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[Articles Home]  [Add Article]  

Resonance Schmesonance!

from Don Keith, N4KC on March 16, 2011
View comments about this article!

Resonance Schmesonance!
By Don Keith, N4KC

www.n4kc.com www.donkeith.com

I’m not trying to get a war started. Or troll for comments. All I’m really trying to do is help others in our hobby—not just newcomers—understand one of the basic concepts of radio frequency transmission: antenna system resonance. Understand it and use it to their benefit so they may better enjoy our wonderful hobby.

There, I said it. RESONANCE. Notice, though, that I used the phrase antenna system resonance. I know of no one using only an “antenna” to send electromagnetic waves whirling off into the sky. They likely have much more between the output stage of their final amplifier (not just a “kicker” but the amplifier inside your radio) and the ionosphere. Much more than just what we typically refer to as an “antenna.” And all that stuff in the chain affects that fleeting Holy Grail we call “resonance.” (By the way, anyone who responds by talking about a “resonate antenna” will be promptly flailed with a length of old left-over RG-59 coax! “Resonate” is a verb. “Resonant” is an adjective.)

Let me start the melee with a strong statement: achieving a perfectly resonant antenna system is virtually impossible. By “antenna,” I mean a transducer—a thingy that changes one form of energy into another, and for our purposes, we’ll call it an antenna (but I really mean an “antenna system”) that changes AC current into electromagnetic waves. The system at resonance forms a more-or-less tuned circuit, which throws in equal doses of inductive reactance and capacitive reactance. At resonance, they cancel each other out, leaving only resistance. And I’m talking two kinds of resistance: loss and radiation. For the purposes of this little conversation starter, let’s ignore loss—which is not usually a big factor at HF frequencies—and concentrate on the good stuff…radiation resistance, something we all want to conjure up as much of as we can.

Now, ponder for a moment all the possible variations of capacitive and inductive reactance that might be swirling around from the rear end of your radio, the jumper to the above-mentioned “kicker,” all the guts inside the amp, the jumper to the antenna matching device (I’m philosophically opposed to the term “antenna tuner” because you are NOT tuning the antenna with that box at all!), the innards of the “tuner,” the feedline, the hank of wire or aluminum that we call an “antenna,” all the various connectors and insulators and maybe even a balun, your kid’s swing set, the neighbor’s metal-roofed garage, and even the sunspot-influenced stuff God put up in the sky above you. Gosh, even the dirt in your yard enters into the equation. And your neighbor’s yard. And all the way beyond the horizon. All part of your antenna “system!”

My, my, my. Hard to imagine it would ever be possible to bring those two forces of reactance to a point where they perfectly cancel each other out and allow every microwatt of power from your little transmitter to shoot off your antenna, launched in the direction of that highly-prized DXpedition. But it can happen. Not very easily. But, technically, it can happen.

That’s one of the things you bought that matching device for in the first place. You can make it appear to your radio that you have that perfect resonance out there, stretched between two shade trees or clamped to a mast on top of the tower. With those controls on the front of the matchbox, you can adjust its internal components, thus presenting to your transmitter the exact value of impedance—the two reactances canceling each other out—that the rig wants to see. (I know. The matching device can go out there closer to the feedpoint, too, and would work better in many situations, but that’s beyond the scope of this conversation starter.)

But just for grins, let’s say Jupiter aligns with Mars and you happen to cut the antenna perfectly, have precisely the correct length of feedline, the ground and earthworms in it present the right amount of conductivity, and Junior’s swing set is exactly the correct distance from the antenna feedpoint. Capacitive and inductive reactance balance beautifully, wiping each other out, leaving only the good stuff: delightful radiation resistance.

Whooppee! You have achieved a resonant antenna system! The much-worshipped standing wave ratio is 1:1 (Our inane fixation on SWR is fodder for another article. In fact, I wrote one. You can find it HERE or at my web site: www.n4kc.com). You are emitting about as much of your precious RF into space as you possibly could manage, based on the immutable laws of physics.

Then you go and do something dumb, like QSY up or down the band a couple of hundred kilocycles, chasing a DX station or to talk with a buddy. Aw, heck! The aerial is no longer resonant. Either Mr. Capacitive or Mr. Inductive have the upper hand. The needle on the SWR meter sways disturbingly upward. Impedance dips toward zero ohms or zooms toward the sky, abandoning “50 ohms” completely. You begin worrying about your considerable investment in your nice radio.

Aw, in truth it’s probably no big deal on 40 meters or lower wavelengths. A dipole cut for the middle of the band on 40 or above will probably still work okay from one end to the other. But it won’t be resonant. No, it won’t.

Heaven forbid you try to use that dipole on some other band that is not an odd harmonic of the one for which you cut it. Resonant? Not by a long shot. And maybe so far off that your radio spits and sparks.

Oh, you might be able to adjust that matchbox so the radio is fine with everything. But signals suddenly seem weaker. People ignore you when you call them. You scream and squawk but the DX stations no longer seem to hear you. The radio thinks there is a resonant aerial out there in the backyard, but you and the RF gods soon know different.

“But wait, OM,” you say. “You told us resonance did not matter. Were you trying to get a fight started after all?”

Well, I did say that, and maybe I should have clarified it a bit. Within reason, resonance is not necessary to communicate with relative effectiveness. The men who went to the moon used decidedly non-resonant antennas in their radio communications. Few AM broadcast stations have truly resonant antennas. They use capacitors and coils—sound like that “antenna tuner” on your desk?—to get a match to their towers/antennas. Only thing is, once they start transmitting on their assigned frequency and have everything set, they don’t have to change anything. As opposed to you, you QSYing, band-hopping fool, you. That is, they don’t have to adjust anything until something else changes, like the ground system starts to deteriorate.

So why do we work so hard to make resonant antenna systems if it doesn’t matter?

It actually does, in some cases. Even if you can get your matchbox to present a lovely 50-ohm load into a ten-penny nail, it will not be nearly as efficient a radiator as a dipole cut to frequency. You probably want to achieve something a bit closer to resonance than that!

If you use a feedline that has higher loss when presented with standing waves, then you would want your antenna to be a lot closer to resonance. Again, that is true, even if your lovely antenna matching device seems to have all that mess worked out. That’s coax I’m talking about, folks. Handy and pretty as the stuff is, it will not work nearly as well if presented with a load that is way off from 50 ohms of impedance.

There are alternatives. Open-air-dielectric feedline is the best. Or window line. It’s cheap, virtually ignores standing waves, and allows you to use one non-resonant-in-most-places antenna across a broad part of the radio spectrum. It has its quirks, too, I’ll grant you. But learn more and you will see what I mean. The same above-mentioned article talks about this stuff and why it can be an important part of your antenna farm.

So here is what I am saying:

1. It is very difficult to achieve perfect resonance in an antenna system, but it can be done.

2. But is it really worth it?

3. If you do devise a resonant antenna system, once you venture up or down the band a ways, or you jump to another band, you are moving farther and farther from Shangri La. Results may deteriorate rapidly.

4. An antenna matching device can allow you to use a very, very non-resonant antenna system, but the result may or may not be a good one.

5. With the proper circuitry (antenna matching components) and a feedline that is not a stickler for resonance, you can still use a very, very non-resonant antenna with very, very good results.

6. Learn more about SWR and resonance so you don’t become a slave to them, but so you can manage them in such a way that you get the results you want.

Look, maybe you are one of those guys who camps on one frequency on one band all day every day. Fine. Get that dang antenna as close to resonance as you can. Do not invest in a matching device. Feed it with coax. And knock yourself out. Brag that you don’t believe in “antenna tuners.” “I only use resonant antennas!” you expound. Good for you, Chief. Enjoy that narrow little sliver of spectrum while the rest of us flit about across a broad swath of the shortwaves, chewing rags and nailing DX.

See, we want to get a taste of every cycle of spectrum we have available to us. Few of us are able to put up a couple of dozen “resonant” antennas to do so. (To be fair, with a decent multi-band antenna like a hexbeam or fan dipole and enough dipoles to cover 160 through 30, I figure you could get by with six or seven antennas without being too far off resonance. A trap vertical could probably cover 160 through 10, but it ain’t gonna be resonant in many places on some of those longer wavelengths! Some guys even sell multi-band, no-radials-required verticals, but good luck filling your logbook using one of those.)

Fact is, many of us prefer not spending all our operating time worrying about “resonance.” Or fidgeting about standing waves. Wringing our hands as we glare at the SWR meter.

We’d much rather learn how to manage these things, take advantage of the science, and apply it so we can have a perfectly wonderful experience every time we throw the “ON” switch.

Besides, learning and experimenting with this stuff is where a lot of the fun happens anyway.

Member Comments:
This article has expired. No more comments may be added.
 
Resonance Schmesonance!  
by N8NSN on March 16, 2011 Mail this to a friend!
" 5. With the proper circuitry (antenna matching components) and a feedline that is not a stickler for resonance, you can still use a very, very non-resonant antenna with very, very good results. "

Amen.



I really liked this article. A humorous read ladened with facts, made easy to understand, cleverly, in layman terms.

Good Job OM !
 
RE: Resonance Schmesonance!  
by KI7YY on March 16, 2011 Mail this to a friend!
Thank you for an excellent article! Not to be a stickler, but the antenna does not simply appear to the radio as resonant, in fact it is at resonance. The change in reactances in the system is real not just apparent.
I agree with you that the over-emphasis on vswr is unfortunate. 73 and keep the articles coming!
 
Resonance Schmesonance!  
by NA4IT on March 16, 2011 Mail this to a friend!
A totally resonant antenna system is a great thing to have... if you never move the VFO!
 
RE: Resonance Schmesonance!  
by WG8Z on March 16, 2011 Mail this to a friend!
Well said.
Love it when the guy who brags about his
"resnant ann-tanna" signal folds-back into the
noise when a little ice hits.
Long live link couplers and open feeders.

Greg
WG8Z/p/4
Stuart Fl
 
RE: Resonance Schmesonance!  
by K9MHZ on March 16, 2011 Mail this to a friend!
Oh man, when I saw the title of this topic, I thought a new salvo in antenna wars was just unleashed. Turns out to be nicely done so that the anal-retentive OCD notables on here can't pick it apart and dissect it.

But, the thread is still young......

Good reading.

 
Resonance Schmesonance!  
by KX4D on March 16, 2011 Mail this to a friend!
Excellent article!!! I'm not a "techie" and only a hobbyist. However, I've been involved in Amateur radio since 1978 and had been stuck in the "youthful myth" that resonance was achieved at the lowest SWR. My eyes were opened a couple of years ago when I began to study for my Extra (meaning go back and actually learn) when I came to realize that many factors (the radiator, feedline, feedline length, ground, etc.- the SYSTEM) affect efficiency. I sure could have used your wisdom a long time ago...
 
Resonance Schmesonance!  
by N4IR on March 16, 2011 Mail this to a friend!
Right on, Don! I've been preaching this sermon for 20 years or more. Most often I am met with that service on the price list in the barber shop - "Dumb looks....Free".

Jim, N4IR
 
Resonance Schmesonance!  
by KB1GMX on March 16, 2011 Mail this to a friend!
Fun!

As a user of a 92ft inverted L for 80,75, and 40M resonance is not part of that antenna. However an efficient and simple coupler at it's feed point makes it works well. The radio doesn't care that the R is somewhere between 40 and 70 ohms with some small +-J and the coax has an acceptable (under 1.7:1) SWR to keep those that might panic happy. I keep the feed in that range to keep the solid state gear happy. I also run glow in the dark (tube) radios and with their adjustable Pi networks they don't care. That and a coax under 25ft makes it a mostly non factor.

I also run end fed half waves, Oh my. Yes resonant and not 50 ohms or even close (more like 4000!) at the feed point. Yep it has a coupler at the feed point too.

Then there is the 5/8th wave 2m antenna, yep not resonant and has it's own matching gadget too at the base.

In the end it's about getting the output of the final to the metal that radiates. My rule is more metal and higher/taller where possible, couple to it and work stations.

Allison
 
Resonance Schmesonance!  
by VE4EGL on March 16, 2011 Mail this to a friend!
Great article. Well-written and informative.

Now, if you'll excuse me, I have to go reposition my neighbor's earthworms to improve my resonance.
 
Resonance Schmesonance!  
by WA0ZZG on March 16, 2011 Mail this to a friend!
One thing I have learned about HF antenna systems, they are like little kids. Will make a liar out of you every time.
I now live in a condo. No antennas allowed. Doesn't mean I'm off the air. It's a new, large fourplex. I noticed that there's a lot of rain gutter and downspouts connected together. Sneaked a run of coax out to the closest downspout. Also installed a tuned ground system to push off of. Found it even does quite well on 160M. Go figure.
 
RE: Resonance Schmesonance!  
by WX7G on March 16, 2011 Mail this to a friend!
And antenna is not "...a thingy that changes one form of energy into another."

An antenna is fed electromagnetic energy and it radiates electromagnetic energy.
 
RE: Resonance Schmesonance!  
by W4VR on March 16, 2011 Mail this to a friend!
Owners of solid state amplifiers are finding out that 50 ohms at the output connector, and not necessarily a resonant antenna, is mandatory.
 
RE: Resonance Schmesonance!  
by K0BG on March 16, 2011 Mail this to a friend!
Viswaritis. A disease far too many amateurs have in common.

Alan, KØBG
www.k0bg.com

PS: Don.... nice to see you back in your true form!

PSS: When's the next book due at the publishers?
 
Resonance Schmesonance!  
by N4EV on March 16, 2011 Mail this to a friend!
Great job Don!

I learned from Al Henderson K6AJ (SK) and he held the idea that an antenna was some sort of a linear transformer to take the 50 ohm output of our radios and "transform" it to the 377 ohms that he said is the nominal impedance of free space.

Oh well, your article is very good food for thought and I think to the point.

About VSWR, an OM at Collins many years ago said. "SWR will circulate until it is disapated"!
Usually in the tank circuit.

Thanks again
Clayton N4EV
 
RE: Resonance Schmesonance!  
by KE3HO on March 16, 2011 Mail this to a friend!
Great article. People talk about "resonance" as though it was something magical. "Resonance" means nothing more than having a purely resistive feedpoint impedance. An antenna can have a feedpoint impedance of 2500 j0 at resonance and yield a 50:1 vswr with 50 ohm coax.
 
Resonance Schmesonance!  
by K2JVI on March 16, 2011 Mail this to a friend!
Great article. I agree that antennas don't always have to be resonant. I've been using non-resonant antennas for years, namely the old 80 meter dipole fed with ladder line, worked very well. My latest antenna is a version of the DX engineering 43'vertical. But instead of using the 43' vertical, I use two wires, one is a 60' vertical up a tree and the other is a 120' L shaped wire with the high point at 50'. I use a relay to switch between them just ahead of the DX engineering 4:1 balun.
The other balun lead connects to a radial plate with 50 buried radials ranging in lengths 20 to 60 feet. All fed with 100' of RG213 coax and an MFJ versa tuner V in the shack. The antenna works very well on 160-15 meters. I've also worked plenty of DX on 75,40,20,17,and 15 meters. I do notice some loss of efficiency above 15 meters so I've added a 12,10,and 6 meter dipole combo as well. And I don't need the tuner for the dipoles. The way I figure it is this, the loss on the RG213 due to non resonance for the verticals is not too critical on the lower bands, but gets noticeable above 15 meters, hence the dipoles. And its not difficult to make resonant antennas for 12,10, and 6 meters.

 
Resonance Schmesonance!  
by N4RSS on March 17, 2011 Mail this to a friend!
"Whooppee! You have achieved a resonant antenna system! The much-worshipped standing wave ratio is 1:1"

This is not correct. Resonance is when you have zero reactance, as you say, but that doesn't necessarily imply anything about SWR.

You could be resonant with a resulting 100 ohm resistive load and no reactance and have a 2:1 SWR
 
RE: Resonance Schmesonance!  
by N4KC on March 17, 2011 Mail this to a friend!
True, N4RSS, but you get my point.

As to my "transducer" comment, from one source:

An antenna is an arrangement of one or more conductors, usually called elements in this context. In transmission, an alternating current is created in the elements by applying a voltage at the antenna terminals, causing the elements to radiate an electromagnetic field. In reception, the inverse occurs: an electromagnetic field from another source induces an alternating current in the elements and a corresponding voltage at the antenna's terminals.

Michael Faraday is generally credited with discovering the principle of induction in 1831 when he ran an electrical current through a conductor and noted that another parallel conductor showed current flowing in it, though the two conductors were not touching. Did that make Mr. Faraday the first DXer?

Alan, since you asked, the latest book is just coming out in paperback and the next one is to be published in November.

73,

Don Keith N4KC
www.n4kc.com
www.donkeith.com



 
Resonance Schmesonance!  
by KX0R on March 17, 2011 Mail this to a friend!
Don,

Thanks for this one - one of the best pieces ever on EHAM!

When I go backpacking with a 5W rig, I don't have the luxury of carrying more than a few pounds of gear. Seems like I always want to work several bands as conditions change during the day and night. It just isn't practical to carry more than one wire antenna - usually it's just a 40M dipole, an end-fed wire, or if I'm feeling strong, a horizontal loop (full wave on 40M).

Even though it weighs something, I almost always take 35 or 40 feet of window line so I can tune the system to match the ATS3B on whatever band I decide to use. Very often I spend time on 20M, and that (resonant) 40M dipole looks like about 4000 ohms at the center! That gets transformed to something even more awful at the tent end of the line, but the BLT transforms it to 50 ohms with just a little bit of adjusting. On 30M or 17M there's lots of reactance from the non-resonant antenna, so the tuner has to be used to resonate the entire system, so the little mosfets in the ATS3 are happy. It all works very reliably, and I seem to make lots of QSO's on many bands, despite having just one wire.

I've tried other (lighter and smaller) feedlines, and while they work OK when the antenna itself is resonant, the performance on the non-resonant bands isn't close to what can be had with low-loss window line. With QRP you can really tell the difference, and so can everyone else out there.

Don has it right. Believe it, and join us as we flit around from band to band, just adjusting a few knobs and switches, or maybe using an autotuner, without even thinking about the Smith Chart until later...

Tuners can make you free!

George
KX0R
 
RE: Resonance Schmesonance!  
by N4KC on March 18, 2011 Mail this to a friend!
Thanks, George. As you might guess, the impetus for this article was my hearing (yet again) someone on the air bragging about his resonant antennas.

"I'll never have a tuner in my shack!" he declared. "All they do is 'trick' the transmitter into thinking there is a real antenna on the other end of the feed line."

He had a one-by-two callsign, by the way.

If that's his level of understanding, then fine. I just hate for others--and especially newcomers--to hear such and decide HF is not worth it if they have to erect antennas that have to be perfectly resonant and a matching device is not an option.

73,

Don N4KC
www.n4kc.com
www.donkeith.com
http://n4kc.blogspot.com

 
RE: Resonance Schmesonance!  
by K1BXI on March 18, 2011 Mail this to a friend!
""All they do is 'trick' the transmitter into thinking there is a real antenna on the other end of the feed line."

When the antenna "looks" back at the output of the tuner, is it also "tricked" into accepting what it sees?

You bet, and it's no trickery. Perhaps the antenna tuner should be called a "conjugate match system tuner"

Nice read Don, Let's hope the choir is listening and understanding.

John

 
RE: Resonance Schmesonance!  
by KB5QMG on March 18, 2011 Mail this to a friend!
Really enjoyed the read, thanks.
 
Resonance Schmesonance!  
by K6SBA on March 18, 2011 Mail this to a friend!
Don,

Many years ago, Joh Haerle, WB5IIR (sk), wrote a great book called "The Easy Way - HF Antenna Systems." In a very straightforward nontechnical way, John put to rest all the myths (urban and otherwise) about resonant antennas. His mentors were antenna icons such as Walt Maxwell.

Unfortunately the box appears to be out of print, but the first chapter, which thoroughly summarizes John's points, is available on the web at http://www.k4mg.com/Antenna%20Design%20the%20Easy%20Way.htm. I would really encourage hams new to HF (and anyone else for that matter) to read this article before listing to a lot of misinformation from an "experienced" elmer. There is also nothing wrong with knuckling down and plow through the latest edition of Maxwell's "Reflections."

I remember an article/rant on eHam several years ago where the author claimed that antenna tuners "ate" up so much energy that the holes in their enclosures were to vent all the heat. Yea...right.

73 de K6SBA
David in Santa Barbara
 
RE: Resonance Schmesonance!  
by AA4PB on March 18, 2011 Mail this to a friend!
I have an "antenna" that has a 1:1 SWR from 2-30MHz and it is resonant on all those frequencies as well. Zero reactance - only resistance.

It's called a dummy load. Just one problem - it doesn't radiate much power, turns most of it into heat. I guess that indicates that low SWR and resonance doesn't necessarily make a good antenna. In fact, many of the "do it all" commercial antennas on the market work the same way. They turn much of the power into heat and radiate just a little so that they can "look good" on all bands.
 
Resonance Schmesonance!  
by AB0RE on March 18, 2011 Mail this to a friend!
Tuners have been given a bad image because of all the hams that feed their HF doublet that's not resonant anywhere near the ham bands with 100' of RG58 through a wide range antenna tuner, in which case a good portion of the power coming from their transmitter never gets radiated. To make matters worse, they boast "if I can hear 'em, I can work 'em!", never knowing what they're missing.

I don't think the "anti-tuner purists" would take such issue with tuner users if tuners were use the in a more responsible manner.... to flatten out minor to moderate SWR on coax-fed antennas, or to be used in conjunction with low-loss ladderline if their SWR is more than moderately high on the frequencies they intend to transmit on.

And although there is nothing "wrong" with owning or using a tuner, many hams DO leave their transmitter parked on the same frequency (their "section phone net", for example), or they stick to the high bands where the antenna's bandwidth should be acceptable to operate without a tuner. For these hams I can't figure out why they don't just put the extra hour of work into their antenna system to get it resonant with a low SWR on their intended frequency. It sure is nice to not be married to the "tune" button.
 
Resonance Schmesonance!  
by G0GQK on March 18, 2011 Mail this to a friend!
Just buy an ATU and bring the system into resonance anywhere you choose

G0GQK
 
RE: Resonance Schmesonance!  
by N4KC on March 18, 2011 Mail this to a friend!
David, I remember that fellow very well. His rants were in reaction (no pun intended) to an article I wrote extolling the virtues of a good ladder-line-fed dipole as a multi-band antenna.

The irony was that he had some beautifully restored Drake gear. And as we know, that wonderful tube gear had the equivalent of an antenna matching device (or whatever we decide to call it) built right in, and "dipping the plate" and "cranking up the tune knob" were an integral part of operating anytime you ventured up or down the band a ways.

Yet he "never" used a tuner!

73,

Don N4KC
www.n4kc.com
www.donkeith.com


 
RE: Resonance Schmesonance!  
by K1BXI on March 18, 2011 Mail this to a friend!
A good read on tuners by Walt Maxwell

www.w2du.com/Chapter07.pdf

John
 
RE: Resonance Schmesonance!  
by N3OX on March 19, 2011 Mail this to a friend!
"I have an "antenna" that has a 1:1 SWR from 2-30MHz and it is resonant on all those frequencies as well. "

A dummy load is NOT resonant on ANY frequency! Zero reactance is only part of resonant behavior. It's very important to distinguish between NON-resonant purely resistive loads and resonant ones.

Resonance requires *energy storage* beyond the flux of energy that's going to heat and radiation. You need to have extra stored energy in electric and magnetic fields to radiate a given amount of power for most efficient types of HF antenna, and when the storage is balanced just right, then you have resonance.

But if you have a load that just absorbs all the energy you put into it resistively, that is not a resonant load. It is a matched load, and it has 1:1 VSWR but it is not resonant, despite the pure resistance.

An example of a real antenna that's close to totally non-resonant a well matched microwave horn antenna. There is no extra energy stored... electromagnetic waves travel from the transmitter through the waveguide, enter the antenna, and leave the antenna with little to no reflection.

In real horn antennas, especially pyramidal ones, there's a little bit of reflection, and so a SWR that's a bit elevated and possibly some reactance at the radio. But that stuff is more incidental to the operation of the antenna. You don't require large amounts of EXTRA energy stored in fields around the horn itself or in the feedline in order to get it to radiate. This makes the antenna very broadband.

Contrast this to a small mobile antenna, where you have a huge electric field around the whip and a huge magnetic field around the coil, with huge amounts of energy just sloshing back and forth between coil and whip. This is required to radiate just a small amount of power from a short whip. We use a loading coil as a magnetic field storage tank. It's a really BIG storage tank, and if you're just a little bit off because you change frequency, you end up with tons of extra magnetic or electric field and lots of inductive or capacitive reactance. A mobile antenna is very high Q because of all the energy that's stored compared to what's radiated. Very narrowband. And since you need so much stored energy, even a tuner and short coax will kill the efficiency of a really short whip. A tuner is not a sufficiently low loss storage tank for the amount of energy required... and sloshing all that energy back and forth in some coax leads to a lot of losses in the coax.

A resonant half wavelength dipole has fields that are inherently balanced. But the more important thing, related to the thrust of this article, is that half wavelength dipoles and other, longer straight wire antennas don't have much extra energy storage that needs to be compensated. If you're close to a half wavelength long or longer, like a doublet off resonance, you can ***store the required extra energy in your tuner and feedline*** without losing too much of it in the process. You can use stored energy in different ways to transform impedances... so even if the antenna is resonant and a thousand ohms, you can use the feedline and tuner to transform it to 50 ohms.

I think it's important to talk about stored energy, because the issues of feedline loss in a tuned feeder arrangement are related to how much energy you need to slosh back and forth between the tuner and antenna, and how well the feedline works as part of an energy storage tank. And the issues of feedline and tuner SURVIVAL in the face of high voltages and currents are related to energy storage too.

If you need to store a **little** extra energy during part of the cycle and deliver it back to the antenna, like when you're operating your 75m dipole down on the CW portion of 80m, an ordinary tuner and coax will be no problem. The voltages and currents aren't so bad, the loss in the coax and tuner isn't so bad. But if you need to store a LOT of extra energy, like using your 75m dipole on 160m, you're going to incur large losses unless you're very careful to use low loss "storage tanks." Loading coils and no intervening feedline are best in this case. A tuner and open wire might be adequate for low power, but it is really easy to arc or overheat something because of the huge amount of extra energy sloshing around.

A dummy load doesn't store any energy. It eats RF and turns it to heat. A well matched microwave horn and waveguide system stores very little energy. It very effectively accepts RF from the transmitter and spits it out the aperture as radiation. Neither of these behaviors involve resonance, even if the input impedance is purely resistive.

73
Dan


 
RE: Resonance Schmesonance!  
by NZ5L on March 19, 2011 Mail this to a friend!
Well Said!
I have incurred the wrath of many, many "old timers" on the air by arguing those same points! (Never mind that my wire antennas have netted 170+ countries and 4 band WAS at 100W). In most cases, the SWR AT THE ANTENNA was up to 3:1 on the upper bands, 5:1 on 80, and 8:1 or higher on 160. However, SWR at the xmtr end is always kept to 1.5:1 or lower
Instead of worrying about SWR, we should be worried about TSE - Total System Efficiency. This takes into account the quality of coax used, the number and length of radials for the counterpoise(if used) and/or the actual height above ground of the dipoles.
That said, there is a lot to be gained from using lengths (or systems) that produce measurable directional gain at the desired frequency. Coming up with practical ways of doing this has been my main interest in the hobby. I mean, c'mon, anyone can layout a couple of kilobux for someone else's engineering, but what fun is that, after making your 5 band DXCC in 6 months? Making our own radios is a bit daunting these days, except for a few hardy QRP advocates, but building an effective antenna SYSTEM is within the grasp of the newest ham.
 
RE: Resonance Schmesonance!  
by AA4PB on March 19, 2011 Mail this to a friend!
You are right, Dan. I shouldn't have said the dummy load was "resonant". My point was to show, in a simple fashion, a worst case example of how the fact that an antenna has a low SWR does not necessarily mean that it is efficient in terms of radiated energy.

There are all sorts of "tricks" out there to make antennas multi band and they sometimes involve adding some sort of resistive loss ("dummy load") to the system to absorb power in lieu of radiating it.

I also submit that the fact that someone worked some DX with an antenna is not necessarily proof that it is efficient. I've worked DX from a mobile that is likely no more that 10% efficient. I've also worked DX while using an efficient antenna and a transmitter putting out less than 1 watt.
 
RE: Resonance Schmesonance!  
by K4RVN on March 19, 2011 Mail this to a friend!
W7XG
Don said in the article that he really meant an antenna system. If he really said that is your comment unchanged? Just curious as to your view.
 
RE: Resonance Schmesonance!  
by K4RVN on March 19, 2011 Mail this to a friend!
Great article Don. As I understand it an antenna system takes ac current and radiates electromagenetic
energy. Also I liked your definition of
resonant which I believe was an adjective if I remember correctly. Of course I am just a novice on antenna theory and trying to learn.
 
Resonance Schmesonance!  
by KC2KCF on March 20, 2011 Mail this to a friend!
The notion of considering an antenna system, as opposed to an isolated "antenna", is absolutely justified. But, as a consequence, why is there still the need to talk about antenna tuners as if they were something fundamentally separate? There is no reason why a tuner can not be considered integral part of the antenna system. E.g., few people would consider loading coils, capacitive hats, or other structures on their antennas to be "antenna tuners". Just putting the matching circuitry inside a separate box and labeling it "tuner" or "coupler" doesn't make a real difference.

A lot of mystique disappears if antennas are considered for what they really are, and what they are not: they do not convert "AC current" into "electromagnetic waves" - such statements are merely entrenched lingo. Rather, antennas mediate between an electromagnetic wave traveling along a waveguide/transmission line (such as a cable, or a trace on a circuit board) and an electromagnetic wave in free space.

Contrary to popular belief, RF energy (or for that matter, AC electric power) does not travel as electric current through a wire; the energy is in the electromagnetic field in and (more importantly) surrounding the wire(s), and the currents and charges induced in/on the wire(s) merely serve to confine and/or guide the electromagnetic wave.

In the ideal case, the transition from "confined waveguide/transmission line mode" to "free space mode" can be made gentle enough (i.e., tapered over a length scale that is large compared to the wavelength), resulting in a broadband traveling wave antenna (e.g. an exponential feed horn).

When the transition is too abrupt, as is the case with smaller antennas, most of the energy isn't radiated to free space, but reflected back - in other words, the mode conversion is highly reactive. Small antennas use matching arrangements to cancel out this reactance. E.g., the radiating sections of a half-wave dipole serve simultaneously as matching "stubs". It is the frequency dependence of this integral matching arrangement that gives rise to antenna resonances. Fundamentally, this is not any different from using an external resonant tuner to force-feed RF energy to a radiator.

To summarise,

1) Antennas convert electromagnetic waves guided along a waveguide/transmission line structure to/from electromagnetic waves traveling in free space.

2) Mode conversion need not be resonant.

3) Narrowband/resonant responses result from the matching/coupling/tuning arrangements used to force-feed radiators that are ineffective mode converters on their own.

4) There is no fundamental difference whether the resonant matching/coupling/tuning arrangement is contained in a separable unit or implicit in the geometry of the radiators.

4a) The above point notwithstanding, a practical difference between "internal" and "external" matching/coupling/tuning arrangements is that external arrangements usually (but not necessarily) have higher losses.

 
RE: Resonance Schmesonance!  
by K4RVN on March 20, 2011 Mail this to a friend!

To KC2KCF
Not being a really smart guy, I have to weigh what I read. Here is a definition of an antenna which seems to agree with my perception of what I read.Are you saying this is not correct as I think you are?

Definition

antenna

antenna is a specialized transducer that converts radio-frequency (RF) fields into alternating current (AC) or vice-versa. There are two basic types: the receiving antenna, which intercepts RF energy and delivers AC to electronic equipment, and the transmitting antenna, which is fed with AC from electronic equipment and generates an RF field.

 
Resonance Schmesonance!  
by WO4V on March 20, 2011 Mail this to a friend!
For some strange reason, I feel compelled to chime in. I know I may regret this...

I am not trying to upstage Don's excellent article, just adding to the discussion.

I have been taken to task for warning newbies about the "lunatic fringe" who insist that antenna installation MUST adhere to this 'n that and be cut this way and be hung that way, etc. and ad nauseum. So, this is my advice to a new ham, take it for what it is worth...

1. Survey your property and determine how long a piece of wire you can put up in the air, running it through and across trees or whatever supports you may have at hand. Yeah, bare wire CAN touch the trees without catastrophic results. Install the wire. Try to use at least a half-wave length of wire at the LOWEST frequency you intend to operate. I'll leave it up to you how to do this (slingshots, bow and arrow, potato gun, etc.)

2. Decide the point along the wire where you can run a length of ladder or open wire line down to a suitable point where you can install a remote balun. Do not worry if the wire is not the same length on either side. Cut the wire at this point and with a suitable "center" insulator, attach each side of the open wire line to each "side" of the wire you previously installed, which at this point is now an antenna. Make sure that the balun will handle the power you intend to run. 4:1 ratio usually will suffice, I have used 9:1 with OK results.

3. Run the shortest length of quality coax (bigger is better) from your remote balun through your window, wall, or tent flap into your shack. (If your antenna tuner has a built in balun and terminals for ladder or open wire line, you can also run the ladder line all the way down from the antenna to the tuner, but usually this is a pain to do).

4. Attach the coax to a quality antenna tuner (whatever you choose to call it) attached to your rig that will handle the power you intend to run.

5. Practice operating the tuner AFTER reading the instructions or listening to your Elmer(hint: an MFJ 259 antenna analyzer or equivalent will make practicing "tuning" your antenna system easier and will avoid irritating your fellow amateur radio operators with obnoxious "carriers" on frequency. if you don't have one, borrow one. Plan on getting one of your own soon). IF this sounds like too much work, get one of those spiffy automatic tuners that will handle the power you intend to run. Again, read the instructions and be aware that the tuner may not handle all conceivable frequencies you want to operate. Just one of those things...

6. Understand you WILL have SOME losses and don't sweat it. I have worked QRPp through such an antenna system with success. You can always get a bigger amp if this bugs you.

7. Enjoy your station!

Read a few old Lew McCoy antenna articles...

Your mileage may vary...

Dave WO4V
 
RE: Resonance Schmesonance!  
by KC2KCF on March 20, 2011 Mail this to a friend!
k4rvn,

Electromagnetic fields interact with charges (current = moving charge), so it is difficult to talk about one without the other.

In Maxwell's theory of electromagnetism, the fields themselves carry energy (which is why radio waves can transport energy without the need of a medium or "ether"). In comparison, e.g the kinetic energy of the electrons making up the RF current in a wire is negligible (unless one goes to really high frequencies). If an antenna radiates energy in form of electromagnetic waves, this energy comes from the electromagnetic field of the feedline, not the moving charges in the feedline.

Some would argue that distinguishing between the current and the field is nitpicking. But it certainly makes a lot of difference in understanding what's going on. It would be hard to explain otherwise why a piece of metal, when part of an antenna, "converts" an AC current to a radio wave, but does not do it when it is part of a coax cable instead.

The other thing one should realise is that engineering parlance is not always a help to understanding what's going on, and sometimes it's outright misleading if not wrong. Keep in mind, engineering is primarily about applying scientific findings towards a purpose, not about understanding them.
 
Resonance Schmesonance!  
by KL7AJ on March 20, 2011 Mail this to a friend!
Required reading for EVERY ham: "My Feedline Tunes My Antenna" by Byron Goodman. It was first published in 1956 in QST has has been reprinted several times since then. It is the definitive article on this matter. I refer to this article in my treatise, "SWR Meters Make You Stupid" as well.

Thanks for bringing this up and clearly 'splaining it again for the noobies. (And us old bees too!)

Eric
 
Resonance Schmesonance!  
by WA4ZKO on March 21, 2011 Mail this to a friend!
Good one Don.

Now I know why I can't work that DXpedition on my dummy load's perfect match ;-)


73
Jeff
WA4ZKO
 
RE: Resonance Schmesonance!  
by 2E0OZI on March 23, 2011 Mail this to a friend!
Hi Don,

great article as usual! I just made my 50th contact and as a new ham the biggest boost to me came via my wife, who ordered me to take down my "resonant" 20m dipole fed with coax as she hated it in the middle of the garden. So I bought a 901B tuner, put a W3EDP over the roof and down to the back garden, with the 24ft counterpoise and I was FREE to explore other bands. Suddenly I could work my 10w OK from 40 to 15m and its great to be able to talk to some people in the morning, noon and early night. It doesn't work so well on 80m but oh well, at the moment I am having a good time and thats what its all about isn't it?
 
Resonance Schmesonance!  
by N8CMQ on March 26, 2011 Mail this to a friend!
WRONG...
 
Resonance Schmesonance!  
by KG6MZS on March 30, 2011 Mail this to a friend!
"...changes AC current..."

Since you let the pedantic Pandora out of her box with the "resonate" comment, "AC current" is redundant. :)

73 de Eric, KG6MZS

PS; All time winner in this department is "The Los Angeles Angels" which is really "The The Angels Angels."
 
RE: Resonance Schmesonance!  
by KG6MZS on March 30, 2011 Mail this to a friend!
To Dave WO4V -- It took me several years on HF to do virtually everything on the list you recommend. I wish I had started with your fine advice.

I still love learning the "whys" -- thanks for a great article Don.

73 de Eric, KG6MZS
 
RE: Resonance Schmesonance!  
by N4KC on March 30, 2011 Mail this to a friend!
Pedantic Pandora? I won't even suggest what her profession might be!

Ouch, you got me, Eric! I think. We say "AC voltage." "Alternating current voltage" sure sounds odd, but that is what it is. I probably would not want to say "A current," or "D current." So I guess we have to just say "AC" or "alternating current."

Don N4KC
www.n4kc.com
www.donkeith.com
http://n4kc.blogspot.com
www.facebook.com/donkeith


 
RE: Resonance Schmesonance!  
by KG6MZS on March 30, 2011 Mail this to a friend!
:)

Most of us have been guilty of the RAS syndrome ;-)

Thanks for the article!
 
Resonance Schmesonance!  
by W2OZ on March 30, 2011 Mail this to a friend!
One of the more confusing items for newcomers is that the dummies that invented the units for Impedance, Resistance and Reactance used the same units for 3 items that don't add up in a simple way! That is OHMS , prefer using Zohms,Rohms andJohms, cause they ain't the same and it reminds me. Use the explanation of the compass, East and West are like the Resistance Axis, North and South the Reactance Axis this makes Impedance the 'Pythagorean' sum, oh yeah, the square root of the sum of the other 2 squared! Think of the compass, if you go 50 miles east and then turn and go 50 miles north you ain't 100 miles from home, , you are the square root of 5000 or the square root of 2 times 50 miles from home. The second item is , you want to be 50 miles east of home[50 Rohms] and then tune out whatever North/South Johms you have [Reactance] Preferably at the antenna, because the 'Antenna element defines the Field your Precious Power is going to Establish in the Air' The more you zig and zag and droop, the junkier your established field gets. Thirdly , the magic of being more than 1/4 wave above earth cannot be excused away, you are or you ain't! Easy on 20m and higher frequencies, takes effort on 40 and gets very tough on 80 or 160m. If you have a 40m dipole below 35 ft , you will work stations, but become very vulnerable to take off angle and the height of the sun during the day, you will not hear the stations returning your calls from afar. Fourth, use high quality [ceramic] end insulators especially if you are running power, propagation [maxwell's equations] requires both fields, Magnetic as well as Electric to be present and to reinforce each other, changing mag field creates electric field; changing electric field creates mag field, why throw either away ? Fifth, I prefer Solid Copper wire , I find it less noisy than stranded that keeps rubbing on itself, and the same for the feedline, make it yourself from solid copper wire, since I have done this I can copy S0 signals Q5 . Copperweld [copperclad] is junk in my opinion, look inside any commercial transmitter final compartment, 'you will NEVER see stranded wire or copperweld' so why use it, this is from Bob W3KUJ who worked for Western Electric in 1946 putting up shortwave stations.
 
RE: Resonance Schmesonance!  
by N4KC on March 30, 2011 Mail this to a friend!
Skip, I'm with you! And I'm still mad that the early guys made the symbol for voltage "E." And for current "I." V = C X R just makes more sense to me.

I know. I know. "C" was occupied by capacitance, but there ain't any capacitance in Ohm's Law! Who gave capacitance precedence over good old electric current for the letter "C?"

Your compass-point explanation is about as good a one as I have seen, by the way.

Don N4KC
www.n4kc.com
www.donkeith.com
http://n4kc.blogspot.com
www.facebook.com/donkeith


 
Resonance Schmesonance!  
by K3VW on April 11, 2011 Mail this to a friend!
Great article Don ! Hope the VSWR addicts are paying attention. 40 years ago, we didn't have SWR meters but still seemed to make contacts ! It's majic!! Looking forward to your next book. Willy
 
Resonance Schmesonance!  
by KB0GU on April 19, 2011 Mail this to a friend!
I am glad 'ham' radio does not HAVE to have a best oil to run in your motorcycle thread.
Thanks for a great read! Resonates with my thoughts.
GB
 
Resonance Schmesonance!  
by KO0KY on April 22, 2011 Mail this to a friend!
Thanks for an excellent article. I am currently teaching a tech ham class, and we are discussing antennas and feedlines now. This will help me a great deal in explaining the concepts.

Regards,

John - ko0ky
 
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