Phased verticals for portable operation
When working on portable or in DX-
peditions the key concern is how to
maximize antenna performance per kilo
of weight of the antenna to be carried to
the distant location. Antennas also have
to be easy to install and all the
adjustments have to be fast and
straightforward.
One antenna that accomplishes very
well those criteria is the array of phased
verticals. What follows is a description
of the well proven array of two verticals
for 40 meter that we have used in IOTA
contests with great results. Total weight
is less than 7 kilograms and it can be
easily carried in a backpack and you
still have spare space left for the rest of
equipment. Performance is in line with
that of a two elements yagi for 40
meters placed at 20 meters high.
The following implementation was developed thanks to the skills of Duncan,
EA5ON. The two verticals are identical and made of copper wire supported on a
fiberglass rod. Spiderbeam manufactures a very interesting 12 meter fiber
telescopic pole that is perfect for these antennas. The vertical radiator consists
on 10.4 meters long wire that can be placed over the pole with 3M tape or fast
plastic grips, starting at a height of 1.5 meters. Each vertical has two elevated
radials that will start at the 1.5 meter high feed-point of the poles and will run
paralel to the ground or with a slight slope. The length of each radial is also 10.4
meters.
Separation among the two poles determines the shape of the lobe of radiation of
the antena. A good F/B and a convenient lobe are achieved with a separation of
11 meters. The resulting lobe is wide enough for contest, where you want your
signals to be spread on ample areas of
interest with good gain.
It is extremely important to place this antena
very close to the seawater to get the most of
its potential performance. The low angles of
radiation and forward gain are very
dependent on the reflection on the
surrounding “ground”. The pseudo-Brewster
angle for vertical polarized signals is only
low when the conductivity of the “ground” is
high and on this aspect, the best “ground” is
seawater.
The phasing of the two verticals is
performed with a 270º long line of coaxial
cable. You have to be cautious when using
transmission lines as phasing devices as
they only work well when impedances are
closely matched but on this case it is well
proven that they work very well. When using RG213 coax cable with a velocity factor of 0.66 the total lenght is 20.8
meters. A couple of antenna switches can be used to change the direction of the antenna.
On air results of this antenna were amazing. When running just 100 watts from EU-093 at EE5KB, the pile-ups of JA
stations on 40m were memorable.
EE5KB from Tabarca Island EU093 (photo EA5FL)
Azimut plot at 13 degrees of elevation
EE5KB from Tabarca Island EU093 (photo EA5FL)
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