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HF Broadband Antenna

Broadband Antennas:

Broadband VertaLoop (tm) Antenna copyright 2008 HFLINK
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

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.

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.

Installed: Broadband VertaLoop  Feedpoint of Broadband Vertaloop

Photo above left: Broadband VertaLoop installed on a chimney. Photo above right: the feedpoint connections of the Broadband VertaLoop, including the ferrites, the strain relief cords for the wires, the matching unit, and other parts.
Installed: Broadband VertaLoop on chimney
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.
Broadband VertaLoop after camouflage paint and leaf garland added     Broadband VertaLoop at lower height testing SWR
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.

Daimond BB7V modified with resistive matching unit with ground lugs Modification of the Diamond BB7V transformer matching unit. Since the stock matching unit does not provide a connection to the shield of the coax for attachment of wires, it was necessary to add these connection points. The photo at left shows the tapped holes in the bottom part of the unit, with 5/16″-18 threads and “ground lug” bolts with washers. The modification includes tapping all of the 4 bottom ventilation holes of the unit, although only one of these connection points was used in this particular installation. These bolts are for the bottom connection of ground radials and loop wires. Extreme care must be observed when tapping the holes, not to cut into or disturb the internal parts of the matching unit. A small LED light can be placed at one of the holes to assist in viewing the internal parts while working on the modification. All of the bolts, nuts, and washers are stainless steel. The ring terminals for wire connections are plated or tinned copper or brass. It is important to avoid over-torque of the bolts, because the aluminum threads may be stripped if the bolts are tightened too much.
Tapping 5-16-18 hole in Diamond BB7V resistive matching unit   Diamond BB7V resistive matching unit modified by tapping 5/16-18 hole
-end of article on Broadband VertaLoop Antenna

Autotuner Fan Antennas:
ALE Auto Tuner Inverted V Fan Dipole (c)2007 HFLINK
ALE Auto Tuner V Dipole (c)2007 HFLINK
The Autotuner Inverted-V-Fan-Dipole and Autotuner V-Fan-Dipole
Design and Installation Notes by Bonnie Crystal KQ6XA

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 frequenciesare 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 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.

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.

Using Autotuners Without ALE Capability for ALE
Design and Installation Notes by Bonnie Crystal KQ6XA

ALE Autotuner Transmit / Receive Switching System

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.

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.

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.

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.

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.

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.

Some MFJ products provide this T/R switch capability:
MFJ-1708 (RF Sense Transmit/Receive Switch)
MFJ-1026 (1.5-30 MHz Deluxe Noise Canceller)
MFJ-1025 (1.5 – 30 MHz Noise Canceling Antenna)

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.

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.

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.

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.

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.

TFD Terminated Folded Dipole  ( T2FD )
Article by Bonnie Crystal KQ6XA

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 / in·i·tial·ism / iˈniSHəˌlizəm / 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).

T2FD Terminated Folded Dipole Antenna TFD

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 2became 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.

T3FD Terminated 3-wire Folded Dipole TFD

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 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.

T2FD Terminated Folded Dipole Inverted V TFD

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.

TFM Terminated Folded Monopole Antenna T2FM T3FM T4FM T5FM

Article archive 1949: An Experimental All-Band Nondirectional Transmitting Antenna

TFD Antenna 1949 Countryman - An Experimental All-Band Nondirectional Transmitting Antenna

Article archive 1951: Performance of the Terminated Folded Dipole

Performance of the Terminated Folded Dipole - Countryman 1951

Article archive 1953: More on the T2FD

More on the T2FD - Countryman 1953

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 Terminated Square Loop Antenna BTSL

Broadband Butterfly Terminated Dipole Antenna BBTD
3 MHz to 30 MHz
2:1 SWR or less
Article by Bonnie Crystal KQ6XA
Broadband Butterfly Terminated Dipole Antenna BBTD

About the BBTD Antenna
The Broadband Butterfly Terminated Dipole antenna (BBTD) is a type of traveling wave antenna. It is similar to a terminated folded dipole antenna (T2FD), but the BBTD antenna is constructed of equilateral triangle elements, instead of narrow rectangular elements. This geometry enables the following structural and electrical advantages:

  1. Constructed without spreaders.
  2. Radiation efficiency gain approximately +2dB better than a T2FD.
  3. Less visibly obtrusive and more stealthy than a T2FD.
  4. Good NVIS high angle regional performance below 14MHz.
  5. Good DX performance at 14MHz and above.
  6. Lower frequency rolloff knee than T2FD of same length.
  7. Smooth and well-matched SWR curve.
  8. Omni-directional radiation pattern.

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 about half the transmitter power for operation above 3.5 MHz. If utilized below 3.5 MHz, then 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 (zip file)

BBTD Termination Resistor vs SWR curve

Broadband Butterfly Terminated Dipole Antenna BBTD Bow Tie Configuration with 2 supports
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:

MHz Gain dBi
800 ohm
Gain dBi
1000 ohm
1.8 -17.9 -17.3
1.9 -16.7 -16.2
3.0 -6.5 -6.9
3.6 -3.0 -3.8
4.0 -1.6 -2.3
5.0 0.2 -0.2
5.4 0.3 0.1
7.0 -0.5 0.2
9.0 -0.4 -0.5
10.0 -2.0 -2.7
11.0 -0.3 -0.1
13.0 3.2 3.4
14.1 4.0 3.7
15.0 3.7 3.0
17.0 2.3 2.0
19.0 1.8 1.4
21.2 4.9 5.0
23.0 4.6 4.9
25.0 2.2 2.3
27.0 5.3 5.1
28.0 5.2 5.2
29.0 4.9 5.0

Graph of BBTD Antenna Gain vs Frequency
BBTD Gain vs Frequency with Termination 800 and 1000 ohms graph

BBTD Antenna 3D Computer Model Perspective View
BBTD Antenna 3D Geometry 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

Broadband Butterfly Terminated Dipole Antenna BBTD Radiation Pattern configuration Bow Tie

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.

Broadband Butterfly Terminated Dipole Antenna BBTD Inverted V configuration with single support

BBTD Inverted V Pyramid 3D Model Geometry View
BBTD 3D Geometry Perspective View Inverted V Pyramid configuration

BBTD Inverted V Pyramid (Large Size) Model Dimensions
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: 1200 ohms
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 Model Drawing 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 Expanded Size 1200 ohm termination SWR curve

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 Pyramid Large Size gain vs frequency

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.

BBTD Inverted V Pyramid Large Size Radiation Patterns


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