Thursday, May 16, 2013

Antenna Topics: A multi-band half-wavelength sloper covering the 40, 20, 15, and 10 meter amateur radio bands, post #191.

A multi-band half-wavelength sloper antenna.

This has been another beautiful, slightly windy day on Hawaii Island--a perfect time to build another antenna for DX adventure.  Although I've been happy with my 40 meter vertical with tuned counterpoise, I wanted to experiment a bit with another antenna I used frequently in my novice license days almost four decades ago.

I quickly found my antenna experiment log book on the shelf of the radio room and turned to the pages marked "November-December 1977."  Those were some unusually dry months at my old QTH in Honokaa.  I was able to build several working verticals, loops, and slopers for my then new novice station.

By feeding the sloper with 450-ohm ladder line and a 4:1 balun, I was able to cover three novice segments  in the 40, 15, and 10 meter amateur radio bands with few problems.  I knew the antenna would work on 20 meters, but I didn't hold a higher license (i.e. general, advanced, or extra class) to  qualify for that band.  Of course, after the passage of 37 years, I eventually got my general, advanced, and extra class licenses, so the old novice restrictions didn't apply.

Like a child in a toy store, I relished the idea of rebuilding an old antenna that could serve my current license class (Amateur Extra Class).  Since I have a limited budget in my retirement years, I decided to continue my practice of building my own antennas with wire, pvc masts, and parts available locally.  I also build my antennas with another purpose--they are collapsable and transportable for mobile, portable, or emergency use.

MATERIALS:

One MFJ telescoping fiberglass mast, 33-feet long (10.06 meters).  The top of the sloper would be attached to the tip of the mast, with the rest of the antenna running at a 45-degree angle to a tie-off stake.

66.02 feet (20.13 meters) of #14 AWG house wire.  The sloping dipole was designed to resonate at 7.088 KHz, the frequency of the Hawaii Afternoon Net.  During construction of the sloping dipole, the wire would be cut into two equal portions (33.01 feet/10.06 meters).  Each piece would form the elements of the dipole.

Two ceramic or plastic insulators to tie-off the sloping dipole.  One insulator would be at the top of the mast, while the other would drop down at a 45-degree angle to a wooden tie-off stake.

Two small pieces of dacron rope to tie-off the ceramic insulators.

One ceramic insulator at the center of the antenna.  The 450-ohm feed line would be attached here.

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

One W9INN 4:1 balun.  Any 4:1 balun would work.  I happened to have a spare W9INN balun in the shack.

20-feet (6.09 meters) of RG-8X coaxial cable to run from the 4:1 balun to the anti-static discharge unit near the window of the shack.

A 10-foot (3.04 meters) piece of RG-8X cable to run from the static discharge unit  through the window pane and then on to the Drake MN-4 matchbox.  An antenna "tuner" is necessary for this antenna to work properly.

Small coaxial patch cords to connect the Drake MN-4 to the Swan 100-MX transceiver, a dummy load, and a low-pass filter.

ASSEMBLY:

The mast was placed on the ground.  Each antenna element was attached to a ceramic insulator and to the center ceramic insulator.  The top half of the antenna and its corresponding insulator were attached to the tip of the MFJ fiberglass mast and secured with nylon ties.  The bottom element was attached to the center insulator.  The end of this element was attached to its insulator and later tied-off at a wooden stake.

The 450-ohm ladder line was attached to each element, with the center insulator supporting the connection.  All connections were soldered and covered with several layers of vinyl electrical tape.

The mast was hoisted and placed on its wooden support stake.  The support stake was a metal fence post, 6-feet long (1.82 meters).  The post was driven into the ground approximately 2-feet (0.60 meters).  The antenna was brought off the top of the mast at a 45-degree angle and secured to a 5-foot (1.52 meters) wooden stake.

The 450-ohm ladder line was led off from the center connector to the W9INN 4:1 balun attached to the garage.  The feed line remained approximately 16-feet (4.87 meters) off the ground until it reached the balun just below the roof of the garage.  The balun was later wrapped in plastic to protect it from the rain and sun.

20-feet (6.09 meters) of RG-8X was attached to the 4:1 balun and directed down to the anti-static unit below the shack window.  The anti-static unit is attached to an 8-foot (2.43 meters) copper ground rod.

A 10-foot (3.04 meters) piece of RG-8X entered the shack through the window pane and was connected to the Drake MN-4 and the rest of the station equipment.

INITIAL PERFORMANCE:

If you change the direction of the stake supporting the bottom half of the sloping dipole, you can get some directivity to your signal.  Since I planned to aim my signal to different parts of the world, I decided to put stakes facing NW, NE, SW, and SE of my QTH.

Initial tests were encouraging.  With the Drake MN-4 in line, I was able to get a 1.5 to 1 SWR on 40, 20, 15, and 10 meters.  Signal reports varied from 559 to 599 on CW and 54 to 59 on SSB, depending on propagation and time of day.  Because of the recent CMEs from the sun, propagation on 15 and 10 meters has been poor to fair over the past few days.  Most of my contacts were made using less than 50 watts from the old Swan 100-MX.  The rig is old and I didn't want to stress the finals too much.

As is my usual practice, I disconnect and ground the feedline after the operating day is over.  I also lower the mast to reduce visibility and the chance of a lightning strike.  The mast is painted a dull green and seems to blend in well with the surrounding trees and vegetation.  The mast is hardly noticeable from the street.

So far, I'm satisfied with the overall performance of this "homebrewed" antenna.  My cost was minimal because I had most of the materials stored in the garage.  What I didn't have, I could have bought at the nearest hardware or home improvement center.

If you want a simple, multi-band antenna that works, try this sloping dipole.  You won't be disappointed.

REFERENCES:

"A Two band Half Sloper Antenna" http://w5gzt.us/8006032.pdf.
"MF/HF Slopers--ARRL."  http://www.arrl.org/mf-hf-slopers.
"Sloper Antenna Tests."  http://www.hard-core-dx.com/nordicdx/antenna/wire/sloper.html.

If you want the latest Amateur Radio News, please check my news site -- http://kh6jrm.com.  I've included a few news items at the end of this post.

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Thanks for joining us today!

Aloha es 73 de Russ (KH6JRM)

BK29jx15--along the beautiful Hamakua Coast of Hawaii Island