It is appropriate to point out that I knew absolutely nothing about 4 Squares going into this! I knew nothing about phased verticals when I built the phased pair the year before, I studied and learned how to get them to work, so I figured should be able to get the new antenna to work.
This is an antenna that started out as a 2 element phased array, and grew up to be a 4 square in the Summer 2000 station rebuild. The element material came from the tops of W7CY's old 80M 4 square that was built on top of Hy-Towers, thanks Rod! On top of Rod's pieces are elements taken from a KLM 5 EL 20M beam in my pile.
The array is fed by a Comtek Systems ACB-40 Hybrid Coupler (thanks to Jim, K4SQR, for all the help! That's how I learned how to make it work, and the comments of many on the Towertalk reflector). The array has 240 ground mounted radials that are tied into the 80M shunt fed tower radial system, for a total of 300 interconnected radials. What the heck, it's only some free wire (from "Elmer's shed) , my recreational time. The beer was the most expensive part of the ground plane!
It took me about a month to build this antenna. Two weeks to design and build (and rebuild) the elements, get the thing layed out and bases installed (the two existing bases had to be dug up and moved). Two weeks to install the ground plane. All of it part time, evenings after work and weekends. I can readily understand why many would not want to hassle with so many radials, and opt for an elevated radial approach. I knew that this would be my only decent 40 meter antenna, for now, and had the wire and the low traffic space, so I chose to do the minimum recommended "wires on the ground" thing.
I'm very happy I did, it was a fun project and it is a very nice antenna, for someone who can't put a beam up high! No waiting for the rotator to come about, and put the other antennas connected to it in the wrong direction. It definitely delivers the performance to be expected from a 4 square.
Element Base Detail
The base of the elements are attached to 4" x 4" posts with some custom built brackets. One plate is clamped to the post with rectangular u-bolts. Another plate is attached to the base element tube with muffler clamps. The plates have 3/8" dia holes for bolting the element plate to the post plate. Removing the single bolt from the top
bracket allows the element to be rotated down to the ground. The mounting geometry was designed to allow the element to swing down to the ground, while not fouling against the post and allowing the feed jumper to gently swing without kinking or getting caught on anything.
I toyed with the notion that all the elements should be at the same elevation, borrowed a transit from work and figured out that doing so would be a big headache, and put them all the same height above the sloping terrain. I cannot discern any poor performance due to it.
The feedline from the Comtek box has a home made current balun near the element connection, which is made through the coax's PL259 into a chassis mount female mounted on a small bracket screwed to the post. A #12 Flexweave jumper connects to the base of the element with a crimped and soldered lug onto a 10-24 SS stud. The bracket that holds the coax connector has several holes with 10-24 SS studs for connecting the radials via crimped & soldered lugs. There is a ground rod at the base of each element, connected to the radials. I did this to facilitate putting some RF chokes from the elements to ground to bleed off static charges. I have yet to mount these, I had them on the previous phased pair.
There are 60 #18-#20 insulated radials for each element. Some are not visible in the photo due to the color of their insulation. The 4 sets of radials are joined along their intersecting lines by soldered connections to 2 #10 bare solid copper wires that bisect the elements. These bus wires are held at their ends by small rebar stakes to keep them in place. The outer ends of the radial wires are held in place with 6" long galvanized "box nails".
Click on Image for large view
I had to "weed whack" the entire area before installing the radials (same for the 80M system), total of one entire day of thrashing last years growth (did it the previous year for the phased pair). I did not try to bury them as it is very difficult to make grooves in the sandy soil that don't just immediately fill back in. That would have taken forever, and I was running out of time to get everything done before the Fall 2000 season. My experience with the previous pair told me they will get covered quite a bit by natural wild grass and stuff that blows up out of the the valley. I trip over them every once in a while and jerk a nail out of "the beach", say a few choice words, and just fix them and get on with it. I can't wait for nature to have its way with them! Maybe, I'll get bored next summer and buy a case of beer and bury them!
The posts are pressure treated Fir. I added two coats of Thompson's Water Seal to them before they went into the ground, holes are 18" deep with a sack of post mix in each hole. The electrical connections were all made with new clean parts and all were coated with a light film of Dow Corning - High Vacuum Silicone Grease.
The connections were then wiped off and covered with 2 coats of Liquid Electrical Tape.
The soldered radial connections to the bus wires were also coated with Liquid Electrical Tape.
The connections between the element tubing sections were cleaned with Scotchbrite, coated with thin film of silicone grease which was worked into the surface with a small piece of Scotchbrite, then assembled. Having water run down into the joints is a real problem for tapered tubing verticals, so I cleaned the adjacent joint surfaces with lacquer thinner and sealed them with Scotch 33 tape. Then, I painted the elements except for the tip section where it would be tuned.
Finally, the areas of the posts where water might run down them, and short the element mounting brackets to the RF connection brackets, were coated with roofing tar. The element brackets are mounted on the opposite side of the posts from the RF connections, so only the element bracket u-bolts are above the RF brackets.
I have had no problems with this antenna due to rain or snow. The bottom of the elements are ~8" off the ground, and I pay attention to how much snow has fallen, and go out and dig them out when it is necessary, only once this year.
Tuning the Antenna
From my previous experience with the two element phased pair of verticals, I knew that it was pretty pointless to try tuning anything until a substantial part of the ground system was installed. I had done the mechanical element design using the material available with YagiStress, assembled and painted the elements and had them ready to go. I layed the feed and dumped power cable runs in a shallow trench to the center of the antenna and mounted the Comtek box.
Then, installed the entire radial field. Next, all of the elements were installed and the brackets adjusted to fit and work properly, and the element guy stakes were layed out and put in place, the 3/32" Dacron guy lines were installed and cut to length. Essentially, everything was done except for the tuning.
I layed all but one element down to decouple them from the element to be tuned and plugged my Autek RF-1 into the coax connector on the post and dialed each element by itself to resonate at 7.010 Mhz. I picked this frequency by finding out from Comtek that the resonant frequency of the 4 elements together is about 80 Khz higher than the single element resonant frequency. I'm a CW fan, so 7.090 sounded ok to me. The element swr curves were fairly broad, so I did my best to get them all in the 7.000-7.020 range.
Then I put them all up, and took a look at the the input terminal to the hybrid coupler, it looked like 1.5:1 and pretty flat, so I connected the feed and dumped power coax cables and checked it with the transciever in the shack. 1.5:1 and real flat, resonant somewhere around 7.100, "I hope this is ok?" I checked the dumped power and that was 1.5-2 watts with 100 watts going in, "That looks good!" Listened around, it was daytime, but I heard the same signals I could hear with the inverted vee, couldn't tell much about the pattern, as all were high angle relatively local type stuff. Switching directions did make a difference, but it didn't make sense, it seemed that the directions were crossed up. I checked the manual and what I had done. Seemed ok. After listening that night to some DX stations, I was sure the directions were not correct. The next day, I figured out that I had trouble sorting out the manual instructions and did have the feedlines between the box and the elements wrong. I fixed that and the array started working like the direction switch indicated.
That's the end of the tuning story, done! I never changed the elements after the initial tune. I dropped them, sealed and painted them, put them back up, tuned up the guys applied the roofing tar to the base pieces, and the job was done.
Designing the 4 Square Elements
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This was a very interesting experience. The array's swr was pretty flat, below 2:1 from 7.0 to 7.25, and I wondered if it was really right. The amount of power dumped to the dummy load was real low, indicating that it was working properly. The front-to-rear checks provided a wide variety of results. On signals originating from west coast to midwest stations, the F/R ranged from non-existent to fairly decent, 10-20 db. On east coast and dx stations, the results were very encouraging, regularly being 20-30 db, as close as one can call that with an S-Meter, and many signals went from completely undetectable to very copiable with antenna direction changes.
For the first time, at this qth, I was able to detect the different directions of 40 meter noise sources. During the late summer months, the noise from the SE would regularly register S-7 to S-9, coinciding with stateside and sub tropical lightning activity. At the same time, directing the array toward the pacific, I would see S-0 to S2 noise levels.
Later into the Fall season, the SE lightning activity subsided and I was able to hear intermittent residential and power co. noise from the other directions. At this point, I was very sure the array's pattern was as suggested by the antenna models, something like 20-30 db of F/R. Noise and signals in the S-7 to S-9 range in one direction changed to S-0 to S-2 when the array was redirected.
This doesn't always coincide with things one is trying to hear, due to the noise source, but many times is phenominal for being able to hear certain signals.
This type of antenna is known not to be a necessarily high gain antenna, compared to other options, but its real value lies in its exceptional pattern, which by virtue of its noise and unwanted signal rejection, can make the signals it is directed at copiable.
The antennas used for comparison in these evaluations were the 40M inverted vees. The 4 square is almost always better on signal strength and noise rejection. The only time it is not, is when the signal is from a source in the local region. The low inverted vees can be 20-30 db louder than the 4 square on some west coast signals, so they are still around for domestic contests.
I have regular schedules with my Dad, near San Diego, on 40 phone, and find that the 4 square is almost always better, because it knocks out the EU broadcast and east coast qrm, when pointed SE. We have found that the inverted vees are better sometimes, but only a very small portion of the time.