Saturday, May 18, 2013

Antenna Topics: A simple 40 through 10 meter delta loop. Post #192

A simple 40 through 10 meter delta loop.

One of the quietest and most versatile antennas I've used over the past few years has been a 40 through 10 meter delta loop fed with 450-ohm ladder line.  Used with a 4:1 balun, an antenna matchbox (i.e. "tuner), and a few feet (meters) of 50-ohm coaxial cable, this easy to build antenna will give you hours of both local and DX contacts.

I built my original 40 meter delta loop with tuned feeders back in 1977, shortly after I passed my novice amateur license exam.  Since space was at a  premium (small backyard), money in limited supply (I was just starting my broadcast radio career after time in the Air Force), and I was recently married, extra funds for a tower and a super sophisticated rig were unavailable.  Like many of my fellow amateurs, I depended on wire antennas, used rigs, and basic designs to work the world.  My first rig was the venerable HW-101, a rig I must have rebuilt several times.

Anyway, I found simple antennas, such as dipoles, inverted vees, and loops were easy to build, cost me very little, and were more than satisfactory for my needs.  Even though my fortunes have improved since those early days, I still prefer making my own wire antennas.

So, on Friday, I opened my antenna logbook for 1977 and found a simple delta loop design I used in November of that year.  Today (Saturday, 18 May 2013), I rebuilt that antenna with supplies I had in the garage.  The antenna works very well and only took me a few hours to build, erect, and test.

MATERIALS:

One 33-foot (10.06 meters) MFJ fiberglass mast.

Three ceramic insulators.  One positioned at the top of the mast and two placed at the bottom of the delta loop.

Two 6-foot (1.82 meters) metal fence posts to tie off the bottom of the delta loop.  I used two 5-foot (1.52 meters) of dacron rope to tie the bottom insulators to the posts.

One 6-foot (1.82 meters) metal fence post to support the fiberglass mast.

A sufficient length of #14 AWG house wire for the delta loop.  Using the general formula for a loop, 1005/f (MHz)=l(ft), and the chosen frequency of 7.088 KHz for the loop, the delta loop was cut to a length of 141.78 feet (43.22 meters).  Each side of the delta loop would equal 47.26 feet (14.40 meters).

A 50-foot (15.24 meters) length of 450-ohm ladder line.

A W9INN 4:1 balun.

A 20-foot (6.09 meters) piece of RG-8X coaxial cable.  This would run from the 4:1 balun to the anti-static system near the shack window.

A 10-foot (3.04 meters) length of RG-8X coaxial cable.  This cable would run from the anti-static unit through the shack window to the Drake MN-4 antenna matchbox (i.e. "tuner).

Short pieces of 50-ohm coax cable to connect the Drake MN-4 to the Swan 100-MX, the low pass filter, and dummy load.

ASSEMBLY:

The antenna was built on the ground.

I fashioned the antenna wire into a rough triangle shape.  I attached a ceramic insulator to the top of the mast and passed the antenna wire through it to the far right end insulator.  At the lower left insulator, I attached the 450-ohm ladder line, with one wire connected to the wire running towards the top of the mast and the other wire attached to the lower wire running to the far right insulator.  All connections were soldered and wrapped with several layers of vinyl electrical tape.

You can attach the feed line at any corner of the delta loop, depending on what kind of polarization you desire.  I attached the feed line to the bottom left of the delta loop because it made maintenance simpler for me.  I expect my signal will be vertically polarized.

I hoisted the fiberglass mast onto its support stake and tied-off the bottom portion of the delta loop to two stakes.  The sides resembled an equal lateral triangle.

The ladder line was led away from the lower left insulator at approximately 6-feet (1.82 meters) above ground.  The ladder line was attached to the 4:1 balun on the garage wall (approximately 6-feet/1.82 meters) above ground.

The 20-foot (6.09 meters) length of RG-8X was attached to the balun and run to the anti-static unit.  The balun was later covered with thick plastic sheeting to protect it against rain and wind.

From the anti-static unit, I ran a 10-foot (3.04 meters) of RG-8X through the window of the shack and onto the Drake MN-4, the Swan 100-MX, and associated equipment.

PRELIMINARY RESULTS:

Using the Drake MN-4 and the 4:1 balun, I was able to keep the SWR below 1.5 to 1 on 40, 20, 15, and 10 meters.  Although propagation has been down a bit since the last CME from the sun, there have been some excellent contacts using less than 50 watts from the old Swan 100-MX.  Depending on the band and time of day, most CW reports range from 549 to 599 and the SSB reports vary between 54 and 57.  Local interisland contacts usually range from 579 to 599 on CW and 57 to 59 on SSB.

The loop does an excellent job for local area nets with coverage out to about 250 miles (approximately 400 kilometers).  I'm probably getting more horizontal polarization than vertical polarization.  The loop makes an excellent NVIS (near vertical incident skywave antenna).  Those into emergency communications may want to consider a low-level loop for strong local coverage.

So far, I'm satisfied with the performance of the delta loop.  It's quiet, cheap, and simple to make.  I've been thinking of making another delta loop and using the pair as a 2-element beam.  I should get some gain out of this arrangement.  The antenna was an enjoyable project.

REFERENCES:

"How to build a delta loop antenna."  http://www.youtube.com/watch?v=WF1TIfbI8Xo.
"Dual Delata Loop for 10 and 12 Meters."  http://www.hamuniverse.com/kl7jrdualdelta1012.html.
"Delta Loop for HF--W5SDC Homepage."  http://w5sdc.net/delta_loop_for-hf.htm.

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Thanks for joining me today!

Aloha es 73 de Russ, KH6JRM

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