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Thursday, October 31, 2013

A 40-10 Meter sloping Delta Loop Antenna. Post #238.

A one-wavelength loop is one of my favorite antennas.  Loops may be built in a square, circular, rectangular, of triangular form to create an effective, inexpensive antenna.  Loops can be built for single band service using coaxial cable and a quarter wave transformer or for multiple band use employing 450 ohm ladder line fed into a 4:1 balun and then into an antenna transmatch.  A small length of 50 ohm coaxial cable with UHF fittings can be used to connect your transceiver to the transmatch.

For my growing antenna farm at my new homesite in the Puna District of Hawaii Island, I needed an antenna which would give me good local coverage for local state wide nets and a decent signal for DX work.  From my location on Hawaii Island, almost anything beyond Hawaii counts as DX.  I elected to build a simple, one wavelength long sloping delta loop supported by a telescoping fiberglass mast and supported at the bottom ends by two wooden stakes.

In order to cover 40 through 10 meters, I designed the delta loop for the lowest frequency of use.  In this case, that frequency was 7.088 MHz, the meeting place of the daily Hawaii Afternoon Net.  I would operate the loop on its various harmonics with 450 ohm ladder line, a W9INN 4:1 balun, a short length of 50 ohm coaxial cable, and my trusty Drake MN-4 transmatch.  I would use my MFJ 941-E Versa Tuner and my Argosy II transceiver for 30 meter contacts.  For the remaining bands, I could use either the Argosy II or the old Swan 100 MX.

MATERIALS:

One 33-foot (10.06 meters) MFJ telescoping fiberglass mast.  The mast would support the apex of the delta loop.

Three ceramic insulators--one at the apex of the loop and the other two at the bottom two ends of the loop.

#14 AWG housewire.  This is sturdy material and will stand up to the tropical heat and rain.   You could also use whatever wire you have in the shack.  I've found #18 speaker wire from Radio Shack a good alternative wire source.  Using the general formula 1005/f(MHz)=L(feet) and my preferred frequency of 7.088 MHz, the total length of the loop came out to be 141.78 feet/43.22 meters.  Each side of the delta loop would be 47.26 feet/14.40 meters.

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

One W9INN 4:1 balun.

A sturdy transmatch.  I had a Drake MN-4 and a MFJ 941-E Versa Tuner at my disposal.

One 5-foot/1.52 meters wooden support stake for the fiberglass mast.

Two 6-foot/1.82 meter wooden stakes to support the bottom of the delta loop.

Short pieces of Dacron rope to tie off the bottom loop element to its stakes and to attach the upper portion of the loop to the top of the mast.

Basic tools, including a soldering gun, vinyl electrical tape, pliers, and nylon ties.

ASSEMBLY:

The delta loop was built on the ground.

I laid out the antenna wire on the lawn in back of my garage, with each side measuring 47.26 feet/14.40 meters.  The wire was threaded through 3 ceramic insulators.  At the lower right hand corner of the loop, attached the 450 ohm ladder line.  All connections were soldered and covered with several layers of vinyl electrical tape.

I attached the top of the delta loop to the tip of the mast.  The ceramic insulator was secured by nylon ties and vinyl electrical tape. 

I hoisted the mast onto its support stake, pulled the loop away from the mast at about a 45- degree angle, and secured the bottom of the loop to two 6-foot/1.82 meter wood stakes. Short pieces of Dacron rope attached the ceramic insulators to the wooden end stakes.  Some minor adjustments were made so that the delta loop assumed a uniform shape as it came away from the fiberglass mast.

The 450 ohm ladder line ran from the right hand bottom insulator to the W9INN 4:1 balun on the garage wall.  The balun was about 5 feet/1.52 meters) above ground.  At no time was the ladder line allowed to touch the ground.

A twenty-five-foot/7.62 meters length of RG-8X coaxial cable with UHF fittings was attached to the balun. The coaxial cable was run into the shack through a homemade patch panel in the shack window.  The cable was connected to the Drake MN-4 antenna transmatch.  From the transmatch a series of 3-foot/0.91 meter coaxial patch cords connected the transceiver, dummy load, and low-pass filter to the Drake MN-4.  I also added a 33-foot/10.06 meter "counterpoise" wire to the ground lug of the Drake MN-4 transmatch.

INITIAL RESULTS:

With the help of the Drake MN-4 transmatch and the MFJ 941-E Versa Tuner, I was able to get a 1:1 SWR reading on all amateur radio frequencies from 40 through 10 meters.  Daytime coverage on 40 meters is excellent with 57 to 59 reports on ssb and 579 to 599+ on cw.  Despite the loop's proximity to ground, I've been able to get some excellent DX on 20 and 15 meters.  Ten meters has ranged from good to poor, depending on the time of day and propagation.  Most of my DX work on 20 and 15 meters has ranged from 56 to 59 on ssb and 569 to 599 on cw.  I ran the Swan 100 MX at 50 watts and the Ten Tec Argosy II at approximately 20 to 25 watts.

The sloping delta loop is a simple, inexpensive antenna that will deliver good results for both local and DX contacts.  Unlike my vertical antennas, I didn't need a ground radial system to get decent performance.  Wire antennas are fun to build.

REFERENCES:

http://www.k5rcd.org/hor%20loop%20instruct.htm.
http://www.youtube.com/watch?v=WF1Tlfbl8Xo.
DeMaw, Doug (W1FB).  Novice Antenna Notebook.  ARRL, Newington, CT., 06111.  First Edition, 1988.  pp 78-89.
Noll, Edward M. ( W3FQJ).  73 Vertical, Beam, and Triangle Antennas.  Editors and Engineers, Ltd.  New Augusta, Indiana.  Seventh Printing, 1979.  pp 126-138.

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Aloha es 73 de Russ (KH6JRM).

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