Monday, November 25, 2013

Simple Ham Radio Antennas: The sloping 30 through 10 meter delta loop. Post #245

How would you like to build a simple, effective antenna for 30 through 10 meter coverage with some gain over a dipole at a moderate cost?  The answer is as simple as designing, erecting, and using a sloping delta loop antenna designed for 30 meters and fed with 450 ohm ladder line into a 4:1 balun connected to a sturdy antenna transmatch.  The ladder line will permit you to cover frequencies between 10.100 MHz through 29.7 MHz with low SWR.  You can also design the antenna for 30 meter use only by feeding the antenna with 50 ohm coaxial cable in conjunction with a 1/4 wavelength matching section made of 75 ohm coaxial cable.  The latest ARRL Antenna Book has more details on how to make the matching section should you decide for that option.

Now that I have more room for my expanding "antenna farm" at my new home site in the Puna District of Hawaii Island, I can set aside some space for antenna experiments without worrying about HOAs, CC&Rs, or unsympathetic  neighbors.  For many years, I've had to use compromise antennas at my amateur radio station.  They all worked well considering the severe space restrictions at my present location.  Once I complete the housing move next year, I'll have enough room to erect some decent antennas.  I already have a few antennas in place--most of them are well disguised by the tall trees surrounding my property.

Over the past few years, I've found the 30 meter band a welcome escape from the heavily used 20 and 15 meter bands.  The 30 meter amateur radio band is the place for the cw and digital signal enthusiast.  Even with the modest 30 meter sloping dipole I made a few weeks ago, contacts were easy to manage and the band was full during my early morning and late afternoon operating hours.  I wanted to try a full wavelength loop on this interesting band.  I've always enjoyed full wavelength loops because of their modest gain over a dipole, fairly quiet operation, and ease of construction.  With the considerations mentioned in the opening of this post, I decided to build a simple sloping delta loop for 30 meters in back of my Puna District home.  The loop would be used for frequencies ranging from 10.100 MHz to 29.7 MHz, with the main design frequency set for 10.125 MHz--the midpoint of the band.  With 450 ohm ladder line, a 4:1 balun, and my trusty MFJ 941E Versa Tuner antenna transmatch, I could roam around several bands without worrying about excessive SWR.

I started the project early this morning before the arrival of the afternoon showers predicted by the National Weather Service.  I had the following materials on hand:

One 33-ft/10.06 meter MFJ telescoping fiberglass mast.

Three 6-ft/1.82 meters wooden stakes.  One stake would support the fiberglass mast.  Two stakes would support the bottom of the delta loop.

One "ladder lock" connector to support the 450 ohm ladder line and its attachment to the delta loop at the apex of the fiberglass mast.

Two ceramic insulators attached to wooden stakes at the bottom of the delta loop.  The wire would run from the mast apex through the insulators.  Small lengths of dacron rope would tie off the insulators to the stakes.

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

Twenty-five feet/7.62 meters of RG-8X coaxial cable with UHF connectors.

One W9INN 4:1 balun.

One MFJ 941 Versa Tuner antenna transmatch.  Unfortunately, my Drake MN-4 wasn't configured to work on 30 meters.  The old Versa Tuner has given good service as a standby transmatch.

One Ten Tec Argosy II transceiver.  This is the only rig I have that can access 30 meters.

One solar charged deep cycle marine battery to serve as a power supply.

Basic tools, nylon ties, soldering gun, tape, etc.

Enough wire to make a full wavelength antenna for 30 meters.  Using the general formula 1005/f(MHz)=L(ft) and #14 AWG housewire, I cut the antenna for a resonant frequency of 10.125 MHz (the band midpoint). The total length of the antenna came out to 99.25 ft/30.26 meters.  Each side of the three-sided delta loop would measure 33.08 ft/10.08 meters.

ASSEMBLY:

The antenna was built on the ground.

I attached the top of the delta loop to the 450 ohm ladder line with the "ladder lock" device.  The center connector was secured to the top of the fiberglass mast with a short piece of dacron rope.  All connections were soldered and wrapped with several layers of vinyl electrical tape.  The "ladder lock" device with the 450 ohm feed line and its connection to the top of the delta loop was secured to the top of the mast with several nylon ties.  I ran the ladder line down the mast approximately 5 feet/1.52 meters.  I tied off the ladder line to the mast with another nylon tie.

I hoisted the fiberglass mast onto its 6 ft/1.82 meter wooden support stake.

I led the delta loop off at a 45-degree angle from the mast and secured the bottom portion of the delta loop to two 6 ft/1.82 meters wooden support stakes.  The antenna wire was threaded through 2 ceramic insulators, which were attached to the wooden support stakes by 2 inches/5.08 cm of dacron rope.

The delta loop was adjusted for a uniform shape.  The loop was configured as a sloper with the apex of the loop attached to the top of the mast and the two sides swung out at an angle and secured to wooden support stakes. Since the bottom of the delta loop is close to the ground, I attached yellow warning tape along the bottom element of the loop.

The 450 ohm ladder line was led to the W9INN 4:1 balun attached to the garage wall in back of the house. The balun is mounted approximately 6 ft/1.82 meters above ground.

Twenty-five feet/7.62 meters of RG-8X coax with UHF connectors were attached to the balun and run through a window patch panel in the garage.  The coax was then connected to the MFJ 941E Versa Tuner. Short lengths of RG-8X coaxial cable interconnected the Ten Tec Argosy II transceiver to the transmatch, low pass filter, and the dummy load.

After 2 hours of leisurely work, the antenna was done.

INITIAL RESULTS:

Thanks to the MFJ 941E Versa Tuner, I was able to keep SWR near 1.1 to 1 between 10.100 MHz and 29.7 MHz.  I made a few 30 meter contacts late this afternoon, with reports ranging between 569 and 599 using the Argosy II running approximately 20 watts.  Contacts were also made on 20 and 15 meters, with SSB reports ranging from 56 to 59 on 20 meters and 54 to 56 on 15 meters.  Again, power used was near 20 watts from the Argosy II.  I'm sure a little tweaking will be necessary to get the most out of this antenna. So far, results have been satisfactory.  For a homebrewed antenna made from available parts, I really can't complain. Most of the materials can be bought at the nearest hardware store.  You can also substitute pvc pipe, surplus military mast sections, or even a high tree branch for the mast.  This antenna is simple, cheap, and a joy to use.

REFERENCES:

http://www.hamuniverse.com/kl7jrloopnotes.html.

http://www.wikihow.com/Build-Several-Easy-Antennas-for-Amateur Radio.  See section 20 for loop antenna ideas.

http://www.southgatearc.org/articles/g0ftd/loop_antennas/simple-loop-antennas.htm.

http://arrl.org/hf-loop-antennas.

http://www.youtube.com/watch?v=y3-LIQ6G6e4.

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Aloha es 73 de Russ (KH6JRM).

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