Wednesday, September 25, 2013

The W3EDP antenna revisited. Post #229

I'm always looking for interesting antennas to build for my expanding antenna "farm" at my new house lot in the Puna District of Hawaii Island.  Unlike my present location, the new lot has an acre of space to design, build, and locate new antennas.  So, when I take a break from clearing the land of brush and scrub trees, I have time to explore antennas for my modest station.

A few days ago, I ran across an interesting article by William McFadden (WD8RIF) on his "Field Deployable Field Antennas" website.  McFadden wrote about an old classic half-wave length antenna called the W3EDP, a variation of the "Zepp" antennas that were popular in the 1930s.  The original W3EDP article can be found in the March 1936 edition of "QST".  If you're a member of the ARRL, you can access the archives and read about this fascinating antenna.

According to McFadden, the W3EDP antenna is a "Zepp" consisting of a radiator 85 feet/25.91 meters and a "counterpoise" wire of 17 feet/5.18 meters.  The radiator and "counterpoise" wire are attached to 17 feet/5.18 meters of 450-ohm ladder line, which serves as the antenna feed line.  The radiator can be supported by a single mast or tree or in an inverted "L" configuration.  The short "counterpoise" wire should be supported above ground for best results.

McFadden says the modified W3EDP design is easily deployable and can serve as an emergency multi-band antenna.

With all of this in mind, I decided to build one of these classic antennas just for the fun of it.

MATERIALS:

One hundred nineteen (119) feet/36.28 meters of #14 AWG housewire.  Eighty-five feet/25.91 meters would be used as the main antenna element.  Seventeen feet/5.18 meters would be used for the "counterpoise" wire.  And 17 feet/5.18 meters would be used as an additional "counterpoise" wire for the Drake MN-4 transmatch. This was my main alteration to the antenna.

One W9INN 4:1 balun.

Seventeen (17) feet/5.18 meters of 450-ohm ladder line.  This would be my feed line.

A 3-ft/0.91 meters of RG-8X coaxial cable with UHF connectors.  This cable would join the Drake MN-4 transmatch to the W9INN 4:1 balun.  The balun would be connected to the 450-ohm feed line.

One transmatch.  I had a spare Drake MN-4 in the shack.

Short coaxial cable patch cords to connect the Drake MN-4 to the Swan 100-MX transceiver, a low pass filter, and a dummy load.

Two five-foot/1.52 meters wooden stakes to support the "counterpoise" wire running from one side of the ladder line.

One 5-ft/1.52 meters wooden stake to support a fiberglass mast.

Four ceramic insulators.  One insulator would be attached to the tip of a fiberglass mast; the second would be used to tie off the main radiator to a nearby tree; the third insulator would be used to tie off the short "counterpoise" wire to a wooden stake; the fourth would be used to tie off the "counterpoise" wire to the Drake MN-4 transmatch.

One 33-ft/10.06 meters telescoping fiberglass mast.

A slingshot and fishing weight to launch part of the antenna into an inverted "L" configuration.  A 50-ft/15.24 meters piece of rayon rope was used to haul up the "L" and secure the installation to a tree stump.

Basic tools, soldering iron, nylon tie wraps, vinyl electrical tape.

ASSEMBLY:

The antenna was made in the garage next to the radio room.

I measured off the predetermined lengths of each wire, including the 450-ohm feed line.

The main radiator and shorter "counterpoise" wires were soldered to the feed line.  All connections were wrapped with several layers of vinyl electrical tape.

I slipped the feed line through a "homebrewed" patch panel in the shack window.  The feed line was attached to the W9INN 4:1 balun, which, in turn, was connected to the Drake MN-4 transmatch with a 3-ft/0.91 meter length of RG-8X coaxial cable with UHF connectors.

A 17-ft/5.18 meters piece of #14 AWG housewire was attached to the ground lug of the Drake MN-4 transmatch.  This wire was run along the baseboards of the enclosed radio room and tied off with a ceramic insulator.  The end of the wire was wrapped with several layers of vinyl electrical tape.  Hopefully, this step would reduce the chances of someone getting shocked with the high voltage at the end of the wire.  I also hoped the extra wire connected to the ground lug of the transmatch would improve the performance of the short "counterpoise" attached to the feed line.

With the interior connections made, I proceeded to finish the external connections of the antenna.

I attached 33-ft/10.06 meters of #14 AWG housewire to the vertical fiberglass mast which was placed temporarily outside the shack window. The antenna wire was then soldered to one side of the ladder line.  That connection was wrapped with several layers of vinyl plastic tape.  The antenna wire was secured to the mast  with nylon ties.  At the tip of the mast, the wire ran through an opening in a ceramic insulator. The mast was then hoisted onto its supporting wooden stake. The remaining part of the antenna (52-feet/15.85 meters) was run to a nearby tree and secured at the 25-ft/7.62 level with a slingshot and fishing weight.  The rope attached to the fishing weight pulled up the "L" part of the antenna.  The rope was tied off on an adjacent tree stump.

The short "counterpoise" wire was soldered to the 450-ohm feedline  That connection was wrapped with several layers of vinyl plastic tape.  The "counterpoise" wire was then attached to two 5-ft/1.52 meters wooden stakes with nylon ties.  The wire was kept off the ground.

RESULTS:

As predicted by McFadden, the antenna showed a low swr (1.5 to 1) on the 80 meter and 10 meter bands without the counterpoise.  The counterpoise was needed to get a low swr on 15 meters, 20 meters, and 40 meters.  The Drake MN-4 seemed to handle the swr without problems.

In the end, I decided to leave the "counterpoise" wires attached, both inside on the Drake MN-4 and outside with the elevated wires running to the wooden stakes.

I've been able to get low swrs on 80 through 10 meters running about 25 watts cw/ssb from the old Swan 100 MX.

As an experimental antenna, the W3EDP has proven simple to build, highly portable, and easy to set up.  This would make a nice antenna for a mini-dxpedition or emergency use.

I've had decent reports on 40, 20, and 15 meters, with contacts ranging from 559 to 599 on cw and 54 to 57 on ssb.  Nothing spectacular, to be sure...but the antenna works.  Ten meters has been marginal due to propagation problems.  Eighty meters has yet to be tested.  So far, so good.

REFERENCES:

homefrognet.net/~mcfadden/wd8rif/fieldantennas.htm.
http://www.ok1rr.com/index.php/antennas/19-the-w3edp-antenna.
http://www.eham.nt/ehamforum/smf/index.php?topic=80021.0.
http://www.kb6nu.com/the-w3edp-antenna/.
http://www.nc4fb.org/wordpress/w3edp-multi-band-antenna/.
"QST".  March, 1936.  ARRL, Newington, CT, 06111.

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Aloha es 73 de Russ (KH6JRM).

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