METER 4-SQUARE PROJECT
Several years back, I started looking at various directive arrays
for 160 meters. Computer analysis of various configurations didn't
match unsolicited reports from users. On-the-air observations also
showed a great variation in practical results. In order to sort this
all out, I started building "scale models" of these various
configurations. I chose 40 and 30 as practical bands to build and test
these arrays since that size would fit in the yard space I had
available at the time.
Quite a few of the common 4-square variations were built and tried
including the sloping dipoles, dipoles folded back to the support base,
1/4 wave wires sloped from the top of the structure, 1/4 wave wires
bent, elevated radial systems, radials laying on top of the grass, and
buried radials. As well as the physical variations, I tried different
methods of phasing.
The one thing that was common to all the models built and tested was
that the performance was sensitive to the radial configuration. After
much test and measurement it was found that elevated radials could
cause unpredictable variations in the element phasing. With 4 or less
radials, the pattern could be skewed so much that the array was
unusable. I did find that more radials (8 or more) on each element
reduced this sensitivity dramatically. Also physical symmetry of the
radial wire was very necessary. Some of the problem was traced to the
radials of one element coupling to radials of another element in
an unpredictable manner. They would also couple to surrounding objects.
In an antenna dense environment like I had this was an unworkable
To make a long story short, I wound up with buried radials producing
measured results which closely tracked computer models.
A permanent working 40 meter system was then constructed using the
experimental results as a guideline. The phasing system chosen was the
parasitic method. This is essentially identical to the phase sloping
dipoles that have been described in the ARRL Handbook and Antenna Book
for many years. This system will not give quite the forward gain or as
good F/B as the hard phased system but it has several advantages over
the usual phasing method. First of all it is simple. Four relays and
you are done! The lines to each element are cut for about 135°
electrical length and the "front" element is relay selected and fed
directly. The thing is 50 ohms and as broad as 40 meters is wide.
Another interesting feature is that you are not required to have 1/4
wave spacing between each of the 4 elements. 0.2 wavelength spacing is
great and the actual spacing is not critical as long as all four are
the same. Additionally, you can add more elements to give more
switchable directions. Just add additional relays and elements. The
forward gain goes up a little bit as you add elements but it is not
significant. A four element version spaced at 0.21 wavelength was used
for several years at the old AZ QTH before it was disassembled for the
move to WA. On-th-air A/B testing showed it to be consistently 6-8 dB
better that the two element yagi at 80 feet that I had at the time. Of
course, part of that was due to the exceptionally high conductivity
earth I had at that QTH.
This is a photo of the control box. The fifth relay switches in a
matching network for 30 meters. The 40 meter version works very well on
30 if you just match it! You can see that there is not much to it. No
complex networks to adjust. this is just the ticket for those who are
challenged by phasing networks.
After moving to WA, the array was re-assembled using 1/4 wave spacing
since I had more space available. After running the array for two
seasons, I decided to try phasing it by using the traditional 0/90/180
forced feed system. The method used was the Lewellen system and was
designed using the information in ON4UN's fourth edition of "Low-band
DX'ing". The array was computer modeled and the phasing box was
assembled and pre-tuned on the bench for the predicted component
values. It was then connected to the array and the tuning was touched
up using an oscilloscope to verify phase and amplitude.
Here is a photo of the phasing box in place. As you can see, it is very
much more complicated than the parasitic box.
In the above photo you can see the scope probes in place for the
alignment operation. The phasing lines out to the individual elements
are an electrical 1/4 wave. 75 ohm coax works best for this system and
common RG11 has a velocity factor that makes the lines too short to
reach the center! I used a good quality TV cable (Belden 9116) RG6
type. This cable is very low loss and will easily handle well over 1500
watts when used in this application. The only real problem is
connecting to the cable. It has an aluminum shield so you can't solder
to it. I solved the problem by obtaining a high quality brass body F
connector and soldering a shield pig tail to it. I WX-proofed it by
coating the open end with common black ABS pipe cement. The network is
built on a piece of salvaged aluminum and enclosed in a cheap plastic
food container. These containers work OK as long as you spray paint
them to prevent degradation caused by sunlight. There are small holes
in each of the four corners to let condensation out. The holes where
the cables enter the box are sealed with "duct seal" after all the
alignment is done.
Here's the setup for alignment:
The scope is a Tek 7603. RF was supplied by my old trusty FT301 at a
low power output. There is a fifth 4x4 pole in the center of the array
because I wanted to be able to add a fifth element in the center at a
later date if I wanted to without tearing up the radial system.
Here is the element feed point:
There are about 65 1/4 wave long radials under each element. I didn't
bury them, but I hope eventually they will be covered by grass (and
The element support structure:
Each element is supported by a pressure treated 4x4 cemented into the
earth. The holes were about 27 inches deep. No insulators are
necessary. The element itself is fabricated from steel tubing, tapered
buggy whip style, and the joints welded. Several coats of Rustoleum
keep the corrosion in check. This method of fabrication results in a
very strong element at a fraction of the cost of using aluminum. Also
no guy lines to get in the way of the mower!
And finally, the whole array:
Preliminary results compared to the original parasitic system indicate
a better F/B as expected on RX. The overall signal to noise ratio
didn't seem to improve much, as was expected, because of the wide beam
width and the fact that the parasitic system was adequate to begin
with. Forward gain is supposed to be about 1.5 dB better, but that's
pretty hard to judge on the air. At least it's no worse than it was
before! Now that I have the concept verified and am experienced in the
phasing method, I'll have to start working on the 160 model!