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Intensive
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load | The K4MMG 2 METER
QUAD
CONSTRUCTION
TIPS FOR BUILDING
BETTER QUADS
2 Meter 2
Element Quad shown mounted above another antenna with
coax feed
nearest you on left spreader rod.
The
antenna that is below the quad is a 6 meter moxon that is made from
TV tray legs!
Ham Ingenuity at it's
finest!
OBJECTIVE:
Construct a
professional looking and great performing quad
for the two meter
band, or higher frequency.
The intent
of the article is to demonstrate how to build a mechanically
symmetric quad,
using pvc
materials
"Like most of you, I have built a lot of Quad
antennas, from HF through UHF.
It has always bothered me that
the HF quads looked neat in construction,
but my higher
frequency quads did not.
While the higher frequency quads worked
well, they just did not look good.".....Steve
After struggling
with this phenomenon I finally discovered a way to build a quad
that is neat, durable, portable and that will support both
horizontal and vertical polarization across the entire two meter
band. As it turns out, the antenna is easily constructed.
The construction
of this antenna uses readily available materials, from your local
home building store such as ½ " pvc, schedule 40 , associated
components, and 7/16" dowel rods usually 3 feet long.
The coax
and quad wire will be described in the construction
section.
There are photos
below that will be referenced as the details
progress.
PLEASE REVIEW ALL PHOTOS
PRIOR TO BEGINNING
CONSTRUCTION:
This is a two
element quad, the mechanical construction applies to both the
director and reflector.
The location for the quad wires for each
element are obviously going to be different, so this part of the
construction will be described later.
It should be noted the pictures show the quad in the
vertical configuration.
OK, let’s
prepare the support rods. There will be four used, so select
any two, and mark the center,
as you can see in the photo
below:
The purpose is to remove some material so that the
rods are almost flush
when placed over each other as shown in
photo above and below.
Do not cut the rods to
length yet.
Now, let’s make
the part that contributes to the neatness of this quad, "the end
caps" and the center "cross" sections used to support the outer
elements.
They can be seen clearly in the second picture below
and near the end of the article in other photos.
What you
want to do now is to find the center of the end cap and drill a
pilot hole
through 4 (four) of them.
A technique that I
have used is to look inside and find the molding connection, center
punch this and drill the pilot hole. Another technique use a flat
wood drill, (wide enough so that it touches the end cap walls), and
insert it into the end cap, and mark a center point for the pilot
drill. Use some method of measuring the diameter of the support
rod. Select a drill that has a diameter less than the support
rod.
When drilling
the final diameter hole, make sure the end cap is level, secured
mechanically, and most of all apply drill pressure slowly.
DO NOT HOLD IN YOUR HAND WHILE DRILLING.
Next, (picture above), cut 10 pieces of PVC
tubing, 1,1/8 inches long.
Locate a PVC
"T", a PVC "CROSS", 2 prepared support rods, (5) 1,1/8" cut
pieces of tubing and (4) prepared end caps.
Using the pvc
cross, (see picture below), insert one prepared support rod so
that the center cut is centered. Next insert the other
prepared support rod 90 degrees to the other one.
Align
the support rods over each other in the center of the cross .
Onto this, insert a pvc tee,
into this, insert a cut piece of pvc,
onto this place an end cap over
the support rod and push together. On the opposite side insert
a cut piece of pvc into the cross, place
an end cap over the support rod and push together. Using the
two remaining end caps, complete the assembly. Since there is no
precise measurements made, the remaining end caps will have
mechanical interference.
This is part of the key to holding all
this rigid.
In the picture
below, you should notice the PVC "cross" in the center with a
"T" next to it.
This is where the 5th 1,1/8" piece of PVC goes
inside the "cross" and
the "T". There are (5) 1,1/8" pieces per element,
(one in each end cap and one between the "cross" and the "T".
See photo below.
(Note the end caps near the edges of the picture
and
the 1,1/8 inch PVC lengths extending from inside them.
One length of 1,1/8" PVC is hidden from view inside the
joint
between the "cross" and the "T" where the two
black marks come together!)
Repeat this
process for the remaining element. All of the PVC can
be cemented together if you like,
but I
recommend that you wait until the entire quad is assembled and
tested. It also would be a good idea to weatherproof the
dowel, (support), rods if the quad is to be permanently mounted
outside.
Next you will
drill 4 holes in the reflector element support
ends of the quad. From the center of the PVC cross,
measure 15, 3/8", on all 4 support rods. Laying the quad
element on a flat surface, drill a hole in each rod parallel to the
pvc "CROSS". The hole size depends on the size wire that you use. A
large variation in the wire size that I have used will affect the
quads tuning. Using a wire length of 86 inches, thread the wire
through each hole. Strip the ends of both wires, take out slack, and
solder the wires together making one continuous loop of wire.
Now for the
driven (director) element.
LOOK AT THE PHOTOS.
From the center of the cross,
measure 13,7/8" on all 4 support rods.
Again lay the quad
element on a flat surface. Drill 4 holes parallel to the pvc "CROSS"
on the rod that is coming out of the "T". Drill another hole 3/16
inch below the previously drilled hole. This is where the coax will
attach. Using a wire length of 76 inches, place one end through the
"T" dowel, tie a knot so that it won’t come out, thread the
remaining wire through the holes, ending at the other hole in the
"T" thread the wire through this hole, and tie a knot in it as well.
Make sure the wire is not sagging.
Attaching the elements to the boom:
To
attach the quad elements to each other using a,"boom", cut 2 pieces
of pvc tubing 6,3/4" long, and insert into a pvc "T".
See
picture of "boom" assembly below and the previous picture
above:
The "boom" is the
horizontal length of PVC in the picture above
which is attached
to each quad section on the ends. The support for the quad
leading to the mount
is at the top in the picture but in final assembly will
be on the bottom.
The method of how you mount the quad from this point
to
your set up is left up to you.
With the quad element " T’S" facing each other, slip the
element sections onto the ends of the quad boom while aligning up
the driven and reflector. Refer to pictures.
If you
are going to use this as a portable device, and are going to use
both horizontal and vertical ,
I recommend that after the quad
is tuned, marking your location of the "T's" on the boom, drilling a
small hole, and inserting a nail in both ends to hold your place. If
you don't do this, after use and ,
if you use it portable, the
pvc will loosen. If the quad is to be permanent, pvc cement it,
ONLY AFTER IT HAS BEEN CHECKED
OUT.
ATTACHING THE
MATCHING COAX
(See photo below)
Cut a piece of RG59 (
75 ohm non foam) coax to 13.34 inches. Strip both ends ¼ inch. At
the driven element, where the two knots are, solder the center
conductor to one wire, and shield to the other wire. Tape the coax
to the outside of the dowel, on the side opposite the boom. Now
attach a length of low loss 50 ohm coax, RG8X , or better. Shield to
shield, center conductor to center conductor. Prior to sealing these
connections, check the antenna out first. Route the coax over the
CROSS and along the boom and down your own vertical mounting method.
Use either tape or tie wraps, (not to tight).
Matching section connection
to feed line can be seen at left in the photo.
Your quad
should look like this:
CHECKING IT OUT:
Mount your quad at least 6 feet
off the ground, away from large metal objects.
My results were
<1.5/1 across entire two meter band using a MFJ 269 analyzer.
Forward gain about 5dB, (S meter), noise on F/B and complete
null side/side. As with all antenna projects, your tests results
will vary depending on your particular location, construction
methods, and distance from other stations, etc.
If you want to cut the extra
length from the end of the dowel rods, this would be the
time.
Weather proofing should be done at
this time.
MATERIALS
10 ft. of ½ pvc, schedule 40
3- ½ " T s"
2- 1/2 "CROSS’s"
8- ½ end caps
4- 7/16 x3’ dowel rods
1- ____ RG 59 coax, (non
foam)
1- A/R___ RG 8X coax " your
length"
1- Length of quad element wire,
#18 gage,13.5 feet total feet
Note: this is great wire for a lot of antenna
projects.
Vendor = You can find PolyStealth 18 under Antenna Wire
at http://www.therfc.com/antenna.htm
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Formulas used:
(See notes about formulas
below)
Director length = 79 inches,
246/146
x12x4= 80.8 inches
(Actual length for
use is 76 inches for proper matching)
Reflector
length= 82.6 inches
246/146 x12 x4 =80.8inches + 5%=
85.05 inches
Actual length for use is 86
inches for forward gain,
front to back attenuation
Element spacing =
1005/146x.2=16.52
inches
(Note, (.2) in formula above is 2/10 of a wave
length)
Coax matching length =
246/146x12x.66=13.34 inches of 75 ohm non-foam
coax
(Note, (.66) in the formula above is the velocity factor of
the coax I used. Yours may be different.
Look it up and use your
velocity factor.
~~~~~~~~~~~~~~~~~~~~~
Formula notes:
The
above formulas were used to begin, but the wire that I used resulted
in the above noted lengths. Also I have used these formulas for many
years with repeatable results.
CONCLUSION:
This
should be a fun experimental project for all, and is intended
to both continue and to expand the interest of amateur radio antenna
projects.
Constructors should use all known safety
precautions.
As with all experimental projects,
there are no guarantees.
With this in mind I hope you enjoy the
project and its results.
Please direct
any questions or comments to Steve ,
k4mmg@hotmail.com
Quad
Design Program Download, VE3SQB
Editor's Note:
This
project kindly shared by Steve, K4MMG; shows construction techniques
that can be applied to lots of antenna projects, not just to quads.
The techniques that Steve used in this article show us that with a
bit of "thinking" and planning on your part, you can apply your
"expertise" also to come up with novel ways to get that "sky hook"
up and running with greater mechanical stability and looks that even
the XYL might approve of!
Thanks
Steve!
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POWERED BY HAM RADIO!
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