This Quad resembles plumber's delight Delta Loop, but with square quad elements
made using copper water pipe fittings, rather than aluminum tubing.
I got out my old 2 m Plumber's QUAD, and took the following measurements:
(centimeters) Inner Circumference Spacing
Reflector: 216.0 40
Driven : 206.8 -
1st Director: 200.7 39.6
2nd Director: 200.0 41.0
Driven Element=1.007 times free space wavelength at 146 MHz middle
of the 2 meter band. This is less than the standard 1.026
"Loop Factor" built into the often quoted 1005 ft/MHz spec.
Note that the outer circumference would correspond to more than
the 1005 ft/MHz.
The driven quad loop seems to have to be larger to resonate to the
same frequency in free space. That is, first I constructed a test loop
and resonated it by itself, calculated differential ofset to reflector and
director sizes; and was mislead. The loop in the quad
has to be reduced in size to resonate to the same frequency.
My fittings were such, that the cut pipe length corresponds to the
inner dimension, thus the practicality of using inner circumference.
For the pipe fittins I used, the pipe was cut to the length of
the inner circumference by 4. The elements may have a "T" cuppling
in either a side (more symtrical but requires one more fitting) or
a corner. I have used the T in the center of the boom side of the quad.
The T coupling inserts a length equal to the size of pipe being Ted.
Thus subtract a 1/2" and then divide by two to obtain the short pieces.
For the driven element, about another inch is removed to allow a
non-connection for direct feed.
The quad had swr of 1.0 in the center of the 2 meter band,and
was low accross the entire band.
I have used both a UHF chassis female connector to span the driven
element gap;
and also just used brass machine screws with wingnuts to connect
a coax fitted with circular spade lugs, and a piece of 1/2" PVC
jambed on as insulator and physical support. My results improved
when I tuned using the UHF connector.
I used this quad for communication accross the mountain ridges
which encircled my QTH, so I know it both receives well and
has gain to get into repeates up to 200 miles away with my
2.5 watts. But I have not optimized the tuning for front to
back ratio or to eliminate side lobes.
I think a boozoka sleeve balun would be useful for decoupling the
feedline.
I would like to colaborate with other hams interested in
prefecting this design.
Please let me know of your experience building copper waterpipe
2 M quads. Hope this helps.
I should mention that I originally built a 6 element
quad with a screen reflector with redwood 4x4 for fixed QTH,
and the four element version was made portable for packing in my horse
Rowdy's saddle bags, for ridge topping.
My conclusion was that the redwood 4x4 was very useful for
adjusting element spacing, which was not critical.
I also concluded that the screen reflector was not practical,
since it increased the antenna's awkwardness unnecessarily.
I used 10 cm "handles" on the loops to attach them to the boom.
For the fixed QTH QUAD, the redwood boom had
1/2" holes drilled; into which the "handles" were inserted.
For portable quad, I used a boom and mast of 3/4" copper pipe.
I used 3/4 x 1/2" Tees for element to boom attach. 3/4" Tee for
boom to mast. To fit the quad elements into the saddle bags,
I left one side of the boom joints at driven element and 1st
director, and two places on each quad loop unsoldered.
On the boom, I used brass machine screws with wingnuts
through the unsoldered joints. The "top L" of each quad loop
fits down into the "bottom L", so gravity and the press fit
is sufficient on the quad elements.
For fixed location, I soldered all joints.
I lack a good test range to
measure front to back ratio without all the reflected signals
that confuse the pattern.
Or an antenna modeling program for theoretical design.
PS.
Driven Element=1.007 times free space wavelength at 146 MHz middle
of the 2 meter band. This is less than the standard 1.026
"Loop Factor" built into the often quoted 1005 ft/MHz spec.
Calculating the circumference of the outside diameter of the loop,
I estimate the 90 degree elbow fitting to have
1.8 cm radius x 2 pie or 2.7 cm x 4 circumference.
11.3 to 10.8 for an average estimate of 11 centimeters added by elbows.
The driven element is then 2.068 inside and 2.178 outside, versus
a free space wavelength 300/146 of 2.055 meters, for a "loop factor"
of 1.007 inside and 1.060 outside, which straddles the standard 1.026
factor.
Somewhere I have my calculations for this, and my 6 element screen
reflector version. I should mention that I had begun building
using standard formulas, and then had to shorten the driven element
to center the resonance in the middle of the band. I think the
directors would benefit from corresponding shortening.
In working with Yagi, when the bandwidth is widened with thicker
elements, one increases deviation in director and reflector length.
Also, we know that variation of frequency vs length, it is more
important to keep the director shorter than the highest frequency,
and the reflector longer than the lowest frequency.
The standard formulas (ARRL Antenna Book, 1974) give:
Driven Element Loop Factor: 1005 ft/MHz)=1.026
Reflector Factor: 1030/1005=1.025
Director Factor: 975/1005=0.970
Band Top=148/146=1.014
Band Bottom=144/146=.986
Using the Loop Factor of 1.007, and wavelength of 2.
I would estimate
reflector of 2.068 x 1.025 x 1.014 = 2.149 meters
director: 2.068 x .97 x .986=1.978 meters
But even more lengthing of reflector and shortening of
directors may compensate for the thickness of the elements.
In ARRL's 1993 Handbook p.33-35, Loop Yagis for 23 cm,
the difference between the reflectors and directors is
9.829/8.359=1.176, or reflectors about 8.8% longer,
and directors about 8.8% shorter.
In the above formulas, that would be 3% reactive tuning,
1.4% for band widening, and 4.4% for width compensation.
Therefore for making new directors, I would try using
director:
1: 1.960 /4=.49
2. 1.940 /4=.485
3. 1.920 /4=.48
4. 1.900 /4=.475
Don www.qsl.net/n6mce
[email protected]
... 1:125/104 POBox 9739 San Rafael,CA 94912