Choosing the Correct Balun

Choosing the Correct Balun
Baluns: Choosing the Correct Balun
By Tom, W8JI
General Info on Baluns
Balun is an acronym for BALanced to UNbalanced, 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".
Balun Fundamentals and Terms
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.
Balun Ratio
The balun's ratio is normally stated from balanced to unbalanced (just as the words appear in the
acronym). 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 precisely equal and exactly out-of-phase currents. If
the feedline does not have equal voltages, equal currents, and exactly out-of-phase currents at every
point, 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 have exactly equal and opposite currents on the
shield and center conductors. Equal and opposite currents can only flow inside the shield. Coaxial
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.
In both balanced and unbalanced lines, we call vector current difference between the two
Choosing the Correct Balun - Page 1 of 22
Rev. October 26 2009
conductors "common-mode current". Common-mode current causes nearly all feedline radiation
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
balanced nor perfectly unbalanced. Real-world antenna systems most often are somewhere between
perfectly unbalanced and perfectly balanced.
In most cases, baluns are installed as close as possible to a balanced-to-unbalanced transition point.
Current Baluns
Current baluns allow each output terminal's voltage, with respect to "ground" or chassis, to float to
any value required to provide equal currents to each feedline conductor. Current baluns are
universal devices that work with balanced or unbalanced loads equally well. Current baluns add
common-mode isolation between systems connected at each end. While traditionally used as baluns,
they work well as broadband phase-invertors or as an un-un.
Current baluns isolate or add impedance to unwanted common-mode current paths, reducing or
controlling common-mode current. Current baluns are the balun of choice in all but very
specialized situations, because they work better than voltage baluns in most real-world systems.
In the case of a 1:1 ratio current balun, core flux 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 better than baluns that operate at
higher ratios.
Voltage Baluns
Voltage baluns always try to force the output terminals to equal voltages. They sometimes introduce
phase shift between each output terminal and "ground". If the impedance presented at each terminal
is not exactly equal, feedline or load currents will not be equal and opposite. This means the
feedline will radiate.
They also do not provide common-mode isolation. A voltage balun almost certainly guarantees
some feedline radiation (or reception), because there are very few "perfectly balanced" loads or
perfect voltage baluns.
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 impedance directly affects core heating and flux density.
Current baluns, rather than voltage baluns, should be used whenever possible. Current baluns
provide better balance and often have lower loss. Current baluns, especially 1:1 ratio baluns,
Choosing the Correct Balun - Page 2 of 22
Rev. October 26 2009
tolerate load impedance and balance variations much better than voltage baluns. Current baluns can
also be used as isolators or un-un's.
Unless otherwise noted, DXE Baluns are current-type baluns.
Systems Requiring Antenna Tuners
Antenna systems requiring antenna tuners or matching networks often have very high voltages or
currents 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
voltages are very high, the worse of both conditions appearing at one point in the system.
In some installations, coaxial cable connects a poorly matched balanced antenna directly to a tuner.
The tuner "matches" the poor antenna system impedance to station equipment. The feedline beyond
the tuner still has very high voltage, current, and loss, even if tuner input has a perfect SWR. With
coaxial feed, any balun would belong at the antenna, not at the tuner.
In other installations, both the antenna and antenna feedline are balanced and the tuner has an
internal or external balun. Unfortunately, most internal tuner baluns are 4:1 voltage baluns, which
we will see is a poor choice. In this case, the baluns should be as close as possible to the tuner.
Less often, balanced tuners are used. Such tuners come in two styles. One is a true balanced voltage
network like the old E.F. Johnson Matchbox. Other better forms include link-coupled homemade
tuners with fully floating tuned circuits, which behave as a more desirable floating current source.
A more recent approach is a balanced network with a balun on the input. While a balanced network
with grounded center is balanced, it is a voltage-type source like the Matchbox. It needs a perfectly
balanced load to function optimally. Balance is not as good as a link-coupled tuner with fully
floating components.
Unbalanced networks with baluns on the input are not what we first 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
balun on the tuner output. Relocating the balun to the input of an unbalanced network does not help
the balun do a better job and complicates tuner construction.
The ideal balanced tuner would have a link-coupled floating balanced network. Nothing else will
assure optimal transmission-line balance. The output network must be ground independent.
Otherwise, it is a resonant equivalent of a voltage balun.
We are often further ahead to place a good 1:1 ratio current balun at the output of a traditional "T"
network tuner. In fact, even though I can build any type of tuner I want, all of my personal high
power tuners are simple "T" networks with good 1:1 ratio current baluns on the output.
Choosing the Correct Balun - Page 3 of 22
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
the balun over the full frequency operating range. As the operating frequency changes, balun
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.
Most baluns inside antenna tuners step the antenna impedance down. Most tuners would work
better if the balun passed the line impedance through without stepping impedance down.
3. 4:1 Baluns inside antenna tuners, which are usually voltage-type baluns, are generally poor
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 than in equivalent current-type baluns.
Based on the above, a 4:1 balun or any voltage-type balun is the wrong choice for use with antenna
tuners in multi-band dipole systems. Most tuners use them because they are cheap, easy to build,
and because almost everyone else uses them.
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Rev. October 26 2009
Special DX Engineering Tuner Baluns
For antenna tuners or systems with high SWR, we have a special balun. This balun uses highvoltage 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
insulation. Our standard Teflon insulated wire does not fail unless voltage significantly exceeds
7,500 volts, while competing baluns using enameled wire fail at less than 25% of that voltage! That
means, for the same mismatched differential load impedance, our standard balun can handle sixteen
times the power of enameled wire baluns before arcing in balun windings!
Tuner baluns (denoted by "T" at the end of the balun part number) may cause a very slightly higher
SWR with a perfectly matched load. Of course, this is when no tuner is required. We do NOT
recommend T-suffix tuner baluns for higher frequencies (above 15 MHz) unless you are willing to
tolerate a slight change in SWR. DXE 1:1 ratio tuner-baluns work equally well and handle the same
power on the tuner input or output, so use them wherever most convenient for your system.
Half-wave Dipoles
A resonant half-wave dipole is typically fed with coaxial feedline and tuned to a specific area of a
band. Its planned use is generally within that band, although it may be useful on other bands (near
odd-harmonics) where feedpoint impedance reasonably matches the coaxial feedline. The wellknown length formula is L (feet) = 468/Frequency (MHz). This formula is an approximation.
Antenna height, leg angles, insulation, wire diameter, and surroundings affect a dipole's resonant
frequency and impedance. It is better to initially make the antenna a few percent longer than
calculated and trim it back to size (higher in frequency), although dangling pigtails will work to
slightly lengthen an antenna (reduce frequency) without adverse electrical 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 "feedline radiation is good",
or pattern change without a balun is insignificant. Many of these claims contradict each other. If one
is true, the other claim argues against it. That is what happens when we justify a questionable
practice.
Indeed there are cases where a balun is not needed at the balanced to unbalanced transition between
coax and dipole, but they are very specific cases where the feedline is suspended in air from the
center of the antenna straight away from the feedpoint, and is grounded ¼ wavelength away from
the feedpoint.
Omitting the balun in other cases will often cause feedline length to affect SWR, increased noise in
the receiver, increased RFI, or any combination of these ill effects. In unlucky cases with higher
Amateur power levels permitted, omission of a balun can cause coaxial shield or connector arcing
to tower legs or other metallic objects.
The best balun for this application is a 1:1 ratio current balun.
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Rev. October 26 2009
The part numbers of the correct 1:1 current baluns would be the DXE-BAL050-H05-A, DXEBAL050-H10-A, or DXE-BAL050-H11-C, depending on power levels.
This antenna can use a coaxial cable feed and the balun is located right at 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 that should be used with this antenna type.
The optional formed plastic piece shown is the DXE-UWA-Kit Center-T which provides the
hardware required for a no-solder mounting for the antenna 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
the antenna wire breaking in most installations.
The top 3/8" diameter hole in the Center-T is used for a rope messenger line which is strung above
the antenna wire and provides support for the balun and feedline. The line can be thin Dacron rope
such as the STI-DBR-94-100 which has a breaking strength of 260 pounds. The use of the
messenger 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 balun hangs lower than desired.
The stress on the wires is higher than usual due to wind or ice loading
The connection from balun to shack is through 50-Ω coaxial cable. Use the lowest-loss coaxial
cable that you can afford, with due consideration of life and mechanical properties.
Choosing the Correct Balun - Page 6 of 22
Rev. October 26 2009
Ladder Line or Open Wire fed Dipoles or Doublets
A Multi-band Dipole or Doublet antenna system is a single length wire antenna useable on virtually
any band where a tuner can provide a match. Efficiency is very good when the antenna is 0.4
wavelengths long or longer. Efficiency drops rapidly with antennas shorter than 0.4 wavelengths.
This is a popular antenna system; many have been built using DX Engineering baluns. A simple
multi-band dipole may be constructed by first choosing the lowest band on which operation is
desired. The overall length of the multi-band dipole antenna should be shorter than one-half
wavelength as shown in Table 1. For best efficiency, ladder line feed and a good antenna tuner
with balanced connections are required. The ideal balun is a 1:1 ratio DX Engineering special
application tuner balun. It can be connected through a short length of coaxial cable to an unbalanced
tuner for tuning the different bands.
Although 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
presented to the balun and antenna tuner. The coaxial cable from the DX Engineering 1:1 Tuner
Balun to the tuner should be kept short; 10 feet or less is best. The recommended 300-Ω ladder line
provides better overall impedances at the tuner and balun, as opposed to typical 450-Ω ladder line.
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
conductor television-style feedline to save money. Losses will increase.
The DXE-LL300 300-Ω ladder feedline for a multi-band dipole must be in odd multiple lengths of
1/8 wavelength on the lowest operating frequency. This helps optimize impedance presented to the
balun and tuner over the frequency range of the antenna. This length can be calculated using the
following formula or use Table 1. The DX Engineering 300 Ω ladder feedline has a VF (Velocity
Factor) of approximately 0.88.
Formula:
Where:
Freq (MHz) = Frequency in Megahertz
0.88 = Velocity Factor of DXE-LL300 300 Ω Ladder Feedline
Multiply the result times the odd multiple (1, 3, 5, 7, etc) to get the correct length closest to your
required feedline length.
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Rev. October 26 2009
Table 1
Recommended Antenna and 300 Ω Ladder Line Feedline Length
for Shortened Multi-Band Dipoles for easier tuning
Frequency
Shortened
Make feedline an Odd Multiple of
Range (MHz)
Dipole (Ft.)
this length in Feet (x 1, 3, 5, etc.)
1.8 - 30
220
60.1
3.5 - 30
110
30.9
5.3 - 30
76
20.4
7 - 30
55
15.4
10.1 - 30
41
10.7
14 - 30
29
7.7
18 - 30
22
6
21 - 30
19
5.2
Note: When using an external balun, the feedline length should be calculated to the balun.
Example: 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. Therefore, 123/3.5 = 35.1 feet.
DX Engineering feedline has a VF of 0.88, so 35.1 ft. x 0.88 = 30.9 ft. per 1/8-wavelength.
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. x 3).
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.
If you need to splice ladder line together for longer lengths, use the DXE-LLC-1P Ladder Line
Coupler.
If you have excess ladder line, it can be zigzagged while suspended in air, but it can't be closer than
a few conductor widths to metallic objects and cannot be coiled on itself or laid on the ground. If it
is necessary to pass closely to a metallic object, twist the line to partially balance the effect on both
sides of the feedline. Ideally, the feedline should be brought away 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 losses. For instance, 600-Ω
feedlines tend to present wider load impedance variations at the tuner in multi-band applications
than lower impedance feedlines. In addition to better impedance performance, the 300-Ω line has
less wind drag than 450-Ω window line.
Coaxial cable has too low of an impedance, higher initial matched loss, and significantly higher
SWR on bands where the antenna feedpoint impedance is high.
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Rev. October 26 2009
True open wire feedlines are much more difficult to build and maintain. Their 500-Ω to 800-Ω
impedance allows low-loss multi-band operation, but band-to-band impedance variations at the
balun and tuner are greater. 300-Ω transmitting feedline is a better choice, since it moderates multiband impedance extremes and still offers significantly less loss than coaxial cable in this
application.
Why you don't want to use coaxial cable when the SWR is high. For each 100 feet of coaxial
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-58 or RG-8X, have even more loss. Plus, the
SWR shown here is measured at the antenna, not at the radio. At the radio, SWR would
measure significantly lower because the lossy feedline absorbs reflected power.
Additional Info on Feedline Length with Multi-band Dipoles: Feedline length is critical to
antenna tuning and performance. Always choose a feedline (connects the antenna to the balun, in
this instance) that is 1/8th wavelength or some odd-multiple of 1/8th wavelength long on the lowest
band. The table above shows the correct dimensions for the antenna and feedline for your Multiband Dipole Antenna when using DX Engineering Ladder Line. Make the feedline any ODD
multiple of the lengths shown.
The best balun for this application is a 1:1 ratio current balun.
A 1:1 balun has the widest operating frequency range, lowest core stress, and provides the best
overall balance of any balun for given cost, size, and weight.
The DX Engineering part number of the correct unit would be the DXE-BAL050-H10-AT Current
Balun or the DXE-BAL050-H11-CT Current Balun depending on power levels.
Choosing the Correct Balun - Page 9 of 22
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-toband. 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
current baluns.
Ladder line fed antennas should be constructed according to the chart. The balun should be located
near the tuner, keeping the coaxial cable between it and the tuner as short as possible. Avoid
routing the line parallel and close to other conductors or structures for any significant distance.
Keep feedline length inside a dwelling as short as possible to reduce 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 other equipment to cause an RF burn.
Even when properly done, this arrangement will subject the coaxial line between the tuner and
balun to very high standing waves and high voltage and/or current. You should use good low-loss
coaxial line and keep the coaxial line as short as possible. RG8/X and smaller will not do a proper
job. Belden RG-213 or equivalent is the minimum size that handles the higher voltages and currents
properly.
DX Engineering baluns have significantly higher common-mode impedance and larger effective
core area than other similar designs. They are much more effective antenna tuner baluns than
standard bead or air-core baluns.
Choosing the Correct Balun - Page 10 of 22
Rev. October 26 2009
Conventional or True Windom Antennas
The True or Conventional Windom antenna, shown below, is fed with a single-wire line, and fed as
an unbalanced system against a reasonable RF ground or counterpoise. The feed is similar to a longwire antenna, except the horizontal wire is fed with a few percent offset from the center.
Single Wire Windom Feed.
Red "D" in DX indicates same phase (positive phase) output terminal on that side.
When you use a single wire feed, ground the unused balanced terminal to the counterpoise or radial
system. DO NOT connect that system to the station ground. Isolating the station ground from the
antenna ground will keep unwanted RF off station equipment, and reduce potential problems with
unwanted RF in the house.
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Rev. October 26 2009
Balanced Feed Windom Antennas Off-Center Fed Dipoles
Another, more popular version of a Windom antenna, shown below, is fed with open wire or ladder
line. It is sometimes called a "balanced feed" Windom, even though it is actually an "Off-Center
Fed" dipole.
Properly installed Windom balanced feed or off-center fed antennas have impedances in the 200400 Ω range at resonant frequencies. 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
are low, are 4:1 baluns.
Unless otherwise labeled, DX Engineering 4:1 ratio baluns have the advantage of being current
baluns. Current baluns, as mentioned earlier, can be used to feed unbalanced loads or balanced
loads.
When using a balanced feed system the length of the feedline is the same as shown in the table for
the Multi-band Dipoles above, an odd-eighth-wave depending on the lowest frequency used.
The best balun for the Windom or Off-Center Fed Dipole is a 4:1 ratio current balun.
The DX Engineering part number of the correct balun would be the DXE-BAL200-H10-A or the
DXE-BAL200H11-C.
Off-Center fed antennas have a large amount of feedline when compared to a conventional dipole.
This means they are more sensitive to their surroundings than a center fed dipole. It isn't unusual to
have to take additional steps to decouple the feedline when using antennas that are not fed in the
center.
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Rev. October 26 2009
End or Non-symmetrically Fed Antennas
Antennas that are end-fed or asymmetrically fed almost always cause unwanted current on feedline
shields.
Examples would be a "dipole" or vertical, either symmetrically or asymmetrically constructed,
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
along or through the antenna.
Commercial examples of this are Gap, MFJ, HyGain, and Cushcraft "no radial" verticals, as well as
Force 12 vertical dipoles. In 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.
50 Ω Broad Band Antennas
One manufacturer of log-periodic antennas suggests running the feedline along a boom that is "hot"
with RF, which means the shield of the coaxial cable is coupled directly to one conductor of a "hot"
transmission line! In this case, the DXE-FCC050-H05-A Feedline Current Choke should be placed
at the point where the feedline leaves the antenna boom, but before it reaches the tower.
Feedline Current Choke: Use with any vertical or horizontal antenna that is coaxially fed. The RF
isolated SO-239 at the top of the DXE- FCC050-H05-A Feedline Current Choke provides a high
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,
shortened or loaded antennas using the coaxial cable as a counterpoise, verticals with few or
shortened radials, full-size dipoles using the feedline shield as the “other leg” of a dipole, so-called
Choosing the Correct Balun - Page 13 of 22
Rev. October 26 2009
‘end-fed’ dipoles which use the feedline as the other half of the antenna, and even regular dipoles if
the feedline parallels the antenna element for any appreciable distance. In all of these cases, a DXEFCC050-H05-A Feedline Current Choke will greatly reduce unwanted or harmful feedline
radiation or reception. The DXE- FCC050-H05-A Feedline Current Choke should be installed
several feet away from the radiating antenna. In all cases, it must be installed before the feedline is
routed against other cables, a metallic mast, or a tower.
What are the benefits of using a Feedline Current Choke?
The above antenna examples usually have very high common-mode feedline currents which often
lead to:
•
•
•
RFI problems, either with the amateur equipment or consumer devices
Noise picked up by the feedline being conducted to the antenna
Signals picked up by the feedline decreasing the directivity of the antenna system, especially
front-to-back ratio.
While most common advice is to improve the station's RF ground, the root of the problem is in the
poor isolation of the feedline from antenna currents. If you wish to reduce feedline radiation and
improve reception, a Feedline Current Choke is a good idea. In these examples adding a DX
Engineering DXE- FCC050-H05-A Feedline Current Choke at the point where the feedline exits
the area of the antenna will substantially reduce unwanted feedline radiation or reception. This is
something a station ground cannot do, no matter how good it is. The feedline current choke is not
recommended for use on high SWR systems.
Quarter-Wave Vertical Antennas
Any antenna directly fed with a coaxial line against a ground system, like a quarter-wave vertical,
depends on the ground system being at zero volts with respect to earth. Unless the ground
connection point is held solidly at zero volts, current will be introduced onto the feedline shield.
Vertical 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
operating position via the feedline unless a feedline current choke is used. Not only does this
unwanted current cause RFI problems, it also reduces antenna system efficiency.
With a ground-mounted vertical using a smaller ground system, and especially with poor radial
systems, there is the need for a feedline choke or current balun system to keep unwanted currents
off the outside of the feedline shield.
The correct location for a choke system is at the base of the vertical portion of the antenna.
For raised quarter-wave verticals with elevated radials, the correct item to use is the Feedline
Current Choke. This should be positioned UNDER the radials at the feedpoint of the raised
Choosing the Correct Balun - Page 14 of 22
Rev. October 26 2009
vertical. The coax should not parallel a radial, but should exit midway between radials.
The DX Engineering Feedline Current Choke is model DXE-FCC050-H05-A.
For ground mounted quarter-wave verticals, the best device for this application is a 1:1 ratio
current choke.
The DX Engineering part number of the correct Vertical Feedline Current Choke would be the
DXE-VFCC-H05-A or the higher power DXE-VFCC-H10-A.
Below is a picture of the DX Engineering DXE-VFCC-H05-A Vertical Feedline Current Choke
(VFCC) used with the Hustler BTV family of vertical antennas. Notice that the VFCC housing is
insulated from the radial system.
Insulated Choke System for use with Hustler Antenna and Radial Plate.
The braid is sized for use with the Tilt-Base and Radial Plate.
When installing a Hustler antenna the best way to do it is with a Radial Plate and a minimum of 16
radials that are ¼-wavelength at the lowest frequency of operation. The installation of 30 radials is
highly recommended. The DX Engineering DXE-VFCC-H05-A Vertical Feedline Current Choke
is mounted on the DXE-VFCC-BRKT Insulated Mounting Bracket which is attached to the
antenna support post, and is connected to the antenna feedpoint and directly to the DXE-RADP-1P
Radial Plate.
For various reasons, people sometimes install the Hustler antennas with no radials or with an
inadequate number of radials. This is not recommended, but it happens. As a result, the antenna
uses the coaxial cable as a radial and by doing so, introduces current to the braid of the feedline,
which can travel to the operating position with the results mentioned above.
In order to reduce the current on the feedline in these situations it is still possible to use the DXEVFCC-H05-A Vertical Feedline Current Choke. In this case, attach the terminal that would
normally go to the Radial Plate to the frame of the antenna support or mounting pipe.
Sometimes, as the coaxial cable feedline travels through the near-field of the antenna, the current
can be re-introduced to the feedline after the balun. In that case, a DXE-FCC050-H05-A Feedline
Current Choke may be inserted into the feedline at the radio shack end of the feedline.
Choosing the Correct Balun - Page 15 of 22
Rev. October 26 2009
Loop Antennas - Horizontal and Vertical
Closed-loop antennas have moderately low impedances if they are about 1 wavelength in
circumference. They present low feedpoint impedances at all multiples or harmonics of the initial
resonant frequency, as opposed to dipole antennas that have low feedpoint impedances only at ODD
multiples of the initial resonant frequency. Loops make better multiband antennas.
There are three common operating conditions for a loop antenna:
Loop Antenna #1 - Operation near fundamental resonance - A Single Band Loop:
When a Horizontal Full-Wave Loop is operated near resonance on the full-wavelength band a 4:1
balun works very well. Using good-quality 50 Ω coaxial cable to the shack from the balun, SWR at
resonance will normally be below 1.5:1. An external antenna tuner will generally not be required;
the radio's internal tuner can be used if needed.
Typical SWR Plot of full-wave horizontal loop at approximately 60 feet above average ground
using DX Engineering 4:1 balun. Operation is safe for balun and coaxial feedline over the
entire band.
Horizontal Full-Wave Loop: The best balun for operation at resonance is a 4:1 ratio current
balun.
The part number of the correct balun would be the DXE-BAL200-H10-A.
Choosing the Correct Balun - Page 16 of 22
Rev. October 26 2009
Vertical Full-Wave Loop: The best balun for operation at resonance is a 2:1 ratio current
balun.
The DX Engineering part number of the correct balun would be the DXE-BAL100-H11-C for any
power levels and operating environment where the resonant impedance of the system is around
100 Ω.
Loop Antenna # 2 - Operation moderately far from resonance or on harmonics:
When operating a Vertical or Horizontal Loop moderately far from resonance or on harmonics,
average SWR will be lowest using a 4:1 balun. An example of this is operating a loop cut for 3.7
MHz near the bottom or top of the band, or using a 3.6 MHz loop on 7.2 MHz. When operating
moderately close (within 200 kHz) of resonance, losses will be reasonable. Good quality coaxial
cable should be installed between the balun and the loop. An external tuner can be used at the
operating position, be sure SWR without the tuner is under 5:1.
On the left is an SWR Plot of full-wave horizontal loop at 60 feet, resonant at 3.54 MHz while
using a DX Engineering 4:1 balun. On the right is the 40 meter SWR plot.
The plots above show with a DX Engineering 4:1 balun and reasonably good coaxial cable,
you can operate a loop over most of 80 and all of 40 meters. This system is generally good on
80, 40, 20, 15 and 12 meters.
Choosing the Correct Balun - Page 17 of 22
Rev. October 26 2009
Vertical or Horizontal Loop: The best balun for operation moderately far from resonance or
on harmonics is a 4:1 ratio current Tuner Balun.
The DX Engineering part number of the correct balun would be the DXE-BAL200-H10-AT or the
DXE-BAL200-H11-CT depending on power levels and operating environment.
Loop Antenna # 3 - Operation far from resonance: When operating the loop on random
unplanned frequencies far from resonance, use the balanced feedline with the lowest impedance and
loss available (DXE-LL300-1C 300 Ω ladder-line is best). Place the balun as close to the tuner as
possible. Use a 1:1 Tuner Balun. Use as short a coaxial cable as in a multi-band dipole system.
Vertical or Horizontal Loop: The best balun for operation far from resonance is a 1:1 ratio
current Tuner Balun.
A 1:1 balun has the widest operating frequency range, lowest core stress, and provides the best
overall balance of any balun for given cost, size, and weight.
The DX Engineering part number of the correct balun would be the DXE-BAL050-H10-AT or the
DXE-BAL050-H11-CT depending on power levels and operating environment.
Some Notes on Feedline Length When Using a Loop Far From Resonance: Feedline length is
critical to antenna performance. Try to choose a feedline that is a multiple of 1/2 wavelength long
on the lowest band, and make the loop antenna for the lowest band on which you will operate.
Choosing the Correct Balun - Page 18 of 22
Rev. October 26 2009
Make Feedline Any Multiple of This Length in Feet
Full-Wave
Lowest Frequency on
Select Column Corresponding to Correct Velocity
Loop Dipole
which the antenna will be
Factor of Your Feedline. Velocity Factors shown are
(ft)
used (MHz)
for DX Engineering Ladder Line
1005/f
0.91 (450 Ω ladder)
0.88 (300 Ω ladder)
1.8
558
248.6
240.4
3.5
287
127.9
123.7
7
144
63.9
61.8
10.1
100
44.3
42.8
14
72
32.0
30.9
18
56
24.9
24.0
21
48
21.3
20.6
24.9
40
18.0
17.4
28
36
16.0
15.5
Table 3 - Length of Feedlines for Multi-band Full Wave Loops
Choosing the Correct Balun - Page 19 of 22
Rev. October 26 2009
Long-Wire Antennas
Long wire antennas are typically horizontal antennas, fed at one end, and well over 1/2-wavelength
long at the lowest operating frequency. The impedance of a long wire antenna varies as the
frequency is changed, but the normally accepted values are from a few hundred to a few thousand
ohms depending on length, height, ground conditions and frequency. The only way to know the
impedance is to measure it or at least model it with antenna software.
A 4:1 balun using good coaxial cable leading to an antenna tuner will provide a relatively wellbehaved installation. The output terminal closest to the red "D" in the DX Engineering label
connects to the antenna. The other terminal connects to the antenna's ground or counterpoise. The
ground ideally would be a modest system of radials. At the very least, an elevated counterpoise
several feet above ground and parallel to the antenna is used. The counterpoise length should be ¼wave on the lowest frequency planned. Multiple counterpoise wires will improve performance. The
case of the balun should be attached to a separate ground rod.
Long-wire Feed using a 4:1 Balun. The antenna ground side should be attached to a radial
system as with a vertical antenna.
Like any other antenna system that involves high SWR, use the shortest length and best
quality coaxial cable possible.
Longwire Antenna: The suggested balun is a 4:1 ratio current choke Tuner Balun.
The DX Engineering part number of the correct balun is DXE-BAL200-H10-AT or the DXEBAL200-H11-CT depending on power levels and operating environment.
Choosing the Correct Balun - Page 20 of 22
Rev. October 26 2009
Rhombic, V-Beam, and Other Broadband Antennas
Some antennas have very little impedance change with frequency. Log Periodic, Terminated
Inverted V's, Terminated V-beam antennas, and Terminated Rhombic antennas are examples of
antennas that have stable feedpoint impedances over very wide frequency ranges. Select a balun
closest to the antenna feedpoint impedance (you'll have to get this from textbooks or modeling), and
use it at the feedpoint or where the feedline from the antenna ends. Be sure the feedline between the
balun and antenna feedpoint matches the antenna impedance as closely as possible.
The balun for a terminated Rhombic, V-Beams and Other high impedance broadband antennas is
the 12:1 model DXE-BAL600-H10A.
Choosing the Correct Balun - Page 21 of 22
Rev. October 26 2009
An Explanation of Our Ratings
SWR
When terminated in the designed output impedance, DX Engineering Baluns have lower SWR
over much wider frequency ranges than competing baluns. Typical SWR curves of DX Engineering
1:1 and 4:1 baluns remain well under 1.3:1 beyond the stated range of operation. Even our least
expensive baluns have lower SWR over much wider frequency ranges than other baluns. The
extremely wide frequency range where SWR is low shows how we carefully select materials,
layout, and the construction process.
Power Rating
DX Engineering Baluns are conservatively rated. Materials are selected to provide substantial
headroom. Baluns are tested to work beyond specified worst case conditions. We specify the power
rating into a 3:1 SWR resistive load in normal ICAS duty. Abnormalities in the system, such as
extremely high common-mode currents, can adversely affect power ratings.
Balance
DX Engineering Baluns, unless specified otherwise, are current baluns. Current baluns try to force
equal and opposite currents, regardless of load balance conditions. Equal antenna currents mean
minimum feedline radiation near the balun.
High common-mode impedance is a very desirable trait in most baluns, since high common-mode
impedance assures the best balance under widely varying load conditions. DX Engineering baluns
have significantly higher common-mode impedance than popular competing baluns, often being
several times better. More important, DX Engineering baluns maintain the high impedance over
wider frequency ranges. Our baluns do a better job of reducing feedline radiation and RF-in-theshack.
Loss
DX Engineering Baluns have such low loss they handle very high power without heating. Losses
in our baluns, when properly terminated, are nearly immeasurable on typical equipment like power
meters. Even greatly mismatched, our baluns' losses remain lower than competing baluns. The extra
power goes to your antenna, rather than overheating and possibly damaging the balun.
Choosing the Correct Balun - Page 22 of 22
Rev. October 26 2009
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