Using the Array Solutions AS80-FS
vertical antenna on 160 meters with a second option to also use it on 80m
with a trap
by Alan Christman, K3LC
This design was simulated using the EZNEC/4 software package, which is
available from Roy Lewallen W7EL.
For maximum efficiency, the height of the antenna was extended to 70
feet, by using all of the aluminum tubing supplied with the antenna. An
extensive ground system was used, consisting of 60radials, each 70 feet
long. Thus, the length of the radials isequal to the height of the
antenna. The soil was assumed to be of average quality, having a
conductivity of 0.005 S/m and a relative permittivity (dielectric
constant) of 13.
To lower the resonant frequency of the antenna from 80 to 160 meters, a
"top hat" consisting of six #12 wires was added to the antenna. These six
wires are attached to the vertical radiator at a height of 59 feet, where
there is a junction between two pieces of aluminum tubing. For resonance
at 1830 kHz, each of the top-hat wires must have a length of 40.4 feet. At
the tip of each top- hat wire, attach a light-weight insulator and
light-weight non-conductive guy material. These guys should be anchored to
theground at a distance of 70 feet from the base of the vertical, which
places them at the outer edge of the radial ground-screen.
According to EZNEC, this antenna configuration yields the following
results:
Resonant frequency = 1830 kHz
Input impedance = 12.49 -j 0.038 ohms
Peak gain = 0.74 dBi at 24 degrees take-off angle
2:1 SWR bandwidth > 60 kHz (using a 12.5-ohm reference)
Using 12.5 ohms as the reference impedance, the SWR values are:
Frequency (kHz) SWR
1800
1.80
1810
1.48
1820
1.22
1830
1.003
1840
1.21
1850
1.46
1860
1.75
If more radials (and/or longer radials) are used, this will increase
the gain of the antenna.
Using the Array Solutions AS80-FS vertical
antenna on both 80 and 160 meters.
Dual-band operation is achieved by adding a "top-hat" to lower the
resonant frequency of the antenna into the 160-meter band, and then adding
a trap to isolate the 80-meter portion of the vertical element. The design
described here produces resonance at 3650 kHz and also at 1830 kHz.
The height of the vertical element is extended to 70 feet, using the
tubing supplied by Array Solutions. An extensive ground system is used in
the computer model, consisting of 60 radials, each 70 feet long. Thus, the
length of the radials is equal to the height of the antenna. The soil was
assumed to be of average quality, having a conductivity of 0.005 S/m and a
relative permittivity (dielectric constant) of 13.
The "top hat" consists of six #12 wires was added to the antenna.
These six wires are attached to the vertical radiator at a height of 59
feet, where there is a junction between two pieces of aluminum tubing. For
resonance at 1830 kHz, each of the top-hat wires must have a length of
28.27 feet. At the tip of each top-hat wire, attach a light-weight
insulator and light-weight non-conductive guy material. These guys should
be anchored to the
ground at a distance of 70 feet from the base of the vertical, which
places them at the outer edge of the radial ground-screen. A trap
(parallel L-C circuit) is placed at the 59-foot level of the vertical
element, just below the point where the top-hat wires are attached. This
trap is composed of a 300 pF capacitor in parallel with a 7.234 uH
inductor. It was assumed that the coil has a Q of 150 at 3.65 Mhz, which
corresponds to a loss resistance of 1.11 ohms. This resistance was
included in the computer model.
According to EZNEC, this antenna configuration yields the following
results:
Resonant frequency = 1830 kHz
Input impedance = 16.09 + j 0.002 ohms
Peak gain = 0.42 dBi at 25 degrees take-off angle
2:1 SWR bandwidth < 60 kHz (using a 16.1-ohm reference, the computed
SWR is 2.02:1 at 1800 kHz and 1.99:1 at 1860 kHz)
Resonant frequency = 3650 kHz
Input impedance = 35.79 - j 0.043 ohms
Peak gain = 0.26 dBi at 25 degrees take-off angle
2:1 SWR bandwidth > 130 kHz (using a 35.8-ohm reference, the
computed SWR is 1.97:1 at 3590 kHz and 1.98:1 at 3720 kHz)
