Wednesday, July 24, 2013

A Multiband "Lazy L" antenna. Post #215

One of my favorite antenna guides is a book by the late Doug DeMaw (W1FB) titled the "Novice Antenna Notebook."  Although it is a slim volume, it contains most of the facts, construction principles, and modifications needed to erect simple, inexpensive, and effective antennas.

I bought the book 25 years ago while I was mentoring (elmering) a newly licensed ham in my neighborhood.  Since I'm not a technical genius, I decided to consult a basic antenna primer that could be used by the new licensee as well as myself.  I wasn't disappointed.  DeMaw's writing is down to earth, clear, and largely without complicated formulas for the beginning ham.  I still have this wonderfully simple volume squeezed in between other antenna tomes, including the ARRL Antenna Book, the ARRL Handbook, and various RSGB publications.

What prompted me to consult DeMaw this late in my amateur radio "career" (I was licensed as a novice back in 1977), was the need to erect a simple multiband antenna that would give good results at a modest cost.  The antenna could also serve as a backup antenna for portable and emergency operations.

According to DeMaw, my self-named "Lazy L" antenna will give "good performance from 40 through 10 meters if it is situated well away from nearby conductive objects, such as house wiring, phone lines and metal buildings.  It may be used also on 80 meters, but the efficiency is lower than on the higher bands."

With that in mind, I built the new "skyhook" in about two hours.  I was in no rush.  I just wanted to get something simple and effective on the air.

MATERIALS:

One 33-foot/10.06 meters fiberglass telescoping mast.  I decided to use an extra MFJ mast stored in the garage.  You could also make a suitable mast from pvc pipe.

A pulley and halyard system to raise the vertical portion of the "Lazy L" to the top of the mast.  The upper portion of the "L" would later be led off the top of the mast at a 45-degree angle.

Three, 5-foot / 1.52 meters wooden posts.  One post would support the mast and the other two posts would support the lower portion of the "L" and act as an elevated radial or counterpoise.

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

A 4:1 balun.  The balun would connect the ladder line to a length of coax entering the shack.

25-feet/7.62 meters of RG-8X coaxial cable.  The coax would run from the balun/ladder line combination to an antenna transmatch in the shack.

A Drake MN-4 transmatch.  Actually, you could use any commercially made "antenna tuner" to complete the antenna system.  I've used my trusty Drake MN-4 since I was first licensed.  It's a good "tuner."

Soldering gun/iron, basic tools.

4 ceramic insulators...two for the vertical section and two for the elevated radial/counterpoise wire.

Transceiver.

ASSEMBLY:

I decided to cut the "Lazy L" to be resonant on 7.088 Mhz, the frequency of the Hawaii Island Afternoon net.  Using the general formula, 468/f (MHz)=L (ft),  I measured and cut two equal lengths of #14 AWG housewire. Each element (the vertical and its elevated radial) came to 33.01 feet/10.064 meters.  I rounded off the measurement to 33-feet/10.06 meters.

I attached a ceramic insulator to each end of the vertical element and the elevated radial/counterpoise.

I pounded in two 5-foot/1.52 meter wooden stakes.  The stakes would support the elevated radial/counterpoise approximately 3-feet/0.91 meters above the ground.

A third 5-foot/1.52 wooden stake would support the fiberglass mast.

A pulley and halyard system to raise and lower the vertical section of the antenna.  I used a brass pulley from the Hilo, Hawaii Ace Hardware store and 75-feet/22.86 meters of dacron rope I found at WalMart.

I attached 50-feet/15.24 meters of 450-ohm ladder line to the vertical element and the elevated radial/counterpoise.  The connections were soldered and covered with several layers of vinyl electrical tape.

I raised the vertical segment of the antenna with the halyard and pulley system.  I then led the vertical element off the top of the mast at a 45-degree angle to the nearest stake supporting the elevated radial/counterpoise.  The antenna took the form a "Lazy L" with the elevated radial/counterpoise running parallel to the ground to the end tie-off stake.  A few short pieces of dacron rope secured the ceramic insulators of the elevated radial to the posts.

The 450-ohm ladder line was routed at a right angle to the sloping vertical element.

The ladder line was attached to the 4:1 balun on the garage wall.  The balun was approximately 7 feet/2.13 meters above ground level.  At no time did the feed line touch the ground.

A 25-foot/7.62 meters piece of RG-8X coaxial cable was connected to the 4:1 balun and led into the shack through a homemade patch panel in the room's window.  MFJ sells several versions of this panel.  I just used a pine board and drilled my own holes.

The coax was connected to the Drake MN-4. Short lengths of RG-8X connected the transmatch to a dummy load, a low pass filter, and the Swan 100-MX.

INITIAL RESULTS:

With the use of the Drake MN-4 transmatch, I was able to attain a SWR of 1:13 to 1 on 40, 20, 15, and 10 meters.  The tuning was a bit "tight" on 20 and 10 meters, but I was able to get SWR readings below 1.5 to 1 in most cases.  I tried the antenna on 80 meters, but I wasn't impressed with the results.

Most contacts were made using 10 watts or less on CW and 20 watts or less on SSB.  Depending on the band selected and the time of day, my CW contacts reported 569 to 599, while my SSB efforts netted reports of 55 to 58.

For a simple, no-frills antenna, the "Lazy L" performs very well.  I had most of the materials on hand, so my financial outlay was minimal.

DeMaw's book is full of easily- built antennas such as mine.  I'm going to build a few more of these basic antennas before the year is over.  Good luck in your antenna building efforts.

REFERENCES:

DeMaw, Doug (W1FB).  "Novice Antenna Notebook".  Copyright 1988.  ARRL.  Newington, CT. 06111. pp. 60-61.
http://www.antennex.com/preview/Folder01/lant/lant.htm.
http://www.eham.net/articles/27401.
http://www.w6sdo.com/160M.html.
http://www.hamuniverse.com/slopinginvl.html.

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Aloha es 73 de Russ (KH6JRM).
BK29jx15--along the beautiful Hamakua Coast of Hawaii Island.