Thursday, January 2, 2014

Simple Amateur Radio Antennas: Your first antenna. Post #252

The New Year is the time of new beginnings.  It's time to try new modes, perhaps a new rig, and even a new antenna.  At the KH6JRM ham shack, the new year got me thinking about the first antennas I built as a novice operator back in 1977.  Some of those halting first steps were a disaster--high swr, no contacts, rf in the shack. You name it, I had it when it came to homebrewed antennas.

Perhaps those of you who are recently licensed can understand my frustration when my knowledge fell a little short in the antenna department.  Thankfully, there are a variety of books, internet sites, and amateur radio clubs that can help the new operator with antenna questions.  But, back in the days when I lived in a fairly isolated location on Hawaii Island, about the only thing I could refer to was the ARRL Antenna Book and my own experimentation.  After a while, my antenna notebooks showed some improvement as I finally understood how antennas are built and used.  Keeping an antenna notebook is a good way to gauge the progress you've made in amateur radio.

All of my early failures and occasional successes were made with simple wire antennas.  As George Woodward (W1RN) mentioned in a June 1983 "QST" article, wire antennas are "easy to build, easy to install, easy to disguise and easy to modify."  Being a man with limited physical dexterity and even lesser financial resources than some, I've stuck to Woodward's advice.  During my 37 year amateur radio "career", wire antennas have served me well. Besides, they are fun to make and relatively inexpensive compared to commercial antennas made of aluminum.

While I was paging through my 1977 antenna notebook, I rediscovered one of my more successful antennas--an antenna I still use today at my home in progress in the Puna District.  For the sheer ease of construction, you can't beat the 40-10 meter Inverted Vee dipole fed with 450 ohm ladder line fed into a 4:1 balun and connected to an antenna transmatch.  This antenna requires only 1 supporting mast and two equal antenna segments cut for the lowest frequency of use.  The ladder line allows you multiband performance with a minimum of materials.

So, during the week preceding the Christmas Holiday, I remade the 40-10 meter Inverted Vee used during my novice license days (1977-1978).  You'll find this antenna produces plenty of local, regional, and DX contacts with power levels below 100 watts.

MATERIALS:

One 33-ft/10.06 meter telescoping fiberglass mast.  I used a spare MFJ mast for this project.

One 5-ft/1.82 meter wooden stake to support the fiberglass mast.

Two ceramic insulators for the ends of the antenna elements.

Fifty feet/15.24 meter of 450 ohm ladder line.

One homebrew center connector for the ladder line.  I made the center attachment from a piece of pvc tubing.

Two antenna elements of equal length for my frequency of choice.  Using the general formula 468/f (MHz)=L (feet) and a chosen frequency of 7.088 KHz (the meeting place of the Hawaii Afternoon Net), the total antenna length came out to 66.02 ft/20.13 meters.  Cutting this length into two equal antenna elements, each segment of the Inverted Vee worked out to 33.01 ft/10.06 meters.  As in my novice Inverted Vee, I used #14 AWG house wire for the antenna elements.

One W9INN 4:1 balun.

Twenty-five ft/7.62 meters of RG-8 coaxial cable with UHF connectors.

One Drake MN-4 antenna transmatch.  I've used this piece of equipment for 37 years without any problems.

Several 3-ft/0.91 meters lengths of RG-8 coaxial cable with UHF connectors for interconnecting station equipment.

My old Swan 100-MX transceiver.  The original Heathkit HW-101 I had as a novice has been gone for many years.

A small step ladder to tie off the antenna elements to nearby trees.




ASSEMBLY:

The antenna was built on the ground.

I attached and soldered each antenna segment to the 450 ohm ladder line.  End insulators were attached to each element.

I attached the homebrewed center insulator to the apex of the fiberglass mast.

I ran the 450 ohm ladder line down the mast to a point 16 ft/4.87 meters above ground level.  The ladder line was secured to the mast by nylon ties.

I hoisted the mast onto its wooden support stake.  The ends of the Inverted Vee were tied off at tree branches near the antenna.  The tie off points were approximately 10 ft/3.04 meters above ground level.  I used a small step ladder to reach the tree branches.

Ideally, the angle of the Vee should be between 90 and 120 degrees.  My angle appeared close to that figure.

I ran the ladder line to the W9INN 4:1 balun, which was attached to the side of the garage, approximately 8 ft/2.43 meters above ground level.

Twenty-five feet/7.62 meters of RG-8 coaxial cable was connected to the balun and then run through a window patch panel in the shack and then connected to the Drake MN-4 antenna transmatch.  Small patch cords interconnected the Swan 100-MX to the Drake MN-4, a low pass filter, and the dummy load.

INITIAL RESULTS:

The 40-10 meter Inverted Vee performed just as well this time as it did back in 1977.  With the Drake MN-4 in the system, I had multiband coverage with an swr below 1.5 to 1 on all bands from 40 through 10 meters.  Reception reports ranged from 56 to 59 on SSB and from 579 to 599+ on CW, depending on the band and time of day.  I was running approximately 25 watts from the old Swan 100-MX.  If I wanted to add 80 meters to the antenna, I could simply add another 33 ft/10.06 meters segment to each element and connect the elements together with clip leads.  Additional supports would be needed to keep the 80 meter segments off the ground.

As a general purpose antenna, the multiband Inverted Vee performs well at a modest cost.  Since I had most of the materials at home, my extended cost was minimal.  As is my usual practice, I nest the antenna mast to ground level when I'm done operating for the day.  This keeps the antenna out of site and reduces the risk of a lightning strike.  All feed lines are disconnected and grounded outside of the shack as well.

If you need an easy, simple, and inexpensive antenna to launch your first signal of the new year, consider the basic Inverted Vee.   You won't be disappointed.

REFERENCES:

Woodward, George.  "Your First Antenna."  QST, June 1983. pp. 33-38.

http://www.arrl.org/your-first-antenna.

http://www.arrl.org/files/Technology/tis/info/pdf/0683033.pdf.

http://www.iw5edi.com/ham-radio/420/a-novice-multiband-vertical-antenna.

http://www.hamuniverse.com/40mcwnvis.html.

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Until next time,

Aloha de Russ (KH6JRM).

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