The AM Forum

A few words on the "Coax vs. Ladderline" issue...
Written by Joe Townsley KC6MCW

If you are interested in constructing a high efficient antenna system, you must follow the rules of mathmatics, physics, and reflection mechanics. I will give a simple explanation and a more complex example of transmission line theory.

The simple rules to remember:

Rule #1

 Use coax only on antennas that are resonate on single bands only! See, 50 ohm coax wants to see a 50 ohm antenna feedpoint impedance.
 
Explanation....
That antenna feedpoint impedance sways away from 50 ohms the moment you QSY away from the resonate frequency. Now say the swr meter on your tuner shows 3:1 and you then simply retune to obtain a 1:1 again. Do you think you are still efficient? Do you think you really have a 1:1 swr on your transmission line? If you answered "yes", then you couldn't be more wrong. The 3:1 swr remains on the transmission line and NEVER goes away! Your tuner is only correcting the mismatch to provide the proper impedance your equipment needs to see (50 ohms) to transfer all the available power. This 3:1 swr on your transmission line is where the loss is! Yes, 3:1 swr is not that bad. This was a simple example. But what you may not realize is when you QSY to another band, the swr on the transmission line may become 40:1, 50:1, or maybe 60:1 swr !!! But wait, why do you only see 2.5:1, 3:1, or maybe a 5:1 swr on your tuner swr meter on these other bands and think that you are still ok? Are you ready? The reason is because you are viewing an swr that also includes all the coax resistive losses.  When there is a 40:1, 50:1, or 60:1 swr on the line, you will NOT see this on your tuner swr meter. The only 2 ways to measure the true swr on the line is to measure the antenna feedpoint impedance directly or calculate it using long math.

Those of you that think there is only half a DB of loss on your coax due to your 2.5:1 swr you are viewing and think your signal is fine and not suffering that much loss to worry about it, I will encourage you to read the book “Reflections II” written by Walter Maxwell. And don’t just skim through it reading the simple stuff and say you read the book. I have read this book 6 times front to back and went through 3 yellow highlighters. This book does have some complicated formulas but if you don’t take the time to understand them and follow what Walter is talking about, you will NOT understand transmission line theory. I know this because that was me. I put the book down after looking through it because it was too complicated. But then in time, I went back to it and learned to understand what I was reading.

When you select a type of coax to use, many of you will look at its losses per 100’. I have heard these quotes when people brag about their low loss cables “I have LMR400...I have hardline…blah blah blah. Sure they exhibit lower losses, yes. But the losses are STILL HUGE when there is a 40:1 swr on the line. (see above). Its simple, don’t use coax of any kind on a multiband antenna system!

Rule #2

Use ladderline, open wire, window line, etc. on antenna systems that will be used on multiple bands! Why? Because of its’ extreme low loss properties.

Explanation….
When there is a 40:1 swr on the transmission line (that never goes away regardless of tuner settings, please see above again) you will want a transmission line that has very LOW losses. My swr on my open wire transmission line is on the order of 19:1 when I operate on 75m. Sure I have a 1:1 between my equipment and the tuner. But the 19:1 swr REMAINS between the tuner and the antenna. My losses are around 2 or 3% and not 38% if I had used the best coax you can buy.

What are the differences of 75, 300, 450, and 600 ohm openwire transmission lines? Here’s the deal, when you construct a multiband wire antenna, you’ll want to put up as much wire as possible. Don’t worry about specific cut lengths. You are constructing a non-resonate antenna system. The antenna feedpoint impedance will change drastically, 200 ohms to 2000 ohms ,when you QSY across the bands, depending on your unique installation. When you are operating on a band that exhibit’s a high complex antenna feedpoint impedance, a transmission line with a higher characteristic impedance will have a lower SWR on it, thus reducing the losses on the line. I have a 19:1 swr on my 600 ohm openwire line when operating on 75m. If I had used 450 ohm, the swr would have been 22:1. If I had used 300 ohm, the swr would have been 26:1...and so on. So my 600 ohm openwire line  is able to handle a much broader impedance swing while keeping the losses low.

Some misconceptions about ladderline, windowline, openwire, etc….
1. Do they radiate?
They only radiate an inch or two. Yes, I have tested this. It is nothing to worry about. The opposing current on the opposite line cancels and keeps the line balanced. Your coax is probably radiating MUCH more due to common mode currents on the outside of the shield.


2. Do they cause RFI in the shack?
No! the RFI is caused my RF current trying to return back to the tuner caused by an incorrect antenna system installation. See, multiband antenna systems are NOT easy. They are not plug and play. You must sharpen your pencil on this type of antenna setup. You are dealing with a complex antenna system that will exhibit very efficient power transfer capabilties on multiple bands.
3. Do they break in the high winds?
Install it correctly and it will be fine. I have had no problems with my openwire setup. And yes, the winds reach 70 mph here at times.
4. Problems with feeding these lines through walls?
Use your head. Its not that difficult. Believe me, it is worth the effort.


So I have attempted to explain a few points to you about transmission lines and their differences. Here are a few more examples to think about:

What kind of transmission line do most high power shortwave broadcast stations use to transfer their power to the antenna systems? Yep, openwire balanced line. Why? Because of the complex impedance their phasing networks exhibit and the long transmission line runs. Remember, low loss and high efficient power transfer is the name of the game here.

So now you have constructed the ultimate multiband antenna system. You have used openwire feedline to minimize the losses due to the high swr on the line. And now you think you are efficient now. Wrong. That nice, expensive,  pretty, commercially made antenna tuner is where your loss is now.  Why? There are baluns in there that exhibit high losses when complex impedances are imposed on them. Remember, baluns work great if they are used within their limits.

This is where a link coupled true balanced tuner comes in. No baluns. No loss.

My opinion on the best antenna system?
A 160m inverted V made with #10 wire up 80 feet, fed with 600 ohm balanced openwire transmission line made with #10 wire at 6” spacing, and matched with a link coupled true balanced tuner. This antenna system will be very efficient on all bands and will exhibit some large gain numbers on the higher bands. And only one support is needed in the center!


I hope this helps anyone who is interested in constructing the ultimate multiband antenna. Why have 5 antennas when 1 will work perfectly!

Joe Townsley
KC6MCW

 
Very good summary, Joe.  This is a keeper for the handbook here.

One comment on using a 160M multi-band flat top on the higher bands...  Yes, on 75M there will be about 2.5db of gain over a half-wave dipole in the broadside direction as a sharp figure eight. However, on 40M the 250’ 160M dipole produces a big bi-directional null broadside and splits into a 4-leaf clover pattern. Gain in those four directions is reduced.  On 20M, there are now eight lobes, like an octopus with eight big nulls and negative gain against a dipole. On 10M there are 16 lobes and 16 nulls, etc. It becomes pot luck as to what areas of the world you cover or null out when on 40M or above.

One suggestion is to use a 180’ flat top (fed with open wire) to cover 160-40M only. The pattern stays as a figure eight with a few db gain broadside on 75 and 40M.  Then put up a second center fed flat top that is about 23’ long for 20-10M. This pattern is also a figure 8 on all bands with a few db gain on 15 and 10M.

Another option is to add legs (fan dipole) for 40M and above  (to the 250’ 160M dipole) to help stabilize the pattern on the higher bands.

It's all about keeping control of the pattern by using a broad figure-8 pattern in your favored directions on all bands.

* Of course, if someone didn’t really care about their directional pattern coverage (or nulls) then the single 160M dipole will do FB on all bands.

Again, good job on the summary, OM!

73,

Tom, K1JJ

Joe,
Rite on..............one of the best descriptions (easy to understand) I have read on the topic.

Bill

I'd  like to find a copy of the book.  I thought it would be available from some of the online booksellers; they list it as "Currently OUT OF PRINT, new release date TBD".  Amazon.com has some used copies available at prices ranging from $168.30 to $399.89 each!  Alibris.com lists similar prices for its used copies.

I find it hard to believe that this book is really selling on the used market at those prices.  That ranks right up there with audiophoolery and their $200 2A3's, $300 wooden volume control knobs and $600 power cords. I recall Walt saying some time ago that a new edition was in the works, but I have heard nothing further on the subject.

Does anyone know of a source of this book at a realistic price?  I think it originally sold for $19.95 per copy.

Joe, Very good.

I wonder sometimes if there's an advantage to hb ladder line that is spaced more than 3 inches to get say 900  or 1000 ohms characteristic Z.  Some of the feedlines from Germany that Array Solutions used to sell had spacers that were 5 or 6 inches at one time.  OTOH, the miss match to the f/p of a 1/2 wave dipole on its lowest frequency would be greater.  Probably 600 ohm feedline is the best compromise between low Z feedpoint and high Z.    You make some great points such as sw bc stations using parallel wire feed to their curtains.   It's hard to go wrong doing what professionals do.   I'm not wild about horizontal wire antennas on 160 however because they have to be so high to eliminate ground loss and then you have a 260 foot span with some possible structural challenges there.  However if a ham has a couple of supports at least 100' high (preferably higher) may as well put up a cloud burner.  Otherwise, I advise a separate 160 vertical antenna of some sort working against ground.  Don't like inverted Vs unless they can be put up so high the ends are at least 50' high, otherwise they have a low average height.  BTW, I followed Tom's advice on the high and low band dipoles and they have worked out very well.  
Another great antenna book is the one that came out in the 1950s by Edmund LaPort (or was it Laporte?).  One of the antenna bibles. 

73

Rob
K5UJ

Don,
I Have a copy.....make me an offer.......
I got it from the ARRL for 19.95...........

This offer goes out anybody..........Im sure Don will not respond.
Im not looking to make money on this......a lot of the stuff in the book is WAY over my head and Im not afraid to admit that.  

Bill

Nice summary of what I've been trying to get across for a long time, Joe!! Thank you for bringing the subject up to date. Some of the chapters of the 2nd ed are available for downloading from my web page at www.w2du.com.

Yes, it's true that the 3rd edition is in progress by CQ Magazine. It's going rather slowly, however, due to a small editing staff that has many tasks other than publishing a book. There are 30 chapters in the new edition, and about three months ago the editor sent me the first eighteen chapters to proof read. I'll have to contact them again to see how the job is progressing. I'll post any new info I learn.

I appreciate your interest, guys!

Walt

Walt.......
What a GREAT book......thanks much (for the stuff I could understand!)
Bill

I offer $40 shipped to Dallas TX. In view if its scarcity and detailed content.

I have personally seen a setup using openwire transmission line with 12" spacing and heard of guys using up to 18". I dont think it would be necessary to go that extreme unless you really have complex impedances that are off the smith chart!

Hi Walt!

Joe Townsley

Opcom...
SOLD.......the book is pristine........contact me off the board at wgr@roadrunner.com  

You will love the book as it is good reading for the brain.

A friend called me on the fone who is a swl and wanted me to try to buy the book for $1000.00. When you snooze, you lose.

OH well..............I can always reconsider  :-\

I'll give this a few days, prune some of the posts regarding the hosstradin' on Walt's book, and move the thread to the Handbook section.

I should have mentioned in the earlier post that the 3rd ed will have everything that appears in both the 1st and 2nd eds, plus several new chapters. So why don't you all wait for the 3rd? As I said, I'll keep you informed.

Walt

Just kidding Bill ;D ;D ;D

Yes.

I've used 24" spacing for 75M.  I used no spacers and simply pulled the two wires tight from the top of the tower to the ground. The feeders canceled well. 24" is a very small fraction of wavelength on 75M. However, on the higher bands it may not be so.

BTW, open wire using no spacers is probably THE most effiecent feedline known to man. There is no dieletric to cause loss current across the line. Except for the end insulators to hold the feeders tight, it uses air.  I used a Hartley oscillator transmitter with it and you could hear the whee-o whee-o  of the carrier swing as the wind blew the feeders to and fro... ;D

T

A few pics of my transmission line with 6" spacing.

Thanks, Walt.  I'm looking forward to when the next edition is ready. That says a  lot about a book when used ones are going for that much more than when brand new, that soon after they go out of print.  Usually a book has to be out of print for many years, and be an extremely rare collectors item, to command that kind of price.  I'm not even sure a mint 1st edition/1st printing original ARRL handbook would bring much more than $400.

Back to the subject of tuning antennas and feedlines; some interesting concepts are discussed in a number of technical books, under the subject of conjugate matching.  The basic idea is to use a feedline that will tolerate substantial SWR without excessive loss, and to do all the tuning at the transmitter end of the feedline, allowing the changes in R + j to efficiently reflect down the feedline all the way to the antenna.  In other words, the antenna, feeders and tuner are all part of a system that is adjustable from one convenient point.

I agree that modern day appliance-tuners that insert a balun between an unbalanced tuning network and balanced open-wire resonant feeders work on what is essentially a bogus concept.

Don,
I believe the concept some people are not grasping is the fact that SWR remains on the transmission line regardless of what you see on a meter in thier store purchased tuner. And this SWR is usually much higher than they think.

"But I can tune all the bands so my coax is fine!"

Yes, a dummy load tunes up good too. It doesn't mean it will be efficient.

Joe

A real whirl example of extreme loss using coax cable is to listen to the 75M band using a 160M coax-fed dipole. (a 2000 ohm impedance fed with 50 ohm coax)  It's down at least 20db from a well matched dipole.  Or to a lesser extent, listen to the 160M band using a 75M coax fed dipole.  (12 ohms impedance fed with 50 ohm line)

The real loss in db could be accurately calculated.

A shack-located  antenna tuner will have no effect on this mismatch UNLESS it is mounted at the antenna's feedpoint.  I suppose this could be done on a tower with a remote tuner - and is done by some.

Or use 40M and 75M coax-fed dipoles for the same type of tests.  

T

Hmmmm,
Looks like some folks are trying complicate this post way beyond what it was meant to be. For the average ham....all this tech stuff might be a little confusing. This is not to say it should be ignored......BUT lets not make a big thing out of something thats NOT THAT COMPLICATED. If one reads Joes post.......u can decide what kind of ant THE AVERAGE HAM wants to put up..........no ifs, ands, or butts. It always amazes me that folks want to complicate things to the point that it will scare the average ham. Again I say..........we are talking to the avarage ham........not some genius that has a degree in math.
Let the flames begin.... :P  

BTW......I do NOT mean anything bad with this post...........just keep it simple....... ;)

Okay.  I'm considering a "fan dipole" no, really a "parallel dipole" of 75/40/20 meter legs fed by one transmission line.  (Maybe I'll be able to get 15 meters too from the 40 meter legs). 

I do not have a balanced tuner.  I have a T network tuner.  If I use RG-213 to feed the center, I am assuming where I have those legs cut for resonance, I will have a good match with low loss.  If i need to stray up and down the band, I am assuming my swr will rise but shouldn't be a big problem for the amplifier output (SB-200).......  Would I really even necessarily need to use the T tuner unless I was feeding my ricebox directly into the antenna and NOT on the resonant freq?
If I feed the DX-60 or the SB-200 output into the system, wouldn't the output "tune" on those units be enough to match okay?

I have some fairly sturdy (14 awg based) 450 ohm windowline.   But wouldn't I need the balun (and it's losses) or a BALANCED tuner (ideally) to use it?

I'm nearly ready to do something as I feel my g5rv is a real compromise, although it's certainly putting my 100 watts carrier out there and giving some nice 20 to 30 db over 9 reports out a few hundred miles in the "ghetto" around 3.885 Mhz.

John KX5JT

Ok, I am dense.

Explain to me please...

Why does the mismatch of the open wire line to the antenna, resulting in a high SWR not matter when the same SWR from using coax does??

Is not SWR, SWR, and therefore resulting losses due to mismatch??

Ok, ants are not my strong point.

                 _-_-bear

Bill
Make copies and sell through a PM so the copyright police don't get involved. $168 is ridiculus!!

I'm definitely all for the real ladder line and 3/8 wave 160M antenna. And I was educated by this forum on the drawbacks of using "multiband antennas" for 40M and higher. If you just want something that works and not get complicated with separate antennas designed for a certain freq range , or there's space limitations, then you got to do what you gotta do.

Fred

I'd say, scan it and post it.  If it's out of print, then it's out of print.

Of course, that helps Walt none.


--Shane

There's a more technical answer, but here's the layman's analogy I like to use:

The difference between openwire and coax is the coax uses a dielectric to position the two wires apart. These create currents across the lines = heat and loss.   The openwire uses spacers that are infrequent, thus not much of the cross current path.

Take a look at the Handbook's swr vs: loss for various feedlines and you will see how different feedlines stack up to swr.

The best feedline in the world (least loss) is two parallel wires suspended without spacers. The worst feedline is two wires separated by a very lossy material to RF, like say, wet wood. Then there's all kinds of materials in between.

The bottom line is lossy materials (coax) cannot tolerate high swr, while air (openwire)  can.

T

Walt has excerpts of his book on his website.  Presumably if he was interested in having his whole book in the public domain, he would have put the whole thing there.  "Out of print" does not mean the book is no longer copyrighted.

Discussing illegally copying and passing the book around, particularly right in front of the author who spent a lot of time on the book, is bad form.

There is a set of curves in most antenna handbooks.   I just checked out my ARRL 1955 Antenna Handbook.    I would send it, but not sure of copyright issues.    The loss of any transmission line at a high SWR is directly related to its loss when it is matched with its characteristic impedance at any given frequency and length.    One diagram shows it all, I am sure the newest antenna books have it.

You can calculate losses for many transmission lines on line.


http://fermi.la.asu.edu/w9cf/tran/index.html

The simple rules to remember:


This is the same sorry stuff that has been screwing up minds for decades. Im not disagreeing with Walt here, in fact I own an autographed 1st Edition.

Multiple bands can easily be fed with a single coax, its done all the time by a lot more hams than those who waste time with open wire. The only benefit of open wire is to achieve gain on higher bands but having multiple nulls as the frequency goes up. If thats tolerable then use it but realize that the other quoted statements below are far from accurate.

The primary reason for the rapid acceptance of coax and the pi network following WW2 was to eliminate or minimize BCI and TVI.




So what? Since this forum membership is limited to 1 to 3 operating bands by most lets start with an 80M dipole or rather 75M. If you want 40M then parallel another dipole from the same feed and dont have it close to the 75M one. You can run at right angles, droop as an inverted vee beneath the 75 as well as other paths. The 40M VSWR will be textbook and allow full band operation even with a fussy SS rig. If you want 80M CW and 75 then run seperate antennas at right angles and get a classic figure W VSWR curve; it wont affect 40M. So far no loss worth talking about. A plus is you now get 30M for free with a reasonable VSWR and loss unless you run several hundred feet of RG-58 thats 50 years old.

For 160M the above can be run as a top loaded vertical with the coax shorted at the shack end and a ground system installed. I dont like that method for several reasons. One is a radial system is a PITA and two, I dont want anything with vertical polarization anywhere near the house to pick up all the man made crud. Its better to wind a pair of homebrew loading coils for another dipole as a better compromise. Any VSWR bandwidth problems wont contribute squat in feedline loss; with low loss coils that loss contribution is minimal.

My own version is a full size 160M inverted vee and both 80 and 75M inverted vees connected at right angles. I know it works since I have over 300 countries on 160 (backed up by verticals when needed) and close to all countries on 80/75 which includes the 1st 5BWAZ from New England. Again 30M is a freebie and Ive around 250 countries there with 100W and often much less.

Any feedline radiation is eliminated by a large ferrite bead current balun that has a high impedance at those frequencies. Lots have been written about that subject for decades. Ferrite beads dont work on OW, they just happily radiate away.






They can absolutely cause RFI in the shack, house and neighborhood. There is no such thing as a perfectly balanced open wire feed in the real world. The closest you may achieve it is a narrow range at the fundemental frequency. Unbalance causes radiation as well as crud pickup on receive which is mostly vertically polarized. How the feed is hung ( how many come down perfectly straight for a quarter wave or more at the fundemental?), nearness to objects, rain, imperfect flatop can all toss the perfect balance out the window....on the fundemental. High VSWR on harmonics will guarantee radiation since it is still there with a tuner. All tuned feeders allow is an easier transformation at the tuner but this doesnt work if you want all the bands.

Unless you are equipped to measure feedline radiation over its total length (read Maxwell, Krause, Jasik, military publications, etc about voltage and current peaks and nulls) dont say it doesnt exist.

What died in the wool OW fanatics never mention is that the ATU is not 100% efficient. In fact if you read the old magazines ( I have QST from 1926 and CQ from Issue 1 plus most of the 2 main Handbooks) the consensus is 70-80% efficient is to be expected.




But not with an ice load and wind at the same time. And not with the store bought garbage.



For many it is very difficult. Obstructions such as a wife and lowering house values stop many from drilling holes. My coaxes run in to the basement below grade. Open wire also has the same lightning protection requirement as any cable entering the house.




Many use coax to fixed direction yagis or LPA's, check out the power handling on the rather common 1 5/8" Andrew cable. Its sufficient for many.

For curtain arrays and other wires fed at some point between the 300-1000' support towers, hoisting coax would be a bit of a chore for a 500KW station dont you think?  Running open wire straight down to a remote building containing phasing and matching components is also common and then coax to the transmitter building. I dont know the weight of 1" phosphor bronze wire but I have to assume it is rather light compared to 2' diameter pressurized copper pipe coax.

While open wire can have its uses for some, such as very long runs to an antenna, and those mired in recreated pre WW2 stations, trying to come out with a blanket statement is just plain wrong and smacks of pure intolerance for other views.

Carl
KM1H

W5HRO,

What kind of tuner are you using?

Joe

Yes! You can construct a multiband antenna system by using the staggered dipole design and feed it with coax. They work great as they present the low impedance the coax wants to see. But, an swr will still exist on the line when you QSY across the band. The statements I presented earlier involves constructing a very efficient antenna system with swr on the line. It would be like building a race engine then running it in the car without putting it on the dyno to fine tune it for that extra 32 HP. Why do that? Just run it, it will work fine! I want things to work the best as possible and not “its good enough, as long as people hear me”.


But what if you or the wife don’t want wires all over the sky or maybe you simply don’t have the property to run dipoles at right angles? The answer is a single wire antenna that can be used on multiple bands.


Compromise it will be yes. The loading coils will create a very high Q which will cause the tuning to be extremely sharp thus creating swr on the line when you QSY 30khz! This article is not about compromised antenna systems but how to construct a multiband wire antenna with high efficiency.


Yes, the ferrite bead choke baluns work great to minimize the common mode returns at the antenna feedpoint when coax is used as long as the antenna feedpoint impedance stays around 50 ohms. The moment you QSY and cause a considerable amount of mismatch at the antenna feedpoint, the ferrite choke balun begins to heat and once again the common mode currents pass back down the line. Ferrite beads are not needed on openwire line. It would not make sense to install them on a line with SWR. They would just heat up.







I have eliminated RFI by constructing chokes on all the lines that enter the shack. Phones lines, Cat 5 internet, TV coax, etc… also there are chokes on every wall outlet. You see, the RFI comes in from the outside.  Has nothing to do with the transmission line. Could it be that the antenna system is radiating so well that now all this RF was a problem? Hmmmmm, makes you think huh?



True, you would have to design a hefty setup for those conditions. If you want to construct an efficient antenna system, you would not purchase the store garbage in the first place.



This type of antenna system will not be for everyone. There are some slick ways to get the line through the walls though. Yes, you would have to implement some lightning protection. As I said, this is not a plug and play system.


It would not make sense to feed a balanced antenna system of higher impedances with skewing capabilities with coax. The point here is that openwire transmission lines work very well for transferring power efficiently with high swr on the line.

Joe Townsley

It amazes me of the flat out ignorance of the avg  Appliance operator Ham.  I just listed to a guy on the air talking about Coax vs ladder line. This fool went on and on saying his Coax feed was better and how he hated the open wire line. He kept saying it makes no difference. The SWR meter is flat on all bands with the coax and with the ladder line.. LOL


On the 600 ohm line from Trueladderline.com

I ran 450 ohm line for a year on my Flat top Zep.  I pulled it down and put up 100Ft of open wire line from Trueladderline.com.   I had a BIG gain on 40 meters to the locals.  I mean big...  This tells me that I have a vertical element now. It works well but the KW matchbox does not like to tune it on 20 much.  I considered going back to 450.

Clark

Clark, before you replace the line...

Just trim, or ad lengths until it tunes where you want it to.

You'll run into the same problem with 450 ohm and 600 ohm line.

Yeah.. I can do that.. I almost never use 20 so it was not much of an issue.  Maybe I will add in a foot or two today for a test. I purchased 200Ft of this stuff.

C

Fred,
I was only kidding about selling the book.... ;)
Back to a multi-band ant. I was told by an old timer may years ago that if u want an all band single wire antenna than put it up as high as possible, feed it balanced line and tune it with a good LINK COUPLED antenna tooner.
Perhaps this is a little over simplified but its based on tried and true practice. Thats what I did and it works on all bands 160 thru 10.(Well....a little iffy on 160, its only 165 ft long) Another point to remember is this ant is for the ham that doesnt have a lot of real estate or other factors that allow for a nice antenna farm such as myself.

Bill

Brian,

After you replace ur 600 ohm with the 450 window line please post something about whether or not ur noise goes away.  I'm interested in the result of this experiment.  I suspect a noise source may have cropped up in the time between ur old feedline and the 600 ohm, but what you plan to do should verify one way or the other.

73

Rob
K5UJ

I have both a quarter wave vertical (with radials) and a dipole @ 110' average height.  The dipole is a half wave for 80m, and thus a quarter wave for 160m.  I get much better results all over N. America with the vertical, except for within a 100 mile or so radius, which is limited by the skip zone.  In Nashville, roughly 50 mi. as the crow flies from here, I am 30 dB stronger with the shortened dipole.

But for receiving, the best solution when using a vertical (or any other antenna for that matter) is to have available one or more separate receiving antennae.  Besides my beverage, I have a rotatable indoor loop for 160.  Nearly every time, the vertical is the worst of the 3, but occasionally it outperforms the rest.  I  have a rotary switch for all my receiving antennas, and when I first contact a station, I always try all the antennas to see which one performs best on receive.


If the horizontal antenna is fed at the mid point, the feeders come off at 90° from the antenna for at least a 1/4λ run and the feedline is kept a reasonable distance away from large metallic objects, the feeders should be essentially balanced.  The frequency of operation has nothing to do with it.

"Unbalance" in open wire feeders actually translates to balanced currents in the feeders plus common mode currents.  Eliminate the common mode and the current in the feeders is perfectly balanced.

If the antenna and feedline are configured as described above, the primary cause of common mode currents and therefore unbalance is that the open wire feeders are trying to function as a Marconi antenna.  This happens most often because the output from the tuner is not isolated from ground.  A Marconi antenna has to have some kind of ground plane to function.  If the open wire feeders are isolated, or "floating free" from ground, there is no opportunity for them to behave like a Marconi.  The most effective way to float the feeders from ground is to use a balanced link-coupled tuner, and do not directly ground the midtap of the secondary coil.  To drain off static discharges from the antenna, ground the mid-tap of the coil through an rf choke.

Those contemporary, bogus, "balanced" tuners that use an unbalanced L, T or Pi-network, feeding a balun that is inserted between the tuner and open wire line, are just begging for common mode currents, feeder current unbalance and feedline radiation.


There will be no more RFI in or nearby the shack with OW line than with coax, if there are no common mode feeder currents, either at the fundamental or harmonic frequencies.  Coax can just as easily have radiation from common mode currents circulating on the outside of the braid.

Think of coax as a three-conductor feedline.  You have the central conductor, the interior of the shield braid and the exterior of the shield braid, each functioning as an independent feedline conductor.  The currents in the central conductor and the interior of the shield braid must be equal and opposite and thus balanced at all times.  Common mode currents reside at the exterior surface of the coax, and the whole thing may radiate as a large-diameter copper tube serving as a Marconi antenna.

It doesn't exist if there are no common mode currents on the feeders.

That is true. No transformer or other coupling device is 100% efficient.  That includes the tank circuits in a transmitter, the modulation transformer in a plate modulated rig, and the output transformer in a hi-fi amplifier. This is why plate efficiency as published in the tube manuals as 75% or 80%, for class-C operation, is unrealistic and never achieved with an actual transmitter.  Expect the tank circuit to be about 90% efficient at best.  But this also holds true for the "transmatches" used to match contemporary transceivers to the antenna and maintain the prescribed SWR limits for the broadband solid state amplifier.  The broadband output transformers in solid state finals have losses, too.

Think of it this way.  In the olden days of vacuum tubes, the transmitter came with a built-in tank circuit, since the output impedance of a tube is far different from the load impedance presented by the feedline.  With the advent of solid state amplifiers, which have an output impedance close enough to the impedance presented by the coax feedline to allow for the use of broadband transformers, the transmitter is now sold minus the tank circuit.  This works OK if the antenna and feeder are matched well enough to present close to a 50Ω non-reactive load, but otherwise, a tank circuit is needed after all.  It is now sold as a separate unit from the transmitter and you have to pay extra for it.  That's exactly what a transmatch is - the final amplifier's outboard tank circuit.

Regarding efficiency, I use 140' of coax to run between the shack and the antenna  tuner shelter at the base of the tower, and open wire line up the tower to the antenna.  When I first installed it, I used some very expensive N.I.B. RG-214/U coax, with silver plated central conductor and double silver coated braid, and supposedly extremely low-loss dielectric.  I got a good deal on it from a satellite TV dealer; I never could have afforded to pay full price. Because of its reputed low loss, it was used in big dish satellite systems to run at microwave frequencies from the LNA in the dish to the down converter.  I ran an efficiency test, assuming that for 160m it would be nearly 100% efficient.  Using a 50Ω dummy load at the far end and after checking to make sure I had 1:1 SWR at the transmitter end, I loaded the transmitter up to exactly 100 watts.  At the far end, the power into the dummy load measured only 93 watts.  I was losing 7% of power at 2 mHz in a 140' length of that super low-loss coax. (It became much worse after rodents chewed holes in the jacket and it got contaminated with water.)

You just have to build it sturdily enough.  I use #10 copperweld both for the antenna and open wire feeders, and it has survived ice and wind for almost 30 years now.  I agree that the store bought stuff, basically TV twin lead with square holes punched in the dielectric ribbon, is garbage not worth bringing home.


Those are non-technical issues beyond the scope of this discussion.


Actually, open wire line is most useful for long runs only if it is operating at a relatively low SWR.  A  long, resonant feedline tends to be very high Q and sharp tuning. The reason is that the long line is a series of quarter-wave resonant sections end-on-end.  The length of each quarter-wave section varies with frequency.  These changes in length are additive over the total length of the line. What might amount to a small percentage of variation across an entire band with a quarter-wave or half-wave resonant feeder system, will amount to a substantial fraction of a wavelength over a feedline several wavelengths long.

Here is an example:  You have an 80m antenna fed with open wire tuned feeders, and you want to operate on one frequency on the CW band and one in the phone band, so you choose 3563 and 3938 kHz (numbers chosen here for easy approximate calculation).  Centred on the middle of the band, 3750 kHz, that range of variation represents 10% of the total frequency/wavelength (3750 kHz plus and minus 5%).  

If you use a quarter wave resonant feeder, when you go from the CW to the phone frequency, the tuner has to compensate for a change in resonant wire length of only 5% of a wavelength (10% of the quarter-wave leg of the antenna plus another 10% of the quarter-wave feeder = 10% of a total wire length of half a wavelength = 20% of a quarter wavelength).  

But say you move the antenna farther away so that now a 1 3/4λ feedline is required.  Adding in the quarter-wave leg of the antenna, we now see that each half of the symmetrical system now consists of two wavelengths of wire. So now, when going from the CW to the phone frequency, the tuner must compensate for a change in resonant wire length of 20% of a whole wavelength.  This calculates to 80% of a quarter wavelength.

Looking at the standing waves on a resonant line, voltage and current loops are exactly a quarter wavelength away from voltage and current nulls.  So in the first case, changing between the two frequencies moves the relative position of the feedpoint 20% along the way between a current loop and a current null. Almost any link coupled balanced tuner could handle that much variation by changing the setting of the split-stator tuning capacitor, without having to tap down on the coil or change from series to parallel tuning.  

But in the second case, the feed point has moved 80% of the relative distance between a current loop and a current null.  Therefore, you would have to toggle between series and parallel tuning to cover those two  frequencies in the same band.  Since any change in frequency moves the loops and nulls a relative distance that  is multiplied by the number of quarter waves between the transmitter feed point of the open wire line and the ends of the antenna,  as the length of the tuned feeders is increased the tuning becomes increasingly more critical, and eventually series or parallel tuning won't hold across the entire band.

The  same phenomenon occurs when using the same feedline and antenna on harmonics to cover higher frequency bands.  You might be able to use one tuner configuration across 160m, but using the same antenna on 10m you might have to change from series to parallel tuning to cover the entire band.

My next project is to build a small enclosure that will house to current meters for my open wire line. This way, I can tune for a balance. 

Anyone have any designes they want to share?  Ideas of what type of meter to use? 

C

Don,

Very well written! Also, here are a few pics of my old homebrew link coupled tuner that shows the differences in line balance by simply the way it is tuned. Also, the ground is connected to the center of the main coil. It clearly shows the reason why the transmission line would radiate! By obtaining good balance, the antenna becomes an efficient radiator and RFI in the shack becomes next to zero. RFI was HUGE in the shack when I tuned it purposely out of balance. And no, the antenna does NOT have to be fed in the center for good balance! My current antenna is an off center fed 200' wire.

Clark,

A pair of current meters would be a great idea!

What do you mean by "tuned it purposely out of balance?"

I was able to tune it out of balance simply by the position of the variable capacitors. I will post a more in depth demonstration showing more detail.

Rob
I think the disadvantage would be that the 450 window line would change tuner settings in various WX conditions. I took a dive for the W7FG ladder and I like the concept of a continous wire that goes from ladder line to antenna wire without splices and a failure point from bad connections, which are plaguing me now.. The 450 ohm doesn't hold up very well in Western PA. Wx.
.......NEVER run ladder line indoors around house wiring or near anything! Talk about noise pick-up WOW!

Fred

I'm still not clear on how you would change the balance of the system when tuning a balanced tuner. Or maybe you are adjusting the two caps independently?

If You dont the tuner correctly, One bulb lights more that the other.

I am going to add a few fee to the feedline and see if it matches better.  I am using 100Ft now and cant pull it any tighter.

C

That makes two of us, Steve.

And isn't the point of using a tuner to provide an essentially balanced output to feed a balanced feedline and antenna? Why use it with an inherently unbalanced antenna, i.e. one that is fed off-center, and then correct for the imbalance with the tuner?

I guess it would work, but the feedline radiation due to the deliberately unbalanced currents flowing from the tuner would be significant. My logic is balanced antenna, balanced feedline, balanced tuner output. At least that's how I do it, but I'm always open to different methods & approachs, etc.

Am I missing something here?

73,

Bruce

While I can't profess the knowledge of some of the fellows here, I have a similar set up and I think he's just stating that the light bulbs prove when its in balance, and he "can" make it out of balance by mistuning.

Ideally you can also "balance" each leg of the antenna with the correct transmatch, allowing you to compensate for different in height above ground, coupling to metal, etc. I use neon bulbs on each feed line point, and tune for equal brilliance, its like the antenna current meter, but cheaper and more buzzardly. The key, as I understand it, is to keep each feed line 180 degrees out of the phase with the other, to cancel out the lines radiating.

You won't find a more knowledgeable (and friendly) fellow than Walt W2DU, we're privileged to have him on here.
I've read his antenna books, as much as I can understand the math with my high school education, and Walt does a very good job explaining how simple and effective balance feed lines can be. Next in line is Kurt Sterba from the "Aerials" series, some great truths distilled down there, in a very humorous, abet acerbic, vein.

Having switched to balance feed lines some years ago, I'd never go back to coax unless it was on a mono-band antenna, even then I'd think twice about it.

Sometimes older and simpler technology is really better!

-Bruce

One thing to beware of with balanced feeders is assuming that you have a  good balance just because both rf ammeters read the same.  The standing waves on the feeders may be skewed from each other.  Naturally, at the feed point they are  going to be close to the same if the feedline is floating from ground and there are no Marconi antenna currents.  You are essentially breaking the resonant wire along with its standing waves at the feedpoint and inserting a generator.  If the generator is ungrounded, there is no place for the current from the two terminals to go except into each of the feeders, and by the laws of physics, the currents in the two wires must be equal in amplitude and opposite in polarity at the exact feed point.  On the lower HF bands, the lengths of wire between the actual output coil and the terminals on the tuner box would be negligible, so if you mount the rf ammeters directly on the box or mount them outboard right at the output terminals, they will read the same, making it appear that the feedline is balanced. In that case, using two meters is a waste; you could do just as well with one. But if the ammeters are placed several feet away from the tuner, maybe just where the feeders go outside through the wall, some unbalance may show up, since the standing waves on the two wires may not be exact mirror images of each other.

A good example of substantial unbalance in the feeders occurs with the end-fed zepp.  If the horizontal antenna wire is exactly an electrical half wavelength, the feeders will be closely, but not perfectly, balanced.  But as you move away from the resonant frequency, the end of the dead feeder still is forced to be at a maximum voltage point, but for the line consisting of the other feeder plus the antenna, the maximum voltage point shifts either out onto the antenna or back on the feed wire towards the transmitter.  The standing  waves are no longer exactly mirror images directly across the feedline from each other, but become offset one from the other.  As you move the rf ammeters away from the point where the tuner feeds the line, this unbalance becomes apparent.  Still, since there is substantial cancellation even in the imperfectly balanced line, the end fed zepp has far less radiation near the shack than would a simple end-fed piece of wire working against ground, or a voltage-fed half wave piece of wire.

Some excellent posts on this thread, indeed. The intelligence of people in this AMfone group is so far ahead of those on the QRZ group it is amazing. Don's posts are exceptionally good. And thank you Bruce, for the nice words--I feel honored to be accepted by this great group!

However, I'm a little concerned about Brian's problem with feedline radiation. Brian, how can be sure your 'balanced' feedline is really radiating? Have you measured it, and if so, how did you perform the measurement? Next, if the system is constructed correctly it will make no difference whether the line impedance is 600, 450, 300, or whatever, with respect to feedline radiation.

On the other hand, let's see what might cause the 'balanced' feedline to radiate. The feedline will radiate somewhat if it is WAY off center, causing unequal currents on the radiator, and thus somewhat unequal currents on the feedline. Another cause could be that one conductor of the feedline is making a poor or non-connection to its antenna terminal. Still another cause could be an open in one of the feedline conductors. As I said above, the impedance of the line has nothing to do with causing it to radiate. As I'm sure you know, feedline radiation is practically zero when the currents in each conductor are equal and out of phase, because the RF fields radiated from each conductor are opposite in polarity, and thus cancel.

Another point that is often misunderstood is that although antenna currents on the radiator result in radiation, antenna currents cease being antenna currents at the junction of the antenna and the feedline, and now become transmission-line currents. When the conductors of the feedline are sufficiently close to prevent radiation, transmission-line currents do not result in radiation. Consequently, with the spacing normally used in open-wire, or other ladder line, no part of the feedline becomes a portion of the radiator.

Coming now to copying book material with respect to copyrighting. For those who have a copy of my book I encourage copying it for others. I'm not interested in royalty money, what concerns me most is that what knowledge I have I can communicate to others in a meaningful way. However, the 2nd ed contains a lot more material than the 1st, and the new 3rd edition contains a lot more than the 2nd, so you must be the judge of what to copy.

Walt

Hi Fred,by dumb luck my ladder line comes in through plexiglass pane in basement casement window and ends about 12 inches later at the flashbox which sits right in front of the window.   Outside the plexiglass pane has banana jacks for the feed so I can pull it away outside if I want to.  So it's mostly low Z coax indoors.   I make my transfer from the W7FG line to the dipoles by using a big tip 150 watt Wahl iron to heat up the joint then I saturate it with silver lead free solder.  Never had a problem but for some reason soldering splices in the W7FG line is harder.  Got to use more flux on them I guess.  

Rob

P.S. Walt tnx for ur work with your FB book & looking fwd to the next edition

Walt, Thanks for posting.  I wonder if you can comment on my situation:

I have a about 130 ft of wire 50ft up horizontal.  The ends are puilled down as my property is not wide enough. About 20 ft on each side of the antenn angles down.

I ran this with 450 ohm line for a year using the KW Johnson tuner.  The line ran out a plastic pipe in the wall the over wooden stakes until going straight up to the antenna.

I lowered the antenna, Cut the 450 ohm line off, Soldered on 600 ohm open wire line.  Ran this through the wall.  This line goes UP the house, over the roof and then arcs to the antenna.

To the locals on 40 meters I gained 20!!! DB.  These guys use Back yard verticals.  On other bands I cant honestly tell the difference.  Why the huge gain on 40? 

By the way, 20 is very hard to tune.. I can get it to 1.8 to 1 but the tuner is out of range and reads 0 and 1 on the Caps. 

Thats fine for you, myself and others that have the room for a Beverage farm. I'll be the first to admit my DX totals would plummet real low if I was stuck with the TX antenna only. My station has been known for its ability to hear on 160/80.



The feedline has to drop vertically and not in the plane of the antenna otherwise antenna mode RF will be coupled. In the real world not many have 130-140' available for 160 and even 60-70' is not an option for 80.  Any deviation from the ideal can have an effect and cause feed radiation.


Easier said than done which is the problem. When you stop spouting strictly theory and then try to apply it to a typical hams yard things fall apart fast.





Id say it contributes to a large degree but just bringing the line into a house and thru a part of a basement full of electrical wiring and copper pipe will cause unbalance. If the shack is at an upper level or attic and right next to the outside wall it is minimized or a non issue. Coax doesnt care where it is run.


  

Thats true for an efficient Marconi. However the basement scenario mentiond avove allows plenty of capacitive coupling to grounded and ungrounded metal.



The more elaborate the tuner the less efficient it can become and becomes a chore to tune and is rather narrowband. Unless you live on a net frequency it becomes a royal PITA to QSY. I tried several iterations of open wire antennas and tuners and always went back to coax. Ive no use for tuners period.

QST finally got off their dead butts in the 90's and did the first indepth evaluation of the commercial tuners. Some with poor LC ratios lost substantial power and MFJ's were notorious for catching on fire when on 160M.  And that was coax to coax!



True but the sleeve balun aka common mode choke has been around for around 40 years now and there is no excuse for coax line radiation.



Im well aware of the issue and wrote a few articles on the subject in the 80's aimed at obtaining high impedance from the sleeve balun as well as being broadbanded.

OTOH OW is a 2 way street having both modes on the surface which often defy removing the common mode.



Which brings us full circle. The Army Signal Corps spent years trying to attain perfection at comm centers during WW2 and after. Bringing OW into the TX building didnt work no matter what they tried for tuners. Why do a few hams with less credentials think they are better?


Many fell for that trap and before RG-214 it was RG-9B. The dielectric is the same as RG-8/213 and that is what determines the loss. And silver plating does squat at HF and even most VHF. All the dual shield offers is close to 100% shielding effectiveness. To eliminate the rodent problem I use all CATV hardline including the 750' run to the Beverage switching center.






Agree. The literature is full of installation details from MF to VHF, past and present. I know a few running in the 750' to a quarter mile range to get to antennas on top of a hill, and in a swamp.


 
Many of the vintage installations were to feed rotary antennas when OW was used right to the feed point. They reportedly worked very well. My contemporay comments are for those monoband antennas that switch to coax thru a stub and balun or thru a LC network. Im sure the balance is far from perfect but a little feedline radiation at almost ground level way out thru the woods is of little consequence. Since those antennas are used by serious contesters and DXers a transition to coax is also done at the house. Nobody wants the hassle of a tunner in those situations.

The feed to my 160/80/75 Inverted vees is about 450' of 3/4" CATV hardline where losses are measured in tenths of a dB even when the 160 VSWR gets to around 3:1 at the high end as its cut for low end DXing. Any pi network can be adapted to the situation at hand as it is, in reality, a tuner.


Ive tried OW at several QTH's over the past 54 years as a ham, none were what I called satisfactory and were mostly something to get up quick after moving that worked to some fashion on many bands. The only tuner that really worked well was a series/parallel affair from a late 40's QST and switching was a Rube Goldberg affair that was part patch panel and part plug in coil swapping. Not exactly QSY convenient.

The bottom line is that OW works for some who remain a minority. You learn to work with what you have with OW or coax. And the last thing that is needed is trying to jam opposing views down anothers throat.

We dont need another war on here.

Carl
KM1H

Walt, That only holds when either a current or voltage peak is at the feedpoint. Otherwise the antenna will attempt to be down at some point on the feedline This will be true if say the antenna is cut for 3900 and you decide to work at 3550. Its more pronounced in the G5RV where feedline radiation is a part of the design and the bottom of the required length feedline usually goes these days into a ferrite balun with choke beads on the coax to the shack.

Then there are tuned feeders and untuned (nonresonant) feeders to contend with and there are pros and cons to both.




Id say that you now have a large vertical component to the radiation.

Carl
KM1H

Very interesting thread.......
As for feedline radiation......u will see in the picture that my feedline is within 5 ft. of my operating position and no rf problems. I run a 4x1 by 833'3 with no problems. In the pic u will see a relay at the top of the picture and its used to switch the balanced line between the tooner on the dryer and a KW matchbox. The spacing of the home made line is 4 inches in the shack and increases to about 7 inches up to the antenna. U can see the change where the feedline goes thru the window. It aint pretty but it works and I didnt use any complicated math the build it ;)

Bill  

BTW.....someone told me that  the feedline spacing had to remain the same or else I would have problems. Looks like nobody told that to the feedline... ::)

Bear,

I will attempt a crude answer to ur question but a caveat:  I am not a physicist or E.E.:

It's important to understand that the virtues of parallel feed can only be enjoyed in a balanced system.  In the visual physical sense, that means antenna symmetry across the feed point, symmetry between the sides of the feed with respect to each other, and a genuine low Z unbalanced, to high Z balanced, matching network.    In my opinion, you can fudge some of this a bit -- maybe the spacing on the feedline wires is something other than 3 inches when making some turns outside, or one side of the dipole is a few feet closer to ground than the other -- these things are not a big deal.  If your current on one side is 97% of the other side the system is essentially balanced.   I get the sense from balanced feedline detractors (elsewhere!) that anything other than total perfection is a useless disaster.  Not true.

In the balanced system, the RF current exciting the dipole is moving in equal but opposite directions.  Because of this the electromagnetic fields, one on each wire oppose each other in their rotation and collapse.  Therefore, the line does not radiate.  Because of the physical construction and design of the line, there is this equal but opposite symmetry, even with high standing currents and voltages, so line loss is still very small.  The air dielectric prevents flashover and damage due to heat (except that Fred seemed to do some window line melting so it might be a good idea to stick with the 600 ohm stuff).   The currents in the line oppose each other because each side takes a turn handling return current with each RF cycle (see http://www.tfcbooks.com/special/antenna.htm (http://www.tfcbooks.com/special/antenna.htm) for a visual diagram of this with the field lines of force about the dipole).

With coaxial cables the RF current flows on the surface of the center conductor and the inside surface of the shell.  The electromagnetic field is propagated through the dialectic and this works fairly well if there are no high voltage and current standing waves on the line although if the line is high quality it may withstand them.  The line is unbalanced because the shield is grounded.   It can work well when the antenna feedpoint Z is relatively close to the coax characteristic Z but there is more loss with high standing waves due to the coax design which has some leakage and resistance losses (how it works here:  http://en.wikipedia.org/wiki/Coaxial_cable (http://en.wikipedia.org/wiki/Coaxial_cable) ).  I'll freely admit to fudging on this last part because I do not intimately understand the inner workings of coax and to be sure, a large air dielectric coax such as heliax may handle an extreme missmatch between it and an antenna without much loss.  In fact LDF6-50A with a vswr of 6:1 has a swr loss of 0.194 dB for 300 feet on 160 meters.  Not bad, but feeding a high dipole with LDF6-50A may be difficult  ;D  My feedline loss calculations were done with this online calculator:  http://www.ocarc.ca/coax.htm (http://www.ocarc.ca/coax.htm)

It's important for AMers that even under ideal condx on low frequencies, a long run of common ham coax such as RG213 can have unacceptable losses (to me at least).   For example, 300 feet of 213 on 160 meters to a 50 ohm load has a loss of 0.78 dB.  That may not seem like much but it is part of accumulated system losses such as loss in the tuner at the feedpoint, and antenna inefficiencies most of us can't avoid.   Unlike some modes such as PSK31 where a ham can get by with a poor antenna, I think for AM losses have to be reduced as much as possible because we are handicapped to begin with due to the power limit.

After doing some thinking about coax v. ladderline, I concluded that there is really not much need for argument because I looked at the pros and cons of each and, assuming a dipole fed with coax and a feedpoint choke balun really does not pick up any common mode noise, the advantages of a balanced system seem to pertain to transmitting (sw bc stations don't have to do any receiving  ;) ) and the advantages of coax seem to favor receiving.   Don sort of beat me to the punch on this but before anyone takes down their ladder line fed dipole and puts up a coax fed one because of RFI, why not use the balanced antenna for transmitting, and set up a separate coax fed rotatable rx loop or small low rx dipole?   I'm going to give one a try -- perhaps that will save me from having to walk around the neighborhood with a noise sniffer.  

73

Rob
K5UJ
 

How true.....how true.....

Carl, I'm sorry, but I have to totally disagree with you concerning the antenna attempting to be down at some point on the feedline. That is one of the mistakes Louis Varney made in describing the action in his G5RV antenna, and which has been repeated over and over by those who swallowed his misleading explanation of the voltage and current distribution along the antenna and feedline. I'm preparing a post concerning the misleading aspects of his presentations that appear to make the G5RV something that it is not, especially the 34 ft open-wire section that he erroneously calls a 'matching section'. It is his incorrect explanation of the current distribution in the OW section of the G5RV feedline that has helped give that antenna a reputation as a superior radiator that it doesn't deserve. The G5RV will not radiate any more RF energy than any other single-wire radiator of the same length when fed with the same power.

In addition, as I've said in previous posts, when the antenna system is truly balanced, radiation from the feedline is insignificant, the G5RV included.

Walt,
If u dont mind.......as u said in an earlier post......I will start to scan your book in pdf format. This will take a LONG time........its a big book!!!

Bill

Suggestion Bill. Why not review the chapters already in pdf on my web page, and then download them. It'll save you a lot of time and effort compared to scanning every chapter. Consequently, I'd only scan the portions of the book that don't appear on the web page. In addition, if you're copying from the 1st edition, there has been some rhetorical editing between that edition and the 2nd. And further, there are more chapters in the 2nd ed than in the 1st.

Walt, I look forward to your post on the G5RV antenna, lots of folks use those, but they never made much sense to me as it was explained. Quite interested in what you have to say.

Bill, good to see you here and thanks for the effort!
As someone else pointed out Walt shares a good amount of his book online, so some the chapters are already in digital form. Will save you some trouble, see w2du.com/Reflections2.html.
Seems that chapters 4 - http://w2du.com/Chapter04.pdf, 7 - http://w2du.com/Chapter07.pdf, and 20 - http://w2du.com/Chapter20.pdf address many of the questions the fellows are asking in this thread.

And thanks Walt for being so magnanimous with sharing the info.
I sure wish the W4RNL site was still "open", I find the current situation confusing to say the least.

-Bruce

I look forward to the post also.  I was talking to Timtron one night last winter.  We talked until 3am.. LOL.  He switched between 4 antennas.  To our amazement the G5RV beat them all to Arizona.  He said he found it in the trash at a hamfest and through it up about 30ft in the air. 

c

Clark, to answer your question about why you gained 20 dB on 40m when you changed to open-wire feedline, I can only think of one reason. You said the radiator is 130'. On 40m this is approximately a full wavelength, which means that the feed-point impedance at resonance will be in the neighborhood of 4000 to 5000 ohms. This impedance presents a huge mismatch to feedlines of 450 ohms or less with plastic insulation, which have much greater attenuation loss than open wire at high values of SWR. On the other hand, going to open-wire the attenuation loss is reduced very significantly, hence the greater signal. But 20 dB? That seems greater than I would expect for that change. There may be another reason that escapes me at the moment.

Walt, that's extremely generous of you to provide permission to copy your book, and truly in the amateur spirit!

And kudos to you also, Bill, for volunteering to copy it; that's very generous of you as well.  As Walt said there's already a fair amount of it already on his website, so save yourself a bit of work  ;D

All you have to do is register....
No more difficult than to register with this site.

This is a VERY simple question to answer, Clark.

Cross polarization = approximately 20 dB.

You now have power being radiated in the vertical plane, and the horizontal plane.

When you said the guys where using verticals, that made sense of it.

Now, the question is, did you have the SAME length, and approximately the same path, or is it both completely different? 

--Shane

It'll give me something interesting to read over the holidays. No telling when III will come out. Good new books are scarce, the rest all seem dumbed down these days.

ah but never mind, Bill may scan it. I can download the existing chapters and read them off the site as well.

thanks,
Patrick

Polarization would make a big difference for local ground-wave coverage, but ionospheric propagation is so turbulent that the polarisation of the signal becomes random at the receiving end.

As for the balanced line coming off the antenna at 90°, I say if everything is truly balanced, it doesn't make any  difference whether the feeders run horizontally, vertically or slanted as long as they remain perpendicular to the antenna. If the antenna and feed line are indeed configured symmetrically, there would be negligible coupling between the radiating antenna and feeders.  Nearby metallic objects such as plumbing, overhead electrical wiring, house wiring, smokestacks, etc may upset the balance, but if there is reasonable separation between antenna system and stray objects, those unbalances would be too negligible to worry about.

   I have been reading this thread with an awe of fascination while I am learning from you antenna gurus. This has been great. That said, I think everybody has it wrong. The solution is far simpler, and on the sinister side. Let me explain. My dear XYL of nearly 25 years has learned how to get me out of the hamshack. She knows which electrical appliances in the home cause RFI such that my joy of listening to the ham bands turns into a maddening session of frustration. I eventually turn off the equipment and come back into the house. There is the wife sitting at the couch looking all pretty and innocent. She asks me if i want to watch a DVD (a chick flick). So in the end, she was not so innocent, and she has smoked me out of the ham shack by creating RFI.

   So Brian, is your noise issue in any way similar to mine? Maybe it is the XYL running a hair dryer for a timed duration after you enter the hamshack? The wife of a ham has to get creative you know.... ;D

73,
Jim
WD5JKO

Good one, Bill
this reminds me of a situation we did a few years ago.....................

the last year that we did the W3F special event station from the Howard County Fairgrounds in West Friendship, Md. Dave (K3ZRF) brought a W7FG complete ladder line fed diaperpole. Al (KZ3AB) shot us up some lines with his easy-hang and the antenner itself went up fairly easily. However............ it left us with another problem. The feedline would only reach the very back of the building (a 100' horse shed)

With no additional feedline in our arsenal, Gary(W2INR), Joe (N2YR) and myself stood there and scratched our heads for a few minutes and came up with "ladder line on the fly" Luckily, Joe had brought a full spol of #12 THHN wire. We spliced it in with wirenuts, and stapled it to the wooden support posts for the building, spacing it at an eyeball 6".

Many of the "ricebox hams" looked at and swore it wouldnt work, and really laughed at wirenut splices. And especially the 100' run of it.

It took my 4x1 transmitter at full strap, noone ever told the feedline that it would'nt work,
the RF didnt care, we had no problems with RF geting into the audio and....................
WE PUT OUT A STRAPPING SIGNAL!!

So the bottom line is that the feedline will work as long as no one tells it otherwise! !   :o  ;D

                                                                  The Slab Bacon

I told my dipole that it was a four-element beam. I have the signal reports to prove it works.   ;)


http://www.amwindow.org/pix/htm/fallfest02/ff4.htm

Steve, those pix were from '02. that was the first year at How Cow. Do you have any from '03? ?  that was the second year up in the barn. Someone took some pix of the feedline, but I dont rememba who it was.

I have run mostly resonant dipoles fed with coax for the last 30 years, but have tried the open wire line, g5rv, trap dipoles, verticles, the B+W folded all band disaster, and other setups.
The G5RV was tunable to a lower swr, but not a great performer on 80 meters.

A well built dipole fed with coax is quite broad banded, has no real power limit, does not need a tuner if run into tube gear, and if put up well, is a maintance free antenna.

In my case, not having much ground, the antenna's are close to the house, so coax runs are under 75 feet.

I really like the no tune part, pick a band, pick a rig (its already tuned up), pick and antenna and go.

No tuners or baluns to worry about or waste any power, no rfi in the shack.
Rain, snow, ice, does not seem to change the swr.

I suspect there are better receive antenna's from a noise standpoint, there are antenna's with gain, and 160 meters is its own thing, and DX is another thing, but for the usual 80 and 40 meter AM operation I do, it seems hard to top a dipole.

If I had room, I would like to try a good 160 meter dipole fed with open wire line and a balanced tuna.
But I dont.

Brett


 

I have always preferred a matched dipole cut and tuned to the frequency band. They always work well.

I have had many problems with multi-band wire antennas fed with open wire, usually due to poor tuner design and high voltage breakdown.

Pat
N4LTA

When I put up my 390 ohm a brown crap window line a put a twist every few feet.   Most pictures I see using real ladder line have long sections running without a twist.    I wonder if that could have some effect with W5HRO's noise pickup.   I think having a twist would reduce pickup and feedline radiation.

Shane, Vertical radiation is not possible from my Open wire line. Thats been pointed out many times.  I think walt explained the gain on 40 meters.

C

I dont have to do that. The line and tuner is balanced. 

C

If we stick to Clarks question and dont go drifting off the subject, a vertical component is a plausible explanation that nobody has presented an acceptable refute.

Its not so much as a polarization issue as it is where the azimuth lobe is situated. With the horizontal at that height there is minimal radiation at the low angles so the local signal is attenuated. With the different feedline there is sufficient unbalance to permit some radiation at a lower angle. Im certain it can be computed with NEC analysis which would show a substantial current (power) node on the feedline. It is the at current node where the maximum radiation takes place. That antenna system has multiple current nodes.



Walt, with all respect, I suggest that you include a series of NEC-4 plots along with that G5RV article using the design exactly as described by Varney.  I too have read of the disagreements and supposed analysis using software. However when working with OW the analysis accuracy of many commercial or free products are not up to the task.  You are old enough  ;D  to remember the current/voltage distribution curves of the antennas and feedlines in the various handbooks as well as engineering books which I believe is still accurate today 8).  Almost all admonished about feedline radiation as well as the necessity of having the feedline drop 90* vertically to minimize radiation. Why the revisionists today want to rewrite these standards is beyond me.

Although I rarely view QST as a bastion of engineering excellence a comment in the December issue caught my eye. "According to the scientific method, a theory must be tested to confirm its validity". Some of what I read on here and elsewhere on the subject neglects those basics.  And dont get me going on Cebik!

Carl
KM1H

And the absolute proof is??

Or maybe its just the operator that is unbalanced ::)  Couldnt resist that one ;D

Carl
KM1H

LOL....    I hope I am balanced.

Because the current on each leg of the feedline is the same.  If that is true, Then the feedline cant radiate.


We can drop the subject.  I dont think we are going to do anything but theorize. I was just trying to learn how changing feedline effected 40 meters.  I think walt hit the nail on the head with my situation.

C

Only if the feedline is unbalanced. We have not determined that the line is unbalanced. My guess is that it is, but I don't see how changing the feedline would create unbalance where (apparently) none or very little existed previously, unless the geometry was changed.

The open wire fed dipole is best configured so that the feed point of the transmission line is near a current or voltage maximum point.  If it is midway between, it can be very difficult to tune.

My first experience with using the 80m dipole as a short dipole on 160 left me with a 3/8 wavelength wire, from the input end of the feedline to the end of the antenna.  I threw together a balanced link coupled tuner using a BC-610 split stator plate tuning capacitor (3/16" spacing, rated at 7kv breakdown).  I tried tapping down on the coil to get it to match the highly reactive load presented by the odd number of eighth wavelengths.  I finally found an adjustment that gave a 1:1 swr at the link when the coil was tuned to resonance, but I couldn't fully modulate over about 100 watts without the 7 kv tuning cap arcing over.

Finally, I added another 60' of open wire that I could switch in using a ceramic knife switch, bringing the total wire length to a half wave.  It loaded perfectly using parallel tuning, and I could run a full kilowatt 100% plate modulated without arcing over the capacitor.  The permanent tuner now uses a 300/300 pf 7 kv variable with a 50 pf 20 kv fixed vacuum capacitor bridged across it.  The coil is the balanced tank coil removed from an old Gates 250 watt transmitter that another ham had gutted.  The extra 60' of open wire is folded like a hairpin and strung between two metal fence posts about 30' apart and resembles a tennis net.

added 2 feet of open wire line.  20 still wont tune lower then 2.0 to 1 SWR.  Feedline length seems to not effect things much. It did change the left cap knob on the KW matchbox.. from 10 to about 25.  Ideas?

C

Started to scan the book. This project will take a while! Besides the time it will take, there will be a wide black line on the spine side of the page. This is because its a book......and I cant get it to lay flat on the scanner unless I pull the book apart page by page which I dont want to do. Even though the line is there, no text will be lost.

Bill

I don't see how you can walk around outside in the near field with some kind of FIM, even one of those cheap meters with a diode connected to a telescoping antenna, and tell the feedline is radiating when the whole area is swamped from RF coming from the antenna itself.  Maybe if you get the dipole way up away and tx with only a few watts but if it is only 50 feet up you'll get these readings but they'll be coming from the antenna and you'll think ur feedline is radiating it seems to me.

Rob

Yeah..  I agree Rob.  If the system is balanced and you check the current on each leg, Its not radiating.

C

BTW.......I think this was covered before on the board but I have found that Foxit Reader beats the Adobe pdf reader hands down for reading the pdf format.
http://www.foxitsoftware.com/pdf/reader/ (http://www.foxitsoftware.com/pdf/reader/)

Bill

Clark, can't remember what your antenna is but on 20 I had trouble getting a match with my KW m/b feeding a 1/2 w. 20 m. dipole. On 14.340 only got as low as 1.9:1.  I added 12 feet of ladder line and that fixed it.   I had a 50 or 55 foot run and increased it to 62 or 67 feet so FWIW maybe you need to add more than 2 feet.   I inserted the extra length in my back yard and temporarily draped it around a 5 foot tall wood step ladder.  I guess I hunched that on 20 where a quarter wave is 16 feet, 12 would be enough to show a change but I got lucky and it was enough to match.  Throw another 10 or 15 feet in there. GL

Rob
K5UJ  

Another Hmmmmmm,
How did this topic get so complicated......is it because the original post was bull or is it because some folks want to impress. I just cant figure it out :-[

Its an internet Forum. 

When you talk on the radio, do you talk about the same subject all night?  :)


I tried everything. This antenn wont tune 20 down flat. Oh well.

Clark

If I start the QSO.......thats where it stays...... ::)

On the air...........not here......

Well, I guess I'll pour a little gasoline on this fire...

what about the mismatch at the antenna feed point??  Coax is 50 ohms normally, but a halfwave dipole is ~72 ohms so right there you've got a mismatch. Small so no problem right?

What about feeding that 72 ohm dipole with 300 (450, 600 etc) ladder line?  now you've got a BIG mismatch. So doesn't a lot of your power get reflected right back down the line? 

If it was to be max efficiency, wouldn't the feed line need to see an antenna with the same impedance?  like folding the dipole with the same spacing as the feed line to get nearly the same impedance???

Truth is, I don't know. My signal gets out, but this bit always made me wonder...

The open wire line is near lossless so the mismatch does not matter.  The only Draw back to the open wire line I can see is that its not easy to setup a true balanced system.  Its been alot of work and a real pain sometimes.

Clark

Ed,
I think your question was covered a little earlier in this thread.......

Bill

Go from 6 inch spaced line to 4 inch spaced line :)  Make a transformer.  The difference in the line spacing will make a Z transformer, and you can fudge the spacing along with the MFJ to get the transformation ratio you want.

Still won't help with your vertical component.   :)

--Shane

Try adding 6 to 8 feet and I bet you will be fine. I used to run 2 Vee beams in parallel with one about 10 feet shorter than the other to lower the q that fixed everything. You are just outside the matchbox tuning range on 20m so it could take close to a quarter wavelength change to get you out of trouble. You can even hang the extra feed line off the match box with the end open. Just be careful as there can be some high voltage at the end. You could short the end but it will change things a lot on other bands.

Aint that the truth. Compare that to the Antennex forum which thinks Cebik was a god. I never saw a bigger collection of fools and poseurs in my life and bailed out fast.

Tower Talk isnt much better and both are owner controlled so that only one side of an issue is tolerated.

Carl

As mentioned the mismatch power loss will be low however the VSWR will still reflect back down the line. As already mentioned this may cause antenna tuning problems as well as radiation.  In the 40's Johnson sold the Q Feed System Q Bars which was simply a 1/4 wave 1/2" tubing transition from the OW line to the feed point. Its impedance is the geometric mean between the feedpoint and OW impedances. Old handbooks had construction details for 1/4" and 1/2" tubing and impedances at various spacings. Monoband of course but it allowed untuned feeders of any length.  I used the concept many years ago to feed a large fixed wire curtain array for 6M with almost 200' of OW and it worked great. At the house end I used a 1/4 wave shorted stub and a coax balun to the KW AM/SSB/CW amp. TVI and RFI all but disappeared.

Carl

Okay I'll have to give it a try.  Unfortunately I can't get close to the dipoles themselves--they're up too high but maybe I can still observe something.  I can tx a carrier on 40 m. with the dipole that's 130 feet long.  I think that will give me current out at the ends.  I can take a f.s. reading and back down the carrier until I barely see the meter move.  then go over to the feedline and take a reading about a foot away and see if there's any signal.  Something to do over the holiday.

Rob

doing it that way - 2 sheets at a time, the aspect ratio will match the CRT screen better.

So far, and over the past 38 years of ham radio, I have preferred coaxial feeders.

I use coax (helical - not solid dialectric) today on all of my antennas, and I suppose anyone who has talked with me knows I get out reasonably well  8)   But, I do decouple the coax from the line using a whole lot of #43 ferrites over the coax, at the antenna feedpoint.  And I use low-loss, usually helical coax cable and nothing with a solid dialectric.

There's just a whole lot less equipment involved with coax feed, and also the RF is carried away from the shack in a convenient manner, without a problem, the coax touching whatever it wants, etc.

I do use a single coax feed for both 160 and 75 meters - with both antennas connected to the same feedline and it works out just great!

Regards,

Steve

Coax is easier:)  I wish I had room for big antennas.

All my verticals use Andrews Heliax. Half inch or 3/8s. I love it..

Clark

But then the reflected wave reaches the feed point end and is reflected back to the antenna where  a little more is radiated and the process repeats itself until all the energy is dissipated into the radiation  resistance of the antenna plus some feed line losses.  The  reflected power does not disappear, except for what is dissipated in the dielectric and the resistance of the wire.  Those reflected wavefronts oscillating back and forth from one end of the feed line to the other is what produces standing waves on the line.

This is equally true with coax, twin lead and open wire.  The solid dielectric stuff wastes the most energy in the process, the reason why it is OK to run open wire at high SWR, but solid dielectric coax need to maintain as low SWR as practicable.

Wow! Walt is like the Jerry Garcia of Amateur radio!!  Freely share the goods!!  It's about the CONTENT not the money!  Love it!

Rob, you can use a long pole with either a 1N34, 6" pickup wire, a .01, and mini coax to a microamp meter; or a NE2 at night as very basic line sniffers. Ive used maybe 20' of aluminum tubing (and old 10M boom) with a 4-5' wooden mop handle stuffed in at the hot end. It may be enough to give some meaninful indication at least over part of the OW run.


As far as ATU's there is an article in Feb 62 QST pg 39 that may be of interest. It also references a good 1942 IRE paper.

Carl
KM1H

Yep. Two feet is not enough to make any substantial change on 20 meters. Two feet is only 0.03 wavelengths. Add something like an eight of a wavelength.

The other thing to keep in mind is that your dipole will probably NOT be 72 Ohms. That is the impedance of a dipole in free space. When a dipole is less than about 0.25 wavelengths above the ground, the impedance is usually less than 72 Ohms. Higher dipoles can have impedances above 72 Ohms, peaking out in the 80-90 Ohm range.

So don't worrry about the mismatch Ed. The loss will be negligible, unless you are using very lossy coax and/or a very long run of it,. Even if your dipole was 72 Ohms, this would only amount to a SWR of 1.44. This SWR results in a whopping 0.01 dB more loss than if you had a perfect match when using 100 feet of RG8 on 3.8 MHz.

You can check you exact situation at the link below.

http://fermi.la.asu.edu/w9cf/tran/index.html

A neon lamp will not give a reliable indication of radiation from the OW feeders.  All it will give is an indication of the intensity of the near field of each of the wires.  By the time you get far enough away to detect the radiated field, it will be far too weak to light up a lamp.

The neon lamp is most useful for determining where the maximum and minimum voltage points are along the feeders.  You might get some idea of feedline balance at a high voltage point by carefully moving the lamp between the feeders,  preferably by sliding it over a spreader, and noting if the null point appears exactly equidistant between the two wires. 

Something I have found with mine is that even the glazed commercial EF Johnson ceramic spreaders are NOT perfect insulators.  I can hold a neon lamp up to a spreader, and a bright spot appears in the bulb where the glass envelope touches the surface of the ceramic, just as it does when touching a metallic conductor that is hot with RF.

Steve, doesn't that run of heliax up to the dipole feedpoint weigh a lot?

73

Rob

hi Carl, thanks -- I have a few fiberglass poles I can use.

73

rob
K5UJ

Here is a test I have done to find out what caused the RFI in my shack when using balanced line. The test was made on 75m. It made a big difference where the ground was on my link coupled tuner and after installing an ugly coax choke at the tuner input. It didn't make a difference if the transmission line was balanced or unbalanced thus acting as Marconi antenna, a conjugate match was obtained in both scenarios. Also, upon using the SLC, Utah reciever on smeter.net as a remote recieving site with an S meter, I noticed that my signal didn't change much when I went from a balanced to an un-balanced state on my transmission line by changing the ground location and retuning, etc. That would make sense due to my wire antenna is only 40' high and acts as a NVIS system. And when it was in an un-balanced state, the transmission line acted as a Marconi antenna using everything including the neighbors home as the counterpoise causing RFI havic, also performed as a NVIS system! So would it be safe to determine that both antenna systems were efficient but with different side effects?

What was the time period of the tests? Did you quickly switch back and forth while watching the remote S-meter?

Consider this - if your antenna system is producing RFI in your neighbor's stuff, that's RF energy that is not making it to the ionosphere.

Not if the neighbors "stuff" is now part of your antenna system per sei, see it wouldnt really be RFI, but RF voltage/current that is on the other half of the antenna/counterpoise/neighbors home.... and the tests were very fast and over a 2 hour test period to average out the test results due to the changing propagation. I am very confident in the signal results in other words.

well,
       Here is another thougt to ponder................... Is the RFI coming from your feedline or your antenna ???  ??? If it is definately coming of of the feedline, then you have some tweeking and testing to do. But.................

If it is coming off of your antenna it could be a "good" thing. This could mean that you have gotten rid of some of your losses and more RF is getting to the antenna.

If you dont have "RF in the shack" problems, but your neighbor is pissing and moaning about your RFI, it might mean that more RF is going to the antenna and not being wasted heating the feedline.

just something to ponder.....................

A quick note.......
My post about complicating this thread was not meant to belittle anybody.........Its just if u read the original post....in my opinion the post was meant to "uncomplicate" the whole idea of coax vs balanced line.
The technical info posted here is first rate.
No harm intended folks.........I love ya all ;D   

Yes, while there are multiple ways to correct the issue I have presented, the point I was attempting to make was that my signal didnt seem to change either way. Only that I had severe RF in the shack when the transmission line was acting as a Marconi antenna as Don pointed out. It makes perfect sense. The open wire transmission line works ONLY in a balanced configuration and is not possible to operate un-balanced as Walt said. BUT, when the tuner and ground is configured incorrectly, the transmission line becomes a Marconi antenna and no longer functions as a balanced transmission line carrying the RF to the real antenna in the sky. I realize this is getting way off the original topic but I find it very interesting learning to understand what this "RFI" really is. I personally dont believe it is RFI at all but simply just RF on the "other" half of its' antenna aka station cabinets, neighbors home, etc... :)

It is fairly heavy... The center is held up by a tower and a pulley system.  I am guessing the antenna and feedline (with the type 43 cores up there also!) probably weigh at least 25 if not possibly 50 pounds.  The center is somewhat hard to hoist up when near the end.

Regards,

Steve

Technically true, but will your neighbors see it that way.  ;D  I know mine didn't at a previous location. I often tied the two conductors of my open-wire fed dipole together and ran it as a vertical-T against 16 radials. This configuration was superior to the balanced-fed dipole configuration for contacts greater than 300-400 miles on 160 meters.

Steve,
I havent tried that yet on 160 but will soon. BTW, We might be able to hear you out here on the west coast tonight but might have to wait another few hours. I am listening out for you and Tom.

Joe

Listen this weekend, Friday or Saturday night. I'm off to bed now. That four letter word, WORK comes up in the morning.

Steve,
So you do work? I thought you were a prfessional Ham radio operator/mentor/DX op/pile-up cracker.

Fred

I go to a work place......