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Multi-Band Arrays with Active Elements
Only the DX Engineering Active Receive Verticals or vertical
elements with Active Matching Units, with constant 75Ω
impedance and unsurpassed dynamic range across the
frequency range, will allow a user to properly cover more
than one band with the Eight Circle Array.
Considering the available patterns from the Eight Circle
Array, the best possible choice for a two-band array covering
80 and 160 meters is one that is optimized for 80 meters. The
resulting patterns are represented closely to the patterns in
Figure 10
by the “.325-wavelength radius” for 80 meters and
by the “.15-wavelength radius” for 160 meters, with a
narrower pattern and performance exceeding short Beverage
arrays.
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
represented closely to the pattern “.35-wavelength radius”
shown in
Figure 9
.
For example, an array built to cover 160, 80 and 40 meters
has a highest frequency of 7.3 MHz, and 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 9
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.
Examples: 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 section “
Delay
Line
”.
Figure 9
Summary of Contents for DXE-RCA8C-SYS-4P
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