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Author Topic: 10 meter dipole build... which balun?  (Read 4865 times)
KD2AXU
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Posts: 7




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« on: November 19, 2011, 10:32:44 AM »

Building 10 meter dipole. Down to choosing a balun. Will be using a Unadilla 1:1. They offer two models (Unadilla W2AU and W2DU HF Maxi-Balun). Wondering if one was better than the other for my application. Would the W2DU "Maxi" provide better performance over the W2AU?

Thanks.

KD2AXU / Will
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WB2WIK
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Posts: 20599




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« Reply #1 on: November 19, 2011, 12:43:24 PM »

I think it will.  The W2DU "balun" is a true current balun, which is a bunch of ferrite cores slipped over the coax inside it.  The W2AU balun is a voltage balun and I'd much prefer the W2DU design.
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K7KBN
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Posts: 2805




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« Reply #2 on: November 20, 2011, 09:32:08 AM »

Just a suggestion:  try the dipole without a balun for a while, just to see how it behaves.  I know what the books say about a balanced antenna with an unbalanced feedline, but none of the coax-fed dipoles I've made in the past 52+ years has needed a balun.
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73
Pat K7KBN
CWO4 USNR Ret.
K3WEC
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Posts: 260




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« Reply #3 on: November 21, 2011, 07:45:39 AM »

Just a suggestion:  try the dipole without a balun for a while, just to see how it behaves.  I know what the books say about a balanced antenna with an unbalanced feedline, but none of the coax-fed dipoles I've made in the past 52+ years has needed a balun.

This is pretty strong testimony!
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K4RVN
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Posts: 775




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« Reply #4 on: November 21, 2011, 12:27:22 PM »

Bill Orr's Radio Handbook 23rd edition reads to the effect for a halfwave dipole antenna below the vhf region, a balun on hf is not generally required. I have used them with and without. I have run into problems at times and installed a homebrew
coax choke with about 5 turns of coax right below the antenna coax connection to decouple the feed line. The 5 turns should be about 1 ft in diameter. Just coil the coax and use ties to hold its' shape.
To summarize, I agree with K7KBN that you should try it without a balun, as chances are it will be OK. If you were to have problems with the feedline radiating, then wind the coax and make you a choke. The impedance of a dipole is almost a perfect match for 72 ohm coax, but 50 ohm coax such as RG 8x is OK for short runs.

Frank
« Last Edit: November 21, 2011, 03:22:35 PM by K4RVN » Logged
KD2AXU
Member

Posts: 7




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« Reply #5 on: November 21, 2011, 04:51:16 PM »

Thanks for the replies. I plan on using a 50' run of Davis RF Bury-Flex into an inverted V approx 35' up on the roof. After doing a bit more research on the balun, I see that the Unadillas are hit and miss with quality control and many recommend a kit build from the Wire Man. Not too keen on multiple trips up on top the roof so I had a "cry once" and overbuild mindset with this project. What say the hive?
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WB3CQM
Member

Posts: 117




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« Reply #6 on: November 21, 2011, 05:23:13 PM »

Just a suggestion:  try the dipole without a balun for a while, just to see how it behaves.  I know what the books say about a balanced antenna with an unbalanced feedline, but none of the coax-fed dipoles I've made in the past 52+ years has needed a balun.

This is pretty strong testimony!

You know - Your right - Just string the dipole between two trees and do not even worry if you have it measured correctly . Use a tuner and stop worrying about the little things.

That is just what I did in my early days of ham radio.  And why the change ? Well because I think there is a better way.

This is what I suggest - Get a DXEngineering catalog and go to page 33 . Look at the pattern of a antenna with no balun and one with one. Read the simple explanation they have on the reason to use a Balun verse not.

Honestly - You will work station with out a balun .And frankly if you want to use nothing more than a 150 watt light bulb and you will work stations sooner or later. But there is better antenna and systems to use.

All my yagi beams use a balun - My super loop 80 - my 160/80 T's has a 1-2 Unun at feed point in series with a 1-1 balun. The tuning is separated from the coax by a 1-1 balun Made by Balun Designs LLC.Made by KZ5R , which is W2FMI design.  Solid  RF engineering at its finest. I will argue with any one on this one.

I have in fact tested perhaps  more antenna than most hams in this area and every antenna I ever used I worked dx with them. But that don't mean they were all  efficient.

I do view this as a important topic best of luck

73 ,

JIM
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K4RVN
Member

Posts: 775




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« Reply #7 on: November 21, 2011, 07:45:26 PM »

Will,
It is your choice. Here is a site that sells baluns. I will suggest that you use a current balun, not a voltage type.
They have some good information so perhaps you may want to navigate through their site. I am currently using one of their current baluns on a half square 40 meter antenna. It does the job of stopping the feedline coax from radiating and wasting power for me. In General a 10 meter dipole according to William Orr ,W6SAI (SK) a recognized authority on antennas writes in his book that a balun is not generally needed for 50 ohm coax feed to a center fed dipole. I can see that you don't want to be climbing on the roof and a balun sure won't hurt. Good luck on your antenna.

http://www.radioworks.com/cbaltop.html

Frank
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G3TXQ
Member

Posts: 1516




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« Reply #8 on: November 22, 2011, 01:36:21 AM »

I often read advice on forums that you should first try the antenna without a balun and only fit one if it turns out you have a problem. But, on a simple antenna like a dipole, perhaps the most significant potential benefit of a balun is noise reduction on Rx; unless you try the antenna with and without a balun you will never know whether you might have enjoyed a lower Rx noise level.

Steve G3TXQ
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