Tuesday, November 19, 2013

Simple Ham Radio Antennas: The slanting 80 meter delta loop. Post #243

One of the joys of moving out of my cramped quarters at Laupahoehoe to more spacious property (1 acre) in the Puna District is the ability to erect some decent antennas.  For most of my 36 years as an amateur radio operator, I've had to "make do" with compromise antennas that often performed poorly compared to full-sized antennas.  Thanks to 450 ohm ladder line, a sturdy W9INN 4:1 balun, and a trusty Drake MN-4 antenna transmatch, I've been able to get some excellent multi band contacts with the 40 meter inverted v in the backyard and the 40 meter loop under my post and pier house.  I can't complain.  These antennas have done a good job with my older equipment in the shack.

Once I complete the slow move to my new home in the Orchidland Estates, I won't have to worry about lack of space for antennas and any ground systems I might install.  To date, I erected the following antennas at the new QTH:

A 135 ft/41.15 meters long horizontal dipole (the classic "doublet antenna") with ends supported by two Norfolk Pine trees.  The antenna is approximately 50 feet/15.24 meters above ground.  Fed with 450 ohm ladder line into a 4:1 balun and the Drake MN-4 antenna transmatch, the antenna works on any amateur radio band from 80 to 10 meters.  As a general purpose antenna, the doublet is perfect for my  location.

A 20 meter half square antenna.  This two element vertical doesn't require a ground system.  Two vertical antennas are connected at the top of each mast by a 1/2 wavelength phasing line.  A 50 ohm coaxial cable feed line is attached to the upper left hand corner of the system, with 1/4 wavelength vertical wires running down each fiberglass mast.  The antenna is bi-directional and can add an additional 3 to 4 dB gain over a regular dipole.

A 40 meter inverted v antenna fed with 450-ohm ladder line.  Used with an antenna transmatch and a 4:1 balun, I can get good performance from 40 through 10 meters.  Best of all, I don't need a ground radial system.

A homebrewed 10 meter ground plane vertical cut for 28.4 MHz.  The antenna is attached to the top of a 33-ft/10.06 meter fiberglass mast and fed with 50 ft/15.24 meters of RG-8X coaxial cable with UHF connectors.  I use this antenna for monitoring purposes.  As a single band antenna, it works well.

The temporary 40 meter delta loop fed with ladder line has been taken down to make room for the 80 meter sloping delta loop.

This brings me to the current project.

During my amateur radio "career", I've never had a good antenna for 80 meters.  The 80 meter vertical helix I built several months ago performed better than expected, considering the lack of space for a ground radial system at my Laupahoehoe qth.  I knew I could do better if adequate space were available.

Now that my xyl and I are relocating to our new "homestead", space won't be a problem.  So, this past Saturday and Sunday (16-17 November 2013), I built a simple, inexpensive full size 80 meter loop in the spacious back yard of our property.

MATERIALS:

Most of the materials I had at the new location.  I reused the 33 ft/10.06 meter MFJ telescoping fiberglass mast from the old inverted v and adapted it for the 80 meter delta loop.

I also reused two ceramic insulators, one 5 ft/1.52 meters wooden support stake for the mast, and two 6 ft/1.82 wooden stakes from the old antenna to support and tie off the loop elements.

One "Ladder Lock" connector to attach the 450 ohm ladder line and the delta loop elements.  The connector would be attached at the top of the mast, with the loop running below the apex of the mast.

Fifty feet/15.24 meters of 450 ohm ladder line, one W9INN 4:1 balun, and one Drake MN-4 antenna transmatch.  This system would be used to make the 80 meter delta loop capable of use on all amateur frequencies between 80 and 10 meters.

Short lengths (5 ft/1.82 meters) of dacron rope to tie off the bottom portion of the delta loop.

Short lengths (3 ft/0.91 meters) of RG-8X coaxial cable with UHF connectors to attach station equipment (transceiver, low pass filter, dummy load) to the Drake MN-4 antenna transmatch.

Sufficient wire to build the loop.  Using the general formula 1005/f(MHz)=L(ft) and the design frequency of 3.775 MHz, I cut the loop to a length of 266.22 ft/81.66 meters.  Each side of the delta loop measured 88.74 ft/27.05 meters.  I used #14 AWG housewire bought at Home Depot in Hilo.

ASSEMBLY:

The delta loop was built on the ground.

Once the loop was made, I attached the "Ladder Lock" connector with the 450 ohm ladder line attached  to the tip of the mast.

Because of the low height of the loop (the mast was only 33 ft/10.06 meters tall), I decided to make the antenna into a sloping delta loop, a design I had used with the 40 meter delta loop.

I then hoisted the mast onto its support stake, ran the loop at a 45 degree angle from the mast , and attatched the bottom of the loop to its wooden support stakes.  I adjusted the shape of the loop so it resembled a sloping delta.  The antenna is very close to the ground.

I ran the 450 ohm ladder line from the apex of the mast to the W9INN 4:1 balun attached to the garage wall.

Twenty five feet/7.62 meters of RG-8X coaxial cable with UHF connectors ran from the balun to the Drake MN-4 antenna transmatch in the radio room (in the corner of the garage).

To minimize rf in the shack, I attached a counterpoise measuring 66 feet/20.12 meters to the ground lug of the Drake MN-4 transmatch.

INITIAL RESULTS:

With the help of the trusty Drake MN-4, I've kept the SWR below 1.3 to 1 on all amateur bands from 80 through 10 meters.  Obviously, some antenna trimming will be done in the future.  But for now, I have no complaints about the loop's performance.  Depending on the band of choice and propagation, I've received ssb reports varying from 57 to 59+10 and cw reports ranging between 569 to 599 +10.  During the short testing period, I was running between 20 and 50 watts from my old Swan 100 MX.

So far, I'm satisfied with the performance of this slanting 80 meter delta loop.  This was a fun project.  Other than buying some extra antenna wire, I had all of the ingredients for this antenna in my garage.  Sometimes, being a "packrat" pays off.

REFERENCES:

Noll, Edward M. (W3FQJ).  73 Vertical, Beam, and Triangle Antennas. Editors and Engineers.  Indianapolis, Indiana, 46268.  First Edition, 1979.  pp.126-127.

Orr, William I. (W6SAI). and Cowan, Stuart D. (W2LX).  The Radio Amateur Antenna Handbook.  Radio Publications, Inc.  Wilton, CT, 06897.  First Edition, 1978. pp.113-128.

DeMaw, Doug. (W1FB).  Novice Antenna Notebook.  American Radio Relay League, Newington, CT, 06111. First Edition, 1988.  pp.78-90.

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Aloha es 73 de Russ (Kh6JRM).

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