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Author Topic: Which 1:4 balun for unbalanced tuner operation?  (Read 2647 times)
GOUDURIX
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Posts: 206




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« on: October 05, 2008, 06:54:58 AM »

I would like to build (wire) a 4:1 balun to use at the output of my Daiwa CNW-419 unbalanced manual ATU, to tune an 80m long horizontal loop antenna for all-band use, with 450 Ohm ladder line as feedline.

This 240 ft horizontal loop antenna will be hung about 13m high and more or less symmetrical, in a hexagonal setup.

Sevick favors a Ruthroff-type 4:1 HD balun for this application, 21 bifillar turns on a 3 inch powdered-iron core. If the antenna system is well balanced, it should work optimally and have the best low-frequency performance.
If the antenna is less well balanced, then a 2-cored Guanella type 4:1 balun should work better since it will force equal current and voltage on the ladder line.
What is really the best choice of balun? I guess my horizontal loop that willpartly circle my house, be affected by surrounding trees etc will not be perfectly balanced.
Could I use the same Amidon T-300 powdered-iron cores (with low permeability) as advocated by Sevick for the Ruthroff type balun, to make a twin-core Guanella balun?
Which balun would offer the best wideband properties?

PS: the 4:1 Guanella balun can also easily be transformed into a 4:1 Unun by strapping 1 outlet to ground, this is an advantage for this balun giving it more allround usage for other application eg. end-fed wire antennas.

Jan
ON3ZTT
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N3JBH
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Posts: 2358




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« Reply #1 on: October 05, 2008, 07:00:04 AM »

JAn the answer to your question is right here.

http://www.balundesigns.com/servlet/the-78/*NEW*-Dual-Core-4-cln-1/Detail

I doubt you would need anything else
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WB7TDG
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Posts: 69




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« Reply #2 on: October 05, 2008, 07:35:12 AM »

I currently have pretty much the same antenna...a 235 ft horizontal loop up 30 ft m/l using a 4 to 1 voltage balun with a T-300 core and of Sevick's design.
By using homebrew 600 ohm feeders, I have found one particular length of feedline about 14 feet off the ground for balun insertion that gives me an swr of less than 3:1 with the exception of 60 meters which is about 5:1...measured at the balun...for 80 thru 10 meters.
I then use about 20 ft of GOOD coax to my TT 238A tuner. The coax's shield is connected to an 8 ft ground rod just before it enters the shack.
Very quiet recieve...virtually no difference between tuner bypass and tuner engaged positions.
I can also use this antenna, sans tuner, on the lower part of 6 meters without changing feedline length.

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G3TXQ
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« Reply #3 on: October 05, 2008, 08:14:14 AM »

Jan,

I'll ask the same question that Cecil W5DXP asked you on the QRZ forum - are you sure you need a 4:1?

Depending on the feedline length, that antenna/feedline system could present impedances below 50 Ohms at the ATU. Why would you then want to make the impedances lower with a step-down transformer?

If you've not already done so, I'd suggest modelling the antenna and feedline combination before making a decision.

73,
Steve

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WB7TDG
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Posts: 69




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« Reply #4 on: October 05, 2008, 08:42:27 AM »

I used Eznec to model the antenna. Eznec indicates slightly lower swr with much narrower bandwidth using 1:1 balun or 50 ohm feed particularly on 40 and 80 meters.
30 thru 10 meters, with the exception of 60 meters, indicates the 4:1 balun gives me a much better match than 1:1 or 50 ohm feed.
I have verified this in the field. SWR was a bit lower than calculated using Eznec using the 4:1 balun...house sits in the middle of the loop!
Before I was using twin lead all the way to the shack and used a variety of transmatches...homebrew, single ended with balun, link coupled and some commercially made expresively for twin lead....no discernable signal difference on xmit but better signal to noise level on recieve.
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G3TXQ
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« Reply #5 on: October 05, 2008, 09:29:27 AM »

>>WB7TDG wrote: I used Eznec to model the antenna. Eznec indicates slightly lower swr with much narrower bandwidth using 1:1 balun or 50 ohm feed particularly on 40 and 80 meters.<<

Do you mean you modelled your antenna, or that you modelled Jan's antenna? It seems to me there are significant differences.

Jan's antenna is 42ft up - yours is at 30ft.
Jan uses 450 Ohm feeder - yours is 600 Ohm line
Jan's antenna is in a hexagon shape
Neither feedline length is quoted, but it would be a coincidence if they were both the same.

Don't misunderstand me - I'm not saying the choice of a 4:1 is wrong. I'm just advocating modelling the impedances of Jan's system before making the choice.

73,
Steve
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WB7TDG
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« Reply #6 on: October 05, 2008, 09:35:32 AM »

I used my antenna for modeling....his impendences will be different!
Anyone wishing to recieve the eznec file for their examination and comments, send me an email to:
denton@oregontrail.net
and I will be glad to forward it.
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GOUDURIX
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Posts: 206




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« Reply #7 on: October 05, 2008, 09:56:37 AM »

TNX guys.

I did not build the antenna yet....so I plan to use 450 Ohm twinlead with open windows.

I have never played with Eznec before though I have it when buying the ARLL Antenna handbook.

The reason I would prefer using a home built 4:1 Guanella balun is that I can switch it easily to a 1:1 current balun to test my antenna system.

It is only that Sevick - without explaining exactly why, and after stating several times in other chapters that the 4:1 Guanella current balun is superior to the Ruthroff voltage design - prefers a 4:1 Ruthroff balun on T-3002 core for tuner balun use.

Jan
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WB6BYU
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Posts: 13231




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« Reply #8 on: October 05, 2008, 09:57:41 AM »

In my experience, balance usually isn't much of a problem with a loop
antenna.  The current tends to adjust itself so maximum current is at
the point opposite the feedpoint.  As long as your feedline isn't
horribly unbalanced, I don't think that should be a concern.

I've used conventional 4 : 1 baluns right at the loop feedpoint and had
reasonably low SWR at some point on all HF bands.  In your case, as long
as the balun doesn't drop the impedance below, say, 20 ohms on the
lower bands, there shouldn't be much difference between using a 1 : 1
or a 4 : 1 balun.

But then I tend to be the pragmatist.  Try whatever is easiest and see
how it works.   If you think it could be better, try something else and
compare the results.  There is no One Right Answer.
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VK1OD
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Posts: 1697




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« Reply #9 on: October 05, 2008, 12:58:15 PM »


Jan said "It is only that Sevick - without explaining exactly why, and after stating several times in other chapters that the 4:1 Guanella current balun is superior to the Ruthroff voltage design - prefers a 4:1 Ruthroff balun on T-3002 core for tuner balun use."

The following is not to offer an explanation of why Sevick did or did not say something.

A Ruthroff balun has very low common mode impedance.

A Guanella balun has high common mode impedance.

The preference depends on the application.

Whilst many if not most commercial HF ATUs incorporate a Ruthroff balun, a Guanella balun is probably more suited to the application (being for a wide range of HF antennas fed with an open wire feed) where its role is to help reduce common mode feedline current.

(The designs you may see for a Guanella 4:1 balun on a single toroid are flawed, it is not a Guanella balun in that case, but someone else's flawed adaptation.)

Owen
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VK1OD
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Posts: 1697




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« Reply #10 on: October 05, 2008, 05:30:03 PM »


That should have read:

Whilst many if not most commercial HF ATUs that incorporate a balun, incorporate a Ruthroff balun, a Guanella balun is probably more suited to the application (being for a wide range of HF antennas fed with an open wire feed) where its role is to help reduce common mode feedline current.

Owen
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GOUDURIX
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Posts: 206




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« Reply #11 on: October 06, 2008, 02:13:04 AM »

Thank you guys. Well experiment is what I will be doing.
I will also be testing out the 1:4 Guanella balun I'll build, measure its SWR over the whole HF spectrum,and connect 2 balun's back to back to measure its losses.

Something to keep me busy during the dark days ahead.

Jan
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WA3SKN
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« Reply #12 on: October 06, 2008, 05:25:34 AM »

I question the need for a 4:1 balun, and would use a 1:1 current style for this application.
However, if Sevick recommended otherwise... Listen to him!  He is more familiar with, and literally wrote the book on, ferrite core baluns!
73

-Mike.
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N1LO
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Posts: 1039


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« Reply #13 on: October 06, 2008, 06:06:27 PM »

Hello Jan,

I just built a switchable 1:1/4:1 current balun. See my plans at www.qsl.net/n1lo on the Just Build Something page.

It's essentially 2 1:1 Guanella current baluns that can be switched in series or parallel.

GL,

Mark
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GOUDURIX
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Posts: 206




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« Reply #14 on: October 08, 2008, 08:26:04 AM »

Thanks Mark,

I already answered and thanked you yesterday but that answer does not seem to have been posted...strange

yes thanks for your interesting information and your interesting site.

I will build the 1:1-4:1 switchable balun, only I'm still looking for reassurance that I can use T300-2 iron-powder toroids, for heavy duty use. I will certainly need more turns to attain enough choking impedance for the low frequencies, I think a min. of 14 turns.

Would this be correct?

Jan
ON3ZTT
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