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Simple VHF/UHF Ground Plane antennas for under $20 |
These antennas have appeared in numerous publications
over the years, including the ARRL Antenna Book, and are
only limited by your imagination as to their potential
uses. Excellent for local repeater work, APRS, Field
Day, Emergency deployment, Stealth installs, the list
goes on. They are simple to make, simple to assemble,
simple to get the parts for; do you see a pattern here?
The most basic design will be shown first, with a few
very slick improvements later.
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The entire antenna consists of a panel mount
SO-239, some stiff wire (like aluminum welding
wire, brazing rod, 12 GA bare copper wire,
electric fence wire, etc) or thin brass tubing,
some solder, and four 4-40 3/8" long screws,
washers, and nuts
Cut the wires to length in accordance with the
chart provided for the band you want. You will
end up with 5 pieces of wire, 4 the same length
(radials) and one slightly longer (driven
element). Use a good high wattage soldering iron
to tin one end of the driven element
HINT:Cut your radials extra long, mount them on
the SO-239, mark the point to start the bend,
remove the radials, make the 45deg bend, remount
them, then measure and trim to length. When
tuning for lowest SWR, remember that the angle
of the radials affects the value, so feel free
to adjust them anywhere between 30 and 45 deg
for best reading. Also, if tubing is used, one
end of each radial can be soldered to a ring
terminal or hammered flat and drilled |
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There are several ways to attach the radials:
- Bend the wire through the corner hole
and solder in place — Requires a lot of
heat, no longer removable for transport but
better electrical connection
- Use a pair of needle nose pliers to
fashion one end into a tight loop just big
enough for the 4-40 screws to get through —
Takes a little work, can loosen over time
[use split washers for extra tension], but
no soldering
- Solder (or crimp) ring terminals on one
end — clean, professional looking, but may
break over time with repeat bending
Notice that the length of the radials is
measured from the 45 deg bend to the tip, so
which ever way you choose, allow for this extra
length in your calculations. |
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So you've got the antenna built, now, how to
mount it:
- Bend a loop (or solder a ring terminal)
at the top of the driven element, thread
some string through it and hoist it up
- Fabricate an "L" shaped bracket that
uses two of the 4-40 screws to hold the
antenna in place
- Run the feed line up a section of 1/2"
PVC with the antenna sitting on top (quick
and easy, but not optimum for prolonged
exposure to the elements)
- Use the method above, but aquire a PVC
end cap, cut slits in four locations to
allow the radials to slip through and drill
a hole in the top center large enough to
allow the driven element through. Cap can be
held in place with small sheet metal screws
or a pipe clamp. A dab of outdoor sealant
around the vertical element and it should be
pretty weather resistant
- Use a pipe cap as above, but drill four
holes to mount the SO-239 directly to the
pipe cap
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