Antenna Definitions Antenna Theory Home. A Balun is used to "balance" unbalanced systems - i. As an example, consider a coaxial cable connected to a half-wave dipole antenna shown in Figure 1.
Figure 1. An unbalanced transmission line coaxial cable connected to a dipole antenna. In Figure 1, a coaxial cable is connected to a dipole antenna. For a dipole antenna to operate properly, the currents on both arms of the dipole should be equal in magnitude. When a coaxial cable is connected directly to a dipole antenna however, the currents will not neccessarily be equal.
To see this, note that the current along a transmission line should be of equal magnitude on the inner and outer conductors, as is typically the case.
Observe what happens when the coax is connected to the dipole. However, the current that travels along the inner side of the outer conductor IB has two options: it can travel down the dipole antenna, or down the reverse outer side of the outer conductor of the coaxial cable labeled IC in Figure 1.
Ideally, the current IC should be zero. In that case, the current along the dipole arm connected to the outer conductor of the coax will be equal to the current on the other dipole arm - a desirable antenna characteristic. Because the dipole wants equal or balanced currents along its arms, it is the balanced section. The coaxial cable does not necesarily give this however - some of the current may travel down the outside of the outer coax, leading to unbalanced operation - this is the unbalanced section.
The solution to this problem, however you come up with it, is a balun. A balun forces an unbalanced transmission line to properly feed a balanced component. In Figure 1, this would be done by forcing IC to be zero somehow - this is often called choking the current or a current choke.
There are many baluns that have been developed to choke off the outer current and restore balanced operation. Some of the most popular methods are described in the following pages. However, suffice it to remember that a balun forces unbalanced lines to produce balanced operation, despite their inherent asymmetry.Like Ford vs Holden, Canon vs Nikon or Yaesu vs Icom; the world is divided into two camps on how best to connect a resonate wire antenna to a bit of coax.
Until now, my dipole had been direct connected. After much googling and a question on the sota email forum, i found a number of sources that showed how to make a Current Balun and decided this would be the path I would go do.
Both items were soured from Mini-kits in Adelaide. I took the opportunity to get some more connectors for other projects, my wife shakes her head at my large RF connector collection, wherever has the most connectors wins I constantly remind her! Start with a length of Coax, for the RG coax, you need around 45cm free to wind the Toroid up.
You should see around turns on the core. Which can increases the loss of the core. Wind the coax around the core and then cable tie the left hand side at the top of the core, cross over and start on the reverse side. Then repeat the right hand side winding back to the top of the core, and cable tie at the top. With the core done, I moved onto the mounting arrangement, I decided to try and engineer a mount using core flute for portable sota work.
I had purchased some RG BNC connectors and worked this into the core flute making a mount and centre point for dipole wire. I installed the connector into the core flute on a little tab, to allow quick coax connection. Then added some cable ties to mount onto the squid pole.
I then measured out some legs and connected them to the core centre. So, how does it work, i had a chance to use it the other day in the local park for a quick activation on the Pirate Contest, and without any tuning and trimming of the wire its a fraction long with vswr ata peak at 6.
Your email address will not be published. Notify me of follow-up comments by email. Notify me of new posts by email. This site uses Akismet to reduce spam. Learn how your comment data is processed. To Balun or Not to Balun, this is the question?
How to Make a Balun or Unun
Like this: Like Loading Related posts. Thanks W8GMF. Leave a Reply Cancel reply Your email address will not be published.New for March ! One type of balun that is often used in microwave applications is the Marchand balun.
First, we will start with reviewing Nathan Marchand's paper reference provided at bottom of page. If you don't have a copy, ask us nicely and we'll send it.
Then we will develop a Marchand balun design in Microwave Office. Marchand provided an excellent means of converting from coax to two-conductor transmission line. The article was carried in the trade journal "Electronics", which was first published in InGordon Moore published an article with the title " Cramming more components onto integrated circuits " in Electronics, providing insight into the future of integrated circuits which became known as Moore's Law.
Below is a figure of the balun that Marchand presented in Note that nowhere in the article, was it called a balun, we are not sure of the origin of that name. Maybe a reader can tell us The variation in characteristic impedance was calculated to be just a few ohms across bandwidth. Toggle navigation Menu. Filter by alphabets Filter by categories.
Below is Marchand's equivalent circuit model.About Balun Theory The resource is currently listed in dxzone. The main category is Home-made antenna baluns projects that is about Balun Construction. Baluns are devices to balance unbalanced systems. This link is listed in our web site directory since Friday Jul 29and till today " Balun Theory " has been followed for a total of times.
So far received 31 votes for a total score of 6. Baluns are devices to balance unbalanced systems. Rate this resource received 31 votes for a total score of 6. The scale is 1 - 10, with 1 being poor and 10 being excellent. Webmaster, add a Remote rating Related links We thought you might also be interested in these additional resources we selected from the same category: Baluns: theory and projects - All about baluns with photos, projects and instructions, by IZ7ATH HF Home made Balun - A balun is a device that is used at the feedpoint of a balanced antenn Balun Theory - The word balun means balanced-unbalanced: it's used to adapt a balance Balun for HF wire antennas - Schema of a self made balun used to match randmon wire antennas, mainl Visit this link Balun Theory Visit Site Share this resource Share this link with your friends, publish within popular social networks or send it via email.
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The DXZone is the largest human created and maintained library of web sites dedicated to Amateur Radio, currently lists Get our latest news and links in your email. Service provided by Google FeedBurner. Visit Site.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. 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. This makes it difficult to push common mode current into the feed line. On the test bench, the center tapped resistor that is grounded at the center is very close to a dipole.
Common mode current and imbalance in the antenna or center tapped load is limited primarily by the common mode impedance looking into the source the feed line or balun. In a balanced line, both conductors are excited with common mode.
An unbalanced line, the coaxial feed line, behaves in common mode as a single-wire transmission line with the shield as the sole conductor. It's easy to see the actual load a balun or transmission line connects to varies over quite wide extremes in common mode. The load on the balun or transmission line almost never appears as a small floating resistor. In a very small small loop, the antenna behaves like a resistor divider with one side going to a small capacitance.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. 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. 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.
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. 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.Authored by Ian C.Antenna Impedance Matching of Antenna and Wave Propagation by Engineering Funda
Text size: increase decrease. My personal recommendations, thanks. Check out the Amazon Electronic Component Packs page. It may or may not provide wide frequency range impedance transformation depending upon the configuration used. The folded dipole is part of a yagi antenna which looks something like a pole with rods set across it at right angles.
The second last one is folded into an oblong or rectangular shape. A folded dipole exhibits two important characteristics a its bandwidth is good for over an octave e. In earlier days extensive use was made of ohm twin lead ribbon cable to feed the signals to the TV receiver. BTW you can use just a length of ohm ribbon cable to make a folded dipole.
When colour or color if you prefer TV was introduced the ribbon cable often created problems which could be rectified by the use of co-axial cable. This is not strictly correct because coax had earlier uses in TV because of other problems such as ghosting which became intolerable with the introduction of colour. Now ohm coax can be and is made. However 50 and 75 ohm cable is preferred for a variety of reasons. Our folded dipole also exhibits a "balanced" feed characteristic whilst coaxial cable has an "unbalanced" characteristic.
Two problems. Each solved by the use of the balun. Fig 1. Perhaps we should have some clarification about this balanced versus unbalanced jazz. Mentally visualise it this way. If we have a plus 12V D. That could be regarded for our illustrative purposes as the unbalanced 75 ohm input. The only difference is we are dealing with RF which of course is very high A. In so doing we have achieved our two goals, a the impedance transformation and b gone from unbalanced to balanced. Higher power levels require a different approach.
Here's an affiliate link to Amazon's Balun Page. Links above do not imply any particular endorsement of organisation, products or services but are provided as a further aid to information. Google Custom Search.