LOW BUDGET NEWCOMERS’ ANTENNAS
By Ed Lawrence - WA5SWD
Newcomers to Amateur Radio often have severe budget restraints due to competing
demands for spare cash. Here is an inexpensive antenna design for a two-meter
groundplane antenna that is easy to build and won’t break the bank. A second version is
also shown that uses a bulkhead double female to permit the use of custom whips or some
commercial whips, encouraging experimentation. These groundplanes are simple,
rugged, effective, and built from easily available parts. The parts I found cost about $10.
Careful shopping can substantially reduce this price.
A typical ground plane antenna at 146 MHz substitutes three or four wire radials for the
actual ground. A vertical quarter wavelength conductor is fed from the center conductor
of the coaxial feedline. This antenna can be found in almost any antenna reference book.
It is simple and classic. Most importantly, it works well and is easy to build. Study the
photographs, Fig. 1 and Fig. 2.
Fig.1. Version 1 Newcomers Antenna
construction details
Fig 2. Center Detail
Note the 12 mm bead at the far end of the radials. Also note that the red objects at the top
of the left photograph are the ends of a clip lead that I used to support the antenna for the
photo and are not part of the antenna.
For my first version we will need an “L” bracket with holes in it to fit a SO-239, two or
four holes to mount the radials, and two holes to fit the clamp that holds it to the support
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post. We make the radials and the vertical radiator out of 1/16" brass rod. The total cost
will be about $9.00, excluding the support pole and the small hardware.
Version 1 Parts List:
Item
Supplier
Part #
Quantity
Price Subtotal
“L” bracket
Home Depot 44315 04300 1 each
$ 1.21
TV mast clamp
Radio Shack 15-826
1 each
$ 2.49
SO-239 chassis mt Radio Shack 278-0201
1 each
$ 1.99
Plastic beads
MJDesigns 12 mm pearl 5 each
$ 0.08
1/16" brass rod
K&S Eng
# 1160
3 each
$ 0.90
(Brazing rod may be substituted, and is probably cheaper) TOTAL
Careful shopping can substantially reduce these costs!
$ 1.21
$ 2.49
$ 1.99
$ 0.40
$ 2.70
$ 8.79
The “L” bracket has several holes already formed. Use a rat-tail file to enlarge the hole
on the shorter leg to fit the SO-239. Use a 1/8-inch drill bit and gently enlarge the
existing holes in the SO-239. Now position the SO-239 on the bracket and drill matching
holes. Pop rivet in place with the solder cup facing out. Drill four more 1/8-inch holes in
the same leg to mount the radials.
Change to a 1/4-inch or slightly larger drill bit. Drill two holes in the longer leg of the
“L” bracket to match the U-bolt spacing of your TV mast clamp.
Fasten the radials to the “L” bracket. I simply bent the 36-inch brass rod at a right angle
at the 18 inch point and pop riveted it to the bracket. Form the brass rod to fit a tightly as
possible around the shank of the pop rivet before you set the rivet. (Do not try to make a
loop around the rivet and then set it. It won’t work well.) This forms two radials at the
same time. I then soldered the brass rod to the galvanized steel bracket to keep them
from pivoting on the pop rivet, using a 75-watt soldering iron. (A soldering iron is far
more effective that a soldering gun. You may be forced to use a propane torch if you
don’t have access to a big soldering iron.) Solder a 21-inch piece of the brass rod into the
solder cup on the SO-239. Use either a small soldering gun or soldering iron for this last
step.
Mount the completed antenna on a short mast and place it out in a clear area. Try to keep
all extraneous large metal objects at least 10 feet away. Bend the ground radials down
about 45°. If you do not bend the radials downward, the impedance will be low,
somewhere near 35 Ω. Bent at a 45° angle, the impedance will be much nearer 50 Ω and
may also lower the angle of maximum radiation. If one of you who do model antenna do
have data on this difference I would appreciate the information. [Editor's Note:
comparisons between flat radials and bent radials (along with 5/8-wavelength monopoles)
for 2-meters appear at http://www.cebik.com/58.html in Part 2 of a series on the "5/8Wavelength Mystique." Although the elevation angle of maximum radiation does not
change significantly, the sloped radials do produce up to 1 dB additional gain over a
2
"flat-radial" system, since sloped radials act both as a radial system (horizontal
component) and as the lower half of a dipole (vertical component).]
Back to the tuning of this simple antenna. Check the SWR across the band. It should be
better at the low end since the whip is deliberately too long. Each time you trim a little
off the top of the vertical rod the frequency for minimum SWR will move upward in
frequency. Remove only about 1/8 inch at a time, rechecking the SWR after each cut. I
suggest you trim for minimum SWR at 146 MHz. Measure at 144, 146, and 148 MHz.
Take and record the SWR data as you trim the whip. If you are a beginner, I suggest that
you start the habit now of keeping a notebook to log EVERY test you make. Include the
date, your name, purpose of the test, a sketch of the setup and the resulting data and
conclusions. This sounds excessive for simple things but will be well worth the effort
when you want to review your work or have someone else help you with a problem. A
regular 8 ½ x 11 notebook is fine for now, but you may want to move up to a more
formal notebook later.
I want to include a word here about SAFETY. You are working with tools and producing
small, sharp edges. The ends of the brass rods are very dangerous, especially for tender
and non-replaceable items such as eyes, both your own and those of innocent bystanders.
Be careful and do not permit harm to come to people or pets. Think ahead and do not
create hazardous conditions that you cannot control.
Since the ends are hazardous, add eye protection to each exposed end. This can take the
form of either a small loop or a plastic bead. In this design there is no extra rod length to
form a loop, if the 36 inch rod is used and bent mid-point, so use the plastic beads. Bend
a little zig-zag at each tip, heat the rod so it will just melt the plastic and force the bead
onto the zig-zagged rod. Hold the bead until the plastic cools enough to lock itself in
place. Don’t wiggle or the bead may fall off, and you will have to do it over.
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SECOND VERSION
The second version is very similar to the first. The only change is to replace the SO-239
with a bulkhead double female and to solder the vertical radiator into a PL-259. The
parts list is below. Version 2 (in Fig. 3) will cost a little more, since the SO-239
bulkhead connector and the PL-259 Connector cost more than the SO-239 chassis mount.
Fig.3. Version 2 Newcomers Antenna construction details.
Version 2 Parts List:
Item
Supplier
Part #
Quantity
Price Subtotal
“L” bracket
Home Depot 44315 04300 1 each
$ 1.21
TV mast clamp
Radio Shack 15-826
1 each
$ 2.49
SO-239 bulkhead
1 each
?
PL-259 Connector
Radio Shack 278-0188
1 each
$ 3.99
Plastic beads
MJDesigns 12 mm pearl 5 each
$ 0.08
1/16 th brass rod
K&S Eng
# 1160
3 each
$ 0.90
(As before, brazing rod may be substituted.)
LISTED TOTAL
Careful shopping can substantially reduce these costs!
$ 1.21
$ 2.49
?
$ 3.99
$ 0.40
$ 2.70
$10.79
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The Version 2 vertical radiator is very easy to construct. Cut a 21-inch piece of the brass
rod and solder it into the center of the PL-259. Remove the threaded shell of the PL-259.
Tape over the holes in the sides of the connector and fill it with clear epoxy. Wipe any
excess off the threaded portion. After the epoxy has set, reassemble the connector and
screw it onto the top part of SO-239 bulkhead double female. Tune this whip exactly as
you did on the Version 1 antenna. Don’t forget the eye protection beads. We only
achieve safety by planning and by attention to detail.
This simple design can be easily modified to work on other frequencies. Either the
aircraft band centered near 125 MHz or the marine band near 163 MHz would be
reasonable choices. The radial and vertical element lengths would have to be changed
accordingly but the calculations are easy. Refer to the ARRL Antenna Book.
It would be nice to have a cheap way to raise the new antenna to a reasonable height,
since these antennas work best when above the local obstacles. I discovered that chainlink fence tubing comes in 21-foot lengths and is low cost. It has sufficient strength for a
small, light antenna such as the one described in this article. Another advantage is that it
is much lighter than water pipe and is much easier for one person to handle safely.
[Editor's Note: Those who must mount antennas like this one in an attic may form a loop
at the top of the vertical. The loop not only provides safety, but also forms a place for
attaching nylon or other line to hang the antenna below the peak of the roof. For indoor
installations, be certain that the roof is not lined with insulation having an aluminum or
other conductive facing. For indoor use, you may also use #14 house wire instead of the
specified brass rod, since the elements do not need as much rigidity when out of the
weather. 1/16" = 0.0625"; AWG #14 = 0.0641" diameter. Remove all insulation. If left
in place, the house wiring insulation will likely require that you cut the radials and
vertical about 2% shorter than for bare wire or rod. If you leave the insulation in place,
be sure to remove insulation from the radials where they attach to the mounting bracket.
A "hanging" version of Ed's 2-meter antenna does not require the mast U-bolt and only
needs a simple small plate for a model comparable to Version 2.]
A few more words about safety: When erecting ANY antenna, you must be careful not to
contact electrical power lines. Assume that all overhead wires are electrically hot. Even
if you believe that they are telephone lines, don’t take the chance. Violating safety rules
because you are in a hurry can lead to injury or death. —Don’t. –30ED: An earlier version of this article first appeared in the September 2002
Newsletter at the Plano Amateur Radio Klub of Plano, Texas, USA. Author, Ed
Lawrence, modified the article and submitted it to antenneX for worldwide reader
access. Although the articles are not identical, they are close enough that antenneX
obtained “reprint” permission from the club Newsletter Editor, Barry A. Goldblatt.
Readers are invited to visit the club’s site at: http://www.k5prk.org/
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UPDATE
The members of the Plano Amateur Radio Klub recently had an antenna building party
and constructed and tuned nine of these antennas for the graduates of Tech Camp. Instead
of the zigzag bends on each element tip we formed a 1/8 th inch right angle bend after the
bead had been installed. The bead was forced onto the heated bend and twisted slightly,
then allowed to cool.
The SWR after trimming the vertical for resonance at 146 MHz was 1.1:1 or better on
each of the nine antennas. Several were checked at 440 MHz as well. As expected, the
SWR was quite low there as well, also being1.1:1." Ed WA5SWD
BRIEF BIO OF AUTHOR
Ed Lawrence started working as an Electronic Technician in
1958. He has been active in Amateur Radio since 1964 and
presently holds an Extra Class License. Over the years his
writing credits include articles in 73 magazine, QCWA,
various club newsletters and www.antennex.com. Ed has
worked at a lot of interesting places, including North
American Aviation, Lear Stereo Division and Texas
Instruments, from which he retired in 1991. Since then Ed
has worked mostly as a Contract IC Mask Designer on
microprocessor and cell phone chips for many of the major
players. Work locations have varied but include Switzerland,
Ireland, Pennsylvania, Texas, Arizona, Washington and Oregon. Ed also has his
Certified Flight Instructors rating, but is not presently a very active pilot due to his
nomadic life style. Presently Ed works at RFSAW, Inc in the Dallas, Texas, USA area.
There he assists in test and development for RFID Passive Microtags.
antenneX Online Issue No. 67 — November 2002
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