HF Digital Messaging - Emergency / Disaster Relief - Interoperative Communications - Ham Radio
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Broadband Antennas: Diagram above: Broadband VertaLoop as described in this article. Wire loop supported by trees, Diamond BB7V Vertical Element with feedpoint resistive matching unit, "ground" radial wire, metal support pole, coaxial cable, ferrite feedline choke clamps, and grounding points. Concepts and Construction of the Broadband VertaLoop Antenna Design and Installation Notes by Bonnie Crystal KQ6XA Background
The Broadband VertaLoop Antenna was developed for use with Automatic Link Establishment to cover HF frequencies from 3.5MHz to 30MHz continuously with low SWR. The antenna presented here is a convenient combination of the Diamond BB7V vertical antenna (modified) and a large irregularly-shaped quad loop of wire, and a wire radial that is used to fine tune the antenna for best comprimise of low SWR on the various frequencies of operation. The objective was to provide improved performance over just a Diamond BB7V alone, or just a quad loop alone. On the higher HF frequencies, the vertical tends to provide good DX performance, while at the lower and middle HF frequencies the the loop provides higher efficiency. Improving Upon the Broadband Resistively-Matched Vertical The Diamond BB7V is a transformer-matched vertical element antenna that normally uses the coaxial cable as the ground reference plane. In this configuration, both the coaxial cable and the support mast are part of the RF radiating element. This article is intended to show how the efficiency of a transformer-matched vertical may be increased, and to provide various design concepts and ideas for a range of broadband antenna types that can be built using the basic resistive-match method. Expand on the Concepts The antenna described in this article may be seen as a prototype antenna, more as a basis for design and use by radio operators seeking to erect broadband antennas. Keep in mind that exact length of the wires, antenna height, and other aspects of this design may be changed to suit the user's application and the environment that the antenna installation is being built for. Advantage of the Large Loop The advantage of the use of a large loop of wire for this application is that the impedance at any given frequency is usually above 100 ohms. This works in concert with the impedance of the resistance in the matching unit to provide the desired low SWR at 50 ohms nominal impedance for use with standard coaxial cable and HF transceivers. Results The installed Broadband VertaLoop Antenna, as built and documented here, provides SWR below 2:1 over 1.8MHz-30MHz range. The antenna system appears to provide approximately +3dB to +20dB of estimated transmit and receive signal strength advantage (depending upon frequency) over the original Diamond BB7V vertical alone as intended by the manufacturer to be installed. This huge advantage has provided a significant improvement in on-the-air performance for this station's ALE operations in the HF frequency range of 3 MHz -30MHz at the 100W to 200W transmitter power level. |
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 Photo above: Looking up at the antenna complete installation on a residential dwelling chimney, with vertical element, bottom loop wire, radial wire, and top loop wire. |
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Photos
above left and right: The Broadband VertaLoop
being installed. Testing at lower height, being prepared
and tested for SWR, ready for final installation;
including details of the camouflage, the feedpoint
connections, and the wires, cords, and cables. The antenna
element has been painted black and the support pole has
been painted to match the color of the residential
structure, in an effort to minimize the appearance of the
antenna, and blend in with the surrounding vegetation.
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of article on Broadband VertaLoop Antenna |
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Autotuner Fan Antennas: |
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The
Autotuner Fan Antenna and Autotuner Fan-Dipole
Design and Installation Notes by Bonnie Crystal KQ6XA Background Various versions of multi-wire dipole antennas are known and widely used. HF inverted-V antennas called "maypole" antennas, have been utilized with dipoles resonant in the amateur bands. The most common has been the 3.8MHz/7.1MHz resonant version fed with 50ohm coax. Technically, the antenna system consists of two or more dipoles of different lengths arranged radially in inverted-Vee form with a single common feedpoint. There are other configurations possible within the general category of "fan dipoles". Autotuner Problems with Single Wire Antenna Autotuners have been in popular use for both amateur and non-amateur applications, especially when many channels or bands of frequencies are utilized throughout the HF spectrum. Problem frequencies are sometimes found in long single-wire autotuner installations, usually due to combined RF reference plane (tuner ground) and wire resonance resulting in a very high impedance presented to the autotuner. At the problem frequencies, it can take a long time for the autotuner to repeatably find a match, or it may not be possible for it to find an acceptable match. Other problems with the same root cause can lead to excessive RF radiation from the feedline at the transmitter (hot mic syndrome). Sometimes, simply changing the length of the antenna wire slightly is sufficient to move the "problem" to an unused frequency. But changes in the ground conductivity due to rain or other factors can bring the problem back. Multiple Antenna Wires for Fast Autotuning HF-ALE (Automatic Link Establishment) requires fast autotuner action, and the linking functions best when the antenna matching autotuning cycle is completed within a fraction of a second. Application of the multi-wire dipole principle to the autotuner installation provides a solution. In practice, it has been found that there are advantages to certain wire lengths or wire length ratios for autotuner use in the HF spectrum. These ratios of wire lengths present multiple "convenient" lower impedances to the autotuner at any given frequency, enabling it to achieve a matched condition rapidly and repeatably, thereby mitigating "problem frequencies". Autotuner Fan Dipoles in Use for ALE I have developed the two successful versions of an autotuner fan dipole antenna system shown above, through both theoretical and empirical design (trial and error). I am presently using one of these antenna systems on the air 24/7 for ALE, from 1.8MHz to 28MHz. I am using an SG-230 autotuner in this installation, but the principles are the same for most of the common autotuners of similar type. Common Mode Chokes I've set up 3 different SGC autotuner systems at base stations using the ferrite common mode chokes (1:1 balun a misnomer) in the control/DC cables/feedlines, combined with a grounding strap to earth. These techniques keep some of the noise from computers and equipment in the station from being conducted into the autotuner's antenna system on receive, and they help choke off RF currents on transmit from going down the cables into the station. In the first two of those installations, severe RFI was eliminated that was present before the "chokes" were installed. In the third, I installed the chokes during the initial installation, and have not removed them to see how much difference they make. It is important to remember that ferrite must be utilized for both the coaxial feedline choke and the control cable choke. Coiling of the coax doesn't work as a choke "balun" for a frequency agile system, and in fact, it may cause problems on some bands. Grounding Indeed, many operators are content to simply ground the coax and control cable at the station entrance (good practice). I'm from ye olde school of lightning protection (having built broadcast stations and telephone central switching offices in my earlier career), so you will see additional ground straps present near the antenna in my base station antenna designs. I believe that a direct lightning discharge path to earth ground is a good design starting point for basic lightning protection. I also believe that the possible loss in RF efficiency at some frequencies is worth trading for the added safety that earth grounding at the antenna provides. Temporary Portable Installations For temporary portable installations when no chance of lightning hazard exists, the safety ground strap could be eliminated. The common mode chokes and control feedline ferrites may also be eliminated if no "hot mic" RF feedback or RFI is experienced. Feedback and Field Reports Requested There are other possible combinations of wire lengths and configurations that should function in a similar manner. I am interested in the results of others who are using this type of antenna system or derivatives of it. Feedback or field reports may be sent directly to the HFLINK or HFpack groups. |
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Using
Autotuners Without ALE Capability for ALE
Design and Installation Notes by Bonnie Crystal KQ6XA  OVERVIEW Operators have expressed interest in using a wide variety of antenna autotuners for ALE. Many autotuners do not have ALE capability, which requires tuning element bypass switching inside the autotuner. COAXIAL FEED AUTOTUNERS FOR ALE Some types of autotuners are intended for use with antennas fed by coaxial cable. LDG is an example. With these autotuners, a suitable antenna must be used that provides a somewhat lower SWR on the bands of interest. ALE TRANSMIT ANTENNA FOR COAX FEED AUTOTUNERS An offset feedpoint dipole with a 4:1 balun or a coaxial fed fan dipole can provide a good enough match for coaxial autotuners to operate properly and provide the instantaneous tuning required for ALE operation. ALE FEATURE IN AUTOTUNERS Some manufacturers have ALE bypass switching in their autotuners, such as SGC or Icom, but the internal timing may not be adequate for good ALE operation or SSB voice. A SOLUTION FOR ALL AUTOTUNERS To solve all these problems, I've designed and used the autotuner antenna system shown in the diagram, with an external T/R switch, and a separate receive antenna. The basic set up is to enable the autotuner to operate only for transmit, into a good transmit antenna... then, use a separate antenna that does not require tuning, only on receive. This ALE Autotuner Antenna System is for use with all autotuners that do not have internal ALE bypass switching capability... such as SGC, LDG, Icom, Yaesu, etc. It is also possible to use a single antenna, with 2 T/R switches. Both of these systems are shown in the above diagram. T/R SWITCH A suitable coaxial T/R switch may be built homebrew or purchased complete. There are several different types of coaxial switches available on the market. Some transceivers have built-in receive antenna switching, and this can be used without the need for an external T/R switch. SUITABLE MFJ T/R SWITCHES Some MFJ products provide this T/R switch capability: MFJ-1708 (RF Sense Transmit/Receive Switch) http://www.mfjenterprises.com/Product.php?productid=MFJ-1708 MFJ-1026 (1.5-30 MHz Deluxe Noise Canceller) http://www.mfjenterprises.com/Product.php?productid=MFJ-1026 MFJ-1025 (1.5 - 30 MHz Noise Canceling Antenna) http://www.mfjenterprises.com/Product.php?productid=MFJ-1025 COMMENT ON MFJ T/R SWITCHES I have used the MFJ-1026 for this purpose for many years, and therefore I can recommend it. Although I have not used the MFJ-1708, it is probably a more economical solution. PTT T/R SWITCHING For adequate ALE timing, it is recommended that the PTT switching output line of the transceiver is used to drive the T/R switch, rather than RF sensing. PTT transmit switching output is available at the accessory connector of most transceivers, commonly used to key the T/R of linear amplifiers. FERRITE BALUNS AND CHOKES Please note that I recommend ferrite coaxial chokes and ferrite baluns. Although it may be possible to operate without ferrites in the system, the performance on both receive and transmit will be degraded. I do not recommend "coax coil" chokes which are made by winding coax cable on a pipe or by looping coax cable. They do not work for multiband operation, and their effectiveness is dubious for other applications. RECEIVE ANTENNA The receive antenna may be almost any type of antenna that provides low noise. I prefer an inverted V antenna cut for 10MHz. I have also used a vertical whip antenna, and a random wire antenna. Keep in mind that a ferrite coaxial choke should be used both at the feedpoint and on the coax cable just before it enters the building. This prevents local noise from power line, computer, monitor, TV sets, and lighting from being conducted into the antenna from the building. On the receive or transmit antenna, for the ferrite coaxial choke at the building, ferrite clamps can be used, but be sure to use at least 8 clamps in series. CONCLUSION I hope that this information will help to enable more operators to configure a viable ALE antenna autotuner system at their station. Perhaps many already have most of the components necessary, such as a separate receive antenna and a balun or two, and most may only need a T/R switch and some coax jumpers to set it up. Please feel free to discuss this system or other suggestions and comments, on the HFLINK forum. |
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The Terminated Folded Dipole, TFD or T2FD, is one of the most popular antennas for ALE Automatic Link Establishment. It performs well on the air, provides good SWR throughout the entire HF range, and does not require an autotuner or coupler. There are many commercial versions and homebrew flavors of the TFD.This article attempts to cover some of the historic background and evolution of this broadband antenna. What Does T2FD Mean? TFD or T2FD is a term of initialism* that encompasses a classification group of antenna design. Terminated Folded Dipole is a folded dipole in which a resistive and/or reactive termination is inserted in the middle of the exposed loop of the active metallic dipole element circuit, opposite the feedpoint. The terminology and initialism has evolved over the past half-century, as variations in design have sprung forth, combined with the deep affinity among engineers and radio operators for descriptive jargon. The TFD or T2FD antenna is also known as a Squashed Rhombic and it is part of a more general category of Broadband Dipoles. *Note: Definition of initialism noun: An abbreviation consisting of initial letters pronounced separately (e.g., CPU). Acronyms are abbreviations that are blended into pronunciation with syllables as if they were words (e.g., NASA or LASER).  Background History of the Name T2FD Antenna Prior to 1949, the term TFD or TTFD originally stood for Tilted Folded Dipole, Terminated Folded Dipole, Terminated Tilted Folded Dipole, or Tilted Terminated Folded Dipole. see 1949 article snippet below By 1950 or 1951 it was widely known in commercial, military, and amateur radio. The TTFD term was converted to T2FD (T-squared FD) and then T2FD with keyboards lacking superscript (the superscript 2 became a numerical figure 2). Insertion of other higher numerical integers (example: T3FD for a Terminated 3-wire Folded Dipole) into the initialism evolved much later, circa 1985 to 1990, as a shorthand for the number of half-wave elements connected in the active circuit of the dipole. Multi-wire TFDs became popular as they were found to have reduced termination losses, wider bandwidth, and higher radiation efficiency. T3FD, T4FD, etc.  To Tilt or Not to Tilt? The recommended tilt or sloping dipole configuration in the T2FD original design articles purportedly achieved a particular beneficial radiation directional pattern for the application or location in which the antenna was developed, and this was widely carried over by other early experimenters. The tilt was utilized to fix a design problem due to feedline radiation. The original design did not have a balun at the feedpoint, but instead utilized a high impedance open wire feedline. The tilt was later found to be completely superfluous to basic TFD design and performance. The essence of the TFD antenna electrical structure can be applied to most all of the various orientation configurations of normal dipoles. It has a radiation pattern identical to a normal dipole of similar size. Tilt or slope is not necessary to the performance of the TFD. Tilt was found to be undesirable for NVIS and omnidirectional applications. Design requirements calling for tilt configuration or sloped installations are less common in modern installations, while the more popular Inverted-V or flat-top formats tend to be favored.  Yet the Tilt still lives on in antenna mythology and superstition. Some have joked that the Tilt made it a more complex acronym while imbuing black magic... therefore adding perceived value. At this point, most will agree that the TFD reputation benefits from such perceived value mystique, while simultaneously acknowledging that it continues to have many detractors. Below, some of the original articles show how the early T2FD was introduced and started to gain popularity. Terminated Folded Monopole Antenna TFM T2FM T3FM The Terminated Folded Monopole (TFM) is a derivation of the TFD, and it is usually implemented as a vertical antenna over an RF ground plane or a radial system. Like the TFD, the TFM can be designed as a multi-wire or cage antenna. T2FM, T3FM, T4FM, T5FM, etc. The TFM has the same broadband qualities as the TFD, but offers a lower footprint configuration and more omnidirectional pattern for different applications.  Article archive 1949: An Experimental All-Band Nondirectional Transmitting Antenna  Article archive 1951: Performance of the Terminated Folded Dipole  Article archive 1953: More on the T2FD  Broadband Terminated
Square Loop Antenna (BTSL)
Article by Bonnie Crystal KQ6XA The following diagram shows a typical BTSL Antenna configuration, SWR curve, and radiation patterns. The length and impedance is optimized for low SWR in the Amateur Radio HF bands. It is a horizontal loop, constructed of wire. The terminating resistance is 450 ohms, and the balun may be either 9:1 or 12:1 impedance ratio. The SWR in the 4MHz to 6MHz range is better with the 12:1 balun. It is made with the same components commonly found with T2FD or T3FD antennas. The main difference between the T2FD and the BTSL is: the BTSL has superior NVIS performance. However, at lower radiation angles (below 45 degrees) on 7MHz to 30MHz, it breaks into directive beam lobes, mostly favoring the general direction of the resistor termination. This can be either an advantage or undesirable, depending on the user's application and location.  Broadband Butterfly Terminated Dipole Antenna BBTD 3 MHz to 30 MHz 2:1 SWR or less Article by Bonnie Crystal KQ6XA  About the BBTD Antenna The Broadband Butterfly Terminated Dipole antenna (BBTD) was invented by Bonnie Crystal (KQ6XA). It is a type of traveling wave antenna, similar to a terminated folded dipole antenna (T2FD or TFD). But, the BBTD antenna is constructed of triangular or irregularly-shaped elements, instead of narrow rectangular elements. The triangular geometry has many structural and electrical advantages over a common T2FD:
Prototype Construction of a BBTD The first prototype, as shown in the above drawing, was built in 2016 to fit within a horizontal area constraint of 100 feet between 2 supports. The prototype is built as if looking at it from the side in the drawing, with the appearance of a bow tie. It had an SWR design goal of less than 2:1 from 1.8 MHz to 60 MHz. The measured SWR of the prototype is about 1.5:1. It covers 80 meters through 10 meters continuously with no gaps. The prototype utilized a 16:1 balun and an 800 ohm non-inductive resistor termination, but a 1000 ohm resistor is recommended for best SWR over the entire HF range. The resistor should be rated at the full transmitter power. Fed with 50 ohm coax, a tuner is not needed. BBTD Antenna Termination Resistor vs SWR Curve For best SWR, the optimum value of termination resistor is 1000 ohms. The value of resistor is not very critical. Any value between about 800 ohms and 1200 ohms may be utilized. The value of 800 ohms works well for the HF ham radio bands (800 ohms is a commonly available termination resistor for T2FD antennas). The following graph shows the computed SWR curve for either 800 ohms or 1000 ohms. Prototype testing found the SWR is similar to results of the BBTD Antenna NEC2 computer model BBTD_Butterfly_Prototype1_as_built_4s.nec (zip file)   BBTD Bow Tie Configuration The above image shows a side view of a BBTD antenna in the bow tie configuration with 2 flagpole type supports. A simple arrangement of insulated rope or cord provides the taut structural shape of the antenna. The center balun is supported by the upper wires of the antenna, and the resistor termination is suspended below the balun by insulated rope or cord. Stealthy construction using trees is possible with this configuration. Gain and Efficiency of the BBTD The model of the BBTD bow tie configuration prototype has a calculated gain (dBi) as shown in the following table:
Graph of BBTD Antenna Gain vs Frequency  BBTD Antenna 3D Computer Model Perspective View  Operation on the 160 Metre Band The bow tie configuration prototype BBTD with dimensions shown above has a low frequency efficiency knee drop off around 3.5 MHz. With a gain of about -16dB on 160 meters, it is very inefficient. But the SWR is good :) On 160 meters SSB with 100 Watts at night, it can still be expected to work stations out to a radius of about 300 miles. One suggested method to get better performance below 2 MHz is to disconnect the termination resistor with a relay, then use an antenna tuner at the radio. Radiation Pattern of the BBTD Antenna models show that the BBTD bow tie configuration is omni-directional at 14 MHz and below. See the radiation pattern plot image below. At frequencies of 18 MHz and higher, it shows a vague omni X pattern. It is more omni-directional than a dipole of similar size and position. The Inverted-V or other horizontal configurations are expected to exhibit similar patterns. Radiation Pattern Plots for BBTD Antenna in Bow Tie Configuration  BBTD Inverted-V Configuration The image below shows a side perspective view of a BBTD antenna in the inverted V configuration with a single flagpole type support. The bottom sides of the triangular wire elements should be deployed as far above ground as possible, and staked out to anchors with insulated rope or cord. Stealthy or temporary construction using a tree is also possible with this configuration.  BBTD Inverted V Pyramid 3D Model Geometry View  BBTD Inverted V Pyramid (Large Size) Model Dimensions The Broadband Butterfly Terminated Dipole antenna (BBTD) was invented by Bonnie Crystal (KQ6XA). A large size BBTD Inverted V Pyramid configuration is modeled in 4NEC2 . This configuration has a -3dB low frequency knee at 3.5 MHz. The model is designed with the following details: Shape: square base pyramid Feedpoint impedance: 800 ohms (16:1 balun) Termination resistor: 1000 ohms Resistor power rating: Same Watts as transmitter power Watts. Total wire: 488ft Leg wire length: 72ft Horizontal wire length 100ft Height of feedpoint: 30ft Height of termination: 26ft. Height of horizontal wire: 8ft BBTD Inverted V Pyramid (Large Size) Model Diagram with Dimensions  BBTD Inverted V Pyramid (Large Size) SWR Curve The model shows a good SWR, below 2:1 over the entire MF-HF range from 1.5MHz to 30MHz.  BBTD Inverted V Pyramid (Large Size) Gain vs Frequency Graph The model shows a gain of about +5dBi above 13MHz, and good performance on lower frequencies. The efficiency drops off at around 3.5 MHz, where the gain is about -3dBi.  BBTD Inverted V Pyramid (Large Size) Radiation Patterns The model shows that the radiation pattern is substantially omnidirectional at 10MHz and below. At 14MHz and above, it has a broad X or lumpy square pattern, slightly favoring the direction of the horizontal wires.  Mel K6KBE has done a lot of work
field testing and modeling the BBTD Pyramid
Configuration. Please download and read his paper about
optimizing it.
Design and development paper pdf
download:
Photos of a BBTD Antenna Inverted V
Pyramid at Station K6KBE
   Click to ZOOM. above photos ©2017 Mel Farrer K6KBE. Used by permission. |
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A Broadband Butterfly Terminated Dipole Antenna BBTD Inverted V optimized for the 7MHz to 54MHz frequency range The Broadband Butterfly Terminated Dipole antenna (BBTD) was invented by Bonnie Crystal (KQ6XA). For situations where full size BBTD antenna will not fit within the area required, a dimension drawing for a more compact version is presented below. The minimum support pole height is 20 feet (6m) high. It is recommended that the bottom wire be elevated at least 5 feet above the surface of the ground, and preferably higher if possible. This version of the antenna provides excellent performance above 7 MHz, with a mostly omni-directional pattern. Like the full size BBTD, it provides continuous good SWR over the entire 1.8 MHz to 54 MHz frequency range. The termination resistor in the range of 1000 ohms is optimum. A 16:1 balun is required for 50 ohm coaxial feed. For use below 7 MHz, the termination resistor should be rated at the power of the transmitter.  |
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A Broadband Butterfly Terminated Dipole Antenna BBTD Inverted V optimized for the 1.8MHz to 30MHz frequency range For better performance on the 160 meter band, a dimension drawing for a larger version is presented below. The minimum support pole height is 40 feet (12m) high. It is recommended that the bottom wire be elevated at least 10 feet above the surface of the ground, and preferably higher if possible. This version of the antenna provides excellent performance at 1.8 MHz through 5 MHz, with a mostly omni-directional pattern favoring the zenith for NVIS. Like other BBTD antennas, it provides continuous good SWR over the entire 1.5 MHz to 30 MHz frequency range. The termination resistor in the range of 1200 ohms is optimum. A 16:1 balun is required for 50 ohm coaxial feed. The termination resistor should be rated at the power of the transmitter. This version of the BBTD requires a 200 feet by 200 feet area.  |
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A Broadband Butterfly Terminated Dipole Antenna BBTD Inverted V Delta Wing optimized for the 7MHz to 30MHz frequency range For situations where an antenna in a much more compact area is required, a somewhat different configuration may be utilized. This Delta Wing configuration takes half the wire of a normal BBTD, and is similar in size to a common 40 meter band Inverted V dipole antenna. A dimension drawing is presented below. The minimum support pole height is 30 feet (6m) or higher if possible. It is recommended that the termination resistor be elevated at least 10 feet above the surface of the ground, and the bottom ends should be at least 5 feet above ground surface level. This version of the antenna provides fairly good performance at 7 MHz and up, with a mostly omni-directional pattern favoring the zenith for NVIS . Like the full size BBTD, it provides continuous good SWR over the entire 1.8 MHz to 54 MHz frequency range. The termination resistor of 1000 ohms is optimum. The termination resistor should be rated at the power of the transmitter. A 16:1 balun is required for 50 ohm coaxial feed.  |
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A Broadband Butterfly Terminated Dipole Antenna BBTD Version for House Roof or Attic The Broadband Butterfly Terminated Dipole antenna (BBTD) was invented by Bonnie Crystal (KQ6XA). Many HF radio station situations require a hidden or stealth antenna using only a house or building to support the antenna. This BBTD House Roof configuration provides broadband good SWR <2:1 over a continuous wide range of frequencies without requiring a tuner. A skeleton drawing is presented below. The total length of wire is whatever is needed to go around the perimeter of the house or building (plus zig zags and connections). A typical wood frame 40 feet by 40 feet (12m x 12m) house provides a large enough perimeter to support optimum performance from 7 MHz to 54 MHz, with somewhat less efficiency at 3.5 MHz. The efficiency is poor on the 160 meter band, but it still provides a good SWR. This version of the antenna has a mostly omni-directional pattern favoring the zenith for NVIS at the lower frequencies. At 14 MHz and above, it has modest gain favoring the direction of the termination resistor. The termination resistor should be approximately 1000 ohms, and rated at the same Watts of power as the transmitter output power in Watts. A 16:1 balun is required for 50 ohm coaxial feed. The coax cable may be any length.  The BBTD Antenna House Roof version can be utilized with buildings of various shapes and sizes. As a guideline, the more wire around the perimeter, the better the performance will be at lower frequencies (below 6 MHz). The length of wire on each side of the balun to the resistor should be within about 6ft (2m) of the same length, to maintain good SWR and balance of the antenna. Use insulated wire; #18 AWG (1mm) insulated wire is sufficient size for 500 Watts transmitter power. #22 AWG wire is sufficient for 100 Watts. The wire may be formed into a zig-zag, serpentine pattern, bent up and down, or around the corners and crevices of the building. It is very advantageous to elevate the wire as much as possible. The balun and/or termination resistor may be mounted inside the building, and the wires routed through air vents, gable vents, or holes in the walls or eaves. The insulated wire may be placed under or over eaves, or in gutters, or in the attic. Avoid close proximity of the balun or the resistor to AC mains power cables, because of risk and RFI or EMI or RX noise. Do not let any antenna wire touch an AC mains wire, internal or external to the building. Warning: contact with AC mains can kill you. Also, be sure to use good lightning protection.  Broadband Butterfly Terminated Dipole Antenna BBTD Back Yard Inverted V Delta Wing version  Broadband Butterfly Terminated Dipole Antenna BBTD Back Yard Inverted V Delta Wing version |
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16:1 Baluns For Use With Broadband Terminated Antennas There are several types, and various methods, for making 16:1 baluns and ununs for use with Broadband Terminated Antennas. A few types are be presented below. The 16:1 KISS Balun by Mel Farrer K6KBE "You cannot build a simpler 16:1 current balun than this. PERIOD. It takes 4 ea #31 ferrite beads, 28-30" of #16 or 18 AWG teflon wire. NO tape, NO twisted wires, SMALL."  above: Schematic of 16:1 KISS Balun by Mel K6KBE. ©2016 Mel Farrer K6KBE. Used by permission. "16:1 current Balun. Start with 28" of #16 or #18 Teflon wire. Make a single loop pass and tap 50 ohm input wires as shown on 4 each #31 beads. Part 1 of 3"  above: Photo of 16:1 KISS Balun during first phase of assembly. photo ©2017 Mel Farrer K6KBE. Used by permission. "Single start loop and 50 ohm taps. Part 2 of 3"  above: Close-up photo of 16:1 KISS Balun during first phase of assembly. photo ©2017 Mel Farrer K6KBE. Used by permission. "Wrap the rest of the wires around until you come up on the opposite end from 50 ohms. Part 3 of 3."  above: Photo of completed assembly of the 16:1 KISS Balun. Housing and connectors not shown. photo ©2017 Mel Farrer K6KBE. Used by permission. A 16:1 Balun Using A 16:1 Toroidal Unun and 1:1 Ferrite Coaxial Choke  |
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Designing Broadband Antenna Termination Resistors - an article by Bonnie Crystal KQ6XA Over the years, I have designed, modeled, manufactured, and tested various types of single-loop MF-HF-VHF broadband terminated antennas. The process often involved some field testing and tweaking of the resistor value to achieve desired SWR and efficiency results. I found that the selection of termination resistor value in ohms mainly depends on the antenna geometry and balun ratio. This year, I developed an RF engineering shortcut for estimating optimum resistor value, within about +/- 10%. The key to it is what I call a "termination factor", ξ, which turned out to be the number "1.3125" I applied this to make a simple formula that is suitable for application to single-loop T2FD, BBTD, BTSL, or similar antenna designs. For the optimum termination resistor value, here is my formula: R = Z ⋅ ξ Where: R is the desired resistor ohms value, Z is the known high balun characteristic impedance in ohms, ξ is the termination factor 1.3125  A balun with 16:1 ratio usually is designed with a characteristic impedance of 800 ohms : 50 ohms. Example calculation of termination resistor value for an antenna designed with a 16:1 balun: R
= 800 ⋅ 1.3125
R
= 1050 ohms (the desired resistor value)
Z
= 800 ohms (the known high balun characteristic impedance
in ohms for a 16:1 balun)
ξ
= 1.3125 (the termination factor)
:. the optimum termination Resistor value for a 16:1 ratio balun antenna is 800 multiplied by 1.3125 = 1050 ohms. A good solution for the MF-HF 1.8MHz to 30MHz range, is the tubular ceramic non-inductive wirewound resistor with Ayrton–Perry windings . Fortunately, there are suitable vitrious enamel or silicone coated A-P non-inductive resistors available for mounting in free air, and which can be exposed to weather for many years. For safety, the design of termination resistor wattage should be approximately equal to (or greater than) the transmitter maximum power output in Watts. If the resistor termination design is to be confined in a sealed (non-convective) enclosure, the enclosure should be made of high temperature material, and the resistor wattage should be rated at approximately double the transmitter power. The other alternative to the doubled wattage rating for a sealed enclosure, is to mount the resistor in a mineral oil-filled sealed enclosure. I have utilized 1075 ohm resistors and 1000 ohm resistors for 16:1 designs. Both of these values perform well for both SWR and efficiency. It is sometimes difficult to find an exact value power resistor. Any value resistor within about 10% of the optimum calculated value can be utilized. For calculated 1050 ohms, the range within 10% is between about 945 ohms and 1155 ohms. Backyard Broadband Delta Loop Antennas Unbalanced loops can provide fairly good performance while meeting the requirements for CC&R, HOA, condo, or stealth. This type of antenna shows a minimum visual impact to the backyard garden environment when insulated black wire is utilized. The feedpoint and terminations are mounted at convenient points provided by building eave, fence, roof, or wall supports. A single support pole (or convenient tree) for an insulated wire element is needed. The hot side of the 16:1 Unun goes to the highest wire. The lower wire may be run along the fence or even laid upon the surface of the ground. As with most antennas, the higher the wire, the better the signal. An automatic tuning unit (ATU) may be alternatively mounted at the feedpoint, in which case, a termination resistor is not needed.    Homebrew T3FD Antenna:  Feedpoint of T3FD Antenna Build A T3FD Antenna article by Tony Rycko KA2UFO Presented here (PDF file) are design and build notes for a Terminated Three Wire Folded Dipole (T3FD) for 160 to 10 meters based upon works by Cebik, the BUSHCOMM BBA100 series antenna, info from the HFLINK site, and lots of experimentation on my part. Shown are instructions with photos and guidelines to build a multi-band T3FD antenna for ALE use, a bill of major materials, cost information, ideas and test results. The goal is to help hams build it and have some fun with ALE. This T3FD works well, and it's easy to build! If you have room for a 90 FT dipole, try this T3FD. DOWNLOAD FULL ARTICLE PDF: Build_a_T3FD_Antenna_by_Tony_Rycko_KA2UFO  The Balun and termination resistor construction have always been a bit of a mystery and there is plenty of junk science out there, even on some commercial ham sites. I read through everything I could find and experimented with designs found on various sites. The best compilation of information and history I have found is here on the HFLINK site and, additionally, a document by Cebik (see ref). The termination resistor is my own concoction. At first I experimented with the standard 2 leg version (T2FD) like B&W makes. I tried various balun core types, transformer ratios, termination resistor values, lengths, height above ground, leg spacing, bench testing and on the air testing. The 2 leg version worked OK, but the VSWR was a bit higher on some bands than I expected. After all, the object is to have wide-band multi-band operation without the use of an antenna tuner. However, from what I have learned from building the T3FD, I can now make the appropriate improvements for the T2FD.  Larry N0OQA told me about his Bushcomm 3 leg terminated dipole (which he is very happy with) and was kind enough to send pictures, performance and VSWR data. After reading data by Cebik on multi-leg terminated dipoles, the three leg version is an efficiency improvement over the 2 leg and not as cumbersome as 4 or 5 leg versions. That's what I wanted to build and share. - Tony Rycko KA2UFO |
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