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Author Topic: Some words on the Ladderline vs. Coax issue...  (Read 105567 times)
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flintstone mop
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« Reply #25 on: November 16, 2009, 10:12:02 AM »

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
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
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Fred KC4MOP
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« Reply #26 on: November 16, 2009, 10:15:49 AM »

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

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
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K1JJ
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« Reply #27 on: November 16, 2009, 10:25:16 AM »



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

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
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w3jn
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« Reply #28 on: November 16, 2009, 10:48:24 AM »

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.
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« Reply #29 on: November 16, 2009, 10:56:01 AM »

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.
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Steve - WB3HUZ
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« Reply #30 on: November 16, 2009, 10:58:48 AM »

You can calculate losses for many transmission lines on line.


http://fermi.la.asu.edu/w9cf/tran/index.html
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KM1H
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« Reply #31 on: November 16, 2009, 12:03:39 PM »

The simple rules to remember:

Quote
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.

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.



Quote
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.

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.



Quote
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.



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.


Quote
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.


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


Quote
4. Problems with feeding these lines through walls?
Use your head. Its not that difficult. Believe me, it is worth the effort.

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.


Quote
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.


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
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kc6mcw
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« Reply #32 on: November 16, 2009, 12:05:07 PM »

W5HRO,

What kind of tuner are you using?

Joe
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kc6mcw
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« Reply #33 on: November 16, 2009, 01:53:49 PM »

The simple rules to remember:

Quote
Quote
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.

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.

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”.

Quote
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

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.

Quote
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.

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.

Quote
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.

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.






Quote
Quote
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.



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.

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?


Quote
Quote
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.


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

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.


Quote
Quote
4. Problems with feeding these lines through walls?
Use your head. Its not that difficult. Believe me, it is worth the effort.

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.

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.

Quote
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.

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


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ke7trp
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« Reply #34 on: November 16, 2009, 02:02:20 PM »

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


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Are FETs supposed to glow like that?


« Reply #35 on: November 16, 2009, 02:08:06 PM »

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.



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ke7trp
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« Reply #36 on: November 16, 2009, 02:15:48 PM »

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
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KC2IFR
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« Reply #37 on: November 16, 2009, 02:21:17 PM »

Fred,
I was only kidding about selling the book.... Wink
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
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« Reply #38 on: November 16, 2009, 02:52:05 PM »

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
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k4kyv
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« Reply #39 on: November 16, 2009, 02:53:33 PM »


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.

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.

Quote
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... 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.

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.

Quote
They can absolutely cause RFI in the shack, house and neighborhood. High VSWR on harmonics will guarantee radiation since it is still there with a tuner.

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.

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

Quote
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.
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.)
Quote
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...

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

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.


Quote
4. Problems with feeding these lines through walls?
Use your head. Its not that difficult. Believe me, it is worth the effort.


For many it is very difficult. Obstructions such as a wife and lowering house values stop many from drilling holes.
Those are non-technical issues beyond the scope of this discussion.

Quote
...open wire can have its uses for some, such as very long runs to an antenna...

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.




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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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ke7trp
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« Reply #40 on: November 16, 2009, 03:00:04 PM »

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
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kc6mcw
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« Reply #41 on: November 16, 2009, 04:22:15 PM »

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!


* link1.jpg (301.76 KB, 1200x900 - viewed 1047 times.)

* link2.jpg (293.62 KB, 1200x900 - viewed 994 times.)
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Steve - WB3HUZ
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« Reply #42 on: November 16, 2009, 04:37:35 PM »

What do you mean by "tuned it purposely out of balance?"
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kc6mcw
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« Reply #43 on: November 16, 2009, 04:41:56 PM »

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.
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« Reply #44 on: November 16, 2009, 04:45:48 PM »

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
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Fred KC4MOP
Steve - WB3HUZ
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« Reply #45 on: November 16, 2009, 05:14:44 PM »

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?



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.
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ke7trp
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« Reply #46 on: November 16, 2009, 05:21:44 PM »

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
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W2XR
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« Reply #47 on: November 16, 2009, 05:49:57 PM »

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?



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.

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
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Real transmitters are homebrewed with a ratchet wrench, and you have to stand up to tune them!

Arthur C. Clarke's Third Law: "Any sufficiently advanced technology is indistinguishable from magic".
W1UJR
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« Reply #48 on: November 16, 2009, 06:22:30 PM »


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 feed line 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 feed line radiation due to the deliberately unbalanced currents flowing from the tuner would be significant. My logic is balanced antenna, balanced feed line, balanced tuner output. At least that's how I do it, but I'm always open to different methods & approaches, 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
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k4kyv
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Don
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« Reply #49 on: November 16, 2009, 07:19:51 PM »

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.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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This message was typed using the DVORAK keyboard layout.
http://www.mwbrooks.com/dvorak
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