because I'd like to be able to refer back to it without having to connect to the Web. If you'd like a copy, please e-mail me at [my callsign]@arrl.net.

Thanks for the great article.

--Carl
 
RE: SWR Meters Make You Stupid  
by N5XM on March 11, 2010 Mail this to a friend!
You have a wonderful style, and a fine sense of humor. What I really like is that I learned a new word while reading. Blorp! I love it. These are the kinds of things I live for. Rick
 
RE: SWR Meters Make You Stupid  
by K1BXI on March 11, 2010 Mail this to a friend!
Very nice writing style as many others have said Eric. I want you to know that I have printed it out (yes, I added the "1/4's" where needed!) and placed it in my notes along side of Tom's, W8JI. You guys compliment each others writings here on eHam very nicely.

John
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 11, 2010 Mail this to a friend!
JZY:

Here's a surprisingly good Wikipedia article on the reflection mechanics, using Kirchoff's current law.

http://en.wikipedia.org/wiki/Reflections_on_copper_lines#Short_circuit_line


It should be noted that, assuming a perfect, lossless transmission line, you would have INFINITE current flow through a short, which makes for some interesting boundary equations.

The so-called Telegraph Equations deal with these differentials, which are well described in the Wikipedia article.

Eric
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 11, 2010 Mail this to a friend!
K1BXI:

Thanks for the great feedback!

Ernest Hemingway said: "The most essential gift for a good writer is a built-in, shockproof s**t detector. This is the writer's radar and all great writers have had it."

This applies to engineers too. Tom's s**t detector is finely tuned...he keeps me honest. :)

Tom's sometimes been accused of not being open to "new" ideas...especially when it comes to "magical" short antennas. This is not being narrow minded...it's being in contact with reality. Tom is to antennas what I am to transmission lines...we both have the "gift of suspicion." This comes about by no other means than crawling around in the same trenches for YEARS. You get a feel for things...you can SMELL whether something sounds right or not. If it sounds too good to be true...it is.

Anwyay...I'm honored to share JI's space on your bookshelf. :)

Eric
 
RE: SWR Meters Make You Stupid  
by N0YXB on March 11, 2010 Mail this to a friend!
Great article! To those ever critical types who think they could have written a better (or more concise) article on this topic, let's see yours.

Vince
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 11, 2010 Mail this to a friend!
MJ and MZ;

It might be interesting to consider how weird the world would be if the Superposition Theorem didn't work. You could never send audio through a pair of wires, much less a loudspeaker. EVERY possible frequency (whether electrical or mechanical) would require its own individual channel.

Think of a loudspeaker with music coming out of it. You have HUNDREDS or THOUSANDS of individual sine waves making up the composite sound, each with its own phase, as well. And yet a speaker cone can ONLY be in one position at any particular time. Each sound emanating from the speaker maintains its own identity, yet comes through the same "pipe." Amazing...yet it can be no other way. At least in THIS universe.

I think what is missing with a lot of new hams is a COHERENT view of the universe. Everything seems to be a fractionalized "special case" with no underlying laws. The controversy with transmission lines is just one visible case.

Did you know that EVERY example I showed in the article SWR METERS MAKE YOU STUPID can be reproduced PRECISELY with a purely MECHANICAL device? ALL of them. Other than the numbers involved, all wave phenomenon can be demonstrated mechanically...including shorted, opened, and reactive transmission lines. Standing waves, traveling waves....they can all be demonstrated with a rubber band as well as a network analyzer. The Smith Chart works for acoustics as well as twin lead.

Something to think about!

Eric
 
RE: SWR Meters Make You Stupid  
by OLLIEOXEN27 on March 11, 2010 Mail this to a friend!
NB3O,

Life is too short to read this article let alone 'contemplate' the nuances of of swr; voltage vs current; etc. If it works keep it - if it doesn't change it. If that doesn't work find another hobbie.

Thats still my advice.
 
RE: SWR Meters Make You Stupid  
by PHILIP_EX_KC7FWB on March 11, 2010 Mail this to a friend!
NDT:

Why look at reflected power?

If we are talking about the feeder-antenna connection we are interested in it because it tells us a lot about how well matched the feeder is to the antenna.

If you just tweak for maximum power, you will get the same result. However, seeing the difference between 95w and 100w can be difficult, but seeing the reflected power go to zero is generally much easier.

Personally, I would like the Ham community to get away from (V)SWR and start thinking in terms of Return-Loss Ratio (RLR), which basically tells you what proportion of your signal gets bounced back to you -- its expressed in dB.

I think it makes things much easier to understand.

When it comes to using an ATU to match whatever funky impedance I see at the end of a specific length of feeder to the 50 ohms resistive load that my Tx wants to see, there are two ways of doing it, one is with an SWR meter, where I just twiddle the knobs to get the reflected signal as low as I can, which is really (sort of) ok, because it achieves the end result that I want, but an alternative, if you have something like an LP-100 is to look at the Impedance/Resistance/Phase of the signal which tells you a lot about what you need to twiddle to correct.

Personally, I get some satisfaction from knowing what I am doing. But that's just me. As the article points out, its the results which count and you don't need the theory to achieve the results -- especially with an automatic ATU where you just push the button - no need to even twiddle knobs.

The only place where the theory really does help (and the equipment to make appropriate measurements) is when things don't work right. You can always just climb on the roof, or up your tower and tweak stuff, and eventually you will probably succeed, but doing the analysis beforehand, then just climbing up once to make your calculated adjustment is not only easier, but (depending upon what turns you on) may be more satisfying.
 
RE: SWR Meters Make You Stupid  
by WI7B on March 11, 2010 Mail this to a friend!
Eric,

HaH! I did! This was my part of my thesis! Using PVDF and PZT pin transducers meant to be buried and measure earthquakes and underground nuclear explosions. I used them to measure energy transfer in the low=pressure gas phase. The little guys were hopelessly mismatched acoustically, hardly sensitive, but fast and broad (1-5 MHz) compared to microphones.

73,

---* Ken

"Other than the numbers involved, all wave phenomenon can be demonstrated mechanically...including shorted, opened, and reactive transmission lines. Standing waves, traveling waves....they can all be demonstrated with a rubber band as well as a network analyzer. The Smith Chart works for acoustics as well as twin lead.

Something to think about!

Eric"
 
RE: SWR Meters Make You Stupid  
by K3LUE on March 11, 2010 Mail this to a friend!
Yes, I remember in 1960, my long wire antenna that terminated in my Globe Chief Deluxe. I still have scars from rf burns when I touched that little set screw in one of the tuning knobs.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 11, 2010 Mail this to a friend!
"Life is too short to read this article let alone 'contemplate' the nuances of of swr; voltage vs current; etc. If it works keep it - if it doesn't change it. If that doesn't work find another hobbie."

Ordinarily, I wouldn't even dignify this sort of comment with a response. (Obviously SPELLING isn't anything more than a "hobbie" to this poster, either). However, just to set the record straight....

One of our reasons for existence as radio amateurs, as clearly spelled out in Part 97.1, is "...to advance the state of the radio art..."

I take this mandate VERY seriously. Like it or not, every advance of knowledge is a result of "contemplating nuances." No progress was ever made by, "If it works, keep it."

Jerry Sevick, W2FMI, John Kraus, W8JK, Walt Maxwell, W2DU, Lew McCoy, W1ICP, Zack Lau, W1VT, Chuck Hutchinson, K8CH, Tom Rauch, W8JI, not to mention "pre-amateurs" such as Michale Faraday, James Clerk Maxwell, Ernst Lecher, and Joseph Fourier, and countless others have devoted their lives to "comtemplating nuances" and we are all the better off because of it. Such a statement would undoubtedly be insulting to any of them.

We need to remember that Olympic athletes are all AMATEURS. "Amateur" has nothing to do with the level of expertise (though modern interpretation of the term seems to suggest this) but rather the MOTIVATION. We do it because we can contribute something to human knowledge and understanding, not to mention it's just a whole lost of FUN, whether we get paid for it or not (though most of the aforementioned, myself included, ALSO are professionals in the field).

Can you live without contemplating nuances? Certainly...the vast majority of people in the world do that...they just bleat along with the crowd.

Or, as we say up here...."Unless your the lead dog, the view never changes." Some of us LIKE a change of scenery.

"Nuff said.

Eric
 
SWR Meters Make You Stupid  
by K7ZP on March 11, 2010 Mail this to a friend!
Damn.....

Alaskan winters must be really, really long.

Cheers... Frank, K7ZP
 
RE: SWR Meters Make You Stupid  
by HAMMYGUY on March 11, 2010 Mail this to a friend!
Very good article Eric. Your style of writing is excellent and fun to read.

A little long, but it kept me interested the whole way through it.
 
RE: SWR Meters Make You Stupid  
by K9WJL on March 11, 2010 Mail this to a friend!
My Vote says it's another great article from Eric,
Thank You.
73,
Bill K9WJL
 
SWR Meters Make You Stupid  
by WD2I on March 11, 2010 Mail this to a friend!
Excellent article, and yes I think everyone should read "reflections" by Walter maxwell. Another excellent book is The Easy Way, HF Antenna Systems by John Haerle, WB5IIR.
 
RE: SWR Meters Make You Stupid  
by K1DA on March 11, 2010 Mail this to a friend!
With respect to the mechanical aspect of this topic, it is interesting to watch waves strike a flat seawall, which has a different "impedance" than water, and watch how the incoming and outgoing waves interact. Peaks and valleys of a height and depth greater than each alone.
 
SWR Meters Make You Stupid  
by LU2DFM on March 11, 2010 Mail this to a friend!
Best article I've read on this subject ever. Excellent prose and clever explanation by example selection right on the most controverted points.

Eric, please let me know if you authorize a spanish translation to hang out somewhere on the 'net. This article is gold material to prepare a presentation for the club members :-)

Go ahead, please, this kind of deep, long and well written article is what the comunity needs.

Thank you.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 11, 2010 Mail this to a friend!
Hi Fernando:

I sent you an email.

73!

Eric
 
Excellent  
by KA4KOE on March 11, 2010 Mail this to a friend!
Great writing style. Love it. To the VERY FEW bomb throwing detractors to this well composed essay, you are most very welcome to submit an article and let US critique it.

73

Philip
KA4KOE

ps working on a sequel to my "Green Radio Roundup" article that appeared in the April 2006 QST.
 
RE: Excellent  
by N7WS on March 11, 2010 Mail this to a friend!
"We need to remember that Olympic athletes are all AMATEURS."


http://en.wikipedia.org/wiki/United_States_men%27s_national_basketball_team
 
RE: SWR Meters Make You Stupid  
by N0VLJ on March 11, 2010 Mail this to a friend!
I tend to agree that when articles such as this get too long I tend to yawn! The old law of the "Proof is in the Pudding" always applies: e.g. ; I lived in a third floor apartment in a big old house with a G5RV and a Ten Tec Power Mite PM-2 back in the 90's and used a Tuner and cheap Ratshack swr meter and tuned for minimum SWR and worked all kinds of 40m stuff. Using a QRP T-kit 20 meter xcvr with the same setup and worked Guam on my first contact. If something works for you why get your undies in a bundle trying for technical nirvana. Sheesh, people. Get a grip!!!
 
SWR Meters Make You Stupid  
by W4JLE on March 11, 2010 Mail this to a friend!
Great article! I always delight in telling the folks from the church of low SWR that mine is 9:1.
I have long concluded that the SWR meter is the worst thing to happen to Amateur Radio, it is the source of more old wives tales and pseudo experts than any one instrument in use today.
"I know my signal must really be down, I'm showing a 1.7:1 SWR" Heard last night on 75 meters.
 
SWR Meters Make You Stupid  
by W4JLE on March 11, 2010 Mail this to a friend!
Great article! I always delight in telling the folks from the church of low SWR that mine is 9:1.
I have long concluded that the SWR meter is the worst thing to happen to Amateur Radio, it is the source of more old wives tales and pseudo experts than any one instrument in use today.
"I know my signal must really be down, I'm showing a 1.7:1 SWR" Heard last night on 75 meters.
 
SWR Meters Make You Stupid  
by VE7AUL on March 11, 2010 Mail this to a friend!
"It's simple. It's a DOUBLE reflection. The 60 watts of REFLECTED power is RE-REFLECTED from the antenna tuner...actually added IN PHASE with the original forward power."

How then is it possible for a received signal to make it through the transmatch to the radio? How can the matching network tell the difference between unwelcome energy coming toward it that has been reflected by the antenna and rare DX energy that the antenna converted from EM waves to electricity? Charges are charges; none of them have little labels on them saying "I originated at another station so please let me through so that I can get to the receiver."

This has puzzled me for decades.

Brian
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 11, 2010 Mail this to a friend!
"This has puzzled me for decades."

Hi Brian:

Another very perceptive question. I'm so glad so many people are paying attention. This has been a very gratifying article for me because of the discussion we've fomente. :)

As it turns out, the two conjugate matches create a double reflection with originating the other direction too!

Let's modify this setup slightly to simplify the number of components, yet creating double reflections in our favor.

First we need to establish some ground rules, which I think you already understand. But let's just confirm things.

1) In receive mode, the ANTENNA is now a voltage source. The actual correct model for a receiving antenna (should you want to model this with SPICE), is a voltage source with a fixed series resistance (the radiation resistance, presumably.)

2) The receiver has an INPUT impedance equal to 50 ohms, non-reactive (at least for the purposes if this particular setup.


3) Let's eliminate the antenna tuner, but replace our coax sith a half wavelength of 300 ohm twin lead. The half-wave is so we don't have to contend with reactances as wall, We understand that a 1/2 length of any transmission line repeats the load.

4) In the receive mode, the SWR is determined by the load the receiver presents to the transmission line. IN this case we will have a 6:1 SWR on the coax.

Now, since the antenna is now the "transmitter" what impedance does it see? Well, we already established that the transmission line is going to repeat the load impedance, right? It's 50 ohms! Is our antenna happy?

Yup.

Is there a large standing wave on the transmission line?

Yup.

Do we have multiple reflections on the transmission line?

Yup. ONe reflection from the mismatch from the receiver, and another from the mismatch on the antenna. This second reflection ADDS to the power the Antenna (which is now a power source" supplies to the coax!

So it works both ways! Absolutely!

If we want, we can also add a couple of tuners, just to make things complicated, but that's unnecessary. We still will have a conjugate match going both directions!


Cool, eh?

Eric

2)
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 11, 2010 Mail this to a friend!
Brian:

Furthermore...


You may have already demonstrated this without knowing it.. If you have an antenna tuner, you know that if you tune it for maximum RECEIVE noise, it's going to be pretty closely matched for best transmit match, as well. This is assuming, of course, that your transmitter output impedance is the same as your receiver INPUT impedance....at H.F., most modern rigs are pretty close.

Anyway...I'm glad you asked this. If you do know how to do SPICE modeling, you can go ahead and confirm this.

I think where some of the weirdness of this comes about is because people have a hard time thinking of a receive antenna as a power SOURCE. But, indeed it is.

Here's a rustic mechanical analogy. Think of a Colonial era waterwheel in a stream, connected to a drive shaft running a saw blade or a millstone.

What is the source of power, the shaft of the water wheel, or the water flowing by? Well, from the point of view of the water wheel, it is a RECEIVER...ir receives energy from the river. But it SUPPLIES energy to the millstone or sawblade. As far as the "internal" circuitry is concerned, the water wheel shaft is the SOURCE of power.

So it's perfectly legitimate to model a receiving antenna as a generator.

Hope this gives some insight.
Eric
 
SWR Meters Make You Stupid  
by WB4JZY on March 12, 2010 Mail this to a friend!
does the reflection from the receiver side back toward the antenna result in some of this reflected energy being dissipated in the radiation resistance of the antenna?
 
SWR Meters Make You Stupid  
by AI4WC on March 12, 2010 Mail this to a friend!
On second thought, Eric, maybe a DVD with several different shows that exhibit the various principles and concepts would be good, as evidenced by the amount of generally thoughtful comments to this article. I think the comments show that folks are interested. It could be sort of like a long "You Tube" presentation by "DVD Elmer." I would gladly pay a reasonable charge for your trouble.
 
RE: SWR Meters Make You Stupid  
by WA8JNM on March 12, 2010 Mail this to a friend!
Eric,

Skip this if you are tired of glowing comments.

I think there are a great number of hams like me: I have an unexplained, but driving, desire to understand this stuff, but have forgotten all my high school and college math. Moreover, my career is unrelated to the sciences. It therefore is difficult to become reasonably educated about the science underpinning of magic of RF without the math, or the time to relearn it.

I know how difficult it is to write clearly and with personality, especially on technical matters. That is also the challenge of a lawyer, and one at which we routinely fail. You simply excel at it, to my great benefit.

Thanks very much.

By the way, your recommendation for additional reading includes Maxwell's Reflections. At first I thought you were sending be to James Clerk. I gather the younger Maxwell may be a bit more accessible? (grin).

Dave WA8JNM
 
RE: SWR Meters Make You Stupid  
by N7WS on March 12, 2010 Mail this to a friend!
WB4JZY on March 12, 2010 asks:

"does the reflection from the receiver side back toward the antenna result in some of this reflected energy being dissipated in the radiation resistance of the antenna? "

If by dissipated you mean re-radiated, yes.
 
RE: SWR Meters Make You Stupid  
by N7WS on March 12, 2010 Mail this to a friend!
W4JLE on March 11, 2010 writes, not once but twice:

"I always delight in telling the folks from the church of low SWR that mine is 9:1."


Why would you knowingly want to increase the stress and loss on your transmission line?

Certainly there are special cases, stubs and series sections for example, where elevated SWR comes with territory, but as a general rule, these situations are to be avoided.

RF watts are expensive and it seems that today the less capable the amplifier is of driving a mismatch, the more it costs. Why folks want to burn up watts that cost five bucks apiece in tuners and transmission lines is a mystery to me.
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 12, 2010 Mail this to a friend!
JZY:

This is one case where a receiving antenna is different from a transmitting antenna. A perfect transmitting antenna radiates all the R.F. applied to it. A perfect RECEIVING antenna transmits half the power to the load and re-radiates half the power. So any comparison of receive antennas has to START with a 50% power loss as the best case.

With that in mind, however, the antenna in the example I just describe is a perfectly matched antenna. Because of the DOUBLE reflection the antenna sees a perfect 50 ohm termination resistance...so it works just as well as if you had a 50 ohm transmission line.

Interestingly enough, this 50% "loss" in a perfect receive antenna is absolutely consistend with the maximum power transfer theorem. Again, we need to look at the receive antenna as a signal SOURCE with a 50 ohm internal resistance. When do you have maximum power transfer in ANY system? When source resistance equals load resistance. What is the total system EFFICIENCY when you do this? 50%! This works from DC to Daylight!

In the case of a car battery, the internal resistance is HEAT generating, in an antenna it's in the form of RADIATION RESISTANCE, so it's converted into radiated R.F. instead of heat. That's the ONLY difference, however.


Eric
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 12, 2010 Mail this to a friend!
JNM;

I NEVER tire of glowing comments. :) Call me a glutton for punishment. HI!

eric
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 12, 2010 Mail this to a friend!
JNM:

If it'a any consolation, I'm pretty much self-taught...but I've had some great elmers. (Don't tell anyone, but I have precisely HALF of an electrical engineering degree. I answered the call of the wild halfway through college.) I probably wouldn't recommend this career path, but I've never been normal.

Eric.
 
RE: SWR Meters Make You Stupid  
by WI7B on March 12, 2010 Mail this to a friend!
"In the case of a car battery, the internal resistance is HEAT generating, in an antenna it's in the form of RADIATION RESISTANCE, so it's converted into radiated R.F. instead of heat. That's the ONLY difference, however." - Eric

In the final analysis, it is ALL radiated as electromagnetic radiation (EM). Some forms more useful than others. Radiated HEAT is nothing less than higher THz and infrared radiation. But its source is not what is term "radiation resistance"...which is somewhat of a bias term in favor of useful EM... since loss of photons higher in energy than RF from the antenna is also due to a radiative transformation and material resistance.

73,

---* Ken
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 12, 2010 Mail this to a friend!
In the final analysis, it is ALL radiated as electromagnetic radiation (EM

Aye....sadly enough, this is absolutely true. It's just a bit trickier to calculate the radiation resistance of an atom. :)

eric
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 12, 2010 Mail this to a friend!
I had someone complain to me about a heater he had....how inefficient it was.

I told hin, NO....all heaters are 100% efficient....eventually. HI

:)

eric
 
RE: SWR Meters Make You Stupid  
by N0JEF on March 12, 2010 Mail this to a friend!
Fantastic article. So SWR is not really the boogy man? What will the "resonant only" crowd do now?
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 12, 2010 Mail this to a friend!
"Fantastic article. So SWR is not really the boogy man? What will the "resonant only" crowd do now?"


Ancient Quaker proverb: "A man convinced against his will is of the same opinion still."

I remember this time in college we were watching a slow motion MOVIE (not an animation...an actual MOVIE!) of a hummingbird hovering. This guy stood up in class and announced, "Their wings don't really move like that!" He was dead serious.

There is absolutely no hope for a certain percentage of people. I don't try. :)

Eric
 
RE: SWR Meters Make You Stupid  
by W2EP on March 12, 2010 Mail this to a friend!
OUTSTANDING. BET YOU COULD MAKE THE THEORY OF RELATIVITY SUITABLE FOR IDIOTS. I HAVE BEEN AT THIS GAME FOR 50 ODD YEARS AND NEVER HAD AN SWR METER IN THE OLD DAYS. YEAH DREW LOTS OF SPARKS WITH MY PENCIL OFF THE OLD 304TL KW AMP. AND LIT LOTS OF BULBS (BOTH KINDS) TO IMPRESS THE YL'S. THE NAVY WAS NOT TOO HAPPY THAT I BURNED ALL THE FINGER PRINTS OFF BOTH HANDS IN THE PROCESS. LOL USED MY WAR SURPLUS RF AMPMETER IN ONE LEG TO TUNE FOR MAX OUTPUT. STILL HAVE THE DARN THING. THANKS AGAIN. VERY INFORMATIVE AND MOST IMPORTANT UNDERSTANDABLE. 73 CAPT.PAUL
 
RE: SWR Meters Make You Stupid  
by K5END on March 12, 2010 Mail this to a friend!
"...the premise that ALL ionospherically reflected signals are circularly polarized."

Would you agree to "elliptically" polarized?

That might be more accurate semantically, for what it's worth.

73
Larry
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 12, 2010 Mail this to a friend!
Elliptically with a nearly unity axial ratio. :) My article actually goes into this in quite detail.

Stay tuned! *and in the meantime, look at ionograms. :)

Eric
 
SWR Meters Make You Stupid  
by VE7AUL on March 12, 2010 Mail this to a friend!
Hi Eric.

This is one of the most informative eHam articles I have ever seen. I hope management keeps this in a "classics" repository for future use.

"3) Let's eliminate the antenna tuner, but replace our coax sith a half wavelength of 300 ohm twin lead. The half-wave is so we don't have to contend with reactances as wall, We understand that a 1/2 length of any transmission line repeats the load."

But what happens in the more general cases like a quarter wavelength of the same feedline with and without an antenna coupler.

"You may have already demonstrated this without knowing it.. If you have an antenna tuner, you know that if you tune it for maximum RECEIVE noise, it's going to be pretty closely matched for best transmit match, as well. This is assuming, of course, that your transmitter output impedance is the same as your receiver INPUT impedance....at H.F., most modern rigs are pretty close."

Yes I have and this is the mysterious part. I still don't see how the noise energy can get through the transmatch to the radio while the transmitted energy (reflected back from the antenna) gets bounced out toward it again. It looks like the transmatch is treating the two differently even though they are traveling in the same direction but the same physics must apply to both signals.

I don't mean to be a pest but I would really like to get to the bottom of this once and for all.

I am looking forward to your X-O article.

Brian
 
SWR Meters Make You Stupid  
by VE7AUL on March 12, 2010 Mail this to a friend!
Hi Eric.

Cancel my last post. I think I figured it out. The key point to remember seems to be that while receiving you are not transmitting so there is no power going out though the tuner to be superimposed on the received signal coming in from the antenna.

Brian
 
RE: SWR Meters Make You Stupid  
by K9MHZ on March 13, 2010 Mail this to a friend!
Hey Eric,

Maybe a little off topic, but after reading your and Alan's recent posts, I've gotten interested in buying an antenna analyzer. So, here's the $279 question....are the MFJ 259B or 269B(?) units OK? I mean, do you happen to know if the quality is there, or are there better alternatives?

Thanks....great post as usual!

Brad, K9MHZ

Equinox in a week!
 
RE: SWR Meters Make You Stupid  
by W5DXP on March 13, 2010 Mail this to a friend!
"WHERE A TRANSMISSION LINE EXISTS, THE POWER GENERATED BY ANY RADIO TRANSMITTER EQUALS THE FORWARD POWER MINUS THE REFLECTED POWER IN THE TRANSMISSION LINE. ALWAYS."

IMO, it would be better to say that the power delivered to the antenna system by the source equals the forward power minus the reflected power. No one knows exactly how much power is being "generated" and "dissipated" so someone decided to solve the problem semantically by defining the generated power equal to the delivered power. This is one of those "by definition only" situations that warps the bounds of reality. An ideal voltage source, for instance, obviously generates a power of V*I*cos(theta) some of which is dissipated internally in the source resistance.
--
73, Cecil, w5dxp.com
 
RE: SWR Meters Make You Stupid  
by KC0W on March 13, 2010 Mail this to a friend!
Good in depth info.


Tom KCØW
 
RE: SWR Meters Make You Stupid  
by KL7AJ on March 13, 2010 Mail this to a friend!
MHZ:

Those analyzers are both fine instruments, but like everything else MFJ makes, you need to think of them as "Partial kits." MFJ has innovative design and impeccable engineering...it's their assembly process that needs help.
So check the operations FULLY as soon as you get it...and if there's ANY problem, get a replacement immediately. They DO make good on their warrantees.

Eric
 
RE: SWR Meters Make You Stupid  
by KW6LA on March 13, 2010 Mail this to a friend!
Eric,

I do not like reading long winded articles on e-ham, but after the second paragraph I was glued to the
screen. You hit it right out of the ball park on this one ,Bravo ! My only hope is that more Ham’s take
the time to read this very important lesson. I have also witness the funny power on my meter when
running a miss matched antenna. 100 w looked like 125 ……. Boy was I happy for half a second.

Kudos and well done!


KW6LA
 
RE: SWR Meters Make You Stupid  
by AE6RO on March 14, 2010 Mail this to a friend!
I only made it halfway through before nodding off. Is the author promoting or dissing ladder line? To be honest, I really don't care. Without sunspots the transmission line may as well run to a dummy load.

But there ARE sunspots now, you say. Oh, yeah and the solar flux is up to 90 today with, something like 12 sunspots. Huh. 73, John

P.S. Is the author smoking something other than his finals?
 
SWR Meters Make You Stupid  
by K1TN on March 15, 2010 Mail this to a friend!
Holy cow, Eric, nice job! It took me all day to read this, and that was only 23 hours instead of 24 since we switched to daylight stretching time.

It's funny how articles like this seem loooong on line, when they wouldn't seem long at all if they appeared in print. The New Yorker gets away with it every week. I'm not trading my liberry card for a digital "reader" any time soon.

I've solved the transmission line/SWR problem here at The K1TN Superstation -- I don't have a transmission line. Auto tuner to a piece of wire stuck out the winder. But, but, there's all those pesky swurs in the six feet or so of coax from the transmitter to the tuner.

Jim Cain, K1TN
 
RE: SWR Meters Make You Stupid  
by K9MHZ on March 15, 2010 Mail this to a friend!
Thanks for your help, re: analyzers, Eric.

Best,

Brad, K9MHZ
 
SWR Meters Make You Stupid  
by G6UWK on March 15, 2010 Mail this to a friend!
very interesting, as others have said surprising lack of maths for subject and degree of concepts covered and put across.
As the article tries to put across SWR is just a tool to measure mismatch not a God, lets face it did all those agents for SOE/OSS worry about their SWR when transmitting? no they were concerned about the Germans!

Jon
G6UWK

PS. No offence to present day German individuals
 
SWR Meters Make You Stupid  
by K9ZF on March 15, 2010 Mail this to a friend!
Once again, great article Eric!

I have always been interested in antennas, and consider myself pretty knowledgeable, but I still picked up a few things:-)

It's always been my opinion that when you stop learning about a subject, it becomes boring fast.

I can't believe all the people who complained the article was too long! There have been many books written on this subject, and you have to PAY to read those. Get over it! Yes, it took me about 3 sittings to read the entire article. But, I enjoyed every minute of it:-)

I do have a question, if you have the time. I always assumed [there's that word...] that reflected power was dissipated in the transmitters final, which causes failures. As you pointed out, this is wrong. Which I should have known, had I given it any thought. But, operating a transmitter into a poor load will cause it to fail. So what is the real cause of the problem?

I look forward to your next article!

73
Dan
--
Amateur Radio Emergency Service, Clark County Indiana. EM78el
K9ZF /R no budget Rover ***QRP-l #1269 Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla> List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!
 
RE: SWR Meters Make You Stupid  
by VK6RO on March 18, 2010 Mail this to a friend!
"I had someone complain to me about a heater he had....how inefficient it was."

I remember very very clearly my science teacher in high school telling us that "heat loss equals heat gained"

There is no loss in heat transfer is what he was saying.


Thats why a nice 8877 amplifier will keep the shack, and your SWR meter warm on a cold day. HI.

graham vk6ro
 
RE: SWR Meters Make You Stupid  
by KC8YXA on March 20, 2010 Mail this to a friend!
You have opened my eyes now if I can only get my brain to work.
 
SWR Meters Make You Stupid  
by KD7KCP on March 20, 2010 Mail this to a friend!
I understand thank you.
 
RE: SWR Meters Make You Stupid  
by AJ4MJ on March 22, 2010 Mail this to a friend!
Eric,

I used the info in this article to build a speaker wire dipole for portable 40M operations. I don't know the Z0 of the feedline, but I know its VF, so I was able to cut it to exactly half a wavelength. Used a 259B to tune it up, but I didn't even look at the SWR, just found the point where X=0. Kept cutting the antenna until the X=0 point was in the middle of the band. The theory worked beautifully. I had R=72 at the center point and low SWR over the whole band.

To those who say "just use coax and 1/2 wave dipoles", note that sometimes we need to build antennas that fit a certain need. A big roll of RG-58 would weigh a lot more and take up more backpack space than the speaker wire, which has equivalent loss at this frequency. By digging deeper and understanding the theory, we can make things work to our advantage.
 
RE: SWR Meters Make You Stupid  
by WA2JJH on March 25, 2010 Mail this to a friend!
Simply a Brilliant artical. Why did I not see other articals written by you. You do have a gift. Yes, many have the same knowledge. However they have a real crummy atitude.

My first 4 year degree in EE was back in 1982. I sure forgot some concepts covered in "Circuits 3 and "fields and waves. Problem with these EE required
classes is that every professor waste time with much of the applied calulus.

The material you covered in a nice artical, would have about 6 blackboards full of the math derivations.

I too used to work at several commercial broadcast TV stations and one FM. You are very correct. I never saw a single meter labled SWR.
oNLY IN THE ENG TRUCKS, swr meters were used for the 450mhz two way radio.
For that limited application of the "Maximum Power Tranfer theorem, a simple radio, short run of coax, and a 1/4 wave antenna on a single frequency.

We would use a bird model 43. Measure the foward power at the TX and antenna feedpoint. Reverse the direction of the slug. Then measure reflected or reverse power. We did not eve bother plugging in the meter readings into the equation for SWR.

Simple RF common sense was used. The TX foward power at the antenna feedpoint was close enough to the motorola manual said the Max TX output(FM modultion),
we would by almost 100% certain we were matched. Just to double check, the reflected power was noted.
If the reverse power was only a few watts, we took our "union coffee break" A union coffee break is as long as we could make it!!!!!Heck, work slow enough, we got into overtime!!!!
The short cut for the 2gig remote TX, I will not reveal. Too many will get pissed off. The FCC allowed a maximum of 12W out for the old 1978-199o 2 gig ENG band.
One time the cameramen could not get a 2 gig signal out. They sent me to fix it fast. I just put my thumb against N connector after I disconnected it from the Twin Golden Rod dual phased claven cavity driven yagi's. When I told them to swtich on the TX. I would know the problem in a few seconds
I should have received a nifty RF burn on my thumb, the burn should take 1 second of exposure to indicate maximum power transfer :)
The Wolfcoach vans used a cheap way of getting the 12W though 50 feet of simple RG-8. RG-8 has a 3 db loss every 18 feet at 2.2 gig. At the top of the mast, is the end of the tranmission line. 12W is attenuted down to one watt. A 2 gig amp bolted to the antenna array amplifies the 1w back to 12W.
12W will give a bad burn in 1-2 seconds. 1W, the thumb can tolorate about 8 seconds. My thumb did not even get warm. I diagnosed the problem to the coax.
Time was running out for the 6PM news.
Thank god for Radio Shack!!!! Purchased a 50 foot RG-8 CB line. I slapped on PL259-N connector adapters at both ends. I DID NOT CHECK FOR NO STINKING SWR.
I knew to expect an unkown loss from the diaelectric and rf discontinity miss match caused by the PL-259 to N connector adapter.
I still did not care about SWR. I just needed 1/4-1W to drive the 12W PA. I had minutes untill airtime.
Fired up the 2` gig tx. The RX site reported a 54db video S/N ratio.Good enough. 5-4-3-2secOND SILENT COUNTDOWN, LIVE REMOTE SHOT---saved seconds before air.
No SWR meter or live animales were used or killed HI-HI

The directors and producers claimed they saved the show. typical!!!

2 gig for TV use was replaced by KU band satruck, 7 gig terrestrail and of course the Internet.
 
RE: SWR Meters Make You Stupid  
by WA2JJH on April 1, 2010 Mail this to a friend!
I think if you check it out, cheap SWR meters were products for when the old 11M ham band transmuted into
23 channel CB radio back in that late 50's

No CB DUDE would buy a Bird Model 43 with the 3-30mhz low power slug.

Early CB meccas like the OLd Lafayette Radio, allied radio Tandys Radio shack had to make some meter that would give a very relative to where placed in coax line device.
Some device to measure up to 4 watts at 27mhz. I remember a 10 dollar meter all cb stores had.
Relative field strength and SWR in one box. Perhaps that is SWR's legacy.
Many post 1957 Ham rigs never even had an SWR meter.
S units, plate /current/reletive out to peak the load cap. Dip the plate. N0 swr or vswr. vizwar units?
 
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