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wb1ead
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« on: January 08, 2011, 12:52:27 PM »

Hey gang..I'm about to get started on sumptin I've never directly dealt with..a wire array..yup I've been a yagi guy for way too long as the bulk of my activity has been on 10mtrs and above..the balun I've selected is throwing me for a loop..it's a W2AU 4-1 voltage type by Unadilla..no I am not one bit familiar with baluns at all..however the ant I'm considering by K4ABT uses a 4-1 balun at the feedpoint with 50ohm coax connection..I thought it would be helpful b/4 I start by marking the +- sides of the connections as shown on ABTs illustration..this is a brandy new in the pkg balun..well imagine my surprise to find continuity on both sides..no matter where I put the meter probes..you know to me being not too savvy indicates a dead short..is this the way it is?..is a current balun different?..have I got the right one to use?..it's tuff enough for me to "buy" the hocus-pocus of a gamma match..by the way the ant will be 166' long side with 94' short side......just trying to avoid disaster        thanks!   73 de DAVE
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« Reply #1 on: January 08, 2011, 02:30:48 PM »

Dave,

Note;  If you see smoke, you made a mistake,  hope this is helpful Grin

The 4-1 balun should read a short from all terminals, if it doesn't it's NG.

The 4-1 baluns I used for TV antennas (300ohm balanced-75ohm unbalanced) read short across all terminals, thats how I tested them.

A balun is an impedance transformer of sorts.  If your antenna is 200 ohms balanced at the feedpoint, the other side of the balun will show 50 ohms unbalanced (4-1).  If the balun is large enough to handle whatever power you're running it will handle the current.  If it's not big enough, refer to my first statement above.

It should also be noted, there are different types of baluns.  but a typical 4-1 balun is usually balanced to unbalanced.

I personally don't like using baluns on transmitting antennas and avoid using them.
Although, I have made many 4-1 coaxial baluns for wire antennas, but they're only good for one frequency.

BTW, I made many hocus-pocus gamma matches, they do work, strange as it may be.

the real Fred
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Ed/KB1HYS
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« Reply #2 on: January 08, 2011, 02:55:48 PM »

I don't know about the balun model you've selected, is it an air-core balun?  Ferrite baluns tend to be designed with SSB or CW in mind, and get really upset with high duty cycle modes like AM at QRO power levels.  Some baluns make things worse at different frequencies ie: they are not as broad banded as people think. for a single band system running with with one of the usual 100+ watt transmitters you can get them spot on and it's all good.

A good gamma matching network would probably beat a balun for power handling hands down.  They aren't well understood by most (me included) but (I think) it's a shunt feed system that uses a cap to cancel out reactance while the feed point position sets up the impedance. As long as the capacitor you use can handle it, you are good to go up to legal limit.
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73 de Ed/KB1HYS
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The Slab Bacon
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« Reply #3 on: January 08, 2011, 03:46:10 PM »

I prefer a 4:1 balun for just about everything. 1:1s seem to be too sensitive to operating impedance and frequency.

this is mine, it is indestructable!! ! ! ! ! !


* balun!.jpg (55.93 KB, 480x710 - viewed 229 times.)
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Steve - K4HX
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« Reply #4 on: January 08, 2011, 05:58:48 PM »

There is nothing magical about a 4:1 balun. How well it works depends quite a lot of load unbalance and common mode current. The same is true for 1:1 or any other ratio balun. You can make a balun that won't get hot by designing it for poor common mode rejection.

Some good info on an improved design at the link below.

http://home.earthlink.net/~christrask/Trask4to1Balun.pdf
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KA2QFX
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Mark


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« Reply #5 on: January 08, 2011, 09:50:34 PM »

Dave,
   I'm not sure to which K4ABT antenna array you are referring, as he has written about many antennas. So I'm reluctant to advise you regarding what/if any particular balun may be best for your application.  However, I can tell you that Steve's comment is correct and the website he suggested is well researched and accurate. 
A simpler explanatory methodology may also be found here: www.ncarc.net/files/Balun.ppt which was written by an ARRL technical expert for a wider audience.  You are on the right path in determining what balun should be utilized.

But your query and its attendant responses caught my eye for other reasons as well and compel me to comment further, likely to my regret.  I particularly like baluns and their myriad applications.  When I read comments like the following I get a little irked.
"...but they're only good for one frequency."
"...they are not as broad banded as people think."
While neither of these statements is correct, they can be readily defended since such hypotheses seem to agree with observed performance in the field. Such observations serve well to sustain the misunderstanding, misapplication, and worse, the inappropriate sales, of otherwise valuable components.

What is true is that baluns, ununs, and other types of Transmission Line Transformers are designed to operate over specific, fairly narrow, ranges of impedance. It is this fundamental premise that is most often violated leading to inappropriate conclusions regarding their performance. 

For example;
- a 4:1 transformer designed to transform 50 ohms to 200 ohms will NOT work very well in reverse if you try to match a short mobile whip of 12.5 ohms up to 50. 
- a most common mistake people make is thinking that they need to match their 70 ohm dipole fed with 450 ohm ladder line to their 50 ohm system with a 4:1 or 9:1 balun, when in fact what they need is a 1:1 balun. It is ultimately the 70 ohm antenna to which they are coupling, not the line impedance. 
- or following that, since they’re running open wire line, they assume they can now use a tuner to match that antenna on several bands. But off resonance the antenna is no longer near 70 ohms or resistive anymore and even the 1:1 balun will not tolerate that.
I could state such misapplications which give baluns a bad reputation ad infinitum.
Suffice to say, baluns are typically VERY broadbanded, VERY efficient, and absolutley must be applied properly.
If I knew more about your specific choice of antenna design I’d gladly suggest what type of balun you might want to consider. I’m a little surprised the article from a well published source isn’t more specific about what type of balun you should use. Nevertheless, I wish you luck in your endeavor and encourage everyone to learn more about baluns and RF transformers in general, they really are marvelous devices, when applied properly.

Mark
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W2VW
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« Reply #6 on: January 08, 2011, 10:40:14 PM »

Terrance Aloysius Mahoney
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The Slab Bacon
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« Reply #7 on: January 09, 2011, 12:09:37 AM »

I experimented with many types of 1:1 baluns. (My low impedance situation would prolly be happier with a 1:1)  I wound / built a bunch of different designs and swept them to see how well they worked. What I found was quite interesting.

I was looking to see how true to 1:1 they were and also how much reactive component they added to the mix. What I found was quite interesting.............
I swept them from 1.5-15Mhz, and 5-400 ohms, seeing that that was where they would be operating. NONE of the 1:1s would stay 1:1 if you deviated far from the 50 ohm designed charactoristic impedance, and all of them added a considerable reactive component of their own once you got away from 50 ohms.

Most of the 4:1s would stay very close to 4:1 and add a very minimal (but constant irregardless of impedance or frequency) reactive component of their own. some of the 1:1s did some really strange things when you changed the operating impedance.

I finally settled on the basic 4:1 design right from the later ARRL handbooks and just supersized it to handle High power AM. It will take long winded "old buzzard" transmissions from my 4X1 rig into a bad load and never even get warm. It is 10 years old this year.

All of this was brought on by the "necessity is the mutha of invention" syndrome after sending a handful of "store bought" baluns up in smoke and flames, and a long discussion with a fellow AMer who swore to me "baluns dont work, you CANT build a balun that will take that kind of power" I had to prove him wrong.   Grin  Grin   
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Steve - K4HX
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« Reply #8 on: January 09, 2011, 12:21:50 AM »

Read Frank Witt's work on balun measurements over a wide range of Z and the entire HF range.
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KA2DZT
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« Reply #9 on: January 09, 2011, 02:10:06 AM »

Mark,

I see you quoted my comment about a coaxial balun being good for only one frequency.

I was referring to a 1/2 wavelength of coax being connected to the antenna end of you coax.  It's an old system that is in every handbook. Maybe you have never seen it or used one.  I'm sure the setup is only good for whatever frequency you cut the 1/2 wavelength of coax.

I've used them many times and I think they are considered a form of a 4-1 balun but not a broadband type.

Maybe I didn't make my comment as clear as I should have.

Fred
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« Reply #10 on: January 09, 2011, 09:16:50 AM »

I took apart one of the W2AU Unidilla baluns.   The ferrite looks like the ones used in old AM radio loop stick antennas.  They tend to burn out if for some reason, the antenna SWR gets high due to antenna failure or feeding the antenna with RF frequency that the antenna is not designed for.
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wb1ead
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« Reply #11 on: January 09, 2011, 10:51:46 AM »

Thank you all for "enlighting" me on baluns in general..sorry I wasn't able to respond sooner as once more I was off on another "honey-do" errand ystdy..

Mark QFX..hopefully this link will lead ya to the K4ABT ant I have in mind   http://www.packetradio.com/windom.htm  

as an aside I plan to run no more than I can squeeze outta either a DX40 or HT40 for the time being..a Ranger ll is being sought after..a Valiant was passed over as it was beyond a "basket-case"..never was one for QRO..call me a "piss-weaker"..it won't ruffle my buzzardy feathers

I hope you all tolerated my query..seems ya did..on lots of subjects I can hold my own..but this IS unchartered territory for me..some will add maybe that there are better choices than my proposed ant..but given my odd lot size with our home where it's located and no supports on one end leads me there..there will be others in the future..vert/inverted L/loops that CAN be tried but going for simplicity 1st b/4

I'm glad this forum is here..decent answers/gud folks......sincerely thanks!!               73 de DAVE

PS: now I feel a bit dum-dum as I clicked unto the "site" I mentioned for Mark..the paper someone gave me is no where as detailed as this and it is/was a copy of the then current info..on my paper no mention of the type of balun or even half of what's there now..ah well live and learn
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Detroit47
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« Reply #12 on: January 09, 2011, 01:48:59 PM »

I'm surprised no one has said use ladder line and forget the Balun. I'm happy that the folks on this board steered my away from a balun.

N8QPC
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KA2QFX
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Mark


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« Reply #13 on: January 09, 2011, 08:42:02 PM »

Ok Dave, thanks for clarifying which antenna. K4ABT certainly has popularized the Windom.  Indeed, a 4:1 balun is what you need.

I’ll refer to the Trask document which Steve noted earlier. The simple “Voltage Balun” is described in Figure 3. The Ruthroff 4:1 voltage balun.  I believe this is the design noted as the W2AU type balun and is also the design seen in Fred’s picture. It is also the most popular type of 4:1 balun seen inside cheap “T” type antenna tuners to feed balanced lines and end fed wires.  I have no doubt that such a balun will “work” for you given the recommendations from K4ABT, et al.

The other balun, which I prefer is described in Figures 1 and 2 of the Trask paper. The type shown in figure 1 is the same as I use in my “T” tuner.
Seen here:  http://home.comcast.net/~msed01/tuner1.html It uses 4 windings instead of two, on a common ferrite core, creating separated current points isolated from the transmission line.

 Going one better, for your application would be the balun described in Figure 2. It is essentially the same balun from figure one except two separate cores are employed. This allows better operation when a differential in load voltages might be anticipated. This would likely be the case when feeding similar currents into elements of different lengths, as in the Windom.  

This design was successfully implemented by John W2WDX in a QRO application in a fairly densely populated neighborhood where feedline radiation was a primary concern. It works very well.  Where he obtained the balun I do not know. Obviously, from the photos below, some assembly was required. 



I’m sure whatever balun you obtain will perform OK. I think the cutting of the wires is more critical in determining feedpoint impedance, especially for the higher bands, than is the selection of balun.  

Fred,
   Yes, the coaxial delay line type of balun, know it well. I did think you meant a TLT using coax.  I have made those using 75 ohm coax but don’t recommend them.  The 4:1 UNUN on my mobile also uses coax.  My mistake, you’re quite right, the classic coaxial balun is pretty frequency fussy.

And Frank,
   I can’t contest to your findings but you certainly can build baluns that will handle all sorts of power.  I’d be curious as to what type of antenna that balun is feeding and what do think the impedance of the wire you used might be. I suspect it’s pretty close to 100 ohms, which would be the right value for a 50:200 ohm balun.

Steve,
When’d you change your call?

73,
Mark
KA2QFX


* ocfbalun2.jpg (104.45 KB, 375x313 - viewed 140 times.)

* ocfbalun.jpg (100.01 KB, 384x317 - viewed 158 times.)
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Steve - K4HX
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« Reply #14 on: January 09, 2011, 09:36:46 PM »

Also search out Witt's articles on Windoms and some of the feed issues.

In October.
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« Reply #15 on: January 10, 2011, 09:15:16 AM »

Mark,
        I am using 14ga "crappy brown stuff" from the balun to the antenna. I have about 8' of coass (RG-214) between the balun and the tuna. (I had to do it that way as it would be pretty dificult to get the "crappy brown stuff" the last couple of feet to the tuna) there is just too much metal there.

For less that 8' of run, I flat out didnt care what impedance the coass was working at. And I am a firm believer that if you have to sin with coass, it is much better (less loss) to run it at an impedance at or below it's charactoristic operating impedance, as you have less loss from the capacitance of the coax sucking up the power. I just needed the balun to provide a smooth transition from balanced line to coax and handle the power levels I was running. Short sweet and simple. The tuna can load a bedspring, so I wasn't worried about not being able to match it to the transmitter. Especially now that I dont hesitate to pour on the soup!!

Due to the fact that I have a small yard, I had to come up with an entire system that worked for my specific application. And as everyone that I have worked knows,
It does work and work well!

Attached is the antenna that I have used for about 10 or 12 years now. (It's not supposed to work either) But I have used it on 160, 75, and 40 meters without any problems.  Wink  Grin

* short ant.pdf (483.04 KB - downloaded 95 times.)
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« Reply #16 on: January 10, 2011, 09:43:51 AM »

Baluns are fine is they aren't used with a reactive load. When you do parts start trading circulating voltage and current. Sizes must go up.
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« Reply #17 on: January 10, 2011, 10:19:05 AM »

Baluns are fine is they aren't used with a reactive load. When you do parts start trading circulating voltage and current. Sizes must go up.

Or go up in smoke  Grin  Grin
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« Reply #18 on: January 10, 2011, 11:05:07 AM »

Given the choice between running 50 ohm cable at 12 ohms or 200 ohms I'd take the 200. Less resistive loss in the conductors. With any length one piece of mismatched cable could have both 12 and 200 ohms plus a reactive component.
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« Reply #19 on: January 10, 2011, 11:13:22 AM »

Given the choice between running 50 ohm cable at 12 ohms or 200 ohms I'd take the 200. Less resistive loss in the conductors. With any length one piece of mismatched cable could have both 12 and 200 ohms plus a reactive component.

I'm more worried about the reactive loss component. Heavier cable = less resistive loss. As the feedline voltages increase (higher impedance) the capacitive reactance of the coax tends to act like a big cap across the outpoot and soak up the RF like a sponge, not leaving much left to deliver to the load. If the impedance is low (low voltage / high current) then all you have to worry about is minimizing the I2R losses.
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Steve - K4HX
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« Reply #20 on: January 10, 2011, 11:19:29 AM »

For purely resistive loads, on RG-213, you get about 0.75 as much loss for 200 Ohm load at you do with 10 Ohm load. On an 8 foot piece of cable at 4 MHz, this difference is negligible.
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k4kyv
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Don
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« Reply #21 on: January 10, 2011, 11:21:08 AM »

Baluns are fine is they aren't used with a reactive load. When you do parts start trading circulating voltage and current. Sizes must go up.

Another problem is with the ferrous core.  High circulating currents associated with a reactive load can push the core to the limit, to the point where saturation begins to occur. This causes the transformer to become a non-linear transfer device, with the same kind of resulting spurious sidebands, possibly even full-blown splatter, as with an active device (tube or solid state) operating beyond its linear range. Besides overdriving their leen-yar, this could explain why SSB stations sometimes splatter on voice peaks even when the leen-yar is operating within the proper signal range.

Too many hams use the bogus circuit both in homebrew and factory tuners, that consists of an unbalanced PI- T- or L-network that then feeds a toroidal step-up balun, which in turn feeds their tuned "ladder line". This will work properly only when the balun looks into a mostly resistive load within the impedance range of the balun... unlikely to occur across all bands when using open-wire tuned feeders to feed a dipole for use on multiple bands, and unlikely to occur when feeding the OWL, at even a non-reactive, high-Z voltage loop where parallel tuning would normally be used with a conventional link-coupled tuner.

A better place to insert the balun would be between the transmitter and tuner.  It should have a 1:1 ratio unless the tuner input is specifically designed for a higher impedance (300Ω, etc.).  Then the bottom side of the tuning network is disconnected from ground, allowed to float.  Insulated tuning shafts are installed, and insulated feed-throughs are used with the bottom side of the network as well as the top side.  The network is thus forced to operate as a balanced tuner and feeds the open wire line directly without any additional balun.  Better still, design a balanced L, T or PI network with symmetrical split coil and capacitances.

As I recall, this was the topic of a QST article quite a few years ago.
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« Reply #22 on: January 10, 2011, 11:28:07 AM »

For purely resistive loads, on RG-213, you get about 0.75 as much loss for 200 Ohm load at you do with 10 Ohm load. On an 8 foot piece of cable at 4 MHz, this difference is negligible.


that's my whole point!! With an 8' piece of cable who gives a szht what the operating impedance is.  Roll Eyes  Roll Eyes
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« Reply #23 on: January 10, 2011, 11:46:56 AM »

Until you try to put 20 R.F. amperes through it.

For purely resistive loads, on RG-213, you get about 0.75 as much loss for 200 Ohm load at you do with 10 Ohm load. On an 8 foot piece of cable at 4 MHz, this difference is negligible.
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« Reply #24 on: January 10, 2011, 11:53:41 AM »


A better place to insert the balun would be between the transmitter and tuner.  

Work well. The tuner design should be symmetrical to keep the balanced load balanced.

One well known internet warrier went way out of his way to try to prove the balun works equally as well when placed after a T network. He's so busy trying to discredit the nichrome supressor guy (who also wrote a well known QST piece placing the balun before the network) that he's discredited himself.

We all pretty much know nichrome parasitic supressors aren't a cure all for bad tube runs and other problems. Time to give up already.
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