DX Engineering DXE-RFS-SYS-4S User manual

Receive Four Square System
DXE-RFS-SYS-4S
U.S. Patent No. 7,423,588
DXE-RFS-4S-INS Revision 0c
DXE-RFS-SYS-4S Components Shown
© DX Engineering 2020
1200 Southeast Ave. - Tallmadge, OH 44278 USA
Phone: [phone] ∙ Tech Support and International: [phone]
Fax: [phone] ∙ E-mail: [email protected]

2
Table of Contents
Introduction
3
Default Jumper Configuration Settings
18
System Overview
4
Diagram 1 - Default Configuration
19
Features
4
Optimizing the Array
02
Additional Parts Required
5
Front-to-Rear (Null) Optimizing
20
Example of Array Performance
5
Operation
02
Site Selection
7
Normal Receive Four Square Operation
21
Proximity to Transmit Antennas
7
Receive Four Square Troubleshooting
21
Topographical Considerations
8
Site Selection in Relation to Noise Sources
8
Ground System
9
Appendix A - Alternate Configurations
26
Lightning Protection
9
Supplying Power Using the Feedline
26
Sizing the Array
10
Directional Control Using the Feedline
27
Four Square Layout
11
Diagram 2 - Alternate Configuration
28
System Operational Overview
12
Diagram 3 - Alternate Configuration
29
Installation
12
DXE-RFS-3 and Active Element Power
30
Active Antenna Elements
13
Directional Control
30
Active Antenna Feedlines
14
Internal Jumper Selection
30
Delay Lines
14
Default Jumper Configuration
31
Control and Power Connections
16
Technical Support and Warranty
32
Default Configuration
18
Figures
Figure 1 - Site Selection Clear Distance
7
Figure 2 - Layout of the DXE-RFS-SYS-4S Four Square System
11
Figure 3 - Active Element L1MF Jumper Locations
13
Figure 4 - Array Diagonal Dimension
15
Figure 5 - Jumper Locations showing Default Settings
19
Tables
Table 1 - Array Safety Distance Minimums at 1500 watts
8
Table 2 - Array Side Lengths
10
Table 3 - Examples of DLY3 Required Length
15
Table 4 - BCD Directional Control Matrix, “1” Equals +12 Vdc (Default)
27
Table 5 - Differential Voltage Control Matrix
28

3
Introduction
DXE-RFS-SYS-4S - Complete Receive Four Square Array Package for Normal
Spacing or Close Spacing to Transmit Antennas
Complete Receive Four Square Array package for Normal or Close Spacing to Transmit Antenna
W8JI design
Operates from 100 kHz to 30 MHz
Excellent directivity in a small space for better signal-to noise ratio
Switchable in four 90 degree spaced directions
Reduced susceptibility to high angle signals compared to EWE, Flag, Pennant, or K9AY
arrays
Low current DC powered control console allows system operation without AC power mains
DXE-RFS-SYS-4S (U.S. Patent No. 7,423,588) is a complete Receive Four Square Array
Package which includes:
(1) DXE-ARAV4-4P Active Receive Vertical Antennas (4) w/ Internal
Antenna Disconnect Relays
(1) DXE-EC-4 Four Position BCD
Control Console
(1) DXE-RFS-3 Receiving Four
Array Controller
(1) DXE-RG6UFQ-1000 CATV RG6 Style
Coaxial cable, 75 Ω, RG6 Quad Shield,
Flooded for Direct Burial, 1000' Spool
(1) DXE-CPT-659 CATV, RG6
and RG-59 Coaxial Cable Stripper,
Includes 1 Replacement Blade
(1) DXE-EX6XL-25 75 ΩQuad Shield Coaxial
cable Compressions Connectors for
DXE-RG6UFQ RG6 Cable, 25 pack
(1) DXE-SNS-CT1 Crimp Tool for Type F
75 ΩCoaxial cable Compression Connectors

4
System Overview
The DXE-RFS-SYS-4S is an advanced four square receiving system that uses four symmetrically
spaced elements to provide switching for a 4-direction receiving antenna system. This unique
system uses time delay phasing rather than the single band phase shifting used in traditional four
squares. When used with active receive elements, this time delay phasing scheme provides the
correct phase relationship across a wide frequency range producing useful front-to-rear ratio (F/R)
response over octaves of bandwidth.
This system uses directionally-optimized time delays to produce wider and deeper rear nulls. Wide
null areas and a narrow main lobe greatly reduce noise and undesirable signals.
The system is more reliable than a conventional transmitting four square system in receiving
applications. Most transmitting four squares use large, exposed open-frame relays which can
become contaminated or corroded. This system uses sealed relays; contact size is optimized for
receiving applications.
Features
Advantages of the DXE-RFS-SYS-4S Receive Four Square Antenna System over other receiving
arrays include:
Seamless stainless steel RFS-3 enclosure, for enhanced weather resistance
Reduced susceptibility to high angle signals compared to EWE, Flag, Pennant, and K9AY
antennas
Excellent directivity in a small space for better signal-to-noise ratio
Switching of four 90 degree spaced directions
Directivity over a very wide frequency range using DX Engineering’s Active Receive
Antennas
Requires less space than a Beverage antenna. Active elements need only a minimal ground
system
Easier to deploy and maintain than a four direction Beverage antenna system
Using active elements, system allows close proximity to transmit antennas using
transmit/receive sequencer
Enhanced relay contact reliability
Low current DC powered control console allows system operation without AC power mains
This manual will describe the DXE-RFS-SYS-4S Receive Four Square System in detail.
The DXE-RFS-SYS-4S is a sophisticated system that has critical control voltage
and three delay line connections.
Failure to make quality feedline or delay line connections might result in an array
that does not work or performs poorly.

5
Additional Parts Required, Not Supplied with the DXE-RFS-SYS-4S
Four Conductor Power and Control Cable for RFS-3
Four conductor cable (3 plus ground), 22 gauge minimum is required. Economically priced
COM-CW-4 is a four conductor control wire which may be used.
Ground Rods (5/8" x 4 feet) for the Active Receive Vertical elements and the RFS-3 unit.
Mounting pipe for the DXE-RFS-3. The DXE-RFS-3 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. If smaller pipe mounting is desired, the optional DXE-CAVS-1P V-Bolt Saddle
clamp can be used for pipe from 3/4" to 1-3/4" inches OD. Note: JTL-12555 Jet-Lube SS-30 Anti-
Seize must be used on all clamps, bolts and stainless steel threaded hardware to prevent galling and
to ensure proper tightening. The controller can also be mounted on a sturdy wooden post, but
provision for grounding the DXE-RFS-3 unit must be made.
Example of Array Performance
Dedicated receive antennas have better signal-to-noise ratios. Directing the antenna 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 limits on
external noise, antenna directivity (F/R) is the only thing that affects the signal-to-noise ratio.
An average Beverage antenna exhibits about -6 dB gain. You would need two reversible Beverage
systems to obtain 4-direction selectivity and you still would be limited to one or two bands. The
DXE-RFS-SYS-4S system occupies less space, is much easier to install, is less conspicuous and
operates over a wider frequency range with similar or better performance.
A test array, constructed at DX Engineering using the DXE-ARAV4 Active Elements and a side
length of 35 feet, showed excellent performance across a wide frequency range. This side length is
optimal for 40 m, according to Table 2. The array worked from 3 MHz to 15 MHz. As shown on
the following page, the patterns stay clean with good directivity and front-to-rear performance. The
elevation angle is 15 degrees for all patterns. Amplification is required below 3 MHz.
Note: The DXE-RFS Receiving system must 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 and signals into the system. This becomes apparent as reduced
front-to-rear directivity in one or more directions or a higher noise level.
In a different test array with 50 ft side lengths, optimum performance occurred between
3 and 4 MHz. Performance on 7 MHz was also excellent. Amplification was used below
2 MHz. The highest usable frequency was 10 MHz. This array also produced usable F/R ratios
down to the lower end of the AM broadcast band (600 kHz).

6
Increasing the array size increases its sensitivity on the lower frequencies, sliding the performance
curve toward the low frequencies and potentially eliminating the need for amplification.

7
Site Selection
Site selection is important. The DXE-RFS-SYS-4S system can be positioned as close as 1/10
wavelength to transmitting antennas. The DXE-ARAV4 Active Elements are bypassed to ground
when power is turned off. A programmable sequencer, such as the optional DXE-TVSU-1B will be
required with the DXE-RFS-SYS-4S, for close spacing requirements.
Significant pattern distortion or coupling may result from close spacing. To prevent pattern
degradation, reception of re-radiated electrical noise or other interference, separation of 1/2
wavelength (at the lowest operating frequency) is ideal. See Figure 1. The goal is to do the best you
can by balancing all the factors.
The minimum distance to any transmitting antenna from the Four
Square perimeter is 1/10 wavelength. Greater than 1/2 wavelength is
the minimum distance that will limit coupling to other antennas and
the introduction of broadband re-radiated noise and signals.
Figure 1 - Site Selection Clear Distance
Proximity to Transmitting Antennas
The DXE-ARAV3-4S active elements and your transmitting antenna need only minimal physical
separation to maintain safe power levels when the optional DXE-TVSU-1B sequencer 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 1.

8
For example, transmitting legal-limit power output (1500 watts) into an ideal four square
transmitting antenna produces about 6,000 watts ERP (6 dB gain). Because of the increased radiated
power level, nearly 1/2 wavelength minimum spacing between the transmitting and receiving
antenna arrays is required, even when using the optional DXE-TVSU-1B Time Variable Sequencer
Unit to remove power from the active receive antennas used in the receive four square array.
Table 1 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.
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 1 - Array Safety Distance Minimums at 1500 watts
For any DX Engineering Receive Four Square, using the optional DXE-TVSU-1B Time Variable
Sequencer Unit to sequence Active antenna power will ensure that transmitted energy will not cause
damage to the receive system.
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 60 foot diameter array should be within six 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 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 the antennas, if one is required.
Site Selection in Relation to Noise Sources
Because the array is directional across its corners, 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 your location doesn’t have the usual noise sources (power lines, electric fences, etc.), locate the
array so that your transmitting antennas and buildings are off the back or side of the receiving array.

9
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 average gain in the direction of
noise.
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.
Ground System
The ARAV3-4S 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 each
ground system be the same 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. If a good ground cannot be established,
use an optional DXE-RFCC-1 Receive Feedline Current Choke that will further decouple the
feedline from the antenna and reduce common mode current and associated noise from the feedline.
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.

10
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 listed under “Lightning Protection and Grounding.”Use lightning surge
protectors for the coaxial cable feedline and control lines.
Sizing the Array
When using active elements, the array side length can be as small as 1/10 wavelength and up to
about 1/2 wavelength on the highest frequency to be used. Sizes below 1/10 wavelength result in
unusable array sensitivity in the most desired bands. Making side lengths larger than 1/2 wavelength
on the highest frequency will split the main lobe and cause pattern and front-to-back degradation.
Determine the size of the array by considering the availability of appropriate space, frequency
coverage desired and the near proximity to undesirable noise sources, transmitting antennas and
other structures.
If there are no space constraints, follow the array side length recommendations in Table 2 for
excellent performance. Side lengths longer than the optimal lengths shown will move the peak
sensitivity of the array toward the lower frequency. For example, if you are most interested in 160m
performance with occasional use on 80m, make the side lengths longer than the optimal 98 feet
shown for 160m and 80m. This will improve 160m performance, reduce sensitivity on 80m
somewhat, but less than sizing the array exactly for 160m.
Band
Freq - MHz
Optimal Side
Length in Ft
Min. Side
Length in Ft
Max. Side
Length in Ft
160
1.83
135
54
270
80
3.60
70
28
140
40
7.10
35
14
70
160, 80
1.83, 3.60
98
40
192
80, 40
3.60, 7.10
50
20
98
160, 80, 40
1.83, 3.60, 7.10
70
28
137
Table 2 - Array Side Lengths
If you have limited space, a carefully installed and amplified DXE-RFS can be used on multiple
bands with very small side lengths. At smaller side lengths, careful construction using precise
measurements is critical. On a fixed-size array, as frequency is decreased, the array signal output
decreases along with array sensitivity. Eventually the received ambient noise signal level will
decrease to a point where it is below your receiver’s noise floor. This comes from two effects:
Elements become electrically shorter, reducing element sensitivity
Element spacing becomes smaller in electrical degrees, reducing array sensitivity
Side lengths at 1/10 wavelength on 40 m would only be 14 feet. Although usable, amplification
would be required. In addition, the construction of a very small array is extremely critical. Side
lengths must be perfectly symmetrical. The delay lines must be directly measured for electrical
length and cut to exact lengths. The ground system must be effective. Even at this small spacing, the
array will have useful front-to-rear performance and directivity!