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Author Topic: Balun / unun  (Read 9134 times)
K2OWK
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Posts: 1037




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« on: February 05, 2011, 08:47:24 PM »

What is the difference between a balun and a unun?

Thanks,
K2OWK
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N4JTE
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Posts: 1154




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« Reply #1 on: February 05, 2011, 09:59:03 PM »

A balun is used to match an balanced, ie, dipole to unbalanced feedline, coax.
A unun is used mostly for UN balanced antenna matching to UN balanced feedlines, acts as an isolation filter to acheive same results when running that type of antenna system.
Bob
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W5FYI
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« Reply #2 on: February 06, 2011, 04:00:45 AM »

Both are impedance-matching transformers. Baluns have a balanced output and are used to attempt to balance currents on dipoles and to keep the feed lines from becoming radiators. Since vertical and endfed antennas do not have balanced halves, the feeding transformer is called an unun. Unun windings sometimes share a common ground, and they can be designed to match a greater variety of impedances. An HF mobile whip antenna, for example, has a very low feed point impedance. An unun transformer might be used to match the 50 ohm feed line to this kind of unbalanced load.
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WB6BYU
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« Reply #3 on: February 06, 2011, 05:52:19 AM »

From the practical construction perspective for an autotransformer (meaning that there is basically
one winding with the antenna and feedline tapped onto it from different points) the balun would
have the coax shield connected to the middle of the antenna winding (so the antenna is balanced
with respect to the shield) while an un-un would have one side of the antenna in common with
the coax shield (the ground side for both circuit.)

If you use a common 4 : 1 voltage balun with one output terminal grounded to feed a 43' whip,
that means that the RF voltage on the coax shield is 1/2 that applied to the antenna, so there
will be significant common mode current on the outside of the shield.  With an un-un (presuming
you ground the proper terminal) the coax shield is connected to ground at the antenna.  The
latter is certainly the preferred condition.

It is simply a matter of reversing the shield and center conductor connections to the coax.
This could be done with a simple adaptor between the coax and the balun if necessary.
Due to the impedances involved you would be better off getting one of the heavy duty
un-uns designed for this service rather than one of the cheaper 4 : 1 baluns that is
more suitable for use at lower SWR.
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W5DXP
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« Reply #4 on: February 06, 2011, 07:01:57 AM »

What is the difference between a balun and a unun?

Sometimes there's no difference. Here's one that could be either depending upon the connector installed on the left.

http://www.w5dxp.com/121Choke.JPG
--
73, Cecil, w5dxp.com
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K2OWK
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Posts: 1037




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« Reply #5 on: February 06, 2011, 12:39:06 PM »

Thank you for your answers. I guess I need a un-un for a 43 foot vertical.

73s
K2OWK
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K2OWK
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« Reply #6 on: February 06, 2011, 04:22:17 PM »

I have a last comment. I have a balun. As I understand it I can use it as UN-UN if I hook it up correctly for that use. The normal hookup that I read about is to connect the balun output with the antenna connection going to the long wire, and the shield going the shortest distance as possible to the ground (radial system) Is this correct? If I do this will it mater if I use a balun or a UN-UN for a 43 foot vertical wire antenna (S9). If I am correct I will just have to hook it the correct way. The reason for this question is I have a 4:1 balun. If I can not use it in this configuration I would sell it and get a UN-UN. I guess what I am saying is I still have some confusion about the difference, especially since reading the last post from W5DXP who indicated that sometimes there is no difference.

73s
K2OWK
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WB6BYU
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Posts: 13027




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« Reply #7 on: February 06, 2011, 05:50:03 PM »

Cecil's example was a 1 : 1 choke, which can be used as a balun.

What you want for the 43' vertical is an un-un.  If you have a 4 : 1 voltage balun ( I don't
know the model numbers, but someone else on here might) and can open it up then it
probably isn't too difficult to convert it to an un-un, or you can use and adaptor ahead
of it that reverses the coax shield and center conductor.  You still have to make sure that
it is connected the right way - with the coax shield on the ground connection and the
coax center going to the center tap of the coil.
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N8CMQ
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Posts: 353




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« Reply #8 on: February 06, 2011, 06:12:56 PM »

Thank you for your answers. I guess I need a un-un for a 43 foot vertical.

73s
K2OWK

Why? Is it called for?
Is there no impedance circuitry at the bottom already?
Is it a home brew vertical?
It is another point of loss you don't need if it isn't required. I have no idea why you would add an un/un to an unbalanced antenna that is fed with unbalanced line unless you are transforming impedance.
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K2OWK
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Posts: 1037




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« Reply #9 on: February 06, 2011, 08:56:44 PM »

The antenna I am referring to is a S9 43 foot wire vertical Fed with a 50 ohm coax cable. The instructions on this antennas call for a 4:1 UN-UN at the base of the antenna if you want to use a transmitter mounted antenna tuner and 50 ohm Coax. I have an MFJ-949E antenna tuner. If I want to use this tuner on this antenna I will need a 4:1 UN-UN on the antenna base as per S9 instruction sheet. The S9 antenna is a fiberglass telescoping antenna with a 43 foot single wire running inside of it. The ground is a radial system at the base. This antenna has the highest rating of any vertical on the Eham reviews. A perfect 5 out of 5 on all reviews if operated and assembled as per instructions. That is why I am asking all the questions on this antenna and its assembly, before I install it. I would like to make the installation right the first time.

73s
K2OWK
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K7ZRZ
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Posts: 279




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« Reply #10 on: February 07, 2011, 08:22:54 AM »

K2OWK (name?),

A couple of things come to mind for me. I have had the S9 31' antenna and now have the 43' version (also got one of their 43' poles not fitted with the antenna element, just for another support if needed).

If you do not ever intend to increase power above the barefoot 100 watt level, then the low-power Unun form Balun Designs (S9's recommended brand) is a good one to have.  If however you might add an amplifier, you should acquire one of the higher power units (higher cost).   Balun Designs builds a great quality product.  That Unun would also be usable for some other kind of wire antenna type, such as a longwire, or end-fed Inverted L.

It's also likely that, sometime, you will want to put up some kind of standard wire antenna (dipole), so you should keep the Balun that you have for possible use in that kind of application.

In my case, I am feeding (matching) my end-fed wire antennas or 43' vertical with a remote motorized tuner which I constructed, and which eliminates the need for a feedline transformer completely. You can see what I have done at k7zrz.net - click on the appropriate links.

Good luck.
« Last Edit: February 07, 2011, 08:24:57 AM by K7ZRZ » Logged

Brian K7ZRZ
K2OWK
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Posts: 1037




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« Reply #11 on: February 07, 2011, 02:39:41 PM »

Hello K7ZRL. My name is Barry, thanks for the information. I will most likely not use an amp. I have a Yaesu FT-450AT. I know the autotuner will not tune this antenna (It needs a VSWR of 3.5 to 1 or better). I have the MFJ-949E which tunes just about anything on any frequency. I guess the 4:1 UN-UN is necessary to match the remote tuner to the unmatched feed at the antennas. I guess I will try and see what happens.

Thanks for the answers,
Regards,
73s
K2OWK
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ES1TU
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Posts: 290


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« Reply #12 on: February 08, 2011, 03:26:26 AM »

I have a last comment. I have a balun. As I understand it I can use it as UN-UN if I hook it up correctly for that use. The normal hookup that I K2OWK

Barry,

I had the same situation when ZF shipped me balun instead of unun.
If you have an hour, you may go through this lengthy thread http://www.eham.net/ehamforum/smf/index.php/topic,44029.60.html

If you want a short version of how to turn a balun into unun, then take a look at this picture:
http://www.w8ji.com/images/ES1TU/ES1TUunun.jpg
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KZ1X
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Posts: 3227




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« Reply #13 on: February 08, 2011, 06:48:00 AM »

Barry

Have you also considered putting a remote autotuner at the antenna feedpoint?

Devices such as the SGC-239 (you package it) and the MFJ-927 (ready to go) are suitable.  (Others exist, and new ones are coming out too.)

Steve KZ1X/4





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K2OWK
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Posts: 1037




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« Reply #14 on: February 08, 2011, 01:36:39 PM »

Hello Steve, The problem with a tuner at the antenna base is the expense. They are not cheep. I already have an MFJ-949E, and the internal tuner of the FT-450AT. I can use both together as I have in  the past (it works that way with no problem), or just use the MFJ without the internal tuner, that works too. I do not see an advantage of spending  a few hundred dollars for something I already have. I do not know if using an external tuner at the base of the antenna would improve performance. The only advantage I see is automatic tuning when I switch bands. I do not mind manually tuning each band as I use them. Thank you for your suggestion. I read and take into account all recommendations I receive.

Thanks,
73s
Barry
K2OWK
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