The goal for the antenna was to make it easy and inexpensive to build,
easy to transport, and to
make it more efficient than a typical “rubber duck” antenna. After
building a series of antennas, I
have to admit I lost sight of the easy to build, part: I had to back
off from using better antennas
because not everyone has the tools, test gear, accessibility to parts,
and money to build them. I
wanted to offer you all a design that would work first time out with
minimal fuss. So, I went back
to using the tried and true groundplane antenna.
After spending a couple of hours futilely trying to draw construction
diagrams, I dug through the
Stuart archives and found the attached article in Amateur Radio Trader
magazine. (You can use
the formulae in the upper right-hand corner for your marine band radios,
if you want.) The article
is missing a few details, so here they are:
For the nuts and bolts, use stainless steel 4-40 hardware—it can be
found at a hardware store.
The mast can be either wood or PVC, at least 2 meters (or 8 feet) in
length; I suggest using
PVC. To make the mast self-standing, I used 3/4” PVC tubing for the
mast and a 1’ length of
angle iron stock, 1/2” width for each side. I hammered the angle iron
into the ground 6”, then slid
the PVC mast over it. If you want to be able to break down the antenna
down to a 4-foot size,
use two 4’ sections of PVC with a female-to-female connector in between.
Use cable, or “zip” ties, for the tie-downs.
If you use old wire hangers for the radials and elements, make sure
you sand away the plastic
coating at the points where you plan to bolt them to the connector.
I don’t suggest using
hangers at all, but 3/32 brass rod stock: it won’t rust as the steel
will in the hangers.
Cut the radials and radiator for the frequency you plan to use the most,
i.e., if you plan to use
122.75 MHz (aviation band) most of the time, then cut the lengths for
that frequency. You’ll still
be able to use all of the air band to transmit and receive, but by
cutting the antenna for its
resonant frequency, it’ll be most efficient at that frequency.
Speaking of cutting the radials...make sure you cut the radials long,
then trim them down to size
after you mount them to the connector: you have to accommodate the
extra length used on top
of the connector for bolt-down purposes.
For whimsy, put a Jack in the Box antenna ball on top. ?
Parts list:
(5) metal elements, 3/32” brass rod stock or coat hangers
(1) mast, 1” x 8’ length of PVC
(4) sets of screws and nylocks, 4-40 size
(4) cable ties (use an additional two to hold the coax cable to the
mast)
(1) Radio Shack 278-967 20’ length of coax, with PL-259 connectors
on each end
(1) Radio Shack 278-201 SO-239 connector
(1) 278-120 connector (to use to connect the radio end of the coax
to the BNC connector on
your transceiver.
So, for around $25, you’ll have a portable antenna that works tons better
than the rubber duck.
This same antenna—a little more robust in construction—costs over $150
out of the pilot
catalogs!
As always, if you have any questions, send me an e-mail.
Rich, WF7A
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