Tuesday, March 18, 2014

Simple Ham Radio Antennas: The "Fencetenna". Post #266

Building wire antennas is one of the few amateur radio activities that remains fairly inexpensive.  Your nearest hardware store or home improvement outlet is chocked full of wire, connectors, pvc pipe, copper tubing, and basic tools to launch your antenna building efforts.

Whether you make simple dipoles, inverted vees, loops, or even directional vertical arrays, the satisfaction of having built something that links you to your fellow amateurs around the world is beyond compare.  If the antenna doesn't meet your expectations, you can salvage most of your material and try again.  It's all part of a continuing educational experience that can last a lifetime.  Add to this mix a few simple transceiver kits or accessories and you have something that will be your faithful radio companion for many years.

I approach my antenna "adventures" with that sort of mindset, and I'm always on the lookout for intriguing antenna ideas that I can modify for my own use.

Such was the case last week Friday after the Laupahoehoe Community Public Charter School took its annual spring break.  My xyl and I planned a brief visit to our new property in the Puna District to continue work on remodeling our permanent home.  There would also be plenty of time to search for new antenna locations once the building chores got done.  Fortunately, our property is surrounded by a semi-tropical forest of ohia, hale koa, and norfolk pine trees which range from 20 to 60 feet/6.09 to 18.29 meters high. This is a perfect environment for antenna experimentation.  I already have found a place for a multiband inverted vee, an 80-10 meter doublet, and an 80 meter loop antenna.  All of these antennas are fed with 450 ohm ladder line connected to a 4:1 current balun.  A short length of RG-8X ties the system to my trusty Drake MN-4 ATU or the spare MFJ 941-E Versa Tuner II.

A curious feature runs along the north property line of my new home.  The previous owner had erected a 150 foot/45.73 meter, 6 foot/1.82 meters tall redwood fence to divide the property from the nearby forest area.  Why not use these fence to support a new NVIS (near vertical incident skywayve) antenna?  I had plenty of hookup wire (#22 AWG) in the shack, a few ceramic insulators, 75 feet/22.86 meters of RG-8X coaxial cable with UHF connectors, and an old, but serviceable 1:1 current balun.  So, another antenna scheme was hatched.

Earlier this month, I remembered an article by Dave Land (KD5FX) on the "Fencetenna", an all band antenna supported on a wooden privacy fence which was invisible to neighbors and enforcers of HOA and CC&R antenna rules.  This would make a near perfect stealth antenna.  I decided to modify Dave's design and build my own version of the "Fencetenna."

MATERIALS:

The antenna is simplicity itself.  Following Dave's guidelines, I assembled the following items:

One 1:1 current balun.

A convenient length of coaxial cable with UHF connectors.  The fence was approximately 50 feet/15.24 meters from the shack, so 75 feet/22.86 meters of RG-8X would be sufficient for the feed line.

Two non-resonant antenna elements, measuring 70 feet/21.34 meters each.  #22 AWG hookup wire was used for the antenna elements.

Two ceramic insulators and nylon rope to tie off the antenna segments.

Some push pins.

Short pieces of nylon rope to secure the antenna segments to the fence.

Nylon ties to secure antenna elements, the balun, and a portion of the coaxial feed line to the fence.

Various tools, including a soldering gun, wire clippers, pliers, knife, and sandpaper.

Shack equipment, including a Drake MN-4 ATU and a MFJ 941-E Versa tuner II.

Ten-Tec Argosy II, Swan 100-MX, and a Kenwood TS-520.

Heathkit Dummy load and a low pass filter.

ASSEMBLY:

I built the antenna in the garage.

Each antenna segment was soldered to its respective tab on the 1:1 current balun.  All connections were covered by several layers of vinyl electrical tape.

A ceramic insulator was attached to each end of each antenna element.

I positioned the balun horizontally across the top of the fence and secured it to the fence with several nylon ties.

I ran one antenna segment along the top of the fence and secured the attached end insulator with nylon rope and push pins to the top of the fence.

I ran the remaining antenna segment vertically down from the balun to the bottom of the fence, a distance of approximately 6 feet/1.82 meters.  The vertical portion was secured with nylon ties and a push pin.

Once the vertical section was secured, I ran the remaining length of the antenna (64 feet/19.51 meters) along the bottom of the fence and secured the attached end insulator with nylon rope and push pins to the lower portion of the fence.  The bottom element was approximately 1 inch (2.54 cm) above ground.

I then attached the RG-8X coaxial cable to the horizontally placed balun and ran the cable to a point approximately 10 feet/3.04 meter along the top of the fence.  The cable was secured to the fence at this point by nylon ties.

The cable was run to a plastic hook on the garage and then to the patch panel in the shack window.  A 6-foot/1.82 meter section of RG-8X ran from the patch panel to the Drake MN-4 and later to the MFJ 941-E Versa Tuner II.  Small coaxial patch cords connected the Ten Tec Argosy II to the Drake MN-4 ATU, a low pass filter, and the Heathkit Dummy Load.

TESTING:

With the help of the Drake MN-4 and the MFJ 941-E Versa Tuner II, I was able to get a SWR of 1.5 to 1 or lower on 80, 40, 20, 30, 15, and 10 meters.  Performance was excellent for local and regional contacts. Better DX coverage can be obtained with a dipole or with a vertical antenna connected to a proper ground radial system.  But, for a simple, stealthy antenna, the "Fencetenna" is worth a try for those of you confronted with HOA and CC&R restrictions.  Remember, out of sight means out of mind.

Listed below are some additional stealth antenna sources you may find useful:

http://www.bvac.org/pdf/HF_Antennas_by_KD5FX.

http://www.swharden.com/blog/2010-2-07-simple-diy-stealth-apartment-antenna-for-20m-and-40m/.

http://www.g4ilo.com/stealth.html.

http://www.dxzone.com/catalog/Antennas/Stealth/.

Thanks for joining us today!  You can follow our blog community with a free e-mail subscription or by tapping into the blog RSS feed.

Aloha es 73 de Russ (KH6JRM).

BK29jx15--along the beautiful Hamakua Coast of Hawaii Island.
Enhanced by Zemanta