Sunday, February 23, 2014

Simple Ham Radio Antennas: The 10 meter 1/2 wavelength sloper. Post #262

The sloping 1/2 wavelength dipole is one of my favorite antennas.  "Slopers" are good antennas for restricted space areas.  They are simple to build, inexpensive, and exhibit some directivity in the your chosen direction.

According to VK6YSF, VE2DPE, and other amateur radio operators, a properly designed 1/2 wavelength sloper radiates energy at low angles relative to the horizon with vertical polarization.  Slopers don't require a ground radial system and can be fed with a good grade of 50 ohm coaxial cable.  A sloper antenna only requires one tall support (tree, mast, edge of a roof, etc.) and occupies less space that a 1/2 wavelength horizontal dipole.

So, let's build one of these simple, effective antennas for the 10 meter band, centering on 28.4 MHz--right in the middle of the techncian class phone band.

MATERIALS:

One tall support.  In my case, I used a 33-ft/10.06 meter MFJ telescoping fiberglass mast..

One 5-ft/1.52 meter wooden stake to support the fiberglass mast.

One 6-ft/1.82 meter wood stake to tie off the sloper.

Two ceramic insulators, one for the upper portion of the sloper and the other for the bottom portion of the sloper.

One coaxial cable center connector.  I had a spare Budwig HQ-1 center connector in the junk box.  You could also make a center connector from wood, plastic,or another ceramic insulator.

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

Basic tools, including a soldering gun/iron, pliers, wire cutters, vinyl electrical tape.

A length of #14 AWG house wire for the two antenna elements.  Using the general dipole formula of 468/f (MHz)=L(ft) and a working frequency of 28.4 MHz, I cut a piece of wire measuring 16.47 ft/5.02 meters.
This length was cut in half to get each dipole segment.  Each segment then measured 8.23 ft/2.51 meters.

Several 3-ft/0.91 pieces of RG-8X coaxial cable to interconnect shack equipment (rig, low pass filter, dummy load) to the Drake MN-4 antenna transmatch.

Fifty-feet/15.24 meters of dacron rope to tie off the sloper to a nearby wooden stake.  I wouldn't need all of the rope for this antenna, but I decided to use what I needed and coiled up the rest  for use in future sloper antenna projects.



ASSEMBLY:

The antenna was made in the garage and then taken outside to be strung from the fiberglass mast.  Prior to making the antenna, the fiberglass mast was positioned on the ground.

I attached a ceramic insulator to each segment.  The insulator on the lower element would be attached to the wooden support stake by dacron rope.  As mentioned above, the rope length would be kept intact for other sloper projects.

I attached the upper segment of the sloper element to the + side of the Budwig center connector and attached the lower segment to the - side of the Budwig center connector.  All connections were soldered and wrapped with several layers of vinyl electrical tape.

Before I attached the RG-8X coaxial cable, I wound a "choke balun" consisting of 6 turns of the cable measuring approximately 8 inches/20.32 cm in diameter.  The balun was secured by vinyl electrical tape.  I then attached the RG-8X coaxial cable to the center coax connector.  After that, I attached the upper end of the top segment to a ceramic insulator.

Once outside, I attached the upper ceramic insulator to the top of the mast with short pieces of dacron rope.
I then tied some dacron rope to the ceramic insulator at the bottom of the lower antenna segment.

I slowly raised the mast and slipped it over the wooden support stake.

The lower end of the sloper was tied to a 5-ft/1.52 meter wooden stake approximately 30 ft/9.14 meters from the base of the mast.  The RG-8X feed line was run from the sloper at a right angle and secured to the base of the fiberglass mast with nylon ties.

I ran the RG-8X coaxial cable through the shack window and into the Drake MN-4 antenna transmatch. The Ten-Tec Argosy II transceiver, a low pass filter, and the old Heathkit Dummy Load were connected to the transmatch by short pieces of RG-8X patch cable.

INITIAL RESULTS:

Without the Drake MN-4 in the system, the swr measured 1.6 to 1 between 28.3 MHz and 28.5 MHz. With the transmatch in the system, I was able to get a swr of 1.1 to 1 on those frequencies. I was also able to use the lower portion of the band for cw if I adjusted the Drake MN-4 to compensate for the small mismatch between the transceiver and the antenna.

Although 10 meters is a bit uncertain at times, I was able to get some excellent contacts in California, Oregon, and Washington State on 28.4 MHz between 1100 to 1600 local time (2100 to 0200 UTC).  My ssb reports ranged from 53 to 57.  Not terribly outstanding, but usable.  I didn't note much directivity in the antenna when I shifted position of the sloper by moving the wooden support stake.  I may have gained a single "s" unit when I pointed the sloper toward the U.S. mainland.

This was a fun project.

REFERENCES:

http://www.dxzone.com/catalog/Antennas/sloper/.

http://www.dxzone/cgi-bin/dir/jump2.cgi?ID=27575.

ARRL Antenna Book, 18th Edition.

http://hamradiosecrets.com/ham-radio-hf-antenna.html..

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Aloha de Russ (KH6JRM).
BK29jx15--along the beautiful Hamakua Coast of Hawaii Island.
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