Friday, November 16, 2012

The half square is

The half square is

My property has a lot of trees, oops! Antenna supports!

The half square is, in my opinion, the best and easiest antenna to put up and keep up. According to the books it supposedly has a bidirectional pattern. I find it is a vertical omnidirectional antenna with some gain because of the top feed wire and in some directions is better in my opinion.

The horizontal wire on top is a feed line for the vertical element on the other end. The coax by the first element, "feed point" needs to be at about a 45 degree angle or more to the vertical element for a low VSWR at the operating frequency.

The antenna is built using #12 or #14 stranded, black electrical wire with the insulation left on except at the far corner away from the coax where it is necessary to bare it, to wind and solder the corner loop in place. The loop must be soldered, so it will not slide on the element wire; thus keeping the
measurement correct at the corner. Some articles on the internet and books say to use a balun at the feed point, but I have not found this to be necessary in any of my designs.

I use a Budwig center insulator at the feed point myself. I am not saying they are the best I have seen on the market, but this is my preference here as I use them over and over again.

For 40 meters this antenna design will work on 15 meters as is, with no antenna tuner. It will work with an antenna tuner for other bands including 80, 10, 20, 60 etc. meters, since it uses no tuning network at the feed point. An 80 meter version laid sideways about 20 feet high will also resonate on 160 with no tuner.

I have a friend who is in a deed restricted area and has had a 20 meter half square up for over a year now and I have not heard that it has been spotted yet. It uses #22 wire with insulation the same color as the house and is hard to spot at 40 feet from the street.

I use half squares for all bands that I use here in northeastern Georgia. I have a 40 meter half square antenna over my driveway now for about a year and have had no complaints from my XYL.

The double half square is a version that has a little more sideways directionality to it if the three elements are not tapered as if it would be in a beam configuration. The bobtail antenna is basically the same except it is fed at the center element, not at the end corner. The radiating pattern is similar
to the half square, mostly omnidirectional.

If the end elements are set a little shorter "an inch or two", it should have an elongated radiating pattern to it, but the frequency will go higher when tuned.

This antenna needs three mounting points instead of two and will be harder to keep up in a high wind environment, which is why I prefer the half square antenna design.

I put it up leaving the support ropes hang down with the weight of the antenna sagging some. This leaves the antenna go up and down with the wind on the trees so the ropes and antenna do not break.

If you do not have the height for a quarter wave this curtain design can be end loaded to shorten the elements and put up at a lower height than a quarter wave would be; just keep the bottom of the wires above head height for safety. Gain will not be affected much as the radiation is from the top of the vertical wires. Do not load the top wire as it is a 1/2 wave feed line, not a radiator.

I use a compound bow and a fiberglass arrow to shoot a # 20 to #30 pound monofilament line over a tree limb, then tie a rope to the line and pull the rope back over. I then tie the two rope ends together as a loop, and tie the antenna to the rope. I pull the antenna up and tie the rope off to the tree or
another tree near it.

NEVER EVER leave the ground to put up an antenna in a tree! ! It is not safe no matter how high you climb or how big the limbs are! !

These antenna designs are similar, easy and cheap to build.

Material list for a 40 meter half square:

Two trees at least 70 feet apart and about 40 feet tall, or higher.
0ne center insulator
One piece of # 12 or 14 stranded wire with black insulation 40 feet long.
The black insulation will fade to a blackish gray over time; it is not uv protected.
One piece of # 12 or 14 stranded wire with black insulation 120 feet long.
One piece of #14 solid wire with no insulation about one foot long.
Solder for corner loop wire attachment after wrapping on long wire at the correct point. Support point!
Two pieces of rope, one to support antenna at the insulator end and at the other corner where the foot long wire was wrapped with the loop at the 534/F point.
The two wire element ends can just hang as is, in the air above head height when installed.
Do not tie them down; a small weight can be added if necessary, but not required!
Use a good coax. I use RG8x that has an all copper center and braid.
The cheap coax is asking for trouble!

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