Tuesday, October 22, 2013

A 30 Meter Sloping Dipole Antenna. Post #236

The 30 Meter Amateur Radio band (10.100 MHz to 10.150 MHz) is territory for the cw and digital enthusiast.  You can find cw operators around 10.105 MHz and many Japanese hams clustering around 10.130 MHz.  In between, you'll find RTTY, PSK 31, FAX, and other digital modes.  If you're a cw operator, 30 Meters can be the place to make new friendships at a leisurely pace while increasing your sending and receiving skills.

Antennas for this tiny sliver of the rf spectrum are modest and inexpensive to build with many materials obtainable from the nearest home improvement outlet or hardware store.

Over the past few weeks, I've built several 30 Meter antennas for my new house lot in the Puna District, including an inverted vee, a ground plane, a delta loop, and even an inverted "L".  All have worked well.

The latest addition to my growing antenna farm is a 30 Meter halfwavelength sloping dipole.  This variation of the basic horizontal, halfwavelength flat top dipole has proven to be a simple, effective antenna suitable for both home and portable use.

MATERIALS:

One 33-foot/10.06 meters MFJ telescoping fiberglass mast.  I disconnected my 30 Meter inverted vee and used those elements to form the sloping dipole.  The top of the sloping dipole would be attached to the tip of the mast, with the bottom portion being run off at an approximately 45 degree angle to a nearby wooden support stake.

Two ceramic insulators, one for each element of the sloping dipole.

Based on the general formula 468/f(MHz)=L(feet) with a chosen frequency of 10.125 MHz (mid-band), the total length of the sloping dipole worked out to be 46.22 feet/14.09 meters.  Each element of the dipole would be cut to a length of 23.11 feet/7.04 meters.  You may want to cut the wires a little longer to adjust for tuning purposes.  I chose #14 AWG housewire for the antenna elements.

One Budwig HQ-1 center coaxial connector.  I happened to have a spare connector in the junk box.  You could also make a center connector from pvc pipe, plexiglass, or some other sturdy material.

Fifty feet/15.24 meters of RG-8X coaxial cable with UHF connectors.  This would be the antenna feed line.  If you want to run more than a few hundred watts with this antenna, I would recommend a sturdier coax, such as RG-8 or RG-213.

Two 5-foot/1.52 meters wooden stakes.  One stake will support the fiberglass mast.  The other would be used to tie off the bottom end of the sloping dipole.

Basic tools, such as wire cutters, plastic vinyl tape, nylon ties, and soldering equipment.

A transceiver capable of using the 30 Meter amateur radio band.  I used an old, reliable Ten Tec Argosy II for this task.

An antenna transmatch to handle the small amount of SWR in the antenna system.  I had an old MFJ 941-E Versa Tuner for the "tuning" process.

Various coaxial patch cords to connect the transmatch to the transceiver, dummy load, and low pass filter.

A key capable of sending Morse Code.  I elected to use an old J-38 manual key from my days as a novice operator.

ASSEMBLY:

The antenna was built on the ground and later hoisted into position.

I attached the top dipole element to the + terminal of the Budwig coax connector.  I attached the bottom part of the sloping dipole to the - terminal of the Budwig coax connector.  Both connections were soldered and covered with several layers of vinyl electrical tape.

A ceramic insulator was attached to the end of the top element.  The insulator was secured to the tip of the mast with vinyl electrical tape and nylon ties.  A ceramic insulator was also attached to the end of the bottom antenna element.

Before I attached the RG-8X to the Budwig center connector, I wound 8 turns of the coax into a "choke balun" approximately 8 inches/20.32 cm in diameter.  Hopefully, the balun would keep rf off the feed line and out of the shack.

I then hoisted the fiberglass mast onto its wooden support stake.  I led the sloping dipole away from the mast at an approximate angle of 45 degrees.  The lower antenna element was tied off at the wooden stake.  The slope of the dipole was directed to the U.S. mainland (northeast from my location).  I really didn't expect much directivity from the sloping dipole, but the direction was convenient from an aesthetic point of view.  The antenna would slope into my back yard and be unnoticeable from the street.

I ran the coax feed line through a homemade patch panel in the shack window and attached it to the MFJ Versa Tuner.  I also attached a 23.11-foot/7.04 meter "counterpoise" wire to the ground lug of the "tuner."

INITIAL RESULTS:

Thanks to the MFJ 941-E Versa Tuner, I was able to keep the SWR 1.1 to 1 across the entire band.  Obviously, some trimming of the antenna will be necessary, but, for now, I'm satisfied with the performance of this temporary arrangement.  In my location, 30 meters works very well from the late afternoon through late evening.  Reports ranged from 559 to 599 with the Argosy II running about 25 watts.

Thirty meters is a fun place to be.  You can get a lot of contacts with modest equipment and an inexpensive wire antenna built at home.

REFERENCES:

http://www.chem.hawaii.edu/uham/antennas.html.
http://www.arrl.org/files/Technology/tis/info/pdf/9106023.pdf.
http://youtube.com/watch?v=mgEibY3INHo.
http://www.hamuniverse.com/n4jaantennabook.html.
w4rnl.net46/sloper.html.

You can follow our blog community with a free email subscription or by tapping into the blog RSS feed.

Thanks for joining us today!

Aloha es 73 de Russ (KH6JRM).

BK29jx15--along the beautiful Hamakua Coast.