Saturday, February 8, 2014

Simple Ham Radio Antennas: A Low HF Band Triangle. Post #259

Over the past few years, I've built a variety of HF antennas for my amateur radio station.  All of my verticals, inverted vees, dipoles, and loops have been a learning experience, especially when I've been faced with limited resources and space.  Operating from an apartment or a home governed by CC&Rs and HOAs has been a challenge.

Now that I'm slowly moving into a full acre of space in the rural Puna District of Hawaii Island, my space restrictions are gone and there are no committees to oversee my antenna activities.  I count this as a definite blessing.  For the first time in many years, I can build full sized dipoles, verticals with a decent ground system, and large full-wave loop antennas without interference.  Since my new property is surrounded by tall trees approaching 50 feet/15.24 meters, my antennas are well shielded from prying eyes.  When I operate out of my rental home in Laupahoehoe, I'm still hemmed in by utility poles and neighbors.  My antenna efforts at that place are generally stealthy and largely out of sight.

Last Saturday (01 February 2014), I decided to erect another loop antenna in the backyard facing Highway 130, the road running from Hilo to Pahoa.  I prefer full-wavelength loops because they are easy to make, don't require a ground radial system, exhibit some gain over a dipole, and can be fed with either coaxial cable through a quarter-wavelength matching section or 450 ohm ladder line.  The coaxial cable-fed system works best on one band, although other frequencies can be used if an antenna transmatch is inserted into the system.  Multi band coverage is possible with ladder line, a 4:1 balun, and an antenna transmatch.

For this antenna, I decided to use 450 ohm ladder line in conjunction with a 4:1 balun and an antenna transmatch.  The antenna would be used on all amateur radio frequencies between 40 and 10 meters.

I patterned the loop antenna after a design described by Edward M. Noll (W3FQJ) in his book "73 Vertical, Beam, and Triangle Antennas."  Noll called his loop "A Low Band Triangle Antenna."

MATERIALS:

The first item in the construction process was to determine the length of wire required, the type of support needed, and the lengths of 50 ohm coaxial cable and 450 ohm ladder necessary to connect the "Triangle Antenna" to my shack equipment.

Rather than use the standard formula of 1005/f(MHz)=L(ft), I used Noll's recommended formula of 984/f(MHz)=L(ft).  When I used the first formula, my antennas proved to be a bit long and I had to trim excess wire to bring the antenna to resonance and low swr.

Using the latter formula and a design frequency of 7.088 MHz (the frequency of the daily Hawaii Afternoon Net), the total length of wire needed worked out to be 138.82 ft (138 feet, 9.8 inches/42.32 meters.)  The only wire I had in the shack was 150 ft/45.73 meters of Radio Shack AWG #18 gauge speaker wire.  If I split the wire apart, I would have more than enough wire for the triangle antenna.

Three ceramic insulators, one for the apex of the triange at the top of the mast and two for supporting the bottom portion of the antenna.

Six, 6-ft/1.82 meters wooden stakes, one to support the mast, two to support the bottom ends of the triangle antenna, and three to support the ladder line off the ground as it ran to the 4:1 balun and the shack.

One 33-ft/10.06 meters MFJ telescoping fiberglass mast.

One W9INN 4:1 balun.

Fifty-feet/15.24 meters of 450 ohm ladder line and a "ladder lock" device to attach the ladder line to the bottom section of the triangle antenna.

Twenty-five feet/7.62 meters of RG-8X coaxial cable with UHF connectors.

Several 3-ft/0.91 meters lengths of RG-8X coaxial cable to interconnect the transceiver (Ten Tec Argonaut II) with the MFJ-941-E Versa Tuner II, the Heathkit Dummy Load, and a low pass filter.

Various tools, including a soldering gun, tape, wire cutters, dacron rope, pliers, and screwdrivers.

ASSEMBLY:

The triangle antenna was built on the ground.

I arranged the antenna in a general equilateral configuration measuring 46.27 feet (46 feet, 3.24 inches)/14.106 meters on a side.  I threaded the speaker wire through each ceramic insulator, leaving a space open midway through the bottom portion of the triangle antenna.

I attached the 450 ohm ladder line to the "ladder lock" center connector and soldered the free ends of the antenna to their respective leads on the ladder line.  The connections were covered by serveral layers of vinyl electrical tape.

At the connection point, I hammered in a 6-ft/1.82 meter wooden stake to support the antenna/feed line connection.  I also drove in a support stake for the fiberglass mast and the two support stakes which tied off the bottom portion of the triangle antenna.  Small lengths of dacron rope were used to secure the ceramic insulators to the support stakes.

Two remaining wooden stakes were driven into the ground approximately 15-ft/4.57 meters apart.  These stakes would support the ladder line off the ground until it reached the 4:1 balun attached to the garage wall.


I attached the apex of the triangle antenna to the tip of the 33-ft/10.06 meter fiberglass mast and slowly hoisted the mast onto its support stake.

I adjusted the antenna to a uniform, balanced shape and led the ladder line to its remaining support stakes.
I ran the ladder line to the first and second support

At the final support stake, the ladder line was run to the 4:1 balun attached to the garage wall (approximately 8-ft/2.43 meters above ground).

I attached 25-ft/7.62 meters of RG-8X coaxial cable to the 4:1 balun and ran the coax through a patch panel into the shack.  The coax was attached to the MFJ-941 Versa II antenna transmatch.  Small lengths of RG-8X coaxial cable were used to interconnect the rest of the shack equipment--the Ten Tec Argosy II, the low pass filter, and the Heathkit Dummy Load.  I have several other rigs in the shack, but the Ten Tec Argosy II was the only rig capable of using 30 meters.  Same goes for the trusty Drake MN-4 antenna transmatch.

PRELIMINARY RESULTS:

With the Versa Tuner II in the line, I was able to cover 40, 30, 20, 15, and 10 meters with swr readings below 1.5 to 1.  Using 10 to 20 watts from the old Ten Tec Argosy II, I was able to make excellent contacts throughout the state of Hawaii, on the U.S. mainland, and throughout the South Pacific.  CW reports ranged from 559 to 599 and SSB varied between 54 and 59.  For now, this "Low Band Triangle Antenna" works well and has provided hours of enjoyable contacts.  Try a loop antenna.  It's cheap, easy to build, and provides both local and DX coverage.  Have fun!

REFERENCES:

Noll, Edward M. (W3FQJ).  73 Vertical, Beam, and Triangle Antennas.  Editors and Engineers.  Indianapolis, IN, 46268.  Seventh Printing, 1979. pp. 126-127.

http:/www.w5sde.net/delta_loop_for_hf.htm.

http://www.hamuniverse.com/kl7jrloopnotes.html.

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Aloha es 73 de Russ (KH6JRM).

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


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