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Tuesday, April 29, 2014

Simple Ham Radio Antennas: A 5/8 wavelength vertical ground plane. Post #272

According to Edward M. Noll (W3FQJ), "The 5/8-wavelength vertical is a preferred length for the best low angle radiation."  For the higher HF bands (20 through 10 meters), this antenna is easily assembled and requires a small quantity of wire, some ceramic insulators, a suitable mast, 50-ohm feed line or 450-ohm feed line, a simple ground radial system, and a sturdy antenna matchbox or ATU.  Multiband use between 20 and 10 meters is possible with 450-ohm ladder line, ATU, and a balun, while good single band use can be obtained with 50-ohm coaxial cable and an inline or base antenna "tuner".

So, let's build a simple 5/8 wavelength vertical for the 10 meter amateur radio band, centering on 28.4 MHz.  This frequency is at the mid-point of the SSB allocation for Technician Class licensees.  The antenna was built at my new home in the Puna District on 18 April 2014.

MATERIALS:

Using the general formula, 585/f (MHz)=L (ft), our vertical element will measure out to 20.59 ft/6.28 meters.  I rounded the length to 20 feet, 7 inches.  Each of the four slanting radials will be a 1/4 wavelength long or 8.23 ft/2.51 meters.  I rounded off the length to 8 ft, 3 inches.  I used some spare #22 AWG hookup wire for the antenna elements and the radial system.

Four ceramic insulators and nylon rope to tie off the radials.

Five, 5-ft/1.52 meters wooden stakes.  One stake would support the fiberglass mast and the four remaining stakes would support the slanting radial elements.

One 33-ft/10.06 MFJ telescoping fiberglass mast.

One "ladder lock" center connector to support the 450-ohm feed line.

50-ft/15.24 meters of 450-ohm ladder line.

One W9INN 4:1 current balun.

One Drake MN-4 antenna transmatch.

Station equipment:  patch panel in the shack window, low-pass filter, Heathkit Dummy Load, Ten-Tec Argosy II transceiver, solar charged battery power supply, microphone, key, log, miscellaneous connectors, several 3-ft/0.91 meters RG-8X patch cords with UHF connectors, and a "counterpoise" bundle consisting of 1/4 wavelengths of wire for 20, 15, and 10 meters.  The bundle will be connected to the ground lug of the Drake MN-4 antenna transmatch.  I also have a station ground consisting of a 8-ft/2.43 meters long ground rod connected to four 33-ft/10.06 meters buried radials.

Nylon ties, nylon rope, tacks to secure the 450-ohm feed line to the garage wall, and various tools.

ASSEMBLY:

The antenna was built on the ground a later raised into position.

I attached the vertical element to the tip of the MFJ mast and ran the wire to a point approximately 12-ft/3.65 meters above the base of the mast.  The wire was secured to the mast with nylon ties and vinyl electrical tape.  Each radial segment was attached to a ceramic insulator.  A small length of nylon rope was tied to each insulator.  This rope would be used to tie off the radial wires to  nearby wooden stakes.

At the 12-ft/3.65 meter point of the mast, I attached the "ladder lock" device and threaded the ladder line through the appropriate holes in the connector.  One lead went to the vertical element, while the other lead went to the four sloping radials.  All connections were soldered and covered with several layers of vinyl electrical tape.

I carefully hoisted the fiberglass mast onto its support stake.

I then spread out the sloping radials in a uniform pattern (every 90 degrees) and secured each radial to a pre-positioned 5-ft/1.52 wooden stake.  The ladder line was led off from the mast at a 90 degree angle and attached to the outside shack wall.  Even with a little sag in the line, the feed line was kept approximately 10-ft/3.04 meters above ground, well out of the way of children, visitors, and pets.

The ladder line was connected to the wall mounted W9INN 4:1 balun.  Three-feet/0.91 meters of RG-8X coaxial cable ran from the balun to the patch panel in the shack window.  A 6-ft/1.82 meters length of RG-8X coaxial cable with UHF connectors ran from the patch panel  to the Drake MN-4 antenna transmatch.  The Argosy II, low-pass filter, and the Heathkit Dummy Load were interconnected with 3-ft/0.91 meters lengths of RG-8X coax with UHF connectors.  A "counterpoise bundle" was attached to the ground lug of the ATU.

PRELIMINARY RESULTS"

With the Drake MN-4 in the system, I was able to keep swr below 1.3 to 1 throughout  the entire 10 meter band.  Running approximately 15 watts from the old Argosy II, I got excellent cw reports of 579 to 599 and ssb reports of 56 to 59, depending on the time of day.

With a little careful tuning, the 5/8 wavelength 10 meter vertical can do an acceptable job on 20 and 15 meters--better if additional wire is added to each radial wire for those bands.  Ed Noll adds that "a vertical cut for 5/8 wavelength on 10 meters has an electrical length not too much shorter than this value on 15 meters, and it functions as a quarter-wave on 20 meters with just a little base loading."  Although what he says is generally true, I decided to keep this antenna for 10 meters only and not stress the old Drake MN-4 too severely.

As a side note, you can also use this antenna (with a "tuner") to work CB channels as well.  Many families in my new neighborhood have CB transceivers and I sometimes use an old Radio Shack TRC-23 CB set to talk with nearby families.

This was a fun and inexpensive project.  According to some antenna experts, you can expect a 3dB gain over a 10 meter dipole with this 5/8 wavelength vertical.

REFERENCES:

Noll, Edward M. (W3FQJ). 73 Vertical, Beam, and Triangle Antennas.  Editors and Engineers, Indianapolis, IN, 46268.  Seventh Printing, 1979.  pp. 34-35.

Orr, William I. (W6SAI) and Cowan, Stuart D. (W2LX)).  The Radio Amateur Antenna Handbook.  Radio Publications, Inc.  Box 149, Wilton, CT, 06897.  First Printing, 1978.  pp. 108-109.

http://www.qsl.net/w4sat/five8th.htm.

http://www.dx-antennas.com/5-8wavevertical.htm.

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