The K4MMG 2 METER QUAD
CONSTRUCTION
TIPS FOR BUILDING BETTER QUADS
(Graphic intensive -- allow time to
load)
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 AT
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!
