Simple Ham Radio Antennas. An 80 through 10 meter inverted "L" antenna. Post #285.


Would you like to build a simple, effective antenna covering 80 through 10 meters that won’t tax your budget or get strange stares from you neighbors?

How about an easily erected inverted “L” that only requires some house wire, a few insulators, basic tools, a simple fiberglass telescoping mast, a roll of 450 ohm ladder line, a 4:1 current balun, an antenna “tuner”, short lengths of 50 ohm coaxial cable, and a few wooden garden stakes?  The inverted “L” is basically a quarter wavelength of wire divided into an 1/8 wavelength vertical segment and a horizontal 1/8 wavelength segment.  Like all verticals, the inverted “L” requires a ground radial system.

This antenna can be built over the course of an afternoon and won’t cost you much money.  The antenna will deliver excellent local and DX contacts.

As with all my homebrewed antennas, I try to use materials I have around the house, shack, or garage. The nearest hardware store or home improvement outlet carries most of the materials I need in case I run short of a few items.

Materials:

The antenna will be cut for a resonant frequency of 3.500 MHz.  Using the general formula for a vertical (234/f (MHz)=L (ft), I measured out 67-ft/20.42 meters of #12 AWG house wire.  The actual calculated length was 66.85-ft/20.38 meters.  I just rounded off the number to 67-ft/20.42 meters. I cut four elevated radials to the same length.

One, 33-ft/10.06 meters MFJ fiberglass telescoping mast.

Five, 5-ft/1.53 meters wooden stakes.  One stake would support the fiberglass mast and four would support the rudimentary radial system above ground level.

Six ceramic insulators.  One would be attached to the free end of the inverted “L”.  The others would be used to tie off radial wires to pre-positioned wooden support stakes. The remaining insulator would be attached to the top of the mast, so that the horizontal portion of the vertical could be run from the mast apex without damaging the wire.

Fifty-feet/15.24 meters of 450 ohm ladder line.  This would be used as the antenna feed line. When the ladder line is connected to a 4:1 current balun and an antenna transmatch, the antenna would be able to cover all amateur radio bands from 80 meters to 10 meters. Small lengths of RG-8X coaxial cable with UHF connectors would be used to connect the antenna system to the “tuner” and assorted station equipment.
Fifty-feet/15.24 meters of nylon rope would be attached to the free end of the vertical element.  The rope would be shot over a nearby tree limb to create the horizontal portion of the antenna.

Assembly:

The inverted “L” was built on the ground about 35-ft/10.67 meters from the garage/radio room.  A heavy duty electrical cord running from the garage would supply electricity for my soldering gun (Weller type). Thankfully, the day was calm and soldering wasn’t a major chore.

I pounded the first support stake into the ground (about 1-ft/0.30 meters deep).  The four remaining wooden stakes were secured in the same way, approximately 70-ft/21.34 meters from the center stake.

I attached a ceramic insulator to the top of the fiberglass mast using wire and nylon cord.  

I secured the bottom of the vertical element to the fiberglass mast at a height of 5-ft/1.53 meters above ground.  The vertical element was run up the mast and passed through the top ceramic insulator.  The vertical element was secured to the mast with nylon ties.  The remaining wire (39-ft/11.89 meters) would serve as the horizontal portion of the inverted “L”.  A ceramic insulator was attached to the end of the horizontal portion of the antenna.  Fifty-feet/15.24 meters of nylon rope, weighed down with a fishing sinker, was attached to this insulator.

I hoisted the fiberglass mast onto its support stake.

I then soldered one leg of the 450 ohm ladder line to the vertical element.  Four radial wires, measuring 67-ft/20.42 meters each, were soldered to the other leg of the ladder line.  Each connection was wrapped with several layers of vinyl electrical tape.

Once the mast was in position, I used a slingshot to shoot the nylon rope/horizontal element over a tree branch approximately 45-ft/13.71 meters away from the mast.  The branch was around 35-ft/10.67 meters above ground.  Once I pulled the nylon rope over the tree branch and secured it to a nearby tree stump, I adjusted the top wire so it was almost horizontal in relation to the tip of the mast.  The antenna had 28-ft/8.53 meters of vertical space on the mast and 39-ft/11.89 meters of horizontal spread on the top.

I then secured each of the four slightly elevated radials to its pre-positioned stake.

I ran the 450 ohm ladder line to the 4:1 W9INN current balun mounted on the garage wall, about 8-ft/2.43 meters above ground level.  A 6-ft/1.82 meters piece of RG-8X ran from the balun to the window patch panel.  From the patch panel, a 10-ft/3.04 meters length of RG-8X ran to the Drake MN-4 “tuner”.  Short lengths (3-ft/0.91meters) of RG-8X interconnected the Ten-Tec Argosy II, Dummy Load, and Low-Pass Filter to the Drake MN-4.  To be on the safe side, I connected a “counterpoise bundle” consisting of quarter wavelength pieces of wire for each band to the ground lug of the “tuner.”

Initial results:

With the Drake MN-4 antenna transmatch in the system, I was able to get a 1:1 SWR across 80, 40, 30, 20, 15, and 10 meters.  I was able to get contacts from both Hawaiian stations and stations on the U.S. mainland. Reception reports varied between 559 and 599 for CW and 55 to 59 for SSB, depending on the band in use and the time of day.  The best daytime bands were 20 and 15 meters.  Forty and 80 meters were fairly good after sunset.  Ten meters was quite noisy and mostly unusable. Most of the time, I used less than 50 watts output for my tests.

For a simple antenna made with available parts, the modified inverted “L” delivered  hours of fun at minimal cost. Since the antenna is positioned in the backyard near the rainforest, it’s nearly invisible.

Give an inverted “L” a try.  It could be the antenna you’re looking for.

References:

http://www.hamuniverse.com/slopinginvl.html.
http://www.hamuniverse.com/w7lpninvertedl8010.html
http://www.n8sdr.sopmcincy.org/index.php/wire-antennas-that-work.
http://www.antennex.com/preview/archieves/ltv.htm.

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Until next time

Russ (KH6JRM).

BK29jx15–along the beautiful Hamakua Coast of Hawaii Island.







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