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Author Topic: Baluns  (Read 516 times)
M3WCG
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Posts: 6




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« on: March 20, 2005, 07:51:49 AM »

Hi, could someone please explain which balun I should use?
1:1, 4:1 or 6:1?
I'll be working mostly on 80m, and will probably use just the same length of wire from each side, and then some coax going to the rig (no ladder feeder at all.)
If I'm going from 50ohm coax to the balun, and using standard lengths of wire at each side, I'll need a 1:1 won't I?

I look forward to some info!
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W8CAR
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Posts: 109


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« Reply #1 on: March 20, 2005, 08:03:43 AM »

Actually you don't need a balun at all. I have never used baluns on dipoles in my 40 plus years as a ham. A balun MIGHT be used if you really are concerned with maintaining a pattern on an antenna but with a simple dipole it makes little difference. If you want you can make a coil of about 10 turns of coax where it feeds the antenna and this will act as a 'choke' to help keep the feedline from radiating. Again, not needed. Save your bucks for more radio stuff and just put up the dipole sans balun. you'll never notice the difference!!

73
Dan
W8CAR
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M3WCG
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Posts: 6




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« Reply #2 on: March 20, 2005, 08:12:43 AM »

It was more just for the connection from the RG58 to the two wires, to stop any loss from the end of the coax, and so that no moisture can get in.

What is the other way of attaching both elements to the coax?  Just simply splitting it, and soldering / joining the two ends with no sheilding?
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W4TYU
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Posts: 518




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« Reply #3 on: March 20, 2005, 08:50:28 AM »

There are center conectors made just for that purpose. They do not contain a balun.

For my part, I simply loop the coax over the home made center connector so that the open end is down and make the connection to the wires.  

Ole man Jean
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KZ1X
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Posts: 3229




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« Reply #4 on: March 20, 2005, 09:56:09 AM »

"It was more just for the connection from the RG58 to the two wires, to stop any loss from the end of the coax, and so that no moisture can get in."

I have always thought that this is one of the better reasons to use a balun.  Besides potentially making the antenna better-performing (often questionable) the benefit of the balun's better quality physical connection is worth it.  

That being said, you can get center connection gizmos that do the same with no balun built in.  Cheaper.  Not sure where you get them in the UK, but I'd wager the best deals are at rallys, what we refer to as hamfests.  Some things, after all, are the same everywhere.

"What is the other way of attaching both elements to the coax? Just simply splitting it, and soldering / joining the two ends with no sheilding?"

Yes, that's how it's done:  braid to one side, center conductor to the other.  Of course, suitable waterproofing and mechanical strain-relieving is warranted,

At HF, the 'shielding' isn't really doing much of that -- what you'd call 'screening' -- as it's really, in the case of the coaxial cable, more simply the 'other side' of the controlled, unbalanced transmission line.  Just a fancy-shaped conductor.
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WA6BFH
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« Reply #5 on: March 20, 2005, 11:09:09 AM »

I think that the first thing you should do is to pull down the “Radio Handbook” off the shelf and read about why and how Baluns are used. I might suggest that also for the other folks who have so far posted “answers” to your question.

While some of the answers given -- from anecdotal experiences -- could be used, will this explain to you or impart any real information?

The idea that a Balun transformer is used, just to provide an easy method of connection really frosts my fern! If this is the case, we should never use solder to make good low Ohm electrical connections. Lets just wrap the wire around whatever we want to connect it to. Or, maybe we can find some completely different device, intended for a completely different application that will allow for this connection!

I would think that you would want to have REAL KNOWLEDGE and not the anecdotal meanderings of people that will tell you anything that might be on their ‘mind’. Why otherwise would you want to enter a technical and scientific hobby? I would really like you to give me a serious answer!

In case you don’t answer, I would recommend:

The “Radio Handbook” by William I. Orr

“Electronic Communication” by Robert L. Shrader

If you have good math skills also obtain:

“Antennas” by John Kraus

These books will answer the question you asked, as well as provide you with a compendium of knowledge to help you in a long and prosperous Amateur radio avocation and hobby.

Cc: READER & CHRON (hmnew001.doc)
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N6AJR
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« Reply #6 on: March 20, 2005, 12:42:58 PM »

I usually use a 1:1 balun for dipoles just for the ease of hanging it, but you can also solder the center conductor to one wire and the shield to the other or use a pl259 and seal it well, and you can use a 10 turn 6 inch loop as a balun too.

you can also use a center hanger ( with out balun ) or make your own from plastic.

buxcommco.com has a good selection
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K9ZF
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Posts: 76


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« Reply #7 on: March 20, 2005, 12:48:23 PM »

Those are very good books.  I would also add "Reflections" by Walter Maxwell.

I certainly won't claim to be an expert, but here is how I understand the issue.  It is necessarily an over simplification, as there have been many books written on this subject.

To balun, or not to balun, that is the question...  I've actually done it both ways.  If you were planning to use the dipole as a single band antenna then I would agree, you could likely get by without the balun without much problem.  Using the antenna for multiple bands will complicate the problem.

The dipole is a balanced radiator, and you are planning to feed it with un-balanced line.  So you will likely end up with quite a bit of RF on the shield of your coax, and feed line radiation.  Which may, or may not cause problems.  Using a balun, however, will help keep the RF off the shield and minimize feed line radiation.  And normally, you want your antenna to do the radiating, not the feed line.

If I were planning to put up a multi band dipole like you are, here is what I would do:  I would put up as much wire as I could get, preferably a full half wave dipole for the lowest band I planned to operate on, I would then feed the antenna with ladder line to help reduce feed line losses.  Run the ladder line for as much of the run as possible, then use a 1:1 balun and run coax from there to the tuner.  This works well.

You can put the balun at the antenna feed point and use  coax for the entire run, but you will have considerably more loss in your feed line.  Ladder line is much lower loss, and cheaper as well!

I would use a 1:1 balun in this application since you are planning to use a tuner.  Let the tuner handle the impedance transformations, it's much more efficient.

Good luck with your project, and have fun!  Check out the books, they explain it much better than I can:-)  And here is another great resource:
http://www.cebik.com
W4RNL's web site is incredible!  I have spent hours browsing his pages.

73
Dan --

K9ZF /R no budget Rover ***QRP-l #1269
Check out the Rover Resource Page at: <http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
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--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
 ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Maili
AA4PB
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Posts: 12995




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« Reply #8 on: March 20, 2005, 01:07:53 PM »

I assume you know that the length of the two wires is critical. They need to each be 1/4 wavelength long (for a total of 1/2 wavelength) on 80 Meters. That feed point impedance should fall somewhere between 50 ohms and 75 ohms so you don't really need a balan at all. If you do use one then it should be a 1:1 current type balun.

There are many ways to support the coax attachment to the dipole without using a balun. The key point is to keep water from getting into the end of the coax. A blob of coax seal or electronic grade RTV will do that just fine.
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K6AER
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Posts: 3530




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« Reply #9 on: March 20, 2005, 07:49:32 PM »

My Dentron MT-3000A works well with a full wave 160 meter ZEP at 1500 watts. I use it for 160-40 meters. These tuners are not made anymore but can be found on the used market for about $150. It has a high and low power meter for 200.2000 watts and a second VSWR meter. These were manufactured before cross meters became popular. Balanced balun output and three coax outputs plus a 200 watt internal dummy load. Size is 14"D by 14"W by 5"H.

Now of course you can find out about just about any tuner made by looking in the eHam product reviews under the 160 plus categories for Antenna Tuners.
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M3WCG
Member

Posts: 6




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« Reply #10 on: March 21, 2005, 12:15:14 AM »

WA6BFH - Thanks for your advice on books to buy/read.  I'll try and get round to some of them when I can.
There are many reasons why people enter amateur radio, as you well know.  

"I would think that you would want to have REAL KNOWLEDGE and not the anecdotal meanderings of people that will tell you anything that might be on their ‘mind’. Why otherwise would you want to enter a technical and scientific hobby? I would really like you to give me a serious answer!"
I quite agree that it's a scientific and technical hobby, but I don't have a scientific or technical background.  
It's also not purely about the science - I'm more interested in making the contacts, and friends than how I do it, although antennas are a great fascination.

A major part of the hobby is experimentation as well (From the BR68 [UK licence terms] "The Licensee shall use the Station for the purpose of self-training in communication by radio telecommunications, which use includes technical investigations.")

I do appreciate your assistance, although I think you may have taken a simple request for some advice a little to seriously.
I would much rather hear the experience of live amateurs, than read it in a book.

Some amateurs may have taken offence to the way you replied to my original request, but thanks anyway.
Funds are tight, which is why I'm making a homebrew antenna, and can't afford many books on the subject!

73s de M3WCG
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AA4PB
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Posts: 12995




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« Reply #11 on: March 21, 2005, 04:46:00 AM »

Although the references given are good, the fact that you read something in print doesn't necessarily make it so. There has been plenty of mis-information published over the years.
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WB6BYU
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Posts: 13488




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« Reply #12 on: March 21, 2005, 04:08:11 PM »

The choice of balun depends on the impedances you expect
to see on each side.  If you are using 50 ohm coax cable,
a 1 : 1 balun would be used for a 50 ohm antenna, 4 : 1
when the antenna is 200 ohms, etc.  If you are making a
half-wave dipole, the impedance should be close enough
to 50 ohms that a 1 : 1 balun would be the best choice.

(But you didn't say how long the antenna was going to be -
just that you were going to connect wires on each end.
Certainly with some wire antennas, there may be a better
impedance ratio to choose: we are only guessing that you
mean a half-wave dipole.  The more information you can
give us, the easier it is for us to help you.)
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