Microsoft Word ChoosingTheCorrectBalun 22Oct09.doc

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1 Baluns: Choosing the Correct Balun By Tom, W8JI General Info on Baluns is an acronym for BAL anced to Balun balanced, which describes cert ain circuit behavior in a UN transmission line, source or load. Most communi cations applications d eal with two-terminal sources, transmission lines, and load s. 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 year s had confused the issue of just what type of balun was appropriate to each antenn a. This article is an attempt to define in simple terms how to get the most performance from your system, both on receiving and transmitting. and The first thing to realize is that there are two types of baluns: Current Baluns Voltage Baluns . Balun Ratio to unbalanced (just as the words appear in the The balun's ratio is normally stated from balanced acronym). A 4:1 balun has four times the bala nced 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 pr ecisely equal and exactly out-of-phase currents. If the feedline does not have equal vo ltages, equal currents, and exactly out-of-phase currents at every point, the feedline will partially act like an antenna. to balance. Voltage is Current is most important 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. E qual and opposite currents can only fl ow inside the shield. Coaxial line shields also must have zero volts radio-fre quency 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 wi ll cause line radiation, since it flows outside the shielding wall. ced lines, we call vector curr In both balanced and unbalan ent difference between the two Rev. October 26 2009 Choosing the Correct Balun - Page 1 of 22

2 conductors "common-mode current". Common-mode current causes nearly a ll feedline radiation inating common-mode current as close to the and RF-in-the-shack problems. Reducing or elim antenna as possible, and keeping it from reappearing inside the shack, can greatly improve reception tenna. It will also reduce RFI problems. and put more transmitter power in the an -world antenna systems are neither perfectly What many of us fail to understand is most real balanced nor perfectly unbalance d. Real-world antenna systems mo st often are somewhere between d perfectly balanced. perfectly unbalanced an as close as possible to a balan ced-to-unbalanced transition point. In most cases, baluns are installed Current Baluns with respect to "ground" or chassis, to float to Current baluns allow each output terminal's voltage, any value required to provide e qual currents to each feedline conductor. Current baluns are universal devices that work with balanced or un balanced 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 unw anted 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 th an 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 mismat ch. Only common-mode current affects the core. This does not mean current baluns can handle infi nite power or mismatch, but it does mean for equal materials and cost they handl r than baluns that operate at e extremes in impedance much bette higher ratios. Voltage Baluns Voltage baluns always try to fo rce 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 current s will not be equal and opposite. This means the feedline will radiate. They also do not provide common-mode isolati on. 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 w ill always magnetize its core in direct proportion to load voltages. In a voltage balun, load impedan ce directly affects core heating and flux density. Current baluns, rather than voltage baluns, shoul d be used whenever possible. Current baluns provide better balance and often have lower loss . Current baluns, especially 1:1 ratio baluns, Rev. October 26 2009 Choosing the Correct Balun - Page 2 of 22

3 tolerate load impedance and balanc e variations much better than vo ltage 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 ng networks often have very high voltages or Antenna systems requiring antenna tuners or matchi modest power. In many cases, voltage and current currents on transmission lines and baluns, even at 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 impe ent. The feedline beyond dance to station equipm the tuner still has very high voltage , current, and loss, even if tune r input has a perf ect 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 in ternal tuner baluns are 4:1 voltage baluns, which we will see is a poor choice. In this case, the balu ns should be as close as possible to the tuner. a true balanced voltage Less often, balanced tuners are used. Such tuners co me in two styles. One is network like the old E.F. Johnson Matchbox. Other better forms include link-coupled homemade tuners with fully floating tuned circuits, which be floating current source. have as a more desirable A more recent approach is a bala nced 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 firs 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 isolati on is also the same as a traditional current balun on the tuner output. Relocati ng 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-coupl ed 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 out put of a traditional "T" network tuner. In fact, even though I can build a ny type of tuner I want, all of my personal high good 1:1 ratio current baluns on the output. power tuners are simple "T" networks with Rev. October 26 2009 Choosing the Correct Balun - Page 3 of 22

4 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 ra nge. As the operating frequency changes, balun load impedance can range from seve ral 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 impe dance through without stepping impedance down. usually voltage-type bal uns, are generally poor 3. 4:1 Baluns inside antenna tuners, which are performers when presented with mismatched load s. 1:1 current baluns are generally much more efficient and have a much wider opera ting impedance and frequency range. 4. Voltage baluns have restricted frequency response. The "optimum pe rformance" 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. Rev. October 26 2009 Choosing the Correct Balun - Page 4 of 22

5 Special DX Engineering Tuner Baluns we have a special bal un. This balun uses high- For antenna tuners or systems with high SWR, voltage 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 doe s not fail unless voltage significantly exceeds fail at less than 25% of that voltage! That 7,500 volts, while competing baluns using enameled wire load impedance, our standard balun can handle sixteen means, for the same mismatched differential times the power of enameled wire baluns before arcing in balun windings! Tuner baluns (denoted by "T" at the end of the ba lun 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 SW R. 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 t ypically fed with coaxial feedline and tuned to a specific area of a be useful on other bands (near band. Its planned use is generally 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/Frequenc y (MHz). This formula is an approximation. eter, and surroundings affect a dipole's resonant Antenna height, leg angles, insulation, wire diam frequency and impedance. It is better to initially ma ke the antenna a few percent longer than calculated and trim it back to si ze (higher in frequency), although dangling pigtails will work to ce frequency) without adverse elec trical or mechanical affects. slightly lengthen an antenna (redu A popular misconception is because the dipole is res onant, or because the dipole feedline is small in diameter, a balun is not helpful. There are also qu estionable claims that "f eedline radiation is good", or pattern change without a balun is insignificant. Many of these clai ms 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 unba lanced transition between coax and dipole, but they are very specific cases where the feedlin e is suspended in air from the center of the antenna straight away from the f eedpoint, and is grounded ¼ wavelength away from the feedpoint. Omitting the balun in other cases will often cause feed line length to affect SWR, increased noise in these ill effects. In the receiver, increased RFI, or any combination of 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. Rev. October 26 2009 Choosing the Correct Balun - Page 5 of 22

6 The part numbers of the correct 1:1 current baluns would be the , DXE- DXE-BAL050-H05-A , or depending on power levels. BAL050-H10-A DXE-BAL050-H11-C, balun is located right at the dipole element to This antenna can use a coaxial cable feed and the e element receives equal currents and prevents external shield ensure that the each side of th currents. The feedline should route straight away from the antenna center at right angles to the antenna conductor. This will keep the antenna's fi elds from introducing current on the outside of the feedline after it leaves the balun, and will keep the feedline from in troducing 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 Center-T which provides the DXE-UWA-Kit 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 me ssenger 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 th e Inverted-V configuration. • The balun hangs lower than desired. • The stress on the wires is higher th an usual due to wind or ice loading The connection from balun to shack is through 50- Ω coaxial cable. Use the lowest-loss coaxial echanical properties. eration of life and m cable that you can afford, with due consid Rev. October 26 2009 Choosing the Correct Balun - Page 6 of 22

7 Ladder Line or Open Wire fed Dipoles or Doublets nna useable on virtually a single length wire ante A Multi-band Dipole or Doublet antenna system is any band where a tuner can provide a match. Efficiency is very good when the antenna is 0.4 ency drops rapidly with antenna s shorter than 0.4 wavelengths. wavelengths long or longer. Effici en built using DX Engin eering baluns. A simple This is a popular antenna system; many have be hoosing the lowest band on which operation is multi-band dipole may be constructed by first c desired. The overall length of the multi-band di pole 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 idea l 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 throug h 10-meter operation, a dipole around 220 feet long may actually help antenna tuner and balun perfor mance, especially on lower frequencies. This is because standing waves on the transmission line transform or change reactance and resistance presented to the balun and ante nna tuner. The coaxial cable fro m the DX Engineering 1:1 Tuner ladder line Balun to the tuner should be kept short; 10 feet or less is be st. The recommended 300- Ω Ω ladder line. provides better overall impedances at the tuner and balun, as opposed to typical 450- Conductor resistance dominates tran choose the largest diameter smission line losses below VHF, so 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. DXE-LL300 300- Ω ladder feedline for a multi-band dipole must be in odd multiple lengths of The 1/8 wavelength on the lowest ope ize impedance presented to the rating frequency. This helps optim balun and tuner over the frequenc y range of the antenna. This le ngth can be calculated using the following formula or use . The DX Engineering 300 Ω ladder feedline has a VF (Velocity Table 1 Factor) of approximately 0.88. Formula: Where: Freq (MHz) = Frequency in Megahertz Ladder Feedline 0.88 = Velocity Factor of DXE-LL300 300 Ω Multiply the result times the odd multiple (1, 3, 5, 7, etc) to get the correct length closest to your required feedline length. Rev. October 26 2009 Choosing the Correct Balun - Page 7 of 22

8 Table 1 Ω Ladder Line Recommended Antenna and 300 Feedline Length for Shortened Multi-Band Dipoles for easier tuning Frequency Make feedline an Odd Multiple of Shortened Range (MHz) Dipole (Ft.) this length in Feet (x 1, 3, 5, etc.) 1.8 - 30 60.1 220 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 22 6 18 - 30 19 5.2 21 - 30 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. 35.1 ft. x 0.88 = 30.9 ft. per 1/8-wavelength. DX Engineering feedline has a VF of 0.88, so If 90 feet is required to get to your operat ing 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 th e feedline to achieve 1 54.5 feet (30.9 x 5) to maintain the odd 1/8th multiple-rule for length. If you need to splice ladder line t ogether for longer lengths, use the DXE-LLC-1P Ladder Line Coupler . If you have excess ladder line, it can be zigzagged while suspended in ai r, 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, balance the effect on both twist the line to partially sides of the feedline. Id eally, the feedline should be brought away from the antenna at right angles. 250-350 ohm impedance feedlines re sult in less extreme impedan ce changes from band-to-band. They are a good compromise between impedance ex tremes and feedline losse s. For instance, 600- Ω feedlines tend to present wider load impedance va riations at the tuner in multi-band applications than lower impedance feedlines. In addition to better impedance pe rformance, the 300- Ω line has less wind drag than 450- Ω window line. d loss, and significantly higher impedance, higher initial matche Coaxial cable has too low of an SWR on bands where the antenna feedpoint impedance is high. Rev. October 26 2009 Choosing the Correct Balun - Page 8 of 22

9 True open wire feedlines are much more difficult to build and maintain. Their 500- to 800- Ω Ω impedance allows low-loss multi-band operation, but band-to-band impedance variations at the balun and tuner are greater. 300- transmitting feedline is a better choice, since it moderates multi- Ω cantly less loss than coaxial cable in this band impedance extremes and still offers signifi 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 s reflected power. measure significantly lower because the lossy feedline absorb Additional Info on Feedline Le Feedline length is critical to ngth with Multi-band Dipoles: feedline (connects the antenna to the balun, in antenna tuning and performance. Always choose a odd-multiple of 1/8th wave length long on the lowest this instance) that is 1/8th wavelength or some rrect dimensions for the antenna and feedline for your Multi- band. The table above shows the co ing Ladder Line. Make the feedline any ODD band Dipole Antenna when using DX Engineer multiple of the lengths shown. The best balun for this applicati on is a 1:1 ratio current balun. A 1:1 balun has the widest opera stress, and provides the best ting frequency range, lowest core overall balance of any balun fo r given cost, size, and weight. The DX Engineering part number of the correct unit would be the DXE-BAL050-H10-AT Current DXE-BAL050-H11-CT Current Balun depending on power levels. Balun or the Rev. October 26 2009 Choosing the Correct Balun - Page 9 of 22

10 Do not match the balun impedance to the transm ission line impedance. The transmission line is the balun and tuner varies greatly from band-to- grossly mismatched. This means the impedance at band. Tuners have an easier time with modest to high impedances. They don't work well into very more will transform the already low impedances low impedances. A balun with a ratio of 4:1 or This will greatly reduce system efficiency and appearing on some bands to even lower values. reduce tuner power ratings. The 1:1 ratio bal un will just pass the low impedance through. In addition, higher ratio baluns will not handle differe ntial impedance extremes nearly as well as 1:1 current baluns. Ladder line fed antennas should be constructed according to the char t. The balun should be located near the tuner, keeping the coaxial cable be tween it and the tuner as short as possible. Avoid ures for any significant distance. routing the line parallel and cl ose to other conductors or struct elling as short as possible to reduce chances of RF feedback. Keep feedline length inside a dw Coupling directly from the line to sensitive wiri ng can cause distorted transmitted audio, often lfunctions. In severe cases, there may be enough RF described as "RF in the audio" or CW keyer ma present on the microphone, key, or othe r 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. Rev. October 26 2009 Choosing the Correct Balun - Page 10 of 22

11 Conventional or True Windom Antennas The True or Conventional Windom antenna, shown belo w, 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 long- wire antenna, except the horizontal wire is fe d with a few percent offset from the center. Single Wire Windom Feed. Red "D" in DX indicates same phase (positiv al on that side. e phase) output termin 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 stat ion ground. Isolating the st ation ground from the antenna ground will keep unwanted RF off station equipment, and reduce potential problems with unwanted RF in the house. Rev. October 26 2009 Choosing the Correct Balun - Page 11 of 22

12 Balanced Feed Windom Antennas Off-Center Fed Dipoles a Windom antenna, shown below, is Another, more popular version of 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. center fed antennas have impedances in the 200- Properly installed Windom balanced feed or off- 400 Ω range at resonant frequenc 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 ope rated where standing waves on the feed system are low, are 4:1 baluns. Unless otherwise labeled, DX Engineering 4:1 rati o baluns have the advantage of being current be used to feed unbalanced loads or balanced baluns. Current baluns, as mentioned earlier, can loads. e feedline is the same as shown in the table for When using a balanced feed system the length of th the Multi-band Dipoles above, an odd-eighth-wav e 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 la rge amount of feedline when comp ared to a conventional dipole. This means they are more sensitive to their surro undings than a center fed dipole. It isn't unusual to have to take additional steps to decouple the feed line when using antennas that are not fed in the center. Rev. October 26 2009 Choosing the Correct Balun - Page 12 of 22

13 End or Non-symmetrically Fed Antennas most always cause unwanted current on feedline Antennas that are end-fed or asymmetrically fed al shields. vertical, either symmetrically or asymmetrically constructed, Examples would be a "dipole" or 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, HyGai n, and Cushcraft "no radial" verticals, as well as Force 12 vertical dipoles. In DXE- FCC050-H05-A Feedline these cases, a DX Engineering 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 eedline along a boom that is "hot" antennas suggests running the f e is coupled directly to one conductor of a "hot" with RF, which means the shield of the coaxial cabl DXE-FCC050-H05-A Feedline Current Choke should be placed transmission line! In this case, the at the point where the feedlin before it reaches the tower. e leaves the antenna boom, but tenna that is coaxially fed. The RF Use with any vertical or horizontal an Feedline Current Choke: 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 ca ble 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 Rev. October 26 2009 Choosing the Correct Balun - Page 13 of 22

14 ‘end-fed’ dipoles which use the feed line as the other half of the an tenna, and even regular dipoles if appreciable distance. In all of these cases, a the feedline parallels the antenna element for any DXE- FCC050-H05-A Feedline Current Choke will greatly reduce unwanted or harmful feedline DXE- FCC050-H05-A Feedline Current Choke should be installed radiation or reception. The e radiating antenna. In all cases, it must be installed before the feedline is several feet away from th 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 be ing conducted to the antenna • Signals picked up by the feedline decreasing the di rectivity of the antenna system, especially front-to-back ratio. While most common advice is to improve the stati on'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 ntially reduce unwanted feedline ra the area of the antenna will substa diation 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 vol ts with respect to earth. Unless the ground connection point is held solidly at zero volts, current will be introdu ced onto the feedline shield. Vertical antennas with less th an perfect grounds will have When the vertical uses elevated radials, it is di fficult 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 al so reduces antenna system efficiency. With a ground-mounted vertical using a smaller gr ound 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 th e base of the vertical portion of the antenna. radials, the correct item to use is the Feedline For raised quarter-wave verticals with elevated the radials at the feedpoint of the raised Current Choke. This should be positioned UNDER Rev. October 26 2009 Choosing the Correct Balun - Page 14 of 22

15 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 ve rtical antennas. Notice that the VFCC housing is from the radial system. insulated 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 installation of 30 radials is the lowest frequency of operation. 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 r ecommended, 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 positi on with the results mentioned above. the feedline in these situations it is still possible to use the DXE- In order to reduce the current on VFCC-H05-A Vertical Feedline Current Choke. In this case, attach the te rminal that would normally go to the Radial Plate to the frame of the antenna support or mounting pipe. Sometimes, as the coaxial cable f eedline travels through th e near-field of the antenna, the current can be re-introduced to the feedlin e after the balun. In that case, a DXE-FCC050-H05-A Feedline end of the feedline. line at the radio shack Current Choke may be inserted into the feed Rev. October 26 2009 Choosing the Correct Balun - Page 15 of 22

16 Loop Antennas - Horizontal and Vertical dances if they are about 1 wavelength in Closed-loop antennas have moderately low impe circumference. They present low feedpoint impedan ces at all multiples or harmonics of the initial that have low feedpoint impedances only at ODD resonant frequency, as opposed to dipole antennas multiples of the initial resonant freque ncy. 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 : is operated near resonance on the full-wavelength band a 4:1 When a Horizontal Full-Wave Loop Ω coaxial cable to the shack from the balun, SWR at balun works very well. Using good-quality 50 antenna tuner will gene rally not be required; resonance will normally be below 1.5:1. An external 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. : The best balun for operation at resonance is a 4:1 ratio current Horizontal Full-Wave Loop balun. rrect balun would be the DXE-BAL200-H10-A . The part number of the co Rev. October 26 2009 Choosing the Correct Balun - Page 16 of 22

17 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 envi ronment where the resonant impedance of the system is around 100 Ω . Loop Antenna # 2 - Operation moderately far from resonance or on harmonics : oderately far from resonance or on harmonics, When operating a Vertical or Horizontal Loop m 4:1 balun. An example of this is operating a loop cut for 3.7 average SWR will be lowest using a 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 extern al 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. Rev. October 26 2009 Choosing the Correct Balun - Page 17 of 22

18 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 correct balun would be the DXE-BAL200-H10-AT or the The DX Engineering part number of depending on power levels and operating environment. DXE-BAL200-H11-CT : When operating the loop on random Loop Antenna # 3 - Operation far from resonance lanced feedline with the lowest impedance and unplanned frequencies far from resonance, use the ba ladder-line is best). Place the ba DXE-LL300-1C 300 Ω lun as close to the tuner as loss available ( possible. Use a 1:1 Tuner Balun. Use as short a co axial cable as in a mu lti-band dipole system. : The best balun for operation fa r from resonance is a 1:1 ratio Vertical or Horizontal Loop current Tuner Balun. ting frequency range, lowest core A 1:1 balun has the widest opera stress, and provides the best overall balance of any balun fo r 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 feedline that is a multiple critical to antenna performance. Try to choose a of 1/2 wavelength long on the lowest band, and make the loop antenna for the lowest band on which you will operate. Rev. October 26 2009 Choosing the Correct Balun - Page 18 of 22

19 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 0.88 (300 Ω ladder) Ω ladder) 0.91 (450 1.8 558 248.6 240.4 287 127.9 123.7 3.5 7 144 63.9 61.8 100 10.1 42.8 44.3 14 72 32.0 30.9 18 56 24.9 24.0 21.3 21 48 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 Rev. October 26 2009 Choosing the Correct Balun - Page 19 of 22

20 Long-Wire Antennas horizontal antennas, fed at one Long wire antennas are typically end, and well over 1/2-wavelength long at the lowest operating frequency. The impe dance of a long wire antenna varies as the lues are from a few hundred to a few thousand frequency is changed, but the normally accepted va ons and frequency. The only way to know the ohms depending on length, height, ground conditi 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 wi ll provide a relatively well- behaved installation. The output te rminal closest to the red " D " in the DX Engineering label connects to the antenna. The other terminal conn ects 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 para llel to the antenna is used. Th e counterpoise length should be ¼- wave on the lowest frequency planned. Multiple c ounterpoise wires will imp rove performance. The case of the balun should be att ached 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 hi gh SWR, use the shortest length and best quality coaxial cable possible. ratio current choke Tuner Balun. : The suggested balun is a 4:1 Longwire Antenna The DX Engineering part number of the correct balun is DXE-BAL200-H10-AT or the DXE- depending on power levels and operating environment. BAL200-H11-CT Rev. October 26 2009 Choosing the Correct Balun - Page 20 of 22

21 Rhombic, V-Beam, and Other Broadband Antennas Some antennas have very little impedance chan ge with frequency. Log Periodic, Terminated Inverted V's, Terminated V-beam antennas, a nd Terminated Rhombic antennas are examples of antennas that have stable feedpoi nt impedances over very wide fr equency ranges. Select a balun impedance (you'll have to get this from textbooks or modeling), and closest to the antenna feedpoint use it at the feedpoint or where th e feedline from the antenna ends. Be sure the feedline between the balun and antenna feedpoint matches the an tenna 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 Rev. October 26 2009 Choosing the Correct Balun - Page 21 of 22

22 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 wi der frequency ranges than other baluns. The extremely wide frequency range where SWR is lo w 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 speci fied 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 baluns. Current baluns try to force , unless specified otherwise, are current equal and opposite currents, regard . Equal antenna currents mean less of load balance conditions 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 impedan ce than popular competing baluns, often being several times better. More important, DX Engin eering baluns maintain the high impedance over wider frequency ranges. Our bal feedline radiation and RF-in-the- uns do a better job of reducing shack. Loss DX Engineering Baluns have such low loss they handle ve ry high power without heating. Losses in our baluns, when properly terminated, are near ly immeasurable on typi cal equipment like power s remain lower than competing baluns. The extra meters. Even greatly mismatched, our baluns' losse overheating and possibly damaging the balun. power goes to your antenna, rather than Rev. October 26 2009 Choosing the Correct Balun - Page 22 of 22

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