Friday, August 16, 2013

A Full Wavelength Loop for 40 through 10 Meters. Post #222

Having built a series of verticals, inverted vees, half squares, and loops for my amateur radio activities, I decided to "thin the heard" of my less than successful antenna efforts and concentrate on a few antennas that have given me the most contacts and overall satisfaction.

Although I love the ease of assembly and portability of homebrew vertical antennas, I just don't enjoy the labor involved in putting in a ground radial system.  The elevated counterpoise systems I've used have been less labor intensive than the buried radial approach, but, still, there is a lot of wire running around my property which is a safety hazard for children and pets.

The inverted vee antennas are being kept for portable and emergency use.  I have a few telescoping fiberglass masts which make raising these antennas an easy task.

Since I lack the space to erect a 80-Meter horizontal 1/2 wavelength flat top dipole (the familiar "doublet" antenna), I have put that antenna on my lot in the Puna District.  My xyl and I spend the weekends there remodeling our future home.  I'm able to use the various trees on the lot to erect some decent dipoles as well as my successful half square antennas for 40-and 20-Meters.  These antennas will stay because I have adequate space and supports to create a good "antenna farm."

While we're remodeling our new home, I'm still operating my amateur radio station in the confined lot which has been our home for many years.  Because of space limitations and limited areas to run a ground radial system, I've opted to use a full wavelength delta loop for my 40 through 10-Meter activity.

Over the course of the past few weeks, I've modified some of my previous loop designs and have rebuilt a delta loop which performs well, has low SWR, shows some gain over a dipole, and is easy to erect.  To get 40 through 10-Meter coverage, I'm feeding the full wavelength delta loop with 450 ohm ladder line.  The ladder line is coupled to a W9INN 4:1 balun, which is then connected to RG-8X coaxial cable.  The cable enters the shack through a homebrew wooden patch panel in a nearby window.

MATERIALS:

One 33-foot/10.06 meter MFJ telescoping fiberglass mast.  This will support the apex of the delta loop.

Using the general formula for a full wavelength loop (1005/f (MHz)=L (ft) and a chosen frequency of 7.088 MHz, the loop measures 141.78 ft/43.22 meters.  Each side of the equilateral triangle will measure 47.26 ft/14.54 meters.  I used #14 AWG housewire I bought at the Hilo, Hawaii Ace Hardware Store.

Three ceramic insulators to form the equilateral delta loop.

Three 7 ft/2.13 meters wood stakes.  One stake will support the fiberglass mast and the remaining two stakes will support the bottom side of the delta loop.

50 ft/15.24 meters of 450 ohm ladder line. This will be the feedline.

One W9INN 4:1 balun.

25 ft/7.62 meters of RG-8X.

Station tools, transceiver, low pass filter, dummy load, Drake MN-4 transmatch, nylon ties, vinyl electrical tape, soldering equipment, and dacron rope.

ASSEMBLY:

The antenna was built on the ground.  The fiberglass mast was also on the ground.

141.78 ft/43.22 meters of #14 AWG housewire was laid on the ground and passed through three ceramic insulators.  The 450 ohm ladder line was soldered to the bottom left hand section of the delta loop.  That connection was wrapped with several layers of vinyl electrical tape.

I secured the apex of the delta loop and its insulator to the top of the mast with nylon ties and vinyl electrical tape.

I hoisted the mast onto its support stake.  The bottom two insulators of the delta loop were secured to two wooden stakes equidistant from the bottom of the mast.  Dacron rope was used to tie off the bottom of the delta loop.  I made minor adjustments to the loop, so the loop would assume the shape of an equilateral triangle measuring 47.26 ft/14.54 meters for each side.

The ladder line was led to the W9INN 4:1 balun attached to the garage wall.  The ladder line was not allowed to touch the ground.  The height above ground for the ladder line ran from 7 ft/2.13 meters at the support stake to 10 ft/3.04 meters at the balun attachement point on the garage wall.

25 ft/7.62 meters of RG-8X with UHF connectors ran from the balun to the wooden patch panel in the shack window and then onto the Drake MN-4 transmatch.  Small patch cords connected the transmatch to the Swan 100-MX, the dummy load, and the low pass filter.

INITIAL RESULTS:

With the use of the Drake MN-4 transmatch, I was able to get a SWR of 1.3 to 1 across the 40, 20, 15, and 10 Meter Bands.  Using 25 to 50 watts output from the old Swan 100-MX I received reports of 559 to 599 on cw and 55 to 59 on ssb.  The best reports came on 20 meters and 40 meters.  Ten meters was fairly noisy, while 15 meters showed some life in mid afternoon.

I'll be using this loop for a while.  My other antennas have been boxed and stored in the garage.  With only one antenna in the backyard, I'll have some room to experiment with other designs until my xyl and I move to our permanent home.  The antenna performs well and gives me plenty of contacts.

REFERENCES:

http://www.youtube.com/watch?v=JiFllyZzfnUo.
http://www.youtube.com/watch?=7odS9dWcUyE.
http://www.iw5edi.com/ham-radio/?full-wave-loop-antenna,164.
http://www.radioworks.com/nloop.html.

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Thanks for being with us today!

Aloha es 73 de Russ (KH6JRM).

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