Choosing the Correct Balun
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Rev.October 26 2009
is an acronym for 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 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 yearbalun 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: Voltage BalunsBalun Ratio The balun's ratio is normally stated from balancedacronym).A 4:1 balun has four times the balanced impedance as unbalanced impedance.Balanced and Unbalanced Balanced lines and loads, by definition, have equal voltages from each terminal to ground.Each balanced terminal or conductor must also carry prpoint, the feedline will partially act like an antenna.Current is most important to balance.Voltage is less important, although voltage can be important in specific cases.Coaxial feedlines, like balanced lines, must also line shields also must have zero volts radio-frequency electrical potential to "ground" or space around the line at the operating frequency.
Deviations from this ideal case will cause current flow on the outer surface of the shield.This current will cause line radiation, since it flows outside the shielding wall.
ced lines, we call vector current difference between the two Choosing the Correct Balun
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Rev.October 26 2009 conductors "common-mode current".
Common-mode and RF-in-the-shack problems.
Reducing or eliminating common-mode current as close to the antenna as possible, and keeping it from reappearing inside the shack, can greatly improve reception and put more transmitter power in the antenna.
It will also reduce RFI problems.What many of us fail to understand is most real-world antenna systems are neither perfectly d.Real-world antenna systems most often are somewhere between In most cases, baluns are installed as close as possible to a balanCurrent baluns allow each output terminal's voltage, universal devices that work with balanced or uncommon-mode isolation between systems connected at each end.While traditionally used as baluns, Current baluns isolate or add impedance to unwanted common-mode current paths, reducing or controlling common-mode current.specialized situations, because they work better than voltage baluns in most real-world systems.
density or "magnetizing stress" on the balun core is independent of load impedance or load mismatch.
Only common-mode current affects the core.This does not mean current baluns can handle infinite power or mismatch, but it does mean for equal materials and cost they handle extremes in impedance much betterce the output terminals to equal voltages.They sometimes introduce phase shift between each output terminal and "ground".
If the impedance presented at each terminal s will not be equal and opposite.
This means the some feedline radiation (or reception), because there are very few "perfectly balanced" loads or Unlike a 1:1 ratio current balun, a voltage balun will always magnetize its core in direct proportion to load voltages.In a voltage balun, load impedanChoosing the Correct Balun
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Rev.October 26 2009 tolerate load impedance and balance variations much better than voalso be used as isolators or un-un's.
Unless otherwise noted, DXE Baluns are current-type baluns.Antenna systems requiring antenna tuners or matchicurrents on transmission lines and baluns, even at modest power.In many cases, voltage and current are not in phase with each other.
This can produce very high currents at the same place where In some installations, coaxial cable connects a poorly matched balanced antenna directly to a tuner.The tuner "matches" the poor antenna system impeect SWR.With antenna and antenna feedline are balanced and the tuner has an internal or external balun.Unfortunately, most inwe will see is a poor choice.In this case, the baluns should be as close as possible to the tuner.
me in two styles.
One is better forms include link-coupled homemade have as a more desirable A more recent approach is a balabalanced load to function optimally.Balance is not as good as a link-coupled tuner with fully floating components.t might think.
The balun has just as much core stress and flux density when placed at the input as it would have when in the traditional location, on the output.
Common-mode isolation is also the same as a traditional current complicates tuner construction.
assure optimal transmission-line must be ground independent.current balun at the output of a traditional "T" all of my personal high power tuners are simple "T" networks withChoosing the Correct Balun
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Rev.October 26 2009 There are four areas of concern in tuner-matched systems: 1.In a multi-band dipole system, the antenna almost never presents a moderate impedance load to load impedance can range from several thousand ohms to a few ohms.2.Most antenna tuners work best into moderate to high impedances, rather than low impedances.antenna impedance down.Most tuners would work better if the balun passed the line impe3.
4:1 Baluns inside antenna tuners, which are performers when presented with mismatched loads.1:1 current baluns are generally much more efficient and have a much wider operating impedance and frequency range.4.
Voltage baluns have restricted frequency response.The "optimum performance" frequency range is much narrower in voltage baluns tuners in multi-band dipole systems.Most tuners use them because they are cheap, easy to build, and because almost everyone else uses them.
Choosing the Correct Balun
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October 26 2009 For antenna tuners or systems with high SWR, we have a special balvoltage wire and has excellent performance at very high SWR.Even standard DXE baluns are better than many competing baluns, because many competing baluns use thin enamel for wire 7,500 volts, while competing baluns using enameled wiremeans, for the same mismatched differential load impedance, our standard balun can handle sixteen lun part number) may cause SWR with a perfectly matched load.Of course, this is when no tuner is required.
We do NOT recommend T-suffix tuner baluns
equally well and handle the same
wherever most convenient for your system.
within that band, although it may odd-harmonics) where feedpoint impedance reasonably matches the coaxial feedline.The well-known length formula is L (feet) = 468/Frequency (MHz).This formula is an approximation.
eter, and surroundings affect a dipole's resonant frequency and impedance.It is better to initially macalculated and trim it back to size (higher in frequency), although dangling pigtails will work to trical or mechanical affects.A popular misconception is because the dipole is resonant, or because the dipole feedline is small in diameter, a balun is not helpful.There are also questionable claims that "fms contradict each other.If one is true, the other claim argues against it.That is what happens when we justify a questionable
specific cases where the feedline is suspended in air from the center of the antenna straight away from the fwavelength away from Omitting the balun in other cases will often cause feedline length to affect SWR, increased noise in the receiver, increased RFI, or any combination ofAmateur power levels permitted, omission of a balun can cause coaxial shield or connector arcing The best balun for this application is a 1:1 ratio current balun.
Choosing the Correct Balun
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Rev.October 26 2009 The part numbers of the correct DXE-BAL050-H11-C,This antenna can use a coaxial cable feed and the
the dipole element to ensure that the each side of the element receives equal currents and prevents external shield currents.The feedline should route straight away from the antenna center at right angles to the antenna conductor.This will keep the antenna's fields from introducing current on the outside of the feedline after it leaves the balun, and will keep the feedline from introducing noise onto the antenna element.Here is an example of the balun setup thatThe optional formed plastic piece shown is the DXE-UWA-Kitantenna elements and the balun and removes the load of the balun and feedline from the element wire ends.This system will reduce the chances of
in most installations.
The top 3/8" diameter hole in the Center-T is used for a rope meSTI-DBR-94-100messenger line also will keep the antenna element from stretching and changing resonant frequency over time.This is helpful when: The antenna will be used in the Inverted-V configuration.
The connection from balun to shack is through 50- coaxial cable.Use the lowest-loss coaxial eration of life and mChoosing the Correct Balun
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October 26 2009 A Multi-band Dipole or Doublet antenna system is a single length wire ante a match.
Efficiency is very good when the antenna is 0.4 s shorter than 0.4 wavelengths.This is a popular antenna system; many have beeering baluns.A simple multi-band dipole may be constructed by first cdesired.The overall length of the multi-band diAlthough it may not seem logical, for 160 through 10-meter operation, a dipole around 220 feet long may actually help antenna tuner and balun performance, especially on lower frequencies
.This is because standing waves on the transmission line transform or change reactance and resistance m the DX Engineering 1:1 Tuner st.
The recommended 300-Conductor resistance dominates transmission line losses below VHF, so choose the largest diameter conductor you can for a given transmission line size and impedance.
Do not substitute smaller feedline to save money.DXE-LL300 ladder feedline for a multi-band dipole
multiple lengths of ize impedance presented to the following formula or use Factor) of approximately 0.88.
DXE-LL300 Ladder Feedline Multiply the result times the odd multiple (1, 3, 5, 7, etc) to get the correct length closest to your Choosing the Correct Balun
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Rev.October 26 2009 Table 1 Feedline Length for Shortened Multi-Band Dipoles for easier tuningFrequency Dipole (Ft.) this length in Feet (x 1, 3, 5, etc.) 1.8 - 30 220 60.1 3.5 - 30 110 5.3 - 30 76 20.4 7 - 30 10.1 - 30 41 10.7 14 - 30 29 18 - 30 22 6 21 - 30 19
When using an external balun, the feedline length should be calculated to the balun.
To use an antenna from 80 meters to 10 meters, the feedline should be in odd 1/8 wavelength multiples on 80 meters.
The 80 meter band starts at 3.5 MHz.DX Engineering feedline has a VF of 0.88, so 35.1 ft.x 0.88 = 30.9 ft.
If 90 feet is required to get to your operating position, the nearest odd multiple 1/8 wavelength length is 92.7 feet (30.9 ft.
If you needed 110 feet, you would have to add to the feedline to achieve 154.5 feet (30.9 x 5) to maintain the odd 1/8th multiple-rule for length.
Ladder Line r, but it can't be closer than a few conductor widths to metallic objects and If it is necessary to pass closely to a metallic object, twist the line to partially
from the antenna at right angles.250-350 ohm impedance feedlines result in less extreme impedance changes from band-to-band.They are a good compromise between impedance extremes and feedline lossefeedlines tend to present wider load impedance variations at the tuner in multi-band applications to better impedance performance, the 300-impedance, higher initial matcheSWR on bands where the antenna feedpoint impedance is high.
Choosing the Correct Balun
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Rev.October 26 2009 True open wire feedlines are much more difficult to build and maintain.Their 500-impedance allows low-loss multi-band operation, but band-to-band impedance variations at the
transmitting feedline is a better choice, since it moderates multi-band impedance extremes and still offers significantly less loss than coaxial cable in this Why you don't want to use coaxial cable when the SWR is high.cable, you lose half your power at an SWR of 10:1.At frequencies higher than 14 MHz, it's worse.For higher loss coaxial cables, like RG-not at the radio.
At the radio, SWR would measure significantly lower because the lossy feedline absorbs reflected power.ngth with Multi-band Dipoles: Feedline length is critical to antenna tuning and performance.Always choose a this instance) that is 1/8th wavelength or some odd-multiple of 1/8th wavelength long on the lowest rrect dimensions for the antennamultiple of the lengths shown.
The DX Engineering part number ofDXE-BAL050-H11-CTChoosing the Correct Balun
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Rev.October 26 2009 Do not match the balun impedance to the transmission line impedance.The transmission line is grossly mismatched.This means the impedance at the balun and tuner varies greatly from band-to-band.Tuners have an easier time with modest to high impedances.They don't work well into very low impedances.
A balun with a ratio of 4:1 or more will transform the already low impedances appearing on some bands to even lower values.This will greatly reduce system efficiency and reduce tuner power ratings.The 1:1 ratio balun will just pass the low impedance through.
In addition, higher ratio baluns will not handle differential impedance extremes nearly as well as 1:1 near the tuner, keeping the coaxial cable bereduce chances of RF feedback.Coupling directly from the line to sensitive wiring can cause distorted transmitted audio, often described as "RF in the audio" or CW keyer malfunctions.In severe cases, there may be enough RF present on the microphone, key, or otheEven when properly done, this arrangement will subject the coaxial line between the tuner and coaxial line and keep the coaxial line as short as possible.
RG8/X and smaller will is the minimum size that handles DX Engineering and larger effective core area than other similar designs.They are much more effective antenna tuner baluns than Choosing the Correct Balun
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Rev.October 26 2009 The True or Conventional Windom antenna, shown beloan unbalanced system against a reasonable RF ground or counterpoise.The feed is similar to a long-wire antenna, except the horizontal wire is fed with a few percent offset from the center.Single Wire Windom Feed.
ground the unused balanced terminal to the counterpoise or radial system.DO NOT connect that system to the statation ground from the antenna ground will keep unwanted RF off station equipment, and reduce potential problems with Choosing the Correct Balun
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Rev.October 26 2009 Another, more popular version of a Windom antenna, shown below, is line.It is sometimes called a "balanced feed" Windom, even though it is Properly installed Windom balanced feed or off-center fed antennas have impedances in the 200-ies.Depending on the installation, a Windom antenna may have reasonable impedances at several harmonically related frequencies.The best balun for both antennas, assuming they operated where standing waves on the feed system baluns.Current baluns, as mentioned earlier, can When using a balanced feed system the length of the feedline is the same ase depending on the lowest frequency used.The best balun for the Windom or Off-CenterThe DX Engineering part number ofrge amount of feedline when compThis means they are more sensitive to their surroundings than a center fed dipole.It isn't unusual to line when using antennas that are not fed in the Choosing the Correct Balun
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Rev.October 26 2009 most always cause unwanted current on feedline Examples would be a "dipole" or vertical, either symmetrically where the feed cable leaves the antenna near a high voltage point.
This can be because of a marginal counterpoise, because the coaxial cable itself is the counterpoise, or because the feedline routes Commercial examples of this are Gap, MFJ, HyGai these cases, a DX Engineering DXE- FCC050-H05-A Feedline Current Choke placed no more than five feet away from the antenna feedpoint will greatly reduce feedline currents.One manufacturer of log-periodicwith RF, which means the shield of the coaxial cabltransmission line! In this case, the DXE-FCC050-H05-Ae leaves the antenna boom, but Feedline Current Choke: tenna that is coaxially fed.The RF common-mode impedance from 1.8 to 60 MHz.
Examples where this may be necessary are small dipole antennas such as Force 12 vertical dipoles, ble as a counterpoise, verticals with few or using the feedline shield as the other leg of a dipole, so-called Choosing the Correct Balun
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Rev.October 26 2009 the feedline parallels the antenna element for any appreciable distance.In all of these cases, a Feedline Current Choke will greatly reduce unwanted or harmful feedline radiation or reception.The several feet away from th be installed before the feedline is routed against other cables, a metallic mast, or a tower.The above antenna examples usually have very lead to: RFI problems, either with the amateur equipment or consumer devices
rectivity of the antenna system, especially While most common advice is to improve the station's RF ground, the root of the problem is in the improve reception, a Feedline Current Choke is a good idea.In these examples adding a DX Feedline Current Choke at the point where the feedline exits the area of the antenna will substasomething a station ground cannot do, no matter howrecommended for use on high SWR systems.coaxial line against a ground system, like a quarter-wave vertical, depends on the ground system being at zero volVertical antennas with less than perfect grounds will have
When the vertical uses elevated radials, it is difficult to keep current from traveling back to the unwanted current cause RFI problems, it also reduces antenna system efficiency.With a ground-mounted vertical using a smaller grsystems, there is the need for a feedline choke or current balun system to keep unwanted currents off the outside of the feedline shield.For raised quarter-wave verticals with elevated radials, the correct item to use is the Feedline Current Choke.
This should be positioned UNDERChoosing the Correct Balun
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Rev.October 26 2009 vertical.The coax should not parallel a radial, but should exit midway between radials.For ground mounted quarter-wave verticals, the best device for this
The DX Engineering part number of the correct Vertical Feedline Current Choke would be the DXE-VFCC-H05-ADXE-VFCC-H10-ABelow is a picture of the DX Engineering (VFCC) used with the Hustler BTV family of veinsulated from the radial system.Insulated Choke System for use withThe braid is sized for use with the Tilt-Base and Radial Plate.do it is with a Radial Plate and a minimum of 16 DXE-VFCC-H05-A is mounted on the DXE-VFCC-BRKTwhich is attached to the Radial Plate.For various reasons, people sometimes install the Hustler antennas with no radials or with an inadequate number of radials.
This is not rintroduces current to the braid of the feedline, which can travel to the operating posit