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
Installation Notes by Bonnie Crystal KQ6XA
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
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.
|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.
Looking up at the antenna complete installation on a residential
dwelling chimney, with vertical element, bottom loop wire, radial wire,
and top loop wire.
|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.
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
|-end of article on Broadband VertaLoop Antenna
|Autotuner Fan Antennas:
|The Autotuner Inverted-V-Fan-Dipole and
Installation Notes by Bonnie Crystal KQ6XA
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
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
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
length of the antenna wire slightly is sufficient to move the "problem"
unused frequency. But changes in the ground conductivity due to
rain or other factors can bring the problem back.
Multiple Antenna Wires for
(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
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
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
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.
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 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
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
Installation Notes by Bonnie Crystal KQ6XA
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
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
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.
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)
MFJ-1026 (1.5-30 MHz Deluxe Noise Canceller)
MFJ-1025 (1.5 - 30 MHz Noise Canceling Antenna)
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.
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
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
END OF PAGE
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