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Topographical Considerations
Flat land is best. Erecting the receiving array on sloped land or steep hills may degrade
performance. To avoid pattern degradation, antenna elements must have reasonably similar
elevations. It's recommended the ground height difference between any element in the array be less
than 10% of the array diameter. For example, a 100 foot diameter array should be within ten feet of
level. Every effort should be taken to make the elements symmetrical. Elements should all be
identical in construction and grounding, and should be mounted above any potential standing water
line but as close to the ground as possible. In general, the system will not be affected by trees or
foliage as long as the foliage does not contact the element. Ideally, in important receiving
directions, there should be a clear electrical path for at least 1-wavelength. The site should allow a
ground system to be evenly distributed around each antenna, if one is required, as for passive
elements.
Sizing the Array
If there are no space constraints, follow the dimensional recommendations in
Table 4
for excellent
performance.
Only a monoband array may be installed with passive verticals or Active Vertical elements,
but a multi-band Eight Circle Array must be installed with Active Vertical elements.
An Eight Circle Array that is optimized for a certain band will not yield useful results on the next
higher frequency band. If you are using the Active Receive Verticals so that you can obtain
directional receiving performance on two or more bands, the array must be sized for the highest
frequency band. The Active Receive Vertical elements provide the required 75Ω impedance across
multiple bands in order to maintain pattern stability.
A monoband 160 meter optimized Eight Circle Array is sized by multiplying the free space
wavelength at 1.832 MHz of 537 feet/wavelength times the optimum pattern circle radius of 0.327
wavelengths, which yields an optimal circle radius of 175.6 feet. This places the vertical elements
about one-quarter wavelength apart, 134.25 feet.
However, as shown by the patterns of
Figure 9
, an optimized 160 meter Eight Circle Array is not
useable on 80 meters.
If the Eight Circle Array is intended to be used monoband on 80 meter, or if it will be used on 80
and 160 meters, then the best choice for sizing the array is shown at the bottom of
Table 4
. This is
where the free space wavelength at 3.803 MHz of 258.65 feet/wavelength is multiplied by the
optimum pattern circle radius of 0.327 wavelengths, which yields an optimal circle radius of 84.58
feet. This places the vertical elements about one-quarter wavelength apart, 64.74 feet.
