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11-19 of 19 messages
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RE: 43ft multiband vertical - balun to unun
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by VK1OD on November 21, 2008
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Bob,
Further to the discussion about the buried coax.
The question arises whether using a 4:1 unun, 4:1 current balun, or nothing is better.
Premised on a ground mounted vertical, buried radials and buried coax in average to better soil where feed line common mode current will decay quickly...
I think that there is little difference between 4:1 unun, 4:1 current balun since the coax ground can be bonded to the radial system. Both bring balun/unun losses to the solution, hopefully offset by a greater reduction in feed line loss. The reality depends on the length and type of feedline, and the actual balun/unun losses on each band. The Note the feed point impedances are extreme and will be affected by the soil type, nearby structures etc... so it is real hard to make a blanket statement.
Measurement of a range of field installations would be valuable, but assessing balun loss under these conditions is not trivial.
Some things that have emerged from the discussion are:
1. A 4:1 voltage balun (alone) at the feedpoint lacks rational explanation;
2. A 4:1 unun (alone) at the feedpoint reduces line losses and should be worthwhile if that reduction is greater than the unun loss;
3. Buried coaxial feedline should carry less common mode current into the shack;
4. A common mode choke between the radial field and the shack may deal with troublesome residual common mode current.
For most situations with 32+ buried radials and buried low loss feed line, average or better soil, a 4:1 unun with adequate voltage / power rating, and a wide range high power low loss ATU should provide reasonable performance from 40m to 20m, degraded on 80m, and poor on 160m. This could be a very acceptable means of accessing HF for people with constraints on unsightly structures in the yard.
I still prefer the remote auto ATU! Perhaps an innovative supplier will build an auto ATU inside the mounting?
Owen
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RE: 43ft multiband vertical - balun to unun
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by N3OX on November 21, 2008
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"Should one use the 4:1 current balun and force balanced currents or is a 4:1 Unun more desirable? "
Devil's in the details. If you don't have much common mode current on the feedline, and you don't have much transformer loss either way, it's an absolute toss up.
It's hard, like Owen says, to get substantial common mode current to speak of on a feedline with the shield connected directly to the common point of dozens of radials. On average, the naive expectation is that something on the order of 1/(N+1) of the current will flow on the coax shield near the antenna, where N is the number of radials, and it will only be significantly different from that if you don't have enough radials yet ;-)
How about this: A real 4:1 current balun needs two cores. The UNUN needs one. That means you can save some money for the matching system you'll want later ;-)
73
Dan
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RE: 43ft multiband vertical - balun to unun
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by KZ5R on November 21, 2008
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Really appreciate both your and Owen's analysis and comments and Owen I did read your updated page which makes more sense to me each time I read it. Not because of your writings but because I understand more each time.
I would add only one thing. When I wind one of my ununs, I use a set of stacked cores for the additional inductance and higher power handling. My current balun also has two cores but they are individually wound with more interconnects. So material wise, the cost of each is nearly a push, from a time and complexity perspective, the current balun will definitely end up costing more.
Long way of saying that based on both of your comments and my "cost analysis" the unun seems to be a good choice.
Thanks again,
Bob, Balun Designs
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RE: 43ft multiband vertical - balun to unun
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by W8JI on November 21, 2008
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The thing that puzzles me is why anyone would have ever recommended a voltage balun for an unbalanced load in the first place. I never considered anyone would do that.
Another thing that puzzles me is how anyone can say a certain type of balun (or unun) has no core flux. The only way to have no core flux is if the core is doing nothing, and if it can be removed without any change in the system.
For example there are cases where a 4:1 current balun can have zero flux in one core and not the other, and in that case the cores in the zero flux core and windings can simply be eliminated with no change at all in performance. Of course that is only one load condition.
Anyway, I hope the recommendations to use voltage baluns to drive unbalanced loads goes away.
The use of a 4:1 voltage balun in this application is OK. In one output terminal case, one core has zero flux and the other simply acts as an unun. In the other case with terminals reversed, you can have twice the flux density in the one transformer that had none before. So you have to be very careful which direction the balanced terminals are connected.
While it does "waste material" in some cases, it allows the use of poor ground systems without RF in the shack.
An interesting rule is this....if the core flux density is really zero, then the core can be eliminated with no change in operation. Anyone claiming otherwise has missed an important part of how transformers work.
That's as solid as the rule that voltage baluns should never be used to feed unbalanced loads.
Both should send up a red flag that someone has missed an important part of the how the system works.
73 Tom
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RE: 43ft multiband vertical - balun to unun
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by N3OX on November 21, 2008
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"The thing that puzzles me is why anyone would have ever recommended a voltage balun for an unbalanced load in the first place. I never considered anyone would do that. "
Well, it seems maybe Zero Five / Array Solutions has learned the lesson already. They offer a different transformer for the feedpoint and I understand it's a UNUN.
Anyway, it's easy to convert your voltage balun to a UNUN, just move the feedpoint connections... quick and painless, and done.
I think maybe demand outstripped design on this one.
Anyway, there's an N3 over in the TowerTalk part of the forum asking a veeeery similar question to Aadu's. What I wonder is why this is finally popping up now, especially if new Zero-Five + Array Solutions packages are shipping with a UNUN? It should have been a problem for at least someone else before now.
I think the second wave must be buying these antennas, and by the second wave I mean the skeptical guys who finally said "well if EVERYONE loves em..."
Oh well, glad Aadu has a solution and spread the word.
And if you're still wanting to play with actual impedance matching, some reasonable starting point networks are listed here:
http://www.n3ox.net/projects/lowbandvert
I haven't actually tried them with high power but I bet it would work fine with the #10 wire and all.
73
Dan
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RE: 43ft multiband vertical - balun to unun
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by VK1OD on November 21, 2008
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Dan,
When I looked the other day, the 'new' balun had as inadequate a description as the 'old' balun.
We know what was in the old balun because a user took it apart. Given the scarcity of product info, it will probably need the same approach.
That the sellers and buyers apparently don't seem to think it relevant is interesting.
Owen
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RE: 43ft multiband vertical - balun to unun
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by VK1OD on November 22, 2008
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Dan,
At the time of writing... 19:30Z 22/11/08.
Zero Five installation instructions state "A BALUN IS REQUIRED This antenna REQUIRES a 4 to 1 balun be used at the feed point if you are feeding this antenna
with coaxial cable."
A little more searching and it seems the current recommendation from Array Solutions is a "special 5 kW lossless RF Matching transformer (ZF-MB-5K)".
Lossless?
Elsewhere, it is described as a "special ZF-MB-5K matching transformer and choke balun".
It does look Array Solutions have changed their recommendation from the AS-200-T 4:1 voltage balun to some kind of 4:1 current balun.
Back to Array Solution's "lossless" claim. IMHO, it is most unlikely that a ferrite or powdered iron core balun designed to work over 10m to 160m and extreme impedances is zero loss, or could be considered of such low loss to honestly describe it as lossless. It would seem an extravagant claim.
DXE recommend their DXE-BAL200-H10-AT 4:1 current balun for their 43' vertical.
Balun Designs recommending their 4135z 4:1 unun for Zero Five's and DX Engineering's 43' vertical.
Owen
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RE: 43ft multiband vertical - balun to unun
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by N2JEU on November 22, 2008
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The installation manual on the web site has now been updated to match the information on the rest of the Zero-Five web site. Please forgive my tardiness in making the change that Tom requested to both the manual and the site itself.
For any questions about the antenna itself and the design behind it you'll have to ask Tom. I just take care of his web site.
Bob Arnold N2JEU
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RE: 43ft multiband vertical - balun to unun
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by K0OD on November 23, 2008
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Last evening I converted my Array Solutions voltage balun into a current unun as specified on VK1OD's site. It was too cold to do any before/after field strength comparisons. (link to VK1OD's relevant page: http://www.vk1od.net/multibandunloadedvertical/index.htm )
The Bulgarian CW DX contest gave me an ideal laboratory for testing the unun on 40 and 80. Running barefoot, I had no trouble working Europeans on 40 from my QTH in Missouri. Perhaps Qs came easier than before the conversion. This morning I easily worked a JA, and a long path OH6 on 40 CW.
On 80 it was still difficult to be heard in EU. Of course most of the contest stations were running KWs to my 100 watts. No doubt a matching unit at the base or some top loading would help me. (flipping on my KW would have helped more!)
I'll test 20 and 30 today. If my "43 footer" works well on 20, 30, 40 and 60 I'll be happy.
Thanks to ES1TU, W8JI, VK1OD and everyone else. Great threads.
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