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6 Meter / 2 Meter / 440
Tri-Band Sleeved
Collinear Antenna Project
by
W7LPN Rick
Frazier
Here is a Tri-Band 6/2/440 Collinear
antenna that if built properly, using the materials suggested by the
author, should give you years of service.
It is a heavy duty
fiberglass radome style collinear multiband vertical capable
of operating on your choice of 6 meters, 2 meters or the 440 ham
band. The radome enclosure is about 18 feet
long containing the 5 antenna elements. Mother Nature will need
lots of help to harm it!
PREPARATION FOR BUILDING
Supplies &
Suppliers:
Fiberglass Tubing from Max-Gain -
4 sections:
1ea 1 3/4 X 48
3 ea 2 X 48
(Only 2 of the 3ea 2" X 48" sections are used for the
antenna. I used the extra 2" section for later on the
bottom mount)
http://www.mgs4u.com/fiberglass-tube-rod.htm
Tip: PVC CAN BE
SUBSTITUTED for fiber glass tubing, but won't be as
strong.
Galvanized Hardware cloth 1/4 or smaller mesh at any
Hardware store:
3 sections 38.1/4 X 4
2
sections 19.1/8 X 4
20 feet. #18 insulated wire (used for
hookup of elements from bottom to top)
Wooden Dowels- 5
pieces 1 1/4 x 6.
(Used for support of antenna elements inside
radome and to center connecting wires.)
Marine Epoxy
Hot
Glue gun
Staple gun
Assorted hand tools as
needed
Preparing the
dowels:
Drill 5 pieces with 8" x 1/4"
drill bit and drill press.
Tip: If you
don't have a drill press, just use a 4 inch or longer 1/4" drill
bit.
Secure the dowel in a vice upright and drill as carefully as
possible starting centered at one end of a dowel and drill towards
the center of the opposite end. Repeat from the other end. Hopefully
the holes will meet and you will have a 1/4 inch hole all the way
through the dowels. Smaller or larger size drill bits may be used as
long as #18 wire will go through the hole in the dowel easily.
Drill center of dowel end to end as best possible. If you are a
perfectionist, just take the dowels to a local shop that has a drill
press and tell them exactly what you want.
Next, near
the center of the dowels on opposite sides, drill 45 degree angle
holes down into the center hole. Both holes should exit the dowel
near the center 180 degrees apart, (on opposite sides). This is
required so you can pull the #18 insulated wire through the dowels
so it can be fed to the next element. See Drawing below:
Figure 1.
Preparing the coax
end:
5 ft RG-213 with high quality PL-259 at one end.
Strip about 3 inches of insulation back and twist the shielding
together so both conductors may be pulled through the bottom dowel
later. The bottom dowel must be drilled large enough so the
coax can be pushed through it. Leave about Ό inch inner
insulation on the center conductor to isolate them
electrically.
The
Balun:
7 pieces of #43 ferrite beads for balun.
You must slide them over coax now before assembly of
antenna unless you leave the PL-259 off until later.
http://www.amidoncorp.com/
THE BASIC CONSTRUCTION:
The basic
construction of the Tri-Band Collinear consists of an outer radome
of 1 3/4 and a 2 fiberglass tubing (PVC can be used) with a
PVC cap at the top. I purchased the tubing from Max-Gain, and had
them cut to 48 for shipping. The exact length of sections or
placement of the joints in the fiber glass radome is not critical,
as long as you end up with enough total length to house the entire
assembled internal parts. It will be about 18 feet including
bottom support.
To assemble, join the 1
3/4X48 sections with marine epoxy and 2 X 12 sleeve tubing
epoxyed over the joints to reinforce and strengthen it. Total
finished length is about 18 feet. Refer to diagram drawing below
and pictures at bottom or article.
Figure
2.
Notice in the inset in drawing that the center
conductor from coax is connected to the bottom of element
#2. The shield is connected to the bottom decoupling
sleeve shown in gray in the drawing and also to the length of #18
wire that is fed up
through the dowel in the bottom of element #2.
Building the antenna
elements:
The actual antenna consist of
1/4 hardware cloth sections cut 38 1/4x 4 and curled around
1x 6 wooden dowels placed between each element. There should be a
dowel inserted in each end of the mesh sections when done. The top
and bottom sections are 19 1/8 inches long. The other 3 remaining
elements are each 38 1/4 inches long.
If you have
a long enough working area lay out all the mesh on the floor end to
end starting with a 19 1/8 section and ending with a 19 1/8
section.
Element
lengths:
#1 - 19 1/8" (At bottom of
antenna)
#2 - 38 1/4"
#3 - 38 1/4"
#4 - 38
1/4"
#5 - 19 1/8" (At top of
antenna)
1/2" space between each
element.
Place the finished
dowels between each element and at both ends.
First staple the
mesh on the ends to each dowel making one continuous piece, leaving
an electrical separation between elements of about 1/2.
Curl them around the dowels at the ends of the 38 1/4 lengths
by wrapping the 4 around the dowels to form a 1 1/4 mesh and
wooden tube.
The center edges of mesh between the dowels will be
opened a little. Don't worry about that, but make sure the sharp
edges are bent inward slightly. Staying open helps keep it flexible
while inserting it into the tubing later.
The dowels have been
center drilled end to end to run the thin #18 wire through. It
doesn't have to be perfect. This allows you to maintain the thin
wire #18 centered. Think of the thin wire as the center conductor of
a piece of coax and the mess as the shielding.
Connecting the elements:
The thin #18
wire is threaded through the dowels and soldered alternately,
skipping one element at a time and soldered 180 degrees from the
other thin wire connection to separate the connections electrically.
See drawing Figure 1. and Figure 2.
above.
Element#1 drops down over
the open end of the coax as a decoupling sleeve with dowel #1
drilled 1/2" so it slides over the coax.
Solder the shielding
to the upper end of element #1 on the opposite side where you will
solder the center conductor to element #2. At that same spot, a thin
#18 wire is soldered to the shield and threaded through dowel
#2, between elements 1 & 2, up through dowel #2 to element
#3, which is repeated to #5. 45 degree holes in the dowels are there
to pull the shielding downward, and the center conductor up and
outward.
The center
conductor of the coax is soldered directly to element # 2, then a
thin wire from the top of element #2 threaded though dowel (#3) up
and through dowel (#4) and soldered to element #4. Then, the #1
shielding decoupling element (at bottom) conducts to #3, which
conducts to #5. #2 center lead conducts to #4.
In other words, the center conductor
of the coax feed, using #18 wire, is connected to elements
2 and 4 ONLY. The shield of the coax connects ONLY to elements 1, 3,
and 5, using #18 wire.
If you are having trouble understanding
this, just refer to the drawings.
The finished internal
parts are close to 13 feet minus the balun.
I chose to use
the other 48X 2 fiberglass tubing as a bottom mounting stub and to
cover the balun for weather proofing. I slid the 2 tubing up over
the 1 Ύ tubing, 2 feet, to reinforce the base and leave enough to
cover the balun.
The Balun is provided by placing 7 pieces of #43
ferrite beads at 38 below #1 element.
We used spray silicone to
slide the completed "guts" into the radome and held everything in
place with marine epoxy.
Everything is sealed air-tight within
the fiberglass radome.
Here are
some un-scientific "gain" and SWR
readings:
2m - 8.56 dBi
440 - 12.02
dBi
6m - 3.07 dBi
SWR- Taken
from the idiot meter on my FT-857D
Barely shows a mark from
144.1 to 147.9 -1.2 or better.
about 1.4 to 1 for the entire
440 band
6m - Still checking. Seems about 1.7-1.9 to 1.
Im going to get a good SWR
meter!
|
Caution! It is suggested that no more than 100
watts of power be used with this antenna on any band. Higher
levels may damage the antenna or your transmitter! Exact safe power levels have not been
verified! |
References:
If
you are familiar with the Coax Collinear"
(http://www.sadona.com/news/ant_coaxcol.html) made from RG-58 of similar length elements, all
I have done here is used large elements for broader band width and
removed the velocity factor shortening of the coax, borrowed
the thin wire alternating with large diameter elements from the
Simple Collinear"
(http://home.comcast.net/~ross_anderson/sc.htm), and beefed up the wind loading.
Practical reception should be better due to the increased overall
length. This is a very strong antenna. We have joked about mounting
an American Flag on it.
 
Questions?
Email Rick
rickenbrook at clearwire.net
POWERED BY HAM
RADIO!
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