Wednesday, July 2, 2014

Simple Ham Radio Antennas. A 20 meter through 10 meter Vertical Dipole Antenna. Post #284.

One of the joys of moving into a bigger home with a decent back yard (1 acre of mixed brush and trees) is the ability to build the wire antennas I've always wanted.  Like many of my fellow amateur radio operators, I've endured HOAs, CC &Rs, and limited space for most of my 37 years as a ham.  I operated fairly well under these circumstances using stealth antennas from "ground hugging" loops to thin random wires stretching to the nearest tree.

Now that my xyl and I are semi-retired, we have to the time to "fix up" our final home in an area conducive to our various hobbies, including gardening, amateur radio, backyard astronomy, and just plain relaxing.  

Over the past few months, I've begun the erection of my "antenna farm" and the building of my radio room in the garage.  There's a lot of work to be done, but it's enjoyable and gives me exercise.

Last Friday, just before the 2014 ARRL Field Day, I completed a new antenna which may be usable for those facing space limitations.  Although I usually prefer half-wave length horizontal dipoles and inverted vees, I decided to try out a "Vertical Dipole" for 20 meters through 10 meters.  The construction seemed fairly simple and the antenna would give me multiband coverage using ladder line, a 4:1 current balun, and my trusty Drake MN-4 transmatch (tuner).
If I really wanted to get fancy, I could cut a matching section of 450 ohm ladder line, connect that to a balun (1:1 or 4:1), and run 50 ohm coaxial cable to a "tuner".

However, I decided to keep things very simple, since the vertical dipole was only an experiment.  Following the advice of Joel R. Hallas (W1ZR) and his article "How Do You Adjust a Non-Resonant Antenna?" in the July 2014 issue of "QST", I left out the matching section entirely, because as Mr. Hallas states, "The whole matching issue can be sidestepped if you run window line all the way back to a wide range tuner near the radio.  The antenna will  receive with the same pattern and gain, but you won't have to fuss with the match at the antenna feed."  Your transmitted pattern will vary, depending on the band of choice.

So, with that advice in hand I began the 20-10 meter vertical dipole project.

MATERIALS:

One 33-ft/10.06 meters MFJ telescoping fiberglass mast.  This would support the upper and lower vertical elements.

One 20-ft/6.09 meters piece of PVC pipe, 2-inches/5.08 cm in diameter.  This mast would support the ladder line coming off the main mast at a point 16.475 ft/5.022 meters above ground.

Two 5-ft/1.52 wooden support stakes.  One stake would support the main mast.  The other would support the PVC pipe.

Sufficient #14 AWG house wire to make the dipole elements. Using the general formula, 468/f (MHz)=L (ft) and a the lowest frequency of use (14.200 MHz), I cut a length of wire measuring 32.95 ft/10.04 meters.  This was divided into two equal parts to form the vertical dipole elements.  Each element was cut to a length of 16.475-ft (16 feet, 5.7 inches)/5.022 meters.

Three ceramic insulators.  One would support the top vertical element; one would serve as the center insulator; and one would anchor the base of the bottom vertical element.

Vinyl electrical tape, nylon ties, basic tools, soldering gun.

Fifty-feet/15.24 meters of 450 ohm ladder line.  This would be the feed line for the antenna.

One W9INN 4:1 current balun.

10 feet/3.04 meters of RG-8X coaxial cable with UHF connectors.

Several 3-ft/0.91 meters pieces of RG-8X coaxial cable with UHF connectors.

One Drake MN-4 antenna transmatch (tuner).

One Ten-Tec Argosy II transceiver with microphone and straight CW key.

One solar-charged deep cycle marine battery for power.

One "counterpoise bundle" consisting of a quarter- wavelength of wire for each band used (20, 15, 10 meters).  The counterpoise would be attached to the ground lug of the Drank MN-4.

ASSEMBLY:

The antenna was made in the garage and erected outside.

First, I cut each dipole element to the proper length (16.475 feet--16 feet, 5.7 inches/5.022 meters).

A ceramic insulator was attached to the top end of the upper element.  A ceramic insulator was attached to the end of the bottom element.

I then threaded each leg of the 450 ohm ladder line through the center insulator and soldered each free end of the antenna elements to its respective leg of the ladder line.  The connections were covered by several layers of vinyl electrical tape.

The completed dipole was taken outside to the mast, which was on the ground approximately 40-ft/12.19 meters from the shack in the garage.  The shorter 20-ft/6.09 meters PVC mast was on the ground, approximately 33-ft/10.06 meters from the main mast.

Next, I attached the vertical dipole and feed line connection to the telescoping fiberglass mast.  The elements were secured with vinyl electrical tape and nylon ties.  I made sure the center insulator with the attached feed line was thoroughly taped and mated with the mast with several nylon ties.

I then hoisted the main fiberglass mast on its pre-positioned wooden stake and led the feed line to the 20-ft/6.09 meters PVC mast on the ground.  The secondary mast was positioned 33-ft/10.06 meters from the main mast.
  Once the ladder line/feed line was secured to the PVC pipe with nylon ties and vinyl electrical tape, I hoisted the PVC mast onto its pre-positioned wooden stake.  The feed line left the main mast at 90 degrees and maintained that angle until it reached the secondary mast.  The feed line sagged a bit, but it was generally a little more than 16-ft/4.87 meters above ground.

The remaining length of the ladder line was fed under the window ledge of the shack and attached to the W9INN 4:1 balun.  A 10-ft/3.04 meters piece of RG-8X with UHF connectors was run from the balun to the Drake MN-4 transmatch.  Short pieces of RG-8X coax interconnected the Argosy II, Heathkit Dummy Load, and a low-pass filter to the Drake MN-4.

Finally, I connected a "counterpoise bundle" to the ground lug of the Drake MN-4.

INITIAL RESULTS:

With the Drake MN-4 in line, I was able to get a 1:1 swr on 20, 15, and 10 meters.  The antenna pattern is omnidirectional. Using approximately 50 watts of power from the old Argosy II, I was able to get some enjoyable contacts on 20 and 15 meters.  Ten meters was quite noisy and no stations were worked.  On 20 and 15 meters, cw contacts ranged from 569 to 599, and on ssb, reports varied between 55 to 59, depending on the time of day.

All told, not a bad day for an antenna made from parts found at home.  If you lack the space for a multiband antenna, try going up with a vertical dipole.

REFERENCES:

Hallas, Joel R. (W1ZR). "How Do You Adjust a Non-Resonant Antenna?" "QST", July 2014, p.55.

http://www/hamuniverse.com/kl7jrverticaldipole.htm.

http://www.arrl.org/files/file/Technology/tis/info/pdf/9106023pdf.

http://www.arrl.org/hf-vertical.

http://www.wolfington.net/articles/dipole.

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Until next time,

Russ (KH6JRM).