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For a single-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 2
, 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 multiple 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 2
.
Note:
These calculations are in decimal feet, not feet and inches.
Table 2
shows delay line length calculations based on the dimensions for the three most common
bands for a Receive Eight Circle Array.
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
(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 2 - Specific Delay Line Length Calculations for single band arrays.
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 Endfire Cell
adjacent element 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.
The delay line cable can be neatly coiled in a 1-1/2 ft diameter coil. Support the weight of the coiled
cable by taping or securing it to the support pole or mast rather than allowing it to hang from the
connectors.
It is important to use 75Ω feedline to the operating position from the
DXE-RCA8B-1
unit. Do not
use amplifiers, combiners, filters or splitters that are not optimized for 75Ω systems.
Lightning Protection
While amateur radio installations rarely suffer damage from lightning, the best protection is to
disconnect electrical devices during storms. The key to lightning survival is to properly ground
