Thursday, May 23, 2013

Antenna Topics: A simple 10 meter dipole. Post #195

A simple 10 meter dipole antenna.

One of my favorite amateur radio bands is 10 meters.  It's unpredictable, capricious, and fun!  When propagation is favorable, you can works the world at QRP levels.  Basic antennas for this band are simple, cheap, and forgiving.  Most of the parts needed for this antenna can be bought at your neighborhood hardware store or home improvement outlet.

Although 10 meters has been a bit sporatic over the past few days, I've been able to make some good contacts during daylight hours from my location on Hawaii Island--the island with the active Kilauea Volcano.  We live dangerously over here.

MATERIALS:

Two fiberglass or pvc masts, ranging from 20 to 30 feet tall (6.09 meters to 9.14 meters).  These masts will support the 10 meter half-wavelength "flat top" antenna.  Fortunately, my backyard can support two masts approximately 30 feet (9.14 meters) apart.  Anything more requires my dipoles to be in the inverted vee configuration.  For this project, I had two, 33-foot (10.06 meters) fiberglass masts in storage.

One Budwig HQ-1 coax center connector (available from Fair Radio Sales in Lima, Ohio).  You make a center connector out of plexiglass, tough plastic, or even a long, ribbed end insulator.  I had a spare HQ-1 in the shack, so I used that for the center connector.

Two ceramic insulators. These would be used to tie off each dipole element to its mast.

A 6-foot (1.82 meters) wooden or metal fence post to support each mast.

Fifty-feet (15.24 meters) of 50-ohm coaxial cable (RG-8X, RG-8, RG-58).  Since I didn't have any RG-8X around the shack, I used the RG-6 coaxial cable attached to my 15 meter vertical dipole.  I disconnected the inverted dipole and stored it in a plastic storage bin for later use.

A suitable length of #14 AWG house wire for the dipole elements.  I wanted the antenna cut for 28.400 MHz, right in the middle of the novice/technician phone band for 10 meters (28.300 MHz to 28.500 MHz).  Using the general formula for a half-wave flat top dipole (468/f (MHz)=l(ft), I cut a piece of #14 AWG wire to a length of 16.47 feet (5.02 meters).  Each dipole element would be 8.23 feet (2.51 meters) long.

10-feet (3.04 meters) of dacron rope for each end insulator.  The rope would be used to tie-off the dipole elements.

ASSEMBLY:

I built the antenna with both masts nested to the ground.

I attached each dipole element to the center insulator.  Each connection was soldered and wrapped with several layers of vinyl electrical tape to seal out salt air and rain.

Each antenna element was attached to its end insulator.  A 10-foot (3.048 meters) piece of dacron rope attached each element to the top of its respective mast.

I attached the RG-6 coaxial feed line to the Budwig HQ-1 center connector.  The cable already had a "choke balun" from the previous 15 meter vertical dipole.

I hoisted the masts into position, leaving a little sag in the flat-top dipole to account for wind movement.

The antenna height above ground was approximately 31-feet (9.45 meters), allowing for some sag in the antenna.

The RG-6 coax feed line was led off the dipole at a 90-degree angle, finally reaching a plastic hook in the garage.  The hook was approximately 16-feet (4.87 meters) above ground.  The cable was then led to the anti-static unit beneath the shack window.

A 10-foot piece (3.04 meters) of RG-6 coax went from the anti-static unit, through the shack window, and then onto the Drake MN-4, low pass filter, dummy load, and the Swan 100-MX transceiver.

INITIAL PERFORMANCE:

With the Drake MN-4 antenna matchbox ("tuner") in line, I was able to keep SWR below 1.5 to 1 from 28.300 MHz to 28.500 MHz.  I've been able to establish a few mainland U.S.A. and Asian contacts, with reports varying from 549 to 579 on CW and from 53 to 57 on SSB.  I've been running the old Swan 100-MX at 20 to 30 watts.  Nothing outstanding, but I do get contacts on a band that has been "up and down" for several days.  I'll keep the flat top around for a few days and see what it does.  I may also shift the antenna to a vertical dipole arrangement as I did with my 15 meter antenna.  The conversion will be simple and will require only one mast.  In any case, I won't need a ground radial system.

Try a simple 10 meter horizontal dipole...it works; it's easy to build; and it's cheap.

REFERENCES:

http://www.hamuniverse.com/easydipole.html.
http://www.arrl.org/files/file/Technology/tis/info/pdf/9106023.pdf.
http://www.youtuve.com/watch?v=quXF2MHIn-w.
http://www.youtube.com/watch?v=8KHzsKYs

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Thanks for joining us today!

Aloha es 73 de Russ (KH6JRM).

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