[ARC5] Antenna for small yard

[howard holden]

Hi Neil, I have some experience with fence-mounted 80 meter antennas. You certainly do have a "space" issue. I'm assuming the fence is 24 X 12 X 24, giving you perhaps 60 ft for an antenna. You might try a loaded dipole, coils about midpoint in each leg. There are several on-line coil calculators for antennas.   www.smeter.net<http://www.smeter.net> has several good loaded antenna calculators, although you need a computer that can work with DOS for them. The link following works on most any computer however:

http://www.k7mem.com/Electronic_Notebook/antennas/shortant.html

You will find that generally an antenna in close proximity to ground will be somewhat shorter than calculated, but your lot dimensions inferring that your antenna will be in a "U" shape may offset that somewhat. I have an 80 meter dipole sitting on a 7 ft high wood fence. It's length for resonance in the CW portion of the band in only about 120 ft as opposed to the calculated length of 135ish feet, reflecting ground losses. Mine is mostly straight, but one end is bent at 90 degrees for about 15 feet.  The opposite end of the antenna is only 40 ft long from center feed, and has a small loading coil about midpoint.

Will such an antenna work? Yes but you won't be king of the hill. Depending on soil conditions, it will range from primarily a NVIS antenna, to one that has losses, but a better radiation pattern than you might envisage with a very low antenna. With normally 50 to 100 watts I have 20 countries worked with mine on 80, from Japan to Europe to South America from my northern NV QTH. Soil here is very dry, rocky, rather poor in general.

Pointer for mounting on a fence: Get some sort of standoffs to keep the wire physically off the wood. When it rains the losses change, and will detune the antenna. I use vinyl window adjustment screws, which are about 3 inches long, and have a shoulder near the head which is convenient for retaining wire. Thus my wire is about 2.5 inches off the wood. Even with that a heavy rain will detune my antenna down about 200Khz, but I can compensate somewhat with a tuner and still work out OK.

Good luck, it;s an interesting challenge but one you can work through.

73, Howie WB2AWQ/7 Reno NV


On 10/20/2016 1:06 PM, AKLDGUY . wrote:
Can anyone suggest a suitable antenna for 80m designed for low impedance transmitters such as the BC-230 and ARC-5?

My yard is 24 feet (7.2m) x 12 feet (3.6m) with a 5 foot (1.5m) high wooden fence on three sides. The ground is covered with concrete pavers, so burying wires is not an option. I do not want to erect poles, so the fence will be the only support.

I have a 2m J-pole mounted out on the fence with RG-213 coax dropping down and running across to the door. I figured that this might act as "the body" of a plane, so I disconnected the coax from my 2m transceiver and connected the braid to the Ground terminal of the BC-230.

Then I ran out a wire from the BC-230 antenna terminal out to the fence very close to the J-pole. This wire was about 4 feet high, and I figured that the whole thing might approximate a short antenna above a plane body. Unfortunately, no antenna current was indicated on the BC-230's RF ammeter. It normally shows about 0.6 Amp when operated into a 5 ohm dummy load in series with 150pF (ARC-5 transmitter cap).

Is anyone able to model that entire thing as an 80m antenna, or can anyone suggest a better arrangement?

73 de Neil ZL1ANM



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