DX Engineering DXE-RCA8C-4S-INS User manual

Receive Eight Circle Array
Complete System Package
DXE-RCA8C-SYS-4S
U.S. Patent No. 7,423,588
DXE-RCA8C-4S-INS Revision 0a
© DX Engineering 2019
1200 Southeast Ave. - Tallmadge, OH 44278 USA
Phone: [phone] ∙ Tech Support and International: [phone]
Fax: [phone] ∙ E-mail: [email protected]

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Table of Contents
Introduction
3
Are you ready to build your Receive Eight Circle Array?
3
DXE-RCA8C-SYS-4S Complete System Package
4
Additional Parts Required, Not Supplied with the DXE-RCA8C-SYS-4S
4
Eight Circle Layout
4
System Overview
5
Installation
6
Control and Power Connections
6
Receive Eight Circle Active Vertical Elements
8
Ground System
9
Lightning Protection
9
Array Spacing
10
Station Feedline, Active Element Feedline and Delay Line
10
Vertical Element Feedlines
11
Typical DXE-RCA8C-SYS-4S Receive Eight Circle Configuration
12
Delay Line
13
Optimizing the Array
13
Theory of Operation of the Receive Eight Circle Array
14
System Design Features and Benefits
14
Frequency Coverage -vs.- Element Type
15
Receive Antennas - Gain and Efficiency
16
Site Selection
16
Effects on Patterns
17
Site Selection in Relation to Noise Sources
17
Proximity to Transmitting Antennas
18
Examples of Array Performance
19
Multi-Band Arrays with Active Elements
20
Delay Line
21
Topographical Considerations
23
Sizing the Array
24
Receive Eight Circle Troubleshooting
27
Technical Support and Warranty
32

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Introduction
Congratulations on your purchase of the DX Engineering Receive Eight Circle Array System
designed by W8JI, which offers the best directional receiving performance in proportion to the
space required. Advanced design, with a stable, clean, narrow and low-angle pattern in eight
selectable directions, makes the DX Engineering Eight Circle Array the ultimate receiving antenna.
The Eight Circle Array System is an eight element, eight direction-switchable array based on a
four element end-fire/broadside combination of short receiving vertical elements. This antenna
array is capable of delivering pattern directional performance superior to standard or short Beverage
or reversible Beverage systems, and typical three element or four square arrays of short vertical
elements. The DX Engineering Receive Eight Circle Array System offers selectable directional
performance comparable to eight very long phased Beverages, and does it in far less space.
Advantages of this DX Engineering Receive Eight Circle Antenna System over other arrays:
W8JI design with stable, narrow and low-angle pattern
Directional performance varies with circle radius
Included Active Receive Verticals with 8.5 foot elements cover a
single band or multiple bands within 500 kHz to 30 MHz
Excellent directivity in a smaller space than phased Beverages for
better signal-to-noise ratio
Reduced susceptibility to high angle signals compared to phased
Beverage antennas, as well as superior performance over EWE,
Flag, Pennant, K9AY antennas.
Switching console selects one of eight 45° spaced directions
Directivity over a very wide frequency range
Less physical space and less maintenance required than phased Beverage antenna arrays
Enhanced relay contact reliability
DC powered control console allows system operation without AC power mains
The DXE-RCA8C-SYS-4S is a complete Receive Eight Circle Antenna Array Package which may
be installed as a Mono-Band or Multi-Band system using a recommended or alternative array radius
for the frequency coverage desired. A single delay line can be made to accommodate the desired
band or bands of operation according to the information provided in the Delay Line section of this
manual.
Are you ready to build your Receive Eight Circle Array?
We are pleased that you have purchased a Complete Receive Eight Circle Array System Package
model DXE-RCA8C-SYS-4S because you wanted the ultimate receive antenna system complete
with Active Vertical Antenna including mounting hardware and rolls of coaxial cable with
connectors and tools; virtually everything required to install a complete system. Before you proceed
with installation, there are some fundamental concepts that you should know.
1. Have you sized your array to achieve the desired performance within your space? Do you
know where you will be locating your Receive Eight Circle Array? Review the explanation

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of the optimal monoband and multi-band frequency coverage of the Eight Circle Array in
sections entitled Array Performance, Site Selection and Sizing the Array.
2. Are you ready to build your system? Proceed!
The DXE-RCA8C-SYS-4S Receive Eight Circle Array Packages includes:
DXE-RCA8C-1 Receive Eight Circle Array Controller
DXE-CC-8A Special eight position Receive Eight Circle Control
Console modified to provide +12 Vdc for powering the active antennas.
DXE-SSVC-2P Stainless Steel V-Clamp for mounting the RCA8C-1
Receive Eight Circle Array Controller to a mounting post between 1"
and 2" OD
Four DXE-ARAV4-4P (Eight total Active Matching units with Internal
Disconnect Relays, Aluminum Vertical Elements, Insulated Mounting
System and Stainless Steel V-Clamps to be used with customer supplied ground rods for
mounting
DXE-F6-1000 (Two) 1000 Foot Rolls, Coaxial Cable, 75Ω, F6 Flooded Cable
DXE-CPT-659 Coaxial Cable Prep Tool for RG6, F6 75Ω Coaxial Cable, w/extra blade
DXE-SNS-CT1 Snap-N-Seal®Compression Tool for 75Ω coaxial cable connectors
DXE-SNS6-25 Package of 25 Snap-N-Seal®Connectors for 75Ω F6 coaxial cable
Additional Parts Required, Not Supplied with the DXE-RCA8C-SYS-4S
One additional DXE-F6-1000 75ΩCoaxial Cable that may be required for the main
feedline from the station to the array
Five-Conductor Power and Control Cable. The modified DXE-CC-8A Control Console
interfaces to the DXE-RCA8C-1 Eight Circle Array Controller through a 5-wire cable to
select one of eight directions and to power the eight active elements. Economically priced
DXE-CW9S is a 9-conductor control wire which may be used allowing the user to use the
spare wires to double up on power and return lines for current carrying capability.
Eight Circle Layout
The optimized array for single band performance has vertical elements
arranged in a circle with a radius of about 175 feet for 160 meters, or 84
feet for 80 meters, or 44 feet for 40 meters. A two-band array for 80 and
160 meters should also have a radius of about 84 feet. See the Theory of
Operation sections for exact dimensions, options for wider frequency
coverage and guidance in choosing the best orientation.
The default direction of the array with no voltage (BCD 000) places
elements 1 and 6 in front and elements 2 and 5 at the rear, with pairs of
lines through two opposite vertical element pairs (tangents) that point toward the receiving
directions.

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Elements 1, 2 and 5, 6 are selected as the default for a forward direction of North-East for North
America, with elements installed as shown. A mirror image of this element positioning would be a
typical default North-West for European installations.
Figure 1 - Typical Diagram of the DXE-RCA8C-SYS-3P Receive Eight Circle Array System
System Overview
The heart of the DXE-RCA8C-SYS-4S system is comprised of the modified DXE-CC-8A Eight
Position Control Console, the DXE-RCA8C-1 Receive Eight Circle Array Controller, eight DXE-
AVA2 Active Matching Units for your vertical elements and one Delay Cable with F-Connectors
installed. These units interconnect and work together using factory default settings to control the
Receive Eight Circle Array. The modified CC-8A control console uses BCD switching voltages for
the RCA8C-1 to change the receiving direction of the array.
When the modified CC-8A Eight Circle Control Console and the RCA8C-1 Receive Eight Circle
Array Controller are connected as shown in the installation section below and the layout is as
described for North America in Figure 1, the switch positions on the modified CC-8A will switch
the array in the eight directions as shown in Figure 2.
Figure 2

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Installation
The RCA8C-1 Receive Eight Circle Array Controller can be mounted to a customer supplied
galvanized steel pipe driven into the ground at the center of the array. A galvanized pipe ranging
from 1 to 2 inch OD may be used. The length of the controller unit's mounting pipe is dependant on
your location. The standard 1-1/2" galvanized water pipe (with its approximate 1.9" OD) is just fine
for this application and can usually be found at your local home building supply store.
The RCA8C-1 relay unit has been pre-drilled to accommodate up to a 2 inch OD pipe using the
included DXE-SSVC-2P Stainless Steel V-Bolt Saddle Clamp for 1" to 2" OD pipe. An optional
DXE-CAVS-1P V-Bolt Saddle clamp can be used for pipe from 3/4" to 1-3/4" inches OD. The
controller can also be mounted on a sturdy wooden post if provision for grounding the RCA8C-1
unit has been made. Note: JTL-12555 Jet-Lube SS-30 Anti-Seize should be used on all clamps,
bolts and stainless steel threaded hardware to prevent galling and to ensure proper tightening.
The Receive Eight Circle Array Controller unit should be mounted as shown in Figure 3 with cover
upward and the control and coaxial cable connections downward to prevent water from entering the
box. The stainless steel base of the Receive Eight Circle Array Controller unit has weep holes to
allow condensation that may build up inside the unit to leave.
Figure 3 - RCA8C-1 unit mounted to 2" pipe using the included DXE-SSVC-2P V-Clamp
Control and Power Connections
1. Locate the removable green connector on the rear of the modified CC-8A labeled "G A B C D”.
The green connector is a two part connector as shown and the top part can be removed by
pulling it straight off. This will allow easier wire replacement or servicing as needed. When
pushing the removable connector back in place, ensure you press straight inward to fully seat
the connection.
2. Insert the five wire cable on the green connector as shown in Figure 4.
3. The same five wires are connected to the RCA8C-1 removable green connector (G A B C D) as
shown in Figure 5. (“D” is required only for voltage on the element feedlines and should not be
connected for passive vertical arrays.)
4. The modified CC-8A Control Console requires a nominal +12 Vdc fused input (+12 to +14
Vdc, 2 Amps and well filtered) through the 2.1 mm connector on the rear of the unit.

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A 2.1 mm power cord is supplied with unit. The wire with the white stripes is the +12 Vdc.
Outer Connection is GROUND Center Pin is +12 VDC.
Figure 4 - Connections between the RCA8C-1 and the modified CC-8A
The RCA8C-1 uses a removable five terminal plug as shown in Figure 5. The RCA8C-1
connections are labeled “G A B C D”. The terminals use the same connection letters and are
connected G to G, A to A, B to B, C to C and D to D.
On the RCA8C-1 the green connector is a two part connector as shown in Figure 5 and the top part
can be removed by pulling it straight off. This will allow easier wire replacement or servicing as
needed. When pushing the removable connector back in place, ensure you press straight inward to
fully seat the connection.
Figure 5 - RCA8C-1 Green Connector

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Switch Position
G
A
B
C
D
1
GND
0
0
0
1
2
GND
1
0
0
1
3
GND
0
1
0
1
4
GND
1
1
0
1
5
GND
0
0
1
1
6
GND
1
0
1
1
7
GND
0
1
1
1
8
GND
1
1
1
1
Table 1 - Modified CC-8A Output Truth Table
Control lines (usually BCD ) can normally use good quality CAT5e cable (4 twisted pairs of 24
AWG wire) for runs up to 1000 feet. Typical DX Engineering BCD control lines requirements are
+12 VDC at 25 milliamps.
Depending on the number of control lines needed (usually 3 or 4) you can double up the twisted
pairs of CAT5e cable, or use control wire that is at least 22 AWG, allowing runs up to 1500 feet. If
you use a cable with more conductors, it is a good idea to tie the unused conductors to ground.
For longer runs of control cable, use a line loss calculator to ensure you supply the proper control
levels needed.
Approximate BCD Control Line Lengths.
Minimum Copper
Wire Gage (AWG)
Length
24
1,000 feet
22
1,500 feet
20
2,000 feet
Active antenna circuitry needs a good voltage supply to operate properly. When supplying power to
an active antenna, you want to have +12 VDC, 60 milliamps at each active (under load).
CAT5e cable is not recommended when making long runs to power an active antenna since the line
loss in CAT5e cable may not supply the proper operational voltages required for active antennas.
Depending on the required length of your power wire, you will want to use a line loss calculator
(voltage drop with various wire gages) to ensure your power supply (normally +13.6 well filtered
DC) will supply a minimum of +12 VDC, 60 milliamps at each active antenna (under load).
A DX Engineering 4 Square or 8 Circle will require approximately 250 milliamps (only 4 actives
are powered at any one time).
When calculating line length, take into consideration the total number of active antennas being
powered at any one time in your line length calculations.

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Approximate Active Antenna Power Line Lengths (4 active antennas on at any one time).
Minimum Copper
Wire Gage (AWG)
Length
18
300 Feet
16
500 feet
12
1,200 feet
10
2,000 feet
Receive Eight Circle Active Vertical Elements
The DXE-RCA8C-SYS-4S Eight Circle Array is supplied with four DX Engineering model DXE-
ARAV4-2P Active Receive Verticals, which consists of eight identical ARAV4 Active Receive
Vertical Antennas. Featuring the AVA2 Active Matching Units, the ARAV4offers excellent
broadband receiving performance from 100 kHz to 30 MHz. In addition, the ARAV4provides a
clean, low profile installation using aluminum antenna elements. DX Engineering’s unique design
makes it vastly superior to other amplified and traditional active antennas in both strong signal
handling and feedline decoupling. You get significantly better weak signal reception due to lower
spurious signal interference and reduced noise.
The ARAV4 Active Receive vertical matching units ground the antenna element when power is
turned off. The active antennas allow installations with spacing from transmit antennas less than 1/2
wavelength but more than 1/10 wavelength (on the lowest frequency). Close spacing of the array to
transmitting antennas can be done, but will impact overall receive array system performance. Sites
without sufficient land area for proper spacing should use these verticals, which may be installed in
close proximity to transmitting antennas (1/10-wavelength of the lowest transmitting frequency).
This is possible, provided the active units are powered off at least 5 ms before transmitting. An
optional sequencer such as the DXE-TVSU should be used to ensure the correct transmit to receive
switching
Your eight identical DXE-ARAV4 Active Vertical Antennas must be mounted so they are self-
supporting and insulated from the mount. A ground rod may be used as the ground mount. The
vertical element must be connected only to the positive terminal of the AVA2 Active Matching
Units, and the negative terminal must be connected to at least one ground rod. Two ground rods
may be needed in some soils. The Active Receive Verticals normally do not need ground radials,
however, depending upon the conductivity of the soil, in sandy soil or rocky soil installations, wire
radials may be required.
The Active Receive Verticals should be installed with their feed points as close to the ground as
possible but above any standing water. The level of snow cover over the feedpoint and the active
vertical is not an issue. If you are planning to use the array on the 160 meter band, a jumper in the
active antenna matching units may be changed to limit the Active Matching Unit response to the
AM Broadcast Band. Placing a jumper on L1MF will peak the array sensitivity response for use on
160 meter, with little effect on 80 meters. For access to the jumpers in the Active Matching Units,
remove the 2 screws on each side of the case and remove the bottom. The circuit board and jumper
headers will be visible, as shown in Figure 6. By default, there are no jumpers across any pins.

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Place a jumper across L1MF. Normally, jumpering any other positions will not be required for most
operations. Typically, the goal of reducing the array sensitivity
within the AM Broadcast Band is the only reason for adjusting the
jumpers in the Active units. If maximum AM Broadcast Band
reception is desired, or if the array is very far from strong AM
Broadcast signals, then no jumpers should be used. All eight active
elements in the array must have identical jumper settings.
Figure 6 - Active Element L1MF Jumper Locations
See the DX Engineering Active Receive Vertical Antenna user manual for more information about
additional peak response jumper settings.
Ground System
The ARAV4 Active Elements work well with just a single copper ground rod placed as close as
possible to the mounting pipe. The mounting pipe can be used as the system ground if the pipe is an
adequate ground. It is recommended that a 3/4" or larger rigid copper water pipe, although
conventional copper coated steel rods may also work. Depending on soil conductivity, you can
expect better performance with multiple ground rods spaced a few feet apart. Increasing ground rod
depth beyond 5 ft rarely improves RF grounding because skin effect in the soil prevents current
from flowing deep in the soil. Avoid ground rods less than 5/8" OD. A good ground system
improves the array performance and enhances lightning survivability. It is important that the
ground system is identical for each active antenna in the array.
You can test ground quality by listening to a steady local signal. Attach 15 ft of wire laid in a
straight line (away from the coaxial feedline) to the initial 4 ft to 6 ft ground rod. If you observe a
change in signal or noise level, you need to improve the ground. A second rod spaced a few feet
away from the first one may correct the problem or 10 to 12 ground radials, each 15 ft long, should
provide a sufficient ground system for most soil conditions.
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
feedlines and equipment and to maintain the integrity of shield connections. A proper installation
improves lightning protection and enhances weak signal receiving performance.
Consult lightning protection and station grounding information in the ARRL handbooks, or by
referring to the NEC (National Electric Code). The DX Engineering website also has technical and
product information “Lightning Protection and Grounding”. Use lightning surge protectors for the
coax feedline and control lines such as the DXE-RLP-75FF Lightning Protector, Receive 75Ω, DC
Pass, with F Connectors, for the array feedline at the station end single point ground.

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Array Spacing
Performance of the Receive Eight Circle Array can noticeably decrease if structures radiating even
small amounts of noise or signals are within 1-wavelength of the array. There is no detrimental
effect when a higher frequency array of small receiving elements is placed inside the circle of a
lower frequency array of short elements.
Note: The DXE-RCA8C Eight Circle Receiving Array System should be separated from
transmitting or other antennas and structures (particularly metal) by at least 1/2
wavelength. Less separation may cause significant pattern distortion and the
introduction of re-radiated noise into the system. This becomes apparent as reduced
front-to-rear directivity in one or more directions or a higher noise level.
With so many variables involved, there is no optimum or minimum spacing for effects on pattern.
The best practice is to install the array as far as possible from tall conductors or noise sources, or
place potential problems in less frequently used directions. For best pattern, space the system as far
as possible from conductors that might be noise sources or re-radiate unwanted signals. One
wavelength or more is generally ideal, although adequate performance generally occurs with much
smaller spacing, with one-half wavelength minimum recommended.
Station Feedline, Active Element Feedline and Delay Line
It is important to use 75Ωfeedline to the operating position from the DXE-RCA8C-1 unit. Do not
use amplifiers, combiners, filters or splitters that are not optimized for 75Ωsystems. All element
feedlines must be 75Ω and can be any length as long as they are all equal and they should come
from the same roll of cable so they have the same velocity factor (VF).
The weakest link in an antenna system is often the coaxial cable connections. All connections must
be high quality and weather tight to prevent contamination and corrosion, which can cause the
feedline impedance to change. This can affect the signal-to-noise ratio and the directivity of the
array. If the coaxial cable is compromised the shield will then pick up unwanted signals. This is
why the shield connections are most critical. In addition, the RCA8C-1 uses the shield as a ground
return path for the active element power.
If the resistance of the shield increases due to contamination, the active elements may not function
properly. Any splices in the feedline should be high quality and entirely weather tight. Do not use
splices in the delay line cable. The DXE-RCA8C system has been designed to use only 75Ωcoax.
High quality, flooded 75ΩCATV F6 type coax is recommended. The DXE-F6-1000 flooded cable
automatically seals small accidental cuts or lacerations in the jacket. Flooded cable also prevents
shield contamination and can be direct-buried.
Feedline connections must have good integrity and be weather resistant. Highly recommended for
any DX Engineering array, and specifically designed for the DXE-F6-1000 flooded cable is the

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Snap-N-Seal® F connectors, model DXE-SNS6-25 which contains 25 connectors; enough for the
entire array plus spares. Snap-N-Seal® connectors cannot be installed with normal crimping tools or
pliers. The DXE-SNS-CT1 Compression Tool for Snap-N-Seal® 75ΩCoax Connectors is an
essential tool for proper connector installation.
Lightly coat threads of F connectors with pure clear non-hardening silicon dielectric compound,
such as PTX-22058 Permatex Dielectric Grease, to improve reliability of electrical connectors. This
will lubricate threads, seal connector threads from water ingress, and reduce chances of unwanted
bonding or welding of connector threads. If dielectric grease is not used, the potential for damage
to the various connectors may result and is not covered under warranty.
Note: DO NOT use pliers or other tools to excessively tighten the type F connectors; they
do not require high torque to make a good connection. F connectors are very
reliable strong connectors for their size, but carelessness can damage them.
Excessive tightening torque can loosen the chassis mounting-nut, allowing the
connector body to rotate and fracture the mounting tabs on either installation or
removal of the connector. F-connectors require modest torque, typically 6-12 inch-
pounds. 20-30 inch-pounds are FAR too high. That value, although commonly used,
is just wrong. Damage to the various connectors may result and is not covered
under warranty. Use a tool such as the DXE-CIT-1 F Connector Tightening Tool.
Additional weatherproofing protection can be provided when using the PTX-22058
Permatex Dielectric Grease on all coaxial connections. Dielectric grease is ideal for
keeping moisture from entering your coaxial connectors. It also acts as a lubricant
allowing easy connector removal by stopping corrosion of electrical connectors.
Vertical Element Feedlines
Use 75Ω coaxial cable from each antenna element to the
RCA8C-1. The eight feedlines from the RCA8C-1 to the
elements can be any length needed to accommodate the size of
the array, but must all be the same physical length, velocity
factor and type. Note the orientation and numbering of the
elements by using Figure 7.Be sure the appropriate antenna
element is connected to the proper ANT connector on the
RCA8C-1.
Figure 7 - Vertical Elements
Coaxial Connections to the RCA8C-1

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Typical DXE-RCA8C-SYS-4S Receive Eight Circle Configuration
Figure 8
Coaxial Cables are shown in various colors for clarity. Shown with optional DXE-RPA-2 Receive Pre-
Amplifier, DXE-RFCC Receive Feedline Current Choke and optional DXE-CW9S Control Cable.
Power connection to the modified DXE-CC-8A Control Console is not shown.

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Delay Line
The DXE-RCA8C-1 unit has two delay line female F connectors marked DELAY. This connection
pair will require one specific length coaxial cable assembly with male F connectors acting as a
jumper between the two female F connectors.
If you intend to size your array for frequency coverage other than 80 and 160 meter operation, see
the section on “Delay Line”.
The DX Engineering DXE-RCA8C-1 uses a time delay system, not a traditional phasing system.
The delay line length is dictated by array dimensions rather than operating frequency, which allows
for the use of a single delay line for optimum directivity over a very wide frequency range. This
results in phase being correct for a rearward null at any frequency.
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.
Optimizing the Array
To determine if the antenna system output level is the limiting factor, tune the receiver to the lowest
band at the quietest operating time. This is usually when propagation is poor but some signals are
heard. Disconnect the antenna and set the receiver to the narrowest selectivity you expect to use.
Receiver noise power is directly proportional to receiver bandwidth (going from 2.5 kHz selectivity
to 250 Hz selectivity reduces noise by 10 dB). Connecting the antenna should result in a noticeable
increase in noise. If so, the array signal level is sufficient and further optimization or amplification
may not be needed.
If the array is used on 160m or 80m and the array still lacks sensitivity, then the optional DX
Engineering DXE-RPA Receive Pre-Amplifier with high dynamic range will easily compensate for
low signal level. Using a pre-amplifier when sufficient signal is already present may result in
amplification of the noise along with the signal. It is always best to use the least gain possible.
Depending on conditions, a lesser pre-amplifier may be unable to handle the signals of a broadband
antenna, which can cause receiver overload. At times, strong signals require the use of an attenuator
or bypassing the preamplifier. However, the DXE-RPA has better dynamic range than most
receivers and can be used to compensate for a low array signal output, even in high signal locations.
Hint: Using a combination of the RPA antenna pre-amplifier AND receiver front-end
attenuation or RF gain reduction or both, can often provide the best improvement in
signal-to-noise for enhanced reception and ultimate low band DXing.

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Theory of Operation of the Eight Circle Array
The following Sections contain specific information about the fundamentals of the Eight Circle
Array. It contains all of the information needed to make decisions about the band coverage desired,
and how band coverage is affected by the selection of the optimal pattern in relation to the circle
radius. Also included is information discussing the differences between the use passive or active
vertical elements.
System Design Features and Benefits
The DX Engineering Receive Eight Circle Array System designed by W8JI offers the best
directional receiving performance in proportion to the space required. Advanced design makes the
DX Engineering’s Eight Circle Array, with stable, clean, narrow and low-angle pattern in eight
selectable directions, the ultimate receiving antenna.
The DX Engineering Receive Eight Circle Array is the highly sophisticated receive eight circle
system that uses time delay phasing - rather than the conventional narrow-band, frequency
dependent phasing - to provide eight 45 degree spaced directional patterns. The time delay phasing
is directivity-optimized to produce wider and deeper rear nulls and a narrower main lobe. The result
is that noise and undesirable signals are greatly reduced by superior front-to-rear (F/R). The array
forms a clean stable pattern with high directivity over wide bandwidth.
W8JI initially developed and used this array in the 1980’s. This
array started appearing in the 1990’s at larger more advanced low-
band DX stations. The phasing system in this array, as well as the
active element design, offer much better dynamic range and
directivity bandwidth than other later copies.
Unlike unidirectional transmitting arrays using large elements, very
small elements do not create significant mutual coupling related current-
distribution and phase errors. Better control of phase and currents
provides a much cleaner pattern than found on available vertical antenna
transmit arrays.
Time-delay phasing produces a frequency independent rearward null. Additionally, this array
combines independent unidirectional cells across the full width of the array to add additional
broadside directivity. Broadside phasing is also frequency independent.
Phasing remains perfect over very wide frequency ranges. This results in excellent front-to-back
performance on multiple bands, despite using a single delay line with fixed element spacing. The
deep rearward null reduces rearward noise and undesirable signals over very wide frequency ranges.
The rearward null is frequency independent up to element-to-element spacings of just over 1/4-
wavelength.
The DX Engineering RCA8C-1 Receive Eight Circle Array Controller uses sealed relays sized for
receiving applications. (High current contacts, suitable for transmitting, commonly have unreliable

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contact connections at low currents. This is because of the large surface areas and hard contact
materials necessary to support high contact switching currents.) The RCA8C-1 Receive Eight
Circle Array Controller uses sealed relays optimally sized for receiving applications. Contacts are
bifurcated and gold-flashed, substantially improving low signal level switching reliability. The
improved low-level signal optimized bifurcated contacts virtually eliminate non-linearity,
rectification, and other maladies caused by poor relay connections.
The DX Engineering ARAV4 Active Receive Verticals have excellent broadband receiving
performance from 100 kHz to 30 MHz. In addition, they provide a clean, low profile installation.
DX Engineering’s unique design makes it vastly superior to other amplified and traditional active
antennas in both strong signal handling and feedline decoupling. You get significantly better weak
signal reception due to lower spurious signal interference and reduced noise.
Frequency Coverage -vs.- Element Type
The Eight Circle Array uses eight elements to form a clean, narrow beamwidth, low-angle pattern in
eight equally spaced user selectable directions. The elements form the most space-efficient type of
directional array, a broadside-endfire combination. With broadband active elements that are created
with the DX Engineering Active Receive Verticals, this array has an exceptionally good pattern
over at least a 3:1 frequency range. With these broadband active elements this array has unbeatable
performance across a single band.
The Eight Circle Array upper frequency limit for a clean unidirectional pattern is slightly above
where the array is .35-wavelength radius. The frequency of optimum performance is where the
array is approximately .327-wavelength radius. Construction care, element construction, desired
beamwidth, and local noise floor determines the minimum array size in wavelengths. Minimum
useful frequency typically occurs with an array less than 0.1-wavelength radius; although that limit
can be pushed lower with care in some situations. Careful construction will allow useful directivity
over the entire HF range with an exceptionally good pattern over a 3:1 frequency range.
A Special Application
The DX Engineering DXE-RCA8C Eight Circle Array phasing and switching system may also
be used as a unidirectional or bidirectional end-fire/broadside array with the installation of only
four vertical elements, using 1/10 to 1/4-wavelength endfire spacing in combination with 1/4 to
3/4-wavelength broadside spacing.
This limited implementation is for the user who specifically wants a very directional receive
antenna system that is pointed only in one direction, without power required, similar to a single
direction, phased Beverage array. It would also be switchable to a second opposite direction
with DC power, similar to a very long Reversible Beverage.
However, this Active Element end-fire/broadside array alternative to building a phased
Beverage array requires a lot less space and a lot less maintenance! Contact DX Engineering for
more details on the use of the DXE-RCA8C for a four element system.

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Receive Antennas –Gain and Efficiency
One popular misconception is that antenna gain pays equal dividends in receiving and transmitting.
While transmit to receive antenna gain reciprocity applies to changes in absolute signal levels, it
does not apply to signal-to-noise. Once external noise levels are slightly above receiver noise floor,
signal-to-noise ratio is almost entirely a function of antenna pattern. System loss or system gain is
no longer a factor, and excessive gain can actually hurt reception of weak signals.
Efficiency is not a major consideration in dedicated receiving systems. This allows application of
techniques that increase directivity in receive-only systems, techniques generally unworkable or
unacceptable in transmitting antennas. In a Multi-Multi contest station environment, passive receive
elements offer significantly greater dynamic range.
Site Selection
Site selection is important. Three major things upset the pattern and performance of an array. Phase
errors, element impedance errors, and improper spacing. This array’s phasing system uses a
combination of end-fire and broadside phasing. This array forms a clean stable pattern with high
directivity over wide bandwidth. Because of the stable, clean, narrow pattern in eight selectable
directions, this antenna is the ultimate in receiving.
Directing the antenna pattern away from noise sources or toward the desired signal path is the
primary benefit. Antenna gain is a secondary advantage. As frequency increases, the fixed array size
becomes electrically larger in terms of wavelength. The increased electrical spacing produces higher
sensitivity (average gain) even though front-to-rear ratio only changes slightly. On the low bands,
once the receiving system, including the antenna system and the receiver, are hearing the lowest
possible level of local and propagated ambient noise, antenna
directivity (F/R) is the only thing that affects the signal-to-noise ratio.
The default direction of the array with no voltage (BCD 000) places
elements 1 and 6 in front and elements 2 and 5 at the rear. Pairs of
lines through two opposite vertical element pairs (tangents) point
toward the receiving directions. Elements 1, 2 and 5, 6 are selected as
the default, for a forward direction of North-East, with elements
installed as shown for North America. A mirror image of this element
positioning would be a typical default direction of North-West for
European installations.
This array can use active or passive elements. Passive elements provide the greatest dynamic range
and immunity to overload. Active elements provide the widest system bandwidth, but at the expense
of dynamic range.
Receiving antennas work best when they have a clean pattern with narrowest possible lobe, and
minimal spurious lobes. This is because noise generally comes from many directions, while a signal
comes from one useful direction at a time. If a signal comes from multiple angles or directions we
still do not want those directions, because the phase relationship and levels of the multiple path

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single source signal will vary a great deal. This will cause undesirable fading and distortion. We
cannot successfully directly mix multiple antennas for diversity reception for the same reasons we
do not want an antenna to respond to the same signal source over multiple paths, since we cannot
combine randomly varying phase and level signals without increasing fading or reducing signal-to-
noise (S/N) ratio.
There is no detrimental effect when a higher frequency array of small receiving elements is placed
inside the circle of a lower frequency array of short elements.
Note: The DXE-RCA8C Eight Circle Receiving Array System should be separated
from transmitting or other antennas and structures (particularly metal) by at least
1/2-wavelength. Less separation may cause significant pattern distortion and the
introduction of re-radiated noise into the system. This becomes apparent as
reduced front-to-rear directivity in one or more directions or a higher noise level.
Effects On Pattern
As far as pattern goes every directional array, no matter how constructed or designed, will always
interact with surrounding conductors. Adequate spacing is almost entirely dependent on electrical
characteristics of the surrounding conductors for a given style of receiving array.
For example, a given style array of similar dimensions from one company will be similarly affected
by surrounding conductors regardless of element design, for a given style of element. The effect on
pattern depends almost entirely on how much surrounding objects absorb and re-radiate signals, if
the undesired structure is in a null or peak of the receiving array, and how close the systems are in
terms of wavelength.
With so many variables involved, there is no optimum or minimum spacing for effects on pattern.
The best practice is to install the array as far as possible from tall conductors or noise sources, or
place potential problems in less frequently used directions. For best pattern, space the system as far
as possible from conductors that might be noise sources or re-radiate unwanted signals. One
wavelength or more is generally ideal, although adequate performance generally occurs with much
smaller spacing.
Site Selection in Relation to Noise Sources
Because the array is directional, use this example as a guide: If you have a noise source and if your
primary listening area is northeast, locate the array northeast of the dominant noise source. This
ensures the array is looking away from the source of noise when beaming in the primary listening
direction. The second-best location for the array is when the noise source is as far as possible from
either side of the array. If you look at patterns, the ideal location for the array is one that places
undesired noise in a deep null area.
If this receiving array is in an area free of noise sources (power lines, electric fences, etc.), locate
the array so transmitting antennas and buildings are located in a null direction or commonly unused
direction.

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Noise that limits the ability to hear a weak signal on the lower bands is generally a mixture of local
ground wave and ionosphere propagated noise sources. Some installations suffer from a dominant
noise source located close to the antennas. Noise level differences between urban and rural locations
can be more than 30 dB during the daytime on 160 meters. Nighttime can bring a dramatic increase
in the overall noise level as noise propagates via the ionosphere from multiple distant sources. Since
the noise is external to the antenna, directivity can reduce noise intensity.
Consider these things about noise sources:
If noise is not evenly distributed, performance will depend on the gain difference between
the desired signal direction (azimuth and elevation) and gain in the direction of noise.
If very strong noise comes from the direction of a receiving antenna null, improvement in
S/N ratio can be as much as 30 dB or more
If noise predominantly arrives from the direction and angle of desired signals (assuming
polarization of signals and noise are the same) there will be no improvement in the signal-to-
noise ratio.
If the noise originates in the near-field of the antenna, everything becomes unpredictable. This is a
good case for placing receiving antennas as far from noise sources (such as power lines) as possible.
Proximity to Transmitting Antennas
Eight DXE-ARAV4 Receive Antenna Active Vertical active elements, and your transmitting
antenna need only minimal physical separation to maintain safe power levels when the DXE-TVSU
Time Variable Sequencer Unit is used. With 1500 watts output and a unity gain (0 dB) antenna, the
closest active element can be 1/10-wavelength from the transmitting antenna at the lowest
transmitting frequency. Doubling the protection distance quadruples safe power levels. See Table 2.
Band
Unity (0 dB) Gain
3 dB Gain (2x)
6 dB Gain (4x)
160m (1.8 MHz)
55 ft
110 ft
220 ft
80m (3.5 MHz)
28 ft
56 ft
112 ft
40m (7.0 MHz)
15 ft
30 ft
60 ft
Table 2 - Array Safety Distance Minimums at 1500 watts
Table 2 indicates minimum safe distances for the sequenced active array from transmitting antennas
with 0 dB, 3 dB and 6 dB gain (ERP) using a 1500 watt transmitter. Your actual system may vary
according to location and proximity to various objects. Your actual system may vary. Safe distance
will vary depending on operating frequency, antenna polarization and orientation, and
transmitting antenna pattern.
The Receive Eight Circle Antenna System should be separated from transmit antennas and other
metal structures by 1/2-wavelength (or more) at the lowest frequency of operation.
The AVA2 Active Matching Units or ARAV-4 Active Receive Verticals grounds the antenna
element when power is turned off. The active antennas allow installations with spacing from
transmit antennas less than 1/2 wavelength but more than 1/10 wavelength (on the lowest

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frequency). Close spacing of any part of the array to transmitting antennas can be done, but will
impact overall receive array system performance. This is possible, provided the active units are
powered off at least 5 ms before transmitting. Sites without sufficient land area for proper spacing
should use the optional sequencer, DXE-TVSU to ensure the correct transmit to receive switching.
Examples of Array Performance
The DXE-RCA8C eight circle array system occupies less space than phased Beverage arrays and is
much easier to install, is less conspicuous and operates over a wider frequency range with similar or
better performance.
The Eight Circle Array achieves an optimal pattern when the array has a
radius of .327-wavelength. This is represented by this azimuth pattern
labeled as “.325-wavelength radius”, which shows the best combination
of a narrow front lobe and acceptable side lobes. This pattern is true for
any frequency from 500 kHz to 30 MHz for which the array is sized with
a radius of .327-wavelength. This pattern achieves the best Receiving
Directivity Factor (RDF), which is a figure that compares the forward-
lobe gain to the average gain of the antenna array in all directions,
including azimuth and elevation. More information about the rating of
receive antenna systems and Receive Directivity Factor are described in
“ON4UN’s Low Band DXing” by John Devoldere, available from DX
Engineering.
As shown by the patterns of Figure 10, an optimized 160 meter Eight Circle Array is not useable on
80 meters. That is why the best performing Receive Eight Circle is built as a mono-band array.
The ultimate low band receiving antenna would be two Eight Circle Arrays, one optimized for 80
meters built inside of the other optimized for 160 meters. Each is optimally sized for a .327-
wavelength radius, according to the dimensions in Table 5.
The DX Engineering Eight Circle Array offers better directivity than the Receive Four
Square. However, it requires more real estate to accomplish better directivity, which in turn
requires eight selectable directions to cover all directions properly.
Only a monoband Eight Circle Array may be installed with passive vertical elements or active
vertical elements, but a multi-band Eight Circle Array must be installed with Active Vertical
elements.