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The absolute maximum useful directional frequency coverage of the Eight Circle Array is about a
4:1 ratio. A compromise Eight Circle Array System should be sized with its highest frequency
corresponding to an array radius of .375-wavelength, being limited by allowable side lobe levels, as
shown in
Figure 9
.
For example, an array built to cover 160, 80 and 40 meters
has the highest frequency of 7.3 MHz will have a .375-
wavelength radius of about 50.5 feet, which offers excellent
rear rejection on 40 meters, a respectable cardioid pattern on
80 meters, and still offer useable directivity on 160 meters.
The patterns on these bands are represented in
Figure 8
by
“.375-wavelength radius” for 40 meters, just about the same
as the “.2-wavelength radius” pattern on 80 meters and the
“.1-wavelength radius” pattern for 160 meters.
An array sized for the highest frequency of 2.0 MHz with a
.375-wavelength radius of 184.43 feet, would provide the
best pattern (.327-wavelength radius) at 1.744 MHz, but still
offer good directional performance down to 500 kHz. An
array sized for the highest frequency of 21.5 MHz with a
.375-wavelength radius of 17.16 feet, would provide usable
directivity down to 5.3 MHz.
NOTE: An array which is intended to be used over a
frequency range greater than 3:1 requires a different Delay
Line than one intended for a single or two-band system. See
the manual for the
DXE-RCA8B-SYS-3P
Eight Circle
Array Electronics Package, or the
DXE-RCA8B-SYS-4P
Complete Eight Circle Array System Package for details.
Figure 8
