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Longest element
Table I) Total weight, 116 pounds
Wind-load area, 10.7 sq. ft
Required input impedance (mean resistance),
R O = 67 ohms,
Z t = 6-inch jumper No. 18 wire
Average characteristic dipole impedance:
Z a 14 MHz = 450 ohms;
Z a 21 MHz = 420 ohms;
Z a 28 MHz = 360 ohms
'
Mean spacing factor = .0527
Impedance of the feeder:
Z O 14 MHz = 95 ohms;
Z O 21 MHz = 97 ohms;
Z O 28 MHz = 103 ohms
Using a toroid balun at the input terminals and a 72-ohm coax feeder the SWR is 1.4 to 1
(maximum).
The mechanical assembly uses materials readily available from most local hardware stores
or aluminum supply houses. The materials needed are given in Table II. In the
construction diagIam, Fig. 8, the materials are referenced by their respective material
list number. The photograph shows the overall construction picture, and the drawings show
the details. Table III gives the required tubing lengths to construct the elements.
Bibliography
Source material and more extended discussion of topics can be found in the references
given below.
Bergren, The Multielement Quad, QST, May, 1963.
Reynolds, Simple Gamma Match Construction, QST, July, 1957.
Rhodes, The Log-Periodic Dipole Array, QST, November. 1973.
Fig. 8 Construction diagram of log-periodic array. Figure 9 and 10 are shown the method
of making electrical connection to each half element, and at D is shown how the boom
sections are joined.
Figure 9
Figure 10
Figure 11
TABLE I ARRAY DIMENSIONS, FEET
dn!1, n (spacing)
Element # ln h nearest resonant
1 38.0 19 0
d1! 2
!
2 34.2 17.1 3.862 = 14 MHz
d2 !
!3
3 30.78 15.39 3.475 =
4 27.7 13.85 3.13 "
5 24.93 12.465 2.815 "
6 22.44 11.22 2.533 " 21 MHz
7 20.195 10.098 2.28 "
8 18.175 9.088 2.05 "
9 16.357 8.179 1.85 " 28 MHz
10 14.72 7.36 1.663 "
11 13.25 6.625 1.496 "
d11!
!12
12 11.924 5.962 1.347 =
TABLE II MATERIALS LIST for Figure 8
Material Description Quantity
1. Aluminum tubing .047" wallthickness
1" 12' or 6' lengths 126 lineal feet
7/8" 12' lengths 96 lineal feet
7/8" 6' or 12' lengths 66 lineal feet
3/4" 8' lengths 16 lineal feet
2. Stainles steel hose clamps 2" max. 48 ea.
3. Stainles steel hose clamps 1-1/4" max. 26 ea.
4. TV - type U-bolts 14 ea.
5. U-bolts galvanized type
5/16" X 1-1/2" 4 ea.
1/4" X 1" 2 ea.
6. 1" ID polyethelene water servire pipe -
160 psi test approx. 1-1/4" OD 20 lineal feet
A. 1-1/4" X 1-1/4" x 1/8" aluminum angle
6 lengths 30 lineal feet
B. 1" X 1/4" aluminum bar 6' lengths 12 lineal feet
7. 1-1/4" top rail of chain-link fence 26.5 lineal feat
8. 1:1 toroid balun 1ea.
9. 6 32 X 1" stainless steel screws 24 ea.
6 32 stainless steel nuts 48 ea.
No. 6 solder lugs 24 ea.
10. No. 12 copper feeder wire 60 lineal feet
11.
A. 12" X 8" X 1/4" aluminum plate 1ea.
B. 6" X 4" X 1/4" aluminum plate 1ea.
12.
A. 3/4" galvanized pipe 3 lineal feet
B. 1 galvanized pipe mast 5 lineal feet
13. Galvanized guy wire 50 lineal feet
14. 1/4 X 2 turnbuckles 4 ea.
15. 1/4" X 1-1/2" eye bolts 2 ea.
16. TV guy clamps and eye bolts 2 ea.
TABLE III ELEMENT MATERIAL REQUIREMENTS
Element # 1" tubing 7/8" tubing 3/4" tubing 1-1/4" angle 1" bar
Lth. Qty. Lth. Qty. Lth. Qty. Lth. Lth.
1. 6' 2 6' 2 8' 2 3' 1'
2. 6' 2 12' 2 - - 3' 1'
3. 6' 2 12' 2 - - 3' 1'
4. 6' 2 8.5' 2 3' 1'
5. 6' 2 7' 2 - - 3' 1'
6. 6' 2 6' 2 - - 3' 1'
7. 6' 2 5' 2 - - 2' 1'
8. 6' 2 3.5' 2 - - 2' 1'
9. 6' 2 2.5' 2 - - 2' 1'
10. 3' 2 5' 2 - - 2' 1'
11. 3' 2 4' 2 - - 2' 1'
12. 3' 2 4' 2 - - 2' 1'
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