THE 15-METER HALF-WAVE SLOPER ANTENNA
Another easy to build antenna for the 15-meter amateur band is the half-wave sloper. According to Ed Noll, W3FQJ, a sloper antenna “is a slanted half-wave antenna with one end of the antenna attached to mast top and the other end near to ground level.” The antenna displays some directivity in the area of the slope and “displays considerably less signal pickup from its rear.” With additional ground stakes, you can turn the sloper into your favored DX direction and reduce QRM from the opposite direction. At my QTH, I’ve driven three wooden stakes into the ground for easy directivity changeover. Depending on the inventory in your “junk” box, this antenna can be built without much cost to you. If you need wire or pvc pipe, check with your nearest hardware store or home improvement outlet.
A tall support, such as a tree or mast at least 30-feet tall (9.14 meters). I used an old 33-foot (10.06 meters) MFJ fiberglass mast to support the upper end of the sloper.
Two dipole elements cut to frequency. I chose 21.150 MHz for my 15-meter frequency. Each dipole element was cut according to the formula 468/f (MHz). Each element was 11-feet, 1-inch long (3.38 meters). I used #14 AWG housewire for this project. If you will be using this sloper for an extended period of time (over a year), I would recommend a good grade of Copperweld from Davis RF. Although copperweld is a bit hard to handle (it’s very “springy”), it resists environmental conditions fairly well.
Two ceramic or plastic insulators to tie off each end of the sloper. One insulator for the upper element; the other for the lower element.
Three to four wooden ground stakes for the lower end of the sloper. You can change directivity of the sloper by moving the lower antenna element to a different stake.
Wooden stake to support the pvc or fiberglass mast. Nylon ties and dacron rope if necessary to secure the mast.
Installed anti-static and ground system between the coaxial feedline and your radio room.
Assembly is straightforward. I built the antenna on the ground before I hoisted the mast onto its support stake. I attached the upper element to the + side of the Budwig dipole-to coaxial center connector. The lower element was attached to the – terminal of the coaxial center connector. The top element was secured to the tip of the mast with a ceramic insulator; the bottom element was secured to a ceramic insulator and a 5-foot (1.52 meter) wooden stake. All connections were soldered, coated with clear nail polished, and wrapped with several layers of vinyl electrical tape.
Before I attached the 50-ohm coaxial feedline to the center connector, I wound an 12- inch diameter (.30 meter) “choke balun” out of the feedline and attached the balun and feedline to the center connector. The balun should keep rf off the coaxial cable shield and reduce rf problems in your shack.
When all connections were soldered and protected from the elements, I raised the mast onto its wooden stake. I led the coax at a 90-degree angle away from the center connector. I attached the feedline to the static discharge system and used a short piece of RG-8X to connect the antenna system to my trusty Drake tuner (MN-4). Smaller pieces of coax connected the tuner and the dummy load to my Swan 100-MX.
The antenna has performed very well over the past few days. The SWR without using the Drake tuner was 1.7 to 1. I suspect a bit of trimming will be in order to bring this figure down below 1.5 to 1. For now, I’ll use the tuner to handle the small mismatch in the antenna system. Reports during the afternoon hours have been fair to good, with SSB contacts ranging from 54 to 58 and CW QSOs varying between 569 to 589. Not too bad for 20 watts output. The sloper exhibits some directivity when I shift the lower element to another stake.
If you have sufficient space in your backyard, you may find this sloper ideal for your 15-meter activity. It’s cheap, easy to build, and inconspicuous.
Edward M. Noll, W3FQJ. Easy-Up Antennas for Radio Listeners and Hams. Limited Edition, 1991. MFJ Enterprises, Inc., page 110.
N4UJW Antenna Design Lab. http://www.hamuniverse.com/antennas.html.
Amateur Antenna Projects. http:www.ac6v.com/antprojects.htm.
And for the ambitious antenna builder:
A Reduced Size Half Sloper for 160 Meters. Don Kirk, WD8DSB. Reprinted by http://www.iw5edi.com/ham-radio/files/160Half-Sloper-Antenna.pdf.
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Until next time,
Aloha es 73 de Russ, KH6JRM–BK29jx15–along the beautiful Hamakua Coast of Hawaii Island.