Phased 40M Wire Verticals
the 40M twin-vertical antenna array
early 2007, I have had two 40M wire verticals suspended from a rope
between two pines in the forest on the slope below our back yard.
wire verticals are 1/4-wavelength (about 33' tall at 7.050 mhz).
vertical has four 33' raised radials each, feedpoints 10' to 15'
off the ground. The verticals are spaced about 30' apart, and in
switchable end-fire mode they aim at about 30 degrees (northeast
to Europe), or 210 degrees (southwest to the deep South Pacific
experiments to reach Europe
I fed the array at the south vertical, and had a 3/4-wave phasing
line of 75-ohm RG6 running to the north vertical. This produced
a single end-fire pattern to the north (Europe), but this effect
was only slight. I suspect the actual velocity factor of the RG6
required an adjustment to the length of the 3/4-wave phasing line
(removing 2.5 feet).
was also able to feed both verticals with 1/4-wave lines for a bi-directional
broadside (US/JA) pattern.
May 2007, I ran an exact 3/4-wave phasing line of RG-6 between the
verticals, feeding at the south end, supposedly to end-fire at EU
just east of north. Exhibited some gain, but never worked much to
2008, I changed the feed of these verticals to use the Christman
method -- each vertical fed by 84-degrees, and a 71-degree phasing
loop inserted between the antenna feedpoints at the common control
box. All coax is 50-ohm RG-58 for now. Relays gave me switchable
end-fire patterns to the north or south (for either EU or W6 coverage).
schematic for end-fire in two directions
This diagram does not show a second relay used to create a broadside
pattern (simply shorts across the A and B terminals, so each antenna
is fed by the same length of feedline). If you want to keep each
antenna's radial system isolated from the other antenna, use a DPDT
relay instead -- which will let you switch both the shield and the
center conductors of each feedline.
on my two-element 80M verticals for details of the phasing and
2009 -- Interaction
problems with half-square array
had to remove the 40M vertical array in January 2009, however, as
these verticals were too close to my 40M half-square array. They
severely skewed the pattern of the half-squares when beaming East
to the U.S. and Canada.
how skewed the half-square antenna pattern was, when the 40M twin
verticals were in place:
here's the half-square antenna pattern to the East with the 40M
twin verticals removed:
the installation of a SteppIR yagi with 30M/40M dipole, I have decommissioned
the two-element 40M verticals for now. Plan is to eventually resurrect
the array as a three-vertical triangle array for 40M. I am currently
working on a three-vertical triangle for 80M to test the concept.
have two major and seemingly perpetual deficiencies for contesting:
40M access to Europe, and 160M to anywhere. I'm working on addressing
both. The first order of business in this pursuit was to resurrect
the two-element 40M vertical array and get it working properly,
firing NE and SW.
pulled the verticals back into the air in January 2010, but they
didn't work very well. Same old story. Seeing as the array has never
achieved the performance I expected, my next suspect was the Christman
phasing lines. Perhaps I had cut them to the wrong lengths using
the old analog noise bridge.
had to wait until a warm spell in February to get outdoors and bring
the two 84-degree feedlines and 71-degree phasing line inside. There,
I checked all three coax lines with my new Autek VA1 RF analyzer.
Turns out that they were all too long -- as much as 5 inches too
long on the phasing line, and about 3 inches on the feedlines. Enough
to make a significant difference in the antenna's gain and F/B.
the noise bridge had brought me "close" to the required
lengths, but not close enough. The VA1 allowed me to cut them precisely...
well, I probably should have cut the cables an inch or so too short
to compensate for the extra length of the relay leads inside the
switch box, but for now I think I'm "close enough."
how I cut them to the correct length:
the antenna analyzer (VA1 in my case) to one end of a cable, other
end left open. I manually held the coax centre and shield
against the analyzer's connector, so there was no extra length presented
by a PL259 -- even a 1/4-inch of extra length makes a difference.
the coax until the analyzer indicates minimum Z impedance -- this
is where the line is precisely 1/4 wavelength (90 degrees) long,
7.050 mhz, the 84-degree feedline is 90 deg. at 7.554
7.050 mhz, the 71-degree phasing line is 90 deg. at 8.937
recommend using the simple online Christman
calculator to get the correct frequency.
my set up, I'm using ring terminals on each end of the coax lines,
and these only add a tiny bit of extra length to the finished cables.
Using PL-259 connectors would add more length, so take that into
to Europe hasn't been very good lately, but tonight I was hearing
more European countries than I've heard ever before. There is pronounced
front-to-back when switching from NE to SW. The corrected phasing
arrangement has dramatically improved how the array works.
now, I will try out the 40M vertical array in the upcoming 2010
XE RTTY and CQWW WPX RTTY contests.
spring, I may actually take one more attempt at trimming the coax
lines a tiny bit more to allow for the extra length of the connecting
wires inside the phasing box.
vertical wires have been remeasured for resonance at 7.050 Mhz with
the VA1 RF analyzer. They are both exactly 10.127m (33.23 feet)
tall and SWR minimum for each measured at 1.2:1 at the target frequency
-- pretty close to a 50-ohm feedpoint impedance, due to the fact
that the radials slope down from the feedpoint.
both verticals are in place, the system SWR rises to about 1.8:1
to the north, and nearly 2:1 to the south. That's caused by the
expected mutual coupling -- and no doubt some unwanted radial interaction
-- when they're both in the air. The ON4UN's Low Band DXing (Chapter
11-8, part 3.4.2, Fig. 11-7) suggests the common feedpoint impedance
(at the relay) should produce an SWR of 2.3:1 for this array, so
I think I am pretty close, taking into account the sloping radial
book says any suitable matching network could be employed to provide
a good 50-ohm feed. I'm going to just match it at the shack end
with a tuner, and run only low power into this system (a 2:1 SWR
at the relay could burn things with sustained high power, particulary
was taken to arrange the radial wires so none of them overlap. Radials
of one antenna within a few feet of the other antenna's radials
detuned the combined system quite a bit. All radials in this array
slope down from the feedpoints at various angles, depending on where
I've been able to tie off their ends.
need to confirm the length of all the radials, as some broke and
were spliced back together over the past year or two. If a radial
on one of the antennas is significantly off-frequency, that could
explain why SWR is worse in one of the directions. Another explanation:
some radials slope down more than others, which definitely affects
the feedpoint impedance of these elevated antennas (though sloping
radials generally offer the benefit of raising the impedance closer
to 50 ohms).
Recordings of 40M vertical array in action
Northeast -- Here's ES3AX (Estonia) on 7.010 mhz at around
0140z on Feb. 17, 2010. You'll hear him clearly with the 40M array
switched to the Northeast (about 30 degrees) then fade away when
I switch the array to aim Southwest.
Southwest -- This is HK1KRY (Colombia) on 7.010 mhz at
around 0150z. The difference between directions isn't as noticeable
in this one, but it's still prominent.
It starts pointed at EU, then I switch SW (not directly at HK1)
and he comes up quite a bit. He really disappears into the noise
when I switch the array back totoward Europe. You'll hear some fading
on the signal, and I think his bearing is actually on one of the
rear-facing lobes in the cardiod pattern, so he's still fairly strong
at times even off the back quarter.
how the 80M version of this vertical array sounds
A roundup look at the antennas currently in use at the
Wire Vertical Phased Array Project
Simple "from the book" phasing lines, a relay switching
box, and two easy 68' wire verticals with raised radials gives me
a competitive contest signal covering most of the horizon on 80M
Rotatable Dipole Project
Using two fiberglass fishing poles (Crappie poles), some wire and
a few feet of TV twinlead, this linear-loaded dipole is less than
40' from tip to tip, cheap and works well for its size.
Hex Beam Project
Read the construction details for a homebrew hex-style beam. This
is a super performer -- if you want all five upper HF bands, or
don't have the wingspan room for a spider beam or other large-format
Beam Group on Yahoo
A spider beam hot spot. See what other homebrewers
(and spider beam kit builders) are doing to get great signals on
20m, 15m and 10m.
Spider Beam Site
Information about the spider beam from its inventor, Con DF4SA.
See how he has used this outstanding antenna to win CQWW contests
from Portugal. The
spider beam is a serious antenna that, in my opinion, is destined
to be one of the most popular homebrewed tribanders.