[ARC5] Antenna for small yard

Thu Oct 20 22:03:53 EDT 2016

Hi Howard

Thank you for taking the time to reply!

The orientation of the yard is somewhat different than you describe. The
fence runs the entire 24 feet width of the yard. At both ends, the fence
makes a 90 degree turn towards my apartment. At the right end, the turn
gives me another 19 feet of fence back to the corner of my apartment (the
corner of the building).

At the left end, I get another 6 feet of fence before it runs up against a
massive concrete slab running the height of the building (earthquake
strengthening). This short section of fence and the concrete slab divide my
yard from the yard next door.

So, for an approximately balanced antenna, I would have the 24 feet, plus 6
feet at each end right-angled back towards the apartment. Obviously I can
make no use of the concrete slab portion, even though more fence is
available at the other end.

I'm unwilling to mount on stand-offs (I have somewhat of a vandalism
problem here) and don't want anything obvious. In fact, it would be
preferable to have an antenna that I could put out on scheduled AM net
nights (Fridays) and take in at the close of the net. An antenna that is
temporarily suspendable from the fence is preferable.

Your experience gives me hope. I'm not expecting to work DX, as long as I
can get a signal into the WebSDR receiver at Musick Point just across the
harbour from me and log into the net. The BC-230 is only 5W, but I'm using
it to tune up (it has an RF ammeter) in prep for when my ARC-5 transmitter
at 60W is ready to go.

I emphasize that these airplane transmitters were designed to work
into VERY short antennas, so 50 and 75 ohm suggestions fly out the window.
They operated into antennas as short as 3 meter length, working against the
aircraft body with the far end very close indeed to the body.

73 de Neil ZL1ANM

On Fri, Oct 21, 2016 at 1:35 PM, howard holden <holden7471 at msn.com> wrote:

> 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 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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