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Saturday, September 14, 2013

A 10-Meter Half Square Antenna. Post #227

Over the past few weeks, I've been able to erect several antennas on my wife's property in the Puna District of Hawaii Island.  We are remodeling a small home on an acre of land, so there is plenty of space to plant the "antenna farm."

All of my antennas are wire antennas, since I'm at the age where building and climbing towers is out of the question.  I did enough tower climbing when I worked at a commercial broadcast station.  So, my antennas were made of locally procured pvc pipe, #14 AWG housewire, spare coaxial cable and 450-ohm ladder line, homebrew insulators, and few Budwig center coax connectors from Fair Radio Sales.

Fortunately, there are several tall trees on our property that can serve as antenna supports.

To date, my antenna farm consists of an 80-10 meter flat top horizontal dipole (a doublet with two equal segments of 67 feet/20.42 meters).  The dipole is stretched between two Norfolk Pine trees, 50 feet/15.24 meters above ground.  The antenna is fed by 450-ohm ladder line which is connected to a W9INN 4:1 balun and then onto a Drake MN-4 transmatch.  The antenna does an excellent job with some directivity.

The second antenna is an inverted vee with equal legs of 67 feet/20.42 meters.  The apex of the vee rests on a tree branch 50 feet/15.24 meters above ground.  Like the doublet, 450-ohm ladder line is used to give coverage from 80 to 10 meters.  The inverted vee is a good general multiband antenna.

The third antenna on my "farm" is a 40 meter delta loop suspended from a 33-foot /10.06 meters MFJ telescoping fiberglass mast.  Each segment of the loop measures 47 feet/14.32 meters.  The loop is feed in the lower left corner with 450-ohm ladder line.  This antenna covers 40 through 10 meters very well.  I use the loop for local statewide nets.

My fourth antenna is a 15 meter half square using two vertical elements joined at the top by a 1/2 wavelength horizontal phasing line.  The antenna is bidirectional and gives about 3.8 dBi over my old 15-meter vertical. The half square is fed at the top left portion of the left mast with 50 feet/15.24 meters of RG-8X coaxial cable connected to a Budwig HQ-1 center coaxial connector.

My fifth antenna is a 5/8 wavelength vertical cut for 28.4 MHz in the 10-meter band.  The antenna is a piece of #14 AWG housewire measuring 20.59 feet/6.28 meters secured to a 33-foot/10.06 meters MFJ telescoping fiberglass mast.  The ground system consists of 6 elevated radials measuring 20.59 feet/6.28 meters each.  450-ohm ladder lines serves as the feed line.  The ladder line is used in conjunction with a W9INN 4:1 balun and a Drake MN-4 transmatch.  Although 10-meters has been marginal for the past few days, local coverage on Hawaii Island has been excellent.

The final addition to my "antenna farm" was built yesterday--a 10-meter half square antenna.

Since I was impressed by the performance of my 15-meter half square antenna, I decided to build a similar antenna for 10-meters.

BACKGROUND:

The half square antenna is a two element vertical array fed in phase by a top mounted half wavelength horizontal phasing line.  The vertical elements are insulated from ground.  The antenna can be fed at the top of the left mast where the current is maximum.  This location makes a good match for 50-ohm coaxial cable.  The pattern is bidirectional to the plane of the antenna.  The half square antenna has theoretical gain of more than 3 dBi compared to a vertical antenna for the same band.

MATERIALS:

Two supporting structures for the vertical elements.  I had two extra MFJ masts which I pressed into service.

Wire.  I used a spool of #14 AWG housewire for the horizontal phase line and the vertical elements.  Using the general formula 249/f (MHz) for the vertical sections and 502/f (MHz) for the horizontal phasing line, I came up with 8.76 ft/2.57 meters for each vertical element and 17.67 feet/5.38 meters for the horizontal element.

One Budwig HQ-1 center coaxial connector.

Fifty feet/15.24 meters of RG-8X coaxial cable with UHF connectors.

One Drake MN-4 transmatch to handle the small amount of SWR present on the antenna.

Two 5-foot/1.52 meter wood stakes to support the fiberglass masts.

Basic tools, transceiver (Swan 100-MX), low pass filter, dummy load, microphone, and key (J-38).

ASSEMBLY:

The antenna was assembled on the ground.

The vertical elements were secured to the masts with nylon ties.  A ceramic insulator was attached to the bottom of each vertical element.

The Budwig HQ-1 center coax connector was attached to the antenna, with the - terminal going to the left hand vertical antenna element and the + terminal being connected to the horizontal phasing line.  The remaining wire was run down the right hand mast and secured with nylon ties.  A ceramic insulator was attached to the bottom of the right mast.   Each wire was soldered to its appropriate place on the center coax connector and covered with several layers of vinyl electrical tape.  The RG-8X feed line was then atached to the center coax connector.

Each mast was hoisted onto its appropriate wooden support stake.  The masts were adjusted to give the antenna symetry.

The coaxial feed line was run from the top of the left mast to the shack window panel.  The feed line was connected to the Drake MN-4 transmatch.  Shorter coaxial patch cords connected the transceiver (Swan 100- MX) to the transmatch, low pass filter, and the dummy load.

INITIAL RESULTS:

Thanks to the Drake MN-4 transmatch, the SWR was kept below 1.5 to 1 across the 10-meter band.  Running approximately 25 watts from the old Swan 100-MX, I was able to get a few cw and ssb contacts. Although band conditions were not favorable, I was able to establish contacts with both Hawaii Island and mainland U.S. stations.  The antenna should perform well once the band opens up.

This was an enjoyable project.  Best of all, I didn't need an extensive ground system and my building costs were low.  Try a half square antenna...you might be surprised just how good it works.

REFERENCES:

http://www.antennasby n6lf.com/2005/04/halfsquareante.html.
http://va7st.ca/array40.htm.
http://antenna-magic.com/antenna/ant_magi.htm.
http://www.hamuniverse.com/wb3aywcurtainantenna.
"The N4GG Array".  (ars.nc4fb.org/antenna-articles/n4ggl.pdf.)

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Thanks for joining us today!

Aloha es 73 de Russ (KH6JRM).

BK29jx15--along the beautiful Hamakua Coast of Hawaii Island.