Saturday, June 1, 2013

Antenna Topics: A Simple Field Day Antenna

The ARRL (American Radio Relay League) 2013 Field Day is set for Saturday and Sunday, 22 June through 23 June 2013.  This is one of the biggest emergency communications exercises in the country and it attracts thousands of amateur radio operators to field day sites throughout the United States and Canada.  Many DX stations around the world participate in this event, so, if it's DX you're looking for, Field Day may just be the place for you.

Because of work or family responsibilities, many amateur radio operators can't join their clubs at a Field Day site.  Instead, these amateur will operate from their homes, using a variety of emergency power configurations, ranging from generators to solar-charged batteries.  Amateur radio operators specializing in emergency communications will run stations from civil defense headquarters, police stations, and even public schools.

Field Day will give you a taste of an intense, but fun operating experience without the comforts of home.  In years past, I've fought off mosquitoes, assorted insects, thunderstorms, and crowds of curious onlookers as I tried to communicate with fellow amateur operators thousands of miles away.

One of the interesting and intriguing parts of any Field Day experience is the "antenna farm" which is raised when the event begins.  Antennas range from telescoping towers topped with 4-element monoband beams to   vertical beam antennas and oddly-configured loops.  Those amateurs into satellite operations often bring an array of homemade and commercial antennas designed to contact these elusive, fast moving space "birds."

All of the group comraderie, antenna raising, and operating is quite an experience.  But, what do you do if you can't join a club at a Field Day site?  Do you avoid the event?  Of course not.  You dig in and run as a single operator at your home qth, a favorite public park, or at your chosen camp site using emergency power such as solar-charged batteries or a genertor.

What about an emergency Field Day antenna?  Why not make your own portable antenna and take it with you to your special site?  That's what I'm planning to do.

On Field Day weekend, I'll be announcing the June Points Meet for the Big Island Auto Club at the Hilo Drag Strip.  Since the races will run into the evening, I won't be able to spend much time at my club's Field Day site at the Wailoa Visitors Center in Hilo.  So, I'm bringing my emergency portable station with me in the Odyssey van and will operate after the evening's racing program is done.  I'll be spending the night at the track with the security team, so, at least, I'll have company and perhaps a few converts to amateur radio.

Here's my equipment list for my 1E (single operator, emergency power) station:

A Yaesu FT-7 QRP (10 watts) rig that covers 80 through 10 meters (no WARC bands).

A deep cycle marine battery charged by solar panels.  I'll charge the panels during the day and operate battery power after the races are done for the evening.

A "homebrew" 40 through 10 meter half-wave sloping dipole, consisting of two equal lengths of #14 AWG housewire.  I cut the wire for 7.088 MHz.  Using the general formula, 468/f (MHz)=L (ft), the total dipole length measured 66.02 feet/20.12 meters.  The dipole was cut in half to provide a 1/4 wavelength section for each half of the sloping dipole.  Each antenna element measured 33.01 feet/10.06 meters.

Fifty feet (15.24 meters) of 450-ohm ladder line.  This would be my antenna feed line.


One 33-foot (10.06 meters) MFJ telescoping fiberglass mast.  The mast collapses down to a small package and fits comfortably in my van.

Two ceramic insulators...one for each antenna element.

One, five-foot (1.52 meters) wooden stake to tie off the sloper.  The post can be moved to change the directional pattern of the sloper.

One, five-foot (1.52 meters) support stake for the mast.

One large hammer to set the support stake.

Various tools, such as screwdrivers, portable drill, pliers, wire cutters, vinyl electrical tape, nylon ties.

One Drake MN-4 antenna transmatch.

One W9INN 4:1 balun.  The balun and transmatch are needed for the feed line to work properly.

A 25-foot (7.62 meters) piece of RG-6 coaxial cable with "F" to "UHF" connectors.  This cable would run from the 4:1 balun to the Drake MN-4 antenna transmatch.  Small coaxial patch cords would connect the Drake MN-4 to the Yaesu FT-7 QRP transceiver.

One Yaesu FT-7 QRP rig.  You will probably get better results with a more modern rig such as the Yaesu 817ND or an ICOM 703.  I had the FT-7 in the shack as a backup rig.  I use this rig for my portable operations.

Headphones, notebook, pencils, pens.

One deep cycle marine battery and small solar panels for battery charging.

ASSEMBLY:

I built the antenna at home and had it ready for the Field Day weekend.  The antenna is now in the back of the van ready to be used.  I tested the antenna before I packed it away in the van.



All I had to do was attach the 450-ohm ladder line to each antenna element.  One lead went to the top element.  The remaining lead went to the lower element.  All connections were soldered and wrapped with several layers of vinyl electrical tape.

End insulators were attached to each antenna element.

I hoisted the antenna on a temporary wooden stake and attached the lower end of the sloper to a pre-positioned stake facing Northeast.

I ran the feed line to the W9INN 4:1 balun.  Twenty-five feet (7.62 meters) of RG-6 coaxial cable ran from the 4:1 balun to the Drake MN-4 antenna transmatch.  A short length of RG-6 ran from the Drake MN-4 to the Yasesu FT-7 QRP transceiver.

Thanks to the Drake MN-4, I was able to keep SWR below 1.5 to 1 on 40, 20, 15, and 10 meters.  I received acceptable reception reports during my initial tests (559 to 599 on CW and 54 to 57 on SSB, depending on propagation and time of day).

Satisfied that the antenna was working well at 10 watts from the Yaesu FT-7, I disassembled the antenna, collapsed the mast, packed the battery and solar chargers in two large plastic bins, rolled up the feed line, packed the rig and Drake MN-4 in two padded boxes, and put the system in the van.

When Field Day comes, I'll have an emergency antenna that will be easy to erect, tune, and take apart during the event.  The antenna will become part of my permanent emergency "go" kit for HF operations.

If you're going solo during Field Day, you may want to try this simple antenna.

REFERENCES:

http://www.hamuniverse.com/ae5jufielddayantenna.html.
http://www.hamuniverse.com/klybobfielddayant.html.
http://www.kn5l.net/fdantenna/
http://www.k9jy.comblog/2008/05/14/field-day-antennas-5-considerations.

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Thanks for joining me today!

Aloha es 73 de Russ, KH6JRM.

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