Wednesday, October 9, 2013

A simple, portable 40-10 meter vertical antenna with counterpoise. Post #232

How would you like to build a 40-10 meter vertical antenna that could be used in portable or emergency situations?  For the relatively low cost of some housewire, a length of 450-ohm ladder line, some clip leads, a few insulators, a 4:1 balun, a small length of coaxial cable, and an antenna transmatch, you could have a simple multiband antenna that will give you hours of fun on your next mini DXpedition to the nearest public park or in your own back yard.  With a  QRP rig, a deep cycle marine battery, and a few solar panels, you can enjoy a few carefree hours without increasing your electric bill.

I have such a station placed in my Odyssey van.  I can operate when the mood strikes me or when a local emergency is declared.  During the quarterly break from my teaching duties, I decided to unpack my portable station and give it a brief "shakedown cruise" at my new homesite in the Puna District of Hawaii Island.

I wanted to relax a bit after a day's work of clearing the land and making small house repairs, and the portable station in the van would a perfect way to get on the air with a minimum of cost and time.

So, after removing the storage cases from the van, here's what I had:

One Yaesu FT-7 QRP rig.  This is an "oldie but goodie".  If you have a more modern rig such as an ICOM-703, a Yaesu FT-817, or an  Elecraft K-2 or a KX3, so much the better.

One 33-foot (10.06 meters) MFJ telescoping fiberglass mast.

Two insulators, three, 5-foot (1.52 meters) wooden stakes, and 2 alligator clips.

Fifty feet (15.24 meters) of 450-ohm ladder line.  This would serve as the antenna feed line.

Sixty-six feet (20.12 meters) of #14 AWG housewire.  This length would make the antenna resonant around 7.088 MHz (the frequency of the Hawaii Afternoon Net).  With ladder line, a 4:1 balun, and an antenna transmatch, I could use the antenna from 40 to 10 meters.

One W9INN 4:1 balun.  A good source for baluns would be DX Engineering.

An antenna transmatch.  I had a spare Drake MN-4 which I use for portable work.

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

Three, 3-foot (0.91 meters) pieces of RG-8X coaxial cable with UHF connectors.

One deep-cycle marine battery and solar panels.

Basic tools.

Assembly:

I first drove the 5-foot (1.52 meters) wooden support stake into the ground with a hammer.  

I measured 33-feet (10.06 meters) from the mast support stake and drove in another 5-foot (1.52 meters) wooden stake.  This stake would support a slightly elevated radial or counterpoise from the base of the fiberglass mast.

The 66-feet (20.12 meters) of #14 AWG house wire was cut into two equal pieces, 33-feet (10.06 meters) each.  One piece would run up the mast and the other would be lead away from the base of the mast at a slight angle to the second wooden post.

One ceramic insulator would be attached to the tip of the mast and would support the vertical element.  The other would be used to tie off the slightly elevated radial at the second post.  Nylon ties were used to secure the vertical element to the fiberglass mast.

An alligator clip lead was soldered to the bottom portion of the vertical element and to the the left end of the elevated radial.  

I hoisted the mast onto its support stake.

The vertical element clip lead was attached to one side of the ladder line.  The elevated radial clip lead was attached to the other side of the ladder line.  The radial wire was attached to a ceramic insulator and tied off at the distant second wooden post.  The end of the elevated radial was now about 3-feet (0.91 metes) above ground.

I led the ladder line to a third wooden post approximately 50-feet (15.24 meters) away from the base of the mast.  This post kept the ladder line off the ground.

The ladder line was attached to the W9INN 4:1 balun, which was secured to the wooden post with nylon ties.

Twenty-five feet (7.62 meters) of RG-8X coaxial cable was attached to the 4:1 balun.  The coax was run to the Drake MN-4 antenna transmatch.  A 3-foot (0.91 meters) piece of RG-8X coax connected the Drake MN-4 to the Yaesu FT-7.  Small pieces of coax were used to connect a dummy load and low pass filter into the antenna system.

Once I connected the Yaesu FT-7 to the deep cycle marine battery, I had a working station.

Initial Results:

With the Drake MN-4, the W9INN balun, and the 450-ohm ladder line in the antenna system, I was able to get an SWR of 1.2 to 1 on 40, 20, 15, and 10 meters.  Even with low power (under 10 watts) from the venerable Yaesu FT-7, I received good reports from both Hawaii and mainland U.S. stations.  I ran the rig for several hours into the early evening.  The system worked.  Best of all , I made it myself.

Once operating was done, I lowered the mast, disconnected the vertical and radial wires, collapsed the antenna, rolled up the ladder line and coaxial cable, and packed the Yaesu FT-7 into its padded box.  The solar panels and deep cycle marine battery were put in special plastic storage bins.  The wooden stakes were cleaned, dried, and put away with the antenna elements.  With the system safely stored in my van, I was again ready for my next mini DX-pedition.

Resources:

http://www.antennex.com/preview/Folder01/lant.htm.

De Maw, Doug (W1FB) (SK).  "Novice Antenna Book."  ARRL, Newington, CT, 06111. 1988. pp. 60-61.

http://www.hamuniverse.com/slopinginvl.htm.

http://www.vk1od.net/antenna/InvertedL.htm.

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Aloha es 73 de Russ (KH6JRM)

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