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Author Topic: 43ft multiband vertical  (Read 19150 times)
K0OD
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« Reply #45 on: November 19, 2008, 05:46:54 AM »

Ok. It's a voltage balun, rather than a proper current one.

How exactly does that shortcoming harm the vertical's real world performance?
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N3OX
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« Reply #46 on: November 19, 2008, 06:07:19 AM »

K0OD, try drawing out the connections explicitly on paper based on Aadu's picture.

The coax shield is attached at the junction of the two windings, but that's one winding up from the ground radials, like Owen says, your shield will be about halfway in voltage between the earth and the element.  This means a current will flow consistent with the voltage impressed upon the shield and its common mode impedance!  

If you wanted the coax to radiate, that would be fine, but if you lay the coax on the earth and force it to carry a lot of current, the energy it takes to do so is going to be largely dissipated in the earth.

Don't bother think about the phrases "voltage balun" and "current balun."

Draw the circuit from the picture and ask yourself why there's a whole winding between the coax shield and the radials ;-)

Then draw the proposed UNUN configuration based on Owen's and Tom's suggestions (coax shield to radials, coax center to common point between blue and white windings).  You'll see the difference.



73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
ES1TU
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« Reply #47 on: November 19, 2008, 06:07:59 AM »

K0OD:

As I said - I DID work Turkey (1500 miles south of me) on 40m and got signal report 53.

Then again, my answer to the CQ of EA8 (2500 miles west of me) was never heard.

That was on 40m. I'm burning of curiosity how the situation had been if I have had ATU at the vertical base instead of voltage balun.

As I said earlier - nobody heard me on 80m.

ES1TU
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K5YLT
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« Reply #48 on: November 19, 2008, 06:15:39 AM »

<<Why on earth is zero-five using a voltage balun to feed a unbalanced load?Huh

That can't ever be good. How did this go on so long before someone caught it?

The proper way to use that balun would be to wire it as an UNUN. Ground one balanced terminal and common that one with the shield. The center of the coax goes to the center tap. The remaining balanced lead goes to the antenna.

That solves the whole problem.>>

To me the problem is much more than as stated.  Many of the respondents seem intent on pointing fingers at a ZeroFive/Array combination without any regard to what other antenna producers are offering.  DX Eng clearly offers a BAlun with their vertical and no one knows what is actually inside.  They do state the design is a current balun but which is better, unun or current balun?  Maybe a 4:1 voltage balun with a choke balun behind it outside of the near field of the antenna would be a good combination as well.

I think the problem is perhaps a tendency to vilify the manufacturers rather than working with them to improve the product.  I have offered to build several test baluns/ununs and so far have no takers.  On any number of occassions I have changed my product based on the experience and recommendations of my customers and other knowledgeable sources.

Rather than trying to drag down the antenna producer, lets work with them to improve the product.  We in the Amateur Radio hobby need vendors like ZeroFive and Array to help keep the hobby growing.

I realize this is taking the topic away from the original 43ft vertical but I can't help but feel that if we worked with the designers and builders, this topic might be mute. If they show an unwillingness to change then point the finger!

Bob, KZ5R

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W8JI
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« Reply #49 on: November 19, 2008, 06:24:04 AM »

Yes, that is a terrible feed system. It has to drive the shield of the coax with as much voltage as it drives the antenna with.

No wonder the SWR of the antenna is acceptable, the shield of the coax laying on earth makes it a big parallel resistor across the antenna feedpoint.


The question is how such a big glaring mistake in the application got into common use without anyone catching it. Someone should have known.

Since that is a voltage balun the core is always subjected to full magnetizing potential of the voltage across the balun terminals. With the shield loading the system it is like a dummy load paralleling the feedpoint.

The even stranger part is the proportion of voltage exciting the shield would depend on the way the two "balanced" terminals are connected. Connected one way, and the shield is driven by half the antenna base voltage. Flip the two balanced terminals around and the center of the coax ties directly to ground and the antenna is driven by the twice the voltage as drives the shield.

In either case if you ground the shield at the antenna the whle thing shorts the coax out!!! The only power radiating is due to imperfections in the coupling in the winding.

What really is mind blowing about this system is so many people seem to think it is great. This is why you can't trust eHam reviews. A bunch of people apparently think loading up the coax shield is a great antenna, or maybe most of them leave the balun out???

73 Tom


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N3OX
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« Reply #50 on: November 19, 2008, 06:57:11 AM »

"Rather than trying to drag down the antenna producer, lets work with them to improve the product. We in the Amateur Radio hobby need vendors like ZeroFive and Array to help keep the hobby growing. "

Bob, it's very charitable of you to do free design work for a business.  I'm sure they'll be happy with that.  Their profits will be much higher if they get a lot of free engineering instead of having to pay for it.

I have no basic ill will toward the manufacturers.  People like Zero-Five and Array Solutions, and I think they like them for good reason.  People like DX Engineering and even MFJ, both of which have hopped on the 43 foot vertical with 4:1 balun bandwagon.  All of these companies provide products that hams want to buy, for whatever reason.  Mostly it's because they sell, on average, useful products that people are very happy with. So I think amateur radio manufacturers are good to have around, but I do *NOT* think they're sufficiently good to have around to do free design and engineering work for them.  What do I care if they're screwing up their designs?  It doesn't really hurt them as businesses, apparently.  Sales of these units are robust.

What it does hurt are the end users.  I care only about the guy who buys a 43 foot vertical by whatever manufacturer because eHam reviews give it a 5/5 "It's a world beater, flame throwing, badass DX machine" and who get disappointed because no one actually looked at what the balun was *really doing.*  

In the end, I actually want that guy to have a little implicit mistrust for the apparent magic and mystery of commercial antenna designs.  I would rather help educate the ham public that a wire strung up into your favorite 40 foot tree and a $50 transformer you made yourself might do as well or better electrically as $600 worth of stuff from someone else.  

Why would I want to call up various antenna manufacturers and point out the flaws in their antennas, when they're selling a tall stick of aluminum along with the wrong feedpoint transformer for hundreds of dollars and calling it a "multiband" vertical?

If people want to buy their products, more power to 'em.  eHam reviews are plenty of evidence that the products are making people happy on average.  But I think the ball is in their court as far as making improvements to their design.  This thread is here if they want to find it or if you want to tell them about it.  It's a simple matter of a couple of ring terminals and a couple of solder connections to make the change to the UNUN configuration.  

Am I "vilifying" them?  I don't see it that way.  I just want people to have a little nagging N3OX in the back of their head when they go to spend $400 or $600 to "upgrade" their battered trap vertical or Home Depot wire dipole to a shiny, expensive, very impressive looking new antenna.  I want them to ask themselves what they're getting for their money.

Does that hurt the antenna business?  Not one bit if you're in the business of producing a product that's worth the money ;-)  I think in the opinion of many buyers the antennas under discussion *are* worth it, and the businesses under discussion are doing well for selling products people want.

73
Dan






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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W9PMZ
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« Reply #51 on: November 19, 2008, 06:59:35 AM »

My 2 cents.

1.  I have the DX Engineering version.  It uses a current balun.
2.  I have no trees and restriction issues.
3.  I have no illusions about the obama-ness (isn't he a cure all?) this antenna.
4.  It seems to work as good as my Hustler 5BTV on 20M, 40M and 80M.
5.  I have had QSOs on 160M, tuning is sharp.  My 5BTV doesn't do that.
6.  I have had QSOs on 80M with better results off resonance than with the 5BTV.  No I don't want to go readjust the resonator when I want to go to a differernt portion of the band.
7.  On 17M and higher I don't have a beam, nor can I have one.  This antenna on 15M and 10M where I have data from my 5BTV suggests that the 43' vertical isn't a good solution.  But the bands aren't active there anyway due to the lack of global warming from the sunspots (remember, I have no trees and cannot have a tower and beam).

73,

Carl - W9PMZ
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K0OD
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« Reply #52 on: November 19, 2008, 07:05:08 AM »

I understand there will be some radiation from the shield. With a vertical that means some current will be wasted in the feedline. There might be more TVI and RF in shack.

***But how much does this weaken the transmitted signal?*** Are we talking about tenths of a dB or several S-units? These antennas certainly radiate to some extent. 2,000 have been sold.

ES1TU said his signal was several S-units down in comparisons with similar nearby stations. Would the improper balun cause this: "On 80m nobody even heard me (while other stations gave 59+ to each other)."

This interests me because I've been using an Array Solutions (voltage) balun with a DX Engineering 43' vertical. My vertical's SWR (after the balun) is close to what Vk1OD predicts on his web page for a perfect balun. But note that I've never been impressed by the performance of my vertical and have held off reviewing it.

Also, I presume DX Engineering's balun is ok to use with 43 foot verticals; their ads say it's a current balun.
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WA1RNE
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« Reply #53 on: November 19, 2008, 07:55:47 AM »

To me the problem is much more than as stated. Many of the respondents seem intent on pointing fingers at a ZeroFive/Array combination without any regard to what other antenna producers are offering. DX Eng clearly offers a BAlun with their vertical and no one knows what is actually inside. They do state the design is a current balun but which is better, unun or current balun? Maybe a 4:1 voltage balun with a choke balun behind it outside of the near field of the antenna would be a good combination as well.


 >>>  The THUNDERBOLTâ„¢ MBVA-1P is described as using a 4:1 current balun, but why is a 43 foot vertical with a 4:1 balun being used on 160 and 80 meters?

The impedance seen at the output terminals of the balun is mostly reactive, in the order of 15j-630 ohms on 160.

 I doubt many autotuners will be able to deal with this and I wouldn't use this configuration with high power.


  ...WA1RNE
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N3OX
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« Reply #54 on: November 19, 2008, 08:01:29 AM »

"Are we talking about tenths of a dB or several S-units?"

The exact amount depends entirely on the common mode impedance of the shield (so it's extremely installation dependent) and depends on the impedance of the antenna.

Let's look at ES1TU's installation in particular.  He says he has 60 feet of coax.  That's not quite a half-wavelength on 40m.  If he's got it grounded at the shack entrance, and that ground is low impedance, he's basically got that shorting a winding of the balun.  If there's a ground wire back to the shack entrance ground from the antenna radial common point, the impedance appearing across the lower winding is that of a near-half-wavelength shorted transmission line stub with very hefty conductors.  

What could happen in that case?  It could just short out the balun, basically.  A particularly weird thing might be if the slightly capacitive stub formed by the common mode circuit were to resonate with the winding impedance.  

Without modeling the entire system carefully, including the lightning safety ground and *maybe* even the house electrical system, there's no way to say what impedance is connected in parallel to the lower winding of that balun, there's no way to say how much loss that causes in that impedance or in circulating currents in the balun or in core losses.  

It could be nothing, it could be a lot.  

73
Dan

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W8JI
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« Reply #55 on: November 19, 2008, 08:01:40 AM »

K0OD,

The problem with systems that contain a major error like this is the results are unpredictable.

For example if the feedline was a 1/4 wave long or an odd-1/4 wave and suspended in air and grounded at the shack end to a reasonable ground, it would be just like you had a ideal installation with an UN UN or a current balun.

Then there is the opposite case.

If you connected the center conductor side of the balun to the earth side of the antenna and the coax had a very low common mode impedance, then there would be almost no power at all into the antenna. It would all be into the coax.

So the system will NEVER be as good as it could be on any band except maybe one or two and in most cases on some bands it would be pretty poor. Sometimes it might be pretty poor on all the bands, just depending on how the cable is run and what two terminals are connected to what.

This is really a pretty simple and very obvious problem. The performance on any given band is unpredictable because it has the worse situation possible, a voltage balun driving a grossly unbalanced load from a cable with unknown common mode impedance.

An UN UN is a bit better than a current balun, and the worse thing possible to use is a voltage balun.

With a voltage balun, depending on which balanced terminal you connect to what and depending on the coax length and the type of stuff around the coax, the efficiency can vary from virtually nothing to about as good as expected with a proper balun or unun.

It will, no doubt about it, vary from band to band based on cable length, cable surroundings, and what particular terminal is connected to the ground and to the antenna.

Antennas are a funny thing. Some antennas with terrible efficiency make people happy because they load up and people can make contacts. Sometimes that's all that is needed, even if for no additional expense they can work properly.

73 Tom
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N3OX
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« Reply #56 on: November 19, 2008, 08:04:52 AM »

"Many of the respondents seem intent on pointing fingers at a ZeroFive/Array combination "

ES1TU started this thread, and is using this combination, and he posted a picture of the interior of the Array Solutions balun so we could see exactly what's going on.  

In my post on rhetoric, I tried to be a little more egalitarian in spreading the blame around, but

1) I have a hard time keeping up with who's jumping on the 43 foot bandwagon

2) The original poster has a particular problem using the ZF/AS combination, so you'll forgive us for sticking to that with regard to ES1TU's specific problem.  

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K0OD
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« Reply #57 on: November 19, 2008, 08:24:10 AM »

Got it, Tom. I'm also sure ES1TU and others appreciate your taking the time to explain how the balun problem might affect the transmitted signal.

Looks like I'm going to be opening up the balun, or installing a matching network at the base.

Thanks! Jeff  
       
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W8JI
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« Reply #58 on: November 19, 2008, 08:31:18 AM »

This isn't about any particular manufacturer.

It is about the very bad idea of feeding a grossly unbalanced load with a voltage balun, no matter who does it.

Most of us should know better than that, and if we didn't know it we should be clear about it now!

We should never use a voltage balun to feed an unbalanced load because it will always cause a major problem with common mode on the feedline.

Let's stick with the technical problem and not make it specific.

73 Tom
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K6GC
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« Reply #59 on: November 19, 2008, 10:40:27 AM »

Tom & List,

My apologies for posting mis-information on this !  Tom, you are exactly RIGHT, and if I had been thinking with even half my brain I wouldn't have posted something so dumb.

73,

TR, WB6TMY

RE: 43ft multiband vertical       Reply
by W8JI on November 17, 2008    Mail this to a friend!

Even AM broadcast stations avoid 5/8th wave verticals (225 degree). Instead they stay down around 100-120 degrees (below 3/8th wave). There is a myth that 5/8th wave has gain, but Fresnel losses in the earth offset any gain. This does not mean on 20 meters the vertical won't work, it does mean you would probably be much better with a trap antenna that is 1/4 wave long or something 1/2 wave or less.

In the USA, BC stations stopped installing 5/8th wave verticals back in the 30's because of fringe coverage problems. You will still have the Fresnel losses of any vertical at HF.

73 Tom
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