2 Meter 3 Element Quad
The Quad antenna, sometimes called the Cubical Quad, is an
antenna which is used by many
amateur radio operators. We owe
it's development to Clarence C. Moore (patent no. 2,537,191),
W9LZX, (SK), an engineer at HCJB,
(a shortwave missionary radio station in the Andean Mountains). He developed it to resolve
issues with large coronal discharges in the thin air with a beam antenna.
The quad was born!
describes his antenna as "a pulled-open folded
The 3 element
2 meter (designed for 146mhz) quad in this project has a very small
footprint (boom length) of about 32 1/4 inches and according to the
computer guru's out there, it has about 9.45dBi gain with only three
9.45 dBi equates to 9.45 - 2.15 = a whopping 7.3 dbd gain
with over 20db front to back ratio and a 2:1 swr bandwidth of
Let's see a standard dipole do that!
So with 3
elements on a 32 inch boom....you're more than multiplying your
effective radiated power by 5 times! If your 2 meter rig is getting 50
watts to the 3 element quad (assuming no line loss)...the station on the
other ends "thinks" your putting out over 250 watts! That's hard to beat
on such a short boom and only 3 elements. If your rigs puts 75 watts to
the antenna, that's a whopping 375 watts + erp! More than enough to
do some serious repeater "Kerchunking". Put a 5 watt handheld on this
antenna and it acts like over 25 watts erp out!
The standard 3
element yagi gain is about 4 to 5 dbd and is usually longer in boom length
compared to the quad and sometimes difficult to tune for best
than the gain for it's size and unlike most quad designs....
element 2 meter quad design has a major plus going for
point is about 53 ohms....a great match for direct feeding with 50
ohm coax...no baluns, no fuss, no muss.
So how do we build it?
There are many ways to build a quad antenna and the difficult part of
constructing the boom, attaching the support arms, etc will be left up to
your ham ingenuity. Most builders of VHF quads use PVC or wood as
the boom, and wooden dowels, PVC, fiberglass, or some other non-conductive
material for the spreader (support) arms. Wire is used for the element
You be your
own judge and build the antenna out of material that suits your
construction skills and talents....experiment.
are the exact measurements for building the 2 Meter 3 Element
the drawings and the Quad.BAS screenshot supplied below for the
layout and lengths.
To convert to inches, multiply by 12. Design
above for highest gain at 146mhz
ELEMENT LENGTHS FOR #14
WIRE AT 146MHZ:
This design only presents a good match to
50 ohm coax using #14 wire and using the spacings and
lengths below....do not change unless you want to experiment! If you
want to experiment with the design program, see details
total length in inches = 86.76 inches (86
length total inches = 83.05 inches (83 inches)
element length total inches = 79.33 inches. 79 3/8
Reflector to driven element = 14.25
Driven element to director = 18
If you can put any faith in computers, the lengths were
Reflector spreader bar = 30.67 inches
spreader bar = 29.36 inches
Director element spreader bar = 28.04
BUILDING NOTES: Allow yourself a minimum of 31
inches from tip to tip for the spreader supports. If that should happen to
be too long, you can always cut off to fit when done. Remember this is
from one end of the "+" thru the boom to the other end.
It is best to
layout the individual loops for the quad in an exact square pattern so
they won't move. Just take the element length from above, divide by 4 for
each side of the "square". Then measure from one corner to the other and
add an inch or two. Don't "cut" yourself short!
Do not change the total
length of the loops unless you have some really strange swr readings when
done. Do not change the element spacing on the boom!
According to the
calculations, you should have an extremely good match to 50 ohm coax by
You must fit the supports (spreader bars and boom to
the length of the loops...not the other way around. The size wire, lengths
and spacing of the elements are fairly critical for the near 50 ohm
impedance of the feed point. Your measured impedance may be slightly
different due to your construction techniques, etc, but you should be
close according to the program used. See below for the program
information and a source to download it. It is loaded with other
interesting design programs.
Do not allow
the wire elements to sag. They must be secure and in as near a square
pattern as possible on the spreader bars.
The quad can
be fed as in the drawings below for vertical polarization suitable for FM
repeaters, mobiles, etc....or.....turn the feed point to the bottom or the
top for horizontal polarization for ssb work etc. It makes no difference
which side the feed point is on for vertical
Quad shown above in Vertical polarization
Note: The quad
can be mounted with the top and bottom sides horizontal to the earth, but
then it still must be fed from one vertical side in the center of one
side for vertical polarization or from either the top side or bottom
side for horizontal. This makes for difficulties with supporting the
feedline and extra measures must be taken to prevent strain on the coax
connection to the loop. Either way you mount it. it should perform the
Feed point end detail on spreader bar
Attaching the feed line for the driven
There are many ways to attach the feed line to the driven
element while allowing good support for the feed line and also the wire
loops on the end.
One example above on the driven element is to
drill 4 small holes big enough for the loop wire to pass thru and twisted
back on itself giving some strain relief. Then the coax center and shield
is extend out just enough to twist onto the loop ends, soldered and then
the coax ends and the solder connections sealed from the weather. The feed
line can be nylon tied to the spreader bar, taped, etc. In doing this,
remember to keep the exact lengths of the wire loops unchanged. The length
of the radiator loop , (the driven) starts at the coax connection center
conductor, continues around the loop and attaches to the shield. Don't
leave three or four inches of center conductor or shield extended before
it attaches to the wire loop. This will detune the antenna because this
added length becomes part of the radiator!
other element loops can be simply run thru a hole drilled all the way thru
the end of the spreader bars at the appropriate distance from the boom
while maintaining the exact loop length for each element and the square
shape of the antenna. Attach them securely to the spreaders, twist
together the ends and solder. You should have 4 equal length sides on each
element of this 3 element quad. Looking at the finished quad from the side
should look something like this.... |-|-|
You may also want to add a
small 1:1 coax "air" choke consisting of about 3 to 5 turns with the
end of your coax feed line wound into a coil in series with the feed
line near the feed point to help eliminate feed line radiation
similar to the "Ugly
Balun"....your choice. It
might be advisable to us a short length of PVC heavy enough to support the
finished antenna mounted to the boom as a "mast" extended below the
antenna, then attach it to your final support mast. This keeps any metal
mast out of the field of the antenna which could possibly distort it's
pattern. Use a rotor if you need to "aim" it.
You should not have to
"tune" this design....unless the computer program has errors in the
calculation results. The lengths above were taken directly from a GWBASIC
HAMCALC - LATEST
by George Murphy, VE3ERP
77 McKenzie Street,Orillia,
ON L3V 6A6, Canada.
Download the complete Hamcalc program
Follow instructions for
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