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Delay Line
For a single or two-band Eight Circle Array, the required
electrical length of the delay line is based
on the distance between each of the two adjacent elements on the circle. As shown in Table 3 , the
calculation of the electrical length of the delay line is 95% of the physical distance between adjacent
elements or adjacent element distance times 0.95 for a single band or two band array. The electrical
length is then multiplied by the VF of the coaxial cable being used to determining the correct
physical length of the delay line. The result is the correct physical length for the Delay Line in the
right column of
Table 3 .
Careful measurements and the use of 75Ω coaxial cable with a known Velocity Factor (VF) is very
important. We strongly recommended the use of DX Engineering
DXE-6UF-1000 High Quality,
Low Loss, 75Ω F6 type
Direct Bury Coax "Flooded" Coax. The DX Engineering DXE-6UF-1000
75Ω coaxial cable has a nominal VF of 0.85. Keep in mind that solid Teflon® or polyethylene (PE)
dielectric coaxial cable has a VF of approximately 0.66. Foamed coaxial cable cables typically
range anywhere between 0.75 and 0.90 VF, depending on the ratio of air-to-dielectric material in
the cable core. If you do not know the VF of the coaxial cable you are using, you must directly
measure the electrical length of the coaxial cable you have with an analyzer or obtain cable with a
known VF.
Table 3 shows delay line length calculations based on the dimensions for the three most common
Receive Eight Circle Arrays. Note: These calculations are in decimal feet, not feet and inches.
Band Coverage
Desired
Optimal Eight
Circle Array
.327-wavelength
Radius in Feet
Adjacent Element
(Endfire Cell)
Quarter-
Wavelength
Physical Spacing in
Feet
Factored
0.95
Electrical
Length
in Feet
Delay Line
Physical
Length in
Feet
(0.85 VF)
160 meters only
(1.830 MHz)
175.64 134.43 127.71 108.55
80 meters only and
80 +160 Dual-Band
(3.800 MHz)
84.58 64.74 61.50 52.28*
40 meters only
(7.200 MHz)
44.66 34.17 32.46 27.59
Table 3- Specific Delay Line Length Calculations for single band arrays
and a 160m/80m dual-band Array.
For Example : An Eight Circle Array intended to be optimized for 160 meter only operation has
an optimized .327-wavelength radius dimension of 175.64 feet, and Adjacent
Element Endfire Cell spacing of 134.43 feet. The 0.95 factored electrical length is
127.71 feet. Multiply 127.71 by 0.85 (the VF of DX Engineering 75Ω coaxial
cable) to determine the physical length of the delay line.
The correct physical length for this delay line is 108.55 feet, or 108 feet 6-5/8 inches.
An Eight Circle Array intended for frequency coverage over a 3:1 ratio, such as 160/80/40M,
cannot use the standard 95% calculation as detailed above.