There is a tendency to view a balun in much too simplistic terms. The most common errors stem from not fully understanding how the system terminating the balun behaves, and not understanding how that system interacts with the balun. We commonly consider only the load impedance or SWR, and of course RF power levels, when discussing baluns. Load impedance or to a lesser detail SWR describes differential across the line characteristic, and is easily understood and explained.

Power is easily understood. The natural motivation to stay with what we easily understand is the root of misunderstanding baluns. One of the most important things, the common mode voltage driving a balun or common mode impedance of a system, is largely misunderstood or ignored.

Common mode impedance can really be almost anything from a few ohms to several thousand ohms, and is often unrelated to differential impedance.

Perhaps common mode is ignored because it is a bit more complex, inconvenient to measure, and varies greatly even in what appear to be similar systems. At times common mode excitation can be phenomenally high. One antenna design I've worked in particular on comes to mind, because it had the largest spread in voltage and impedance between common mode and differential normal transmission line mode mode I've ever observed.

With a few hundred watts of power, with a differential mode impedance of 50 j0 and SWR, the common mode voltage driving the balun in this troublesome system was several thousand volts.

String of beads 50 beads long would literally shatter or melt through Teflon coax even though the SWR was with only a few hundred watts of transmitter power. In contrast to that system, I worked on a small "magnetic" loop antenna.

The small loop presented a very high common mode impedance with almost no common mode voltage, and even though the loop was a balanced system a good balun made absolutely no difference in performance or common mode current.

For any feed line length, with or without a balun, common mode current on the feed line to the loop was essentially zero. In the above systems, the first example the dipole could be much worse than a balanced balun test load simulated by a center-tapped resistor. The second case, the very small "magnetic" loop, appeared to the feed line almost like a fully floating resistor.

Antenna Balun and Unun

This points to one very real conclusion, a balun test with a fully floating resistor is like the testing the balun in a system were the balun is not needed; a system where the balun serves no useful purpose. The antenna terminals in effect push back against the feed line, just like it is a generator. The other "foothold" is the electrical mass or common mode impedance of the antenna itself, as the antenna behaves like a radial or counterpoise working against the feed line.

In general very large symmetrically fed half-wave antennas have a very low common mode impedance near the antenna. The dipole presents a pretty stiff source voltage at the feed line terminals. Each conductor in the feed line is effectively driven by a voltage that is around half the voltage appearing across the antenna's feedpoint, the electrical mass of the antenna being the footing to push current down into the feed line.

Looking at it this way it is easy to see why the small balanced loop develops very little common mode current under any feed line length condition, and why a dipole can significantly excite the feed line. The loop has a very high common mode impedance, not nearly as low as a small floating resistor, but still high enough make the loop act like a poor counterpoise.A Balun is special type of transformer that performs two functions i.

Baluns are important because many types of antennas dipoles, yagis, loops are balanced loads, which are fed with an unbalanced transmission line coax.

Baluns are required for proper connection of parallel line to a transceiver with a 50 ohm unbalanced output. A balanced transmission line is one whose currents are symmetric with respect to ground so that all current flows through the transmission line and the load and none through ground.

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Note that line balance depends on the current through the line, not the voltage across the line. Here is an example of a balanced line. DC rather than AC is used to simplify the analysis. Below is another example, note that the total current flowing through ground is again 0.

Because the ground current is 0, the ground is not required. Below is another example. Is the line balanced? No — although the voltages are equal and opposite, the currents are not!

A Voltage Balun is one whose output voltages are equal and opposite balanced with respect to ground. Voltages baluns are easily constructed and commonly used in spite of their inability to provide true current balance. This is the simplest voltage balun, consisting of two coils of wire connected as shown below.

The coils may use an air core or a ferrite core. Current flowing through the lower coil induces an equal and opposite voltage in the upper coil. This voltage balun is constructed solely for transmission line and requires two cores.

Unlike the transformer- type baluns, this balun may be used only over a narrow range of frequencies. The extra half wave section causes the voltage at its output to be equal and opposite to the voltage at the input. This voltage balun is similar to thebut uses 3 windings connected in series.

A Current Balun is one whose output currents are equal and opposite balanced with respect to ground. With the exception of the current balun, current baluns are more expensive to construct than voltage baluns and thus are less widely used. Current baluns may be made with RF transformers on ferrite cores or with lengths of transmission line.QRZ Forums.

Just curious, are there recommended applications for a balun besides perhaps an OCF dipole? I know this balun is found in most or maybe all commercially manufactured antenna tuners but I'm wanting to know where it's use might get better results than a N5YPJOct 13, G3TXQOct 13, I've used coaxial half wave baluns on,and MHz Yagi antennas.

They are great for feeding T matches. W1VTOct 13, Others will chime in, and I am only going to offer you what has been said and written about many times over. The typical "breed" of baluns on the market are voltage baluns Ruthroff-balunwhereas the typical balun is a current type Guanella-balun. There are designs for a Guanella current balun.

This would be a better choice for a impedance transformation than the voltage type because the varying electric field and permeable core of a voltage balun causes hysterisis and thus resistive loss heat. It is the same principle that causes a power supply transformer to heat up. Heat is wasted power. The current balun avoids this issue. The baluns in most antenna tuners are voltage types because, really the only reason, they are cheaper. A impedance transformation has useful applications, as you mentioned in an OCF, or any antenna that is intentionally fed at a higher impedance than the characteristic 50 ohms of coax.

Folded dipoles are another example of where a balun would be useful.

All About Baluns (Ask Dave #73)

But the current balun would be the preferred design. Using a on a multiband doublet type antenna would not be a good idea, If the antenna is resonant on any band, the feedpoint impedance would be too low to step down by a ratio of Fifty to seventy ohms would be between 12 and 18 ohms and would present a high VSWR to the transmitter and difficulties for an antenna tuner.

4 1 balun theory

So a transformation would be ideal. Even on bands where the impedance is great for instance if the antenna is near 1 full wavelength on a given bandmany broad-range tuners will be able to handle it. A balun would be useful here, but the losses in a voltage type balun would be an issue.

In most cases that can be described, the balun is as good or better a choice in terms of resistive loss vs. I'm just expressing the same details that others more knowl;edgeable than I will explain. If you're using a wide range tuner feeding balanced line, the "correct" balun would depend on your operating frequency, antenna length and feedpoint, and transmission line length, and can be almost anything.

I found a good article with a thermal image photograph of a voltage balun with RF applied for 5 minutes. The lower permeability of the first core results in heat in the core.

Steve, What, if any, effect does frequency and core matching have on this? My understanding was that if the two cores in a current balun were a matched pair that it would be more efficient over a broader frequency range than a voltage balun. I've seen it stressed that the cores should be matched for the transmission line mode to work properly and for all to be in balance.I needed a simple portable HF antenna. A long wire and some insulators is pretty easy to carry. To connect it to the radio I needed a Balun.

These are such simple things but yet they cost so much from some places. A Balun is used to match a balanced line to an unbalanced line. An Unun is used to match an unbalanced line to another unbalanced line.

4:1 Current Balun

This is a Current Balun. That means it can match a ohm antenna to a 50 feed line.

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If you plan on stringing up a dipole you use 2 equal lengths of wire with the Balun in the middle. You can run the wire straight across the field or better yet use a V shape, either inverted or not. In an inverted V you raise the Balun to a high point on a mast and the elements extend down to the ground.

I prefer a regular V where the Balun is near the ground and the elements extend up to two masts or trees, buildings etc nearby. Even simpler is a long wire end fed antenna. You just need a single wire and a ground rod. Here you need an Unun. The only difference between the Unun and Balun is how you connect the feed line.

Did you use this instructable in your classroom? Add a Teacher Note to share how you incorporated it into your lesson. You need a good large toroid core. You will make a bifilar winding.

This simply means you wind 2 wires at the same time, lying flat and equally spaced. Many people use 2 different colors of wire but its easy enough to figure out with an ohmmeter.

After you are done winding the coil coat it with glue or shellac to keep it together. Now strip all 4 leads and connect your meter to one start and one end lead. These will go to the binding posts.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Amateur Radio Stack Exchange is a question and answer site for amateur radio enthusiasts. It only takes a minute to sign up. I have a 10m dipole and am going to feed it with 50 ohm unbalanced feed line coax.

My understanding is the feed point of this style antenna is about ohms and since it is a balanced antenna I'm thinking I need some type of balun. I'm wondering, is a current balun the same as a choke? Are they the exact same devices internally or are they different internally and just preform the same function? If they are different, do they both keep common mode current off the feed line? If they are the same, why are there two different names? For an antenna, the purpose of a choke balun is to create a high-impedance to common mode currents that would flow on the outside of coaxial cable shielding.

These common mode currents can cause all kinds of problems such as RF in the shack, matching problems, and others. So, minimizing common mode currents is a good thing. Common mode currents arise when you are coupling a balanced antenna to an unbalanced line usually. For example, connecting coax cable to a dipole antenna.

You can use either a balun or a choke balun at the feed point of the antenna or where the balanced part of the system meets the unbalanced part.

The choke balun usually does the same thing as a regular current balun but adds the high impedance path to the common mode currents too. Also, the names Choke Balun and regular current balun are somewhat interchangeable as both are used to do the same thing in ham radio antenna matching: matching coax to balanced antenna and minimizing common mode currents.

Currently, on my meter dipole, I run ohm ladder line to a Current Balun and the remaining 20 feet or so is coax into the shack. In this application, I experimented with both a and a balun to find the best match and overall SWR on my bands of choice I use with this antenna: 80, 40, With the same antenna, I have used my own custom made choke balun made from coax turns through 6 toroids -- about 7 turns of coax through all 6 toroids.

This worked very effectively except for one thing. This balun was heavy and often would be a factor in my antenna coming down in a wind storm so I replaced it. So, in answer to your question specifics: 1 they do not always perform the same function but sometimes they do; 2 A regular current balun internally is very much like a transformer where as a choke balun usually focuses on multiple turns through toroids to provide high-impedance to common mode currents; 3 the names are different and some people distinguish between one thing and another by the names and others do not.

It is usually not a big deal from my experience unless you are buying something but then you look at the data sheet to understand the balun better. The image below is of one of my custom made choke baluns. This is an older one that used only five toroids. The name choke refers to the electrical component, whereas the name current balun refers to the job it is doing.

Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. How is a current balun different from a choke? Ask Question.

4 1 balun theory

Asked 4 years, 4 months ago.To return to the this point, simply use your browser's "Back" button. Voltage-type baluns produce equal and opposite voltages at the balun's balanced port. Since low impedance antennas are current fed, a balun that produces equal and opposite currents at its output over a wide range of load impedances is desirable. There is little to be gained by forcing the voltages of the two antenna halves, whether the antenna is balanced or not, to be equal and opposite compared with the cold side of the balun input.

The antenna field is proportional to the currents in the elements, not the voltages at the feed point. Current-type baluns are not a new idea. They have been used in TV receivers for many, many years.

4 1 balun theory

TV tuners require a very wide bandwidth balun that will work with a severely mismatched antenna, like a TV's so-called 'rabbit ears' antenna. The Current-type balun was the best choice for that application. Unfortunately, when baluns were first popularized for use with wire antennas, a voltage-type design was chosen.

Other balun makers just followed along. It was years before the first true, Current-type baluns appeared on the market. Of course, times change and today you can find entire books devoted to Current-type baluns.

The Radio Works was the first to offer you a full line of Current-type baluns for every application. Baluns do not allow multiband operation of single band, coax fed, antennas They do not make antennas more broadbanded. These are all generalizations and, of course, there may be specific exceptions to any of them. Large cores - prevents saturation and provide the necessary high inductive reactance values on the low bands.

Mechanical considerations: Weather- proofing, rustproof hardware and a strong case to withstand loads.

4:1 balun uses

Balun cases are high quality, heavy-wall, PVC. Eye-bolts, if they are used, are made of stainless- steel. This eliminates any chance of an unreliable connection. Signal distortion and RFI, due to core overload is practically eliminated.

4 1 balun theory

Installing a YK, 4K-LI or T-4 can substantially improve antenna performance by providing the antenna with balanced current and excellent feedline isolation. Beam antennas benefit from improved balanced drive and superior feedline isolation.

An improved radiation pattern is the result. Also, receiver noise may be reduced by eliminating signal pickup by the feedline. You can have the convenience of coaxial cable combined with the flexibility of open wire. The balun is located outside where it belongs.

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This eliminates the complication of routing balanced feeders into the radio room. This type balun has several exceptional features that are not present in other balun designs. For example, in RFI reduction, the most important factors are very high load isolation over a wide bandwidth, extremely low loss characteristics, and wide, low SWR bandwidth.

In this discussion there are four different RF currents flowing on or within a coaxial cable.

Baluns: Choosing the Correct Balun

There is an I 1 current flowing on the center conductor of the cable. Due to the skin-effect, there are two currents flowing on the cable's braided second conductor its shield which surrounds the inner conductor. On the inner surface of the braid, there is the I 2 current. At the antenna end of the coax I 2 divides into I 3 and I 4. Without a device to isolate the antenna from the feed line, the outer surface of the coax's shield is part of the antenna, thus the division in current.

I 3 is radiated by the antenna and I 4 flows along the coax. On its way back down the coax, some I 4 current is radiated, some is conducted back to the transmitter and on to station's ground system, house wiring, etc. A balun or Line Isolator substantially reduces I 4 current.Your JavaScript appears to be disabled. JavaScript is necessary for various functions, such as order checkout, to operate on this web site. Please ensure that JavaScript is enabled. Your web browser appears to be out of date.

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Contact us with your comments - good, bad, great, so-so, or whatever. We want to hear from you! View as PDF. Depending on your browser, you may not be able to view some charts or illustrations contained in this article. To ensure that you see all charts, tables, and illustrations, select the View as PDF link above.

Balun is an acronym for BAL anced to UN balanced, which describes certain circuit behavior in a transmission line, source or load. Most communications applications deal with two-terminal sources, transmission lines, and loads.

This includes coaxial cables, open wire lines and systems working against earth or a ground plane as the "second conductor". The balun has to do a good job and be reliable.

DX Engineering has the expertise to design and build a better balun that will deliver more power to the antenna, be more reliable, and in many cases cost less than products made by others. We also realized that advertising hype over the years had confused the issue of just what type of balun was appropriate to each antenna.

This article is an attempt to define in simple terms how to get the most performance from your system, both on receiving and transmitting. The first thing to realize is that there are two types of baluns: Current Baluns and Voltage Baluns. The balun's ratio is normally stated from balanced to unbalanced just as the words appear in the acronym.

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A balun has four times the balanced impedance as unbalanced impedance.


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