Saturday, December 14, 2013

Simple Ham Radio Antennas: A double extended "zep" for 10 meters. Post #248.

From what I've been hearing today (Saturday, 14 December 2013), amateur radio operators are having a good time on the ARRL 10 meter contest.  Although propagation has been variable on Hawaii Island, the band seemed alive with signals.  Ten meters, like its distant cousins at 160 meters and 6 meters, offers plenty of challenges for amateurs new and old.  When propagation is favorable, both local and DX signals are possible with low power and modest antennas that can fit into a small backyard.

Ten meter events are scheduled throughout the year, sponsored by the ARRL, various national amateur radio groups, and the Ten-Ten group, which promotes the use of 10 meters.

Antennas for 10 meters run the gamut from multi-element beams and ground planes to dipoles and full wavelength loops.  Even though the current ARRL 10 meter contest is coming to an end, it's not to early  to think about ways to improve the signal from your 10 meter antenna.

If you want some gain over a dipole and have about 50 ft/15.24 meters of horizontal space, why not build a double extended zepp antenna for your next 10 meter operation?  The antenna traces its ancestry both to the familiar half wavelength dipole and to the trailing antennas used on the Zeppelin airships of the 1920s and 1930s.

The double extended zepp looks like a conventional halfwave dipole fed in the center with 300 or 450 ohm feed line.  But, unlike the horizontal flat top known to most of us, each antenna element is 5/8 of a wavelength long, which produces a gain of approximately 3 dB over a dipole at the same height.  According to Steve Shorey (G3ZPS), this gain is attained when the extended zep is approximately 0.6 wavelength above ground.

Just before the ARRL 10 meter contest, I built a crude replica of a double extended zepp at my future homesite in the Puna District.  So far, the antenna works very well and gets better reception reports than my 10 meter ground plane.

Here's what I did to make the antenna:

Using the formula 599/f(MHz)=l (ft) supplied by Steve (G3ZPS), I cut two equal lengths of #14 AWG housewire for a chosen frequency of 28.400 MHz in the 10 meter band.  This frequency is quite busy, with many newly licensed technician class licensees testing the waters of SSB operation.  These contacts are always interesting and remind me of the time I first ventured into a "phone" band.  Based on this general formula, each element of the zepp measured 21.09 ft/6.43 meters.

Once I had cut the wire, I began to assemble the antenna on the ground.

I used three MFJ telescoping fiberglass masts to support the antenna.  One mast would support the center connector and the 450 ohm ladder line, while the other two masts would support the zepp elements.

The masts extended out to 33 ft/10.06 meters.  At this height, the zepp would be more than 0.6 wavelength above ground and should give me about 3 dB gain over my 10 meter inverted vee and ground plane.

Three, 5-ft/1.52 meters wooden support stakes for the masts.  Each mast had a halyard and pulley system which would allow me to hoist each section of the antenna to its proper height.

I attached a ceramic insulator to each end of the elements.  A short piece of dacron rope would be used to tie off the insulator to each mast.  The tie off rope was approximately 3 ft/0.91 meters long.  The center connector was the "ladder lock", a device that allows you to attach each wire of the feed line to its respective antenna element.

The ladder lock was secured to the center mast with nylon ties and duct tape.  The ladder line was run down to the midpoint of the center mast (16.5 ft/5.03 meters) and secured to the mast with nylon ties.  All antenna connections were soldered and covered with several layers of vinyl electrical tape.  

I attached each element of the antenna and the center connector to its respective pulley and halyard system.

After each mast was hoisted into position on its support stake, I raised each antenna element to the apex of its mast and tied off the halyard to the base of each mast.  To make adjustments, all I would have to do is raise or lower each element with the halyard and pulley system.

Once I had the masts in place, I ran 50 ft/15.24 meters of 450 ohm feed line to a W9INN 4:1 balun attached to the garage wall (approximately 16.5 ft/5.03 meters above ground at the peak of the garage roof).  The only dangerous part of this installation was using a ladder to get the balun near the top of the roof peak.  A neighbor, who doesn't mind about my amateur radio operations, steadied the ladder while I attached the feed line to the 4:1 balun and ran 25 ft/7.62 meters of RG-8X coaxial cable with UHF connectors through the patch panel in the shack window.

The balun was wrapped in thick plastic to protect the device from the weather.

Once the coax was safely inside the shack, I hooked up the Drake MN-4 transmatch, the Swan 100 MX transceiver, and the dummy load to complete the project.

Based on just a few contacts  Friday (13 December 2013), the double extended zepp works very well with SSB reports running between 56 and 58, using approximately 50 watts output from the old Swan 100 MX. The antenna was oriented northwest to southeast, giving me some decent coverage of the U.S. mainland.

As an added bonus, the ladder line/balun/transmatch combination allows me to transmit a usable signal with low SWR on 20, 15, and 10 meters.  While not a competition grade antenna, it does perform better than my reference 10 meter ground plane and gives me some gain to mainland U.S. areas.  I can change the directivity of the signal by moving the masts, so that the broadside pattern and its lobes reach other parts of the compass.

If you need a new antenna for 10 meters, try a classic double extended zepp.  It's cheap, easy to make, and produces results at modest power levels.


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Thanks for being with us today!

Aloha de Russ (KH6JRM)

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

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Aloha es 73 de Russ (KH6JRM).