Saturday, January 25, 2014

Simple Ham Radio Antennas: Antennas without tuners, part 4. Post #257

So far, the "tunerless" antennas I've built have worked very well.  They have been made with locally available materials from my "junk" box, neighborhood garage sales, and the nearby Ace Hardware Store.  These antennas have consisted of individual dipoles/inverted vees for my bands of preference (40, 20, 15, 10 meters), telescoping fiberglass masts (33-ft/10.06 meters tall), a single RG-8X coaxial feed line, and supporting wooden stakes or tree branches.

Dipoles for each band were built on the ground and were later hoisted into position via a halyard and pulley system.  A "choke balun" made from part of the RG-8X feed line was attached to the mast just below the center connector at the top of the mast.

In my first multiband antenna system, I changed bands by lowering and raising the appropriate antenna into place.  I couldn't change bands by staying in the shack.

My second system was a modified "fan dipole/inverted vee" using multiple dipoles/inverted vees connected to a common connection point at the apex of the mast.  The dipole/inverted vee elements were "fanned" out below the lowest frequency dipole/inverted vee (40 meters).  The 40 meter 1/2 wavelength dipole was nearly horizontal, with subsequent bands run off at an angle below the common connection point.

The third variant of the coax-fed multiband antenna without a "tuner" was a segmented inverted vee, with the main 40 meter elements connected to 20 meter "outrigger" elements by means of clip leads.  The 40 meter segments were cut for the cw portion of the band, allowing for phone (ssb) operation in the upper portion of the 15 meter (21 MHz) band.  The 15 meter antenna would operate on the third harmonic of 40 meters. With the "outrigger" elements connected to the 40 meter elements, the antenna would function as a 3/2 wavelength antenna on 20 meters.  If I wanted to change bands, all I had to do was connect/disconnect the appropriate leads.

Now, for the next phase of the "tuner less" antenna. These next two antennas use both 450 ohm ladder line and 50 ohm coaxial antenna to create a multiband antenna.  Is it possible to do without a "tuner" and still retain the ladder line as a feed line?  Yes, if certain precautions are taken.

Back in 1992, Bill Wright (G0FAH) faced such a problem.  According to Bill, a modified G5RV antenna served as the inspiration for his "tuner less" ladder line/coaxial cable feed system.  I decided to duplicate his efforts at my new homesite in the Puna District.  I found the antenna was useful from 40 through 10 meters, with 40 meter swr measuring 2.4 to 1; 20 meter swr reading 1.5 to 1; and 10 meter swr reaching 2.4 to 1. Bill also had data for 17 and 12 meters, where swrs ranged from 2 to 1 for 18.1 MHz and 1.5 to 1 for 24.9 MHz.  I didn't test these frequencies because my older equipment didn't cover those bands.  I found an antenna transmatch was needed to work 15 and 30 meters.  In essence, I had an antenna which did well on 40, 20, and 10 meters.

I used an inverted vee for this antenna configuration, since suitable trees were not available for this antenna. As with my past antennas, I used several wooden stakes to support the fiberglass mast and to serve as tie off points for the antenna elements.  I managed to find several end insulators, some extra 450 ohm ladder line, an old 1:1 balun, and a good supply of #14 AWG house wire for the antenna elements.

As usual, I built the antenna on the ground and hoisted the inverted vee into position with a halyard and pulley system.

According to Bill here are the general dimensions of the antenna:

94-ft/28.65 meters of #14 AWG wire.  Each element was divided into two equal sections of 47 -ft/14.329 meters.  Ceramic insulators were connected to the end of each element.  A third ceramic insulator would serve as the center connector and support for the 450 ohm ladder line.  Wires connected to the ladder line were threaded through the center insulator and connected to the ladder line.  The connnections were soldered and covered with several layers of vinyl electrical tape.

Then, I rolled out 41-ft/12.50 meters) of 450 ohm ladder line.  The ladder line was soldered to the terminals of the 1:1 balun.

From the balun, I ran 25-ft7.62 meters of RG-8X coaxial cable with UHF connectors to the patch panel in the shack window.  A 6-ft/1.829 meters piece of RG-8X was connected to a Drake MN-4 antenna transmatch in bypass mode.  I would use the "tuners" meter to measure swr and power.  Once that step was done, I would not use the tuner.  The tuner would be available to work 15 meters.  Three-foot/0.91 meters sections of RG-8X would interconnect the Swan 100 MX to a low pass filter and dummy load.

I then hoisted the modified G5RV into position and adjusted the wooden support stakes to give the inverted vee an uniform and balanced appearance.

Test results were good.  I found acceptable swrs on 40, 20, and 10 meters.  The antenna works well and I'm pleased with the mainland U.S. and Hawaii contacts I've received.  Power levels ranged from 20 to 50 watts, cw and ssb.

Another approach:

For the more adventurous hams among us, an experimental multi band antenna using ladder line, a 1:1 balun, and 50 ohm coaxial cable designed by Cecil Moore (W5DXP) may prove interesting.  Cecil's antenna consists of a 130-ft/39.63 meters dipole at a height of 37-ft/11.28 meters fed with lengths of 450 ohm ladder line arranged in a relay and switching system.  Feed line length varies between 91 and 121-ft (27.74 and 36.89 meters).  Cecil says varying the length of 450 ohm feed line for each band (80 through 10 meters) will produce a low swr and maximum power transfer from your transceiver to the antenna.  He uses something called a "ladder line length selector" which adds or removes lengths of feed line depending on the band in use.  Although I haven't built this system yet, it surely looks interesting.

For now, I'll keep the "fan dipole/inverted vee" as a semi-permanent antenna.  I have multi band use with a single feed line without going outside to switch clips or adjust "outrigger" elements.  I'm not getting rid of my antenna transmatches.  They will be used in further antenna experiments.

Have fun building these antennas.  They are inexpensive, easy to build, and don't require a ground radial system.

RESOURCES:  The original article appeared in the June 1995 "QST", number 6.

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Aloha de Russ (KH6JRM).

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

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