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DX Engineering What components do I need for my receive 4-square? The DXE-RFS Receive 4-Square includes the receive 4-square switching unit and a CC-8 Control Console. In addition, you will need 4 broadband vertical elements such as the DXE-ARAV-4P or DXE-ARAV2-4P (for closer spacing) active receive antennas, or you can build your own passive elements for single or two band operation. If you use broadband active elements, you will need an additional 4- conductor control cable. A block diagram of the broadband system is shown here . What type of feedline should I use? Loss is not important. Impedance, reliability, and life are important. We recommend a good quality “flooded” 75 Ω cable suitable for direct burial.. The use of Snap-N-Seal watertight F connectors is also advised. The cable, connectors and crimping tools are available from DX Engineering. What type of elements can be used with the RFS-2? DX Engineering recommends active elements, DXE-ARAV-4P or DXE-ARAV2-4P. The active elements are easy to install, nearly invisible and offers very wide bandwidth (up to four octaves or 16:1 frequency range) and normally requires a minimal ground system. Passive elements are less expensive, but are much more work, require an extensive ground system and normally allow only two band operation. How can I control the RFS-2? The RFS-2 Receive 4-Square is a very flexible design. Directional control is done with a 2-bit BCD interface accessed from the external connector. This interface requires two conductors and a ground. Power for the RFS and active elements is also done from the external connector and requires one additional conductor. The CC-8 provides the operational voltage and the BCD interface. The RFS-2 also has internal jumpers to either control voltage or operational power through the feedline. This option requires additional hardware, such as a DXE-FVC-1 Feedline Voltage Controller. How much area do I need to construct a receive 4 square? For optimum performance the receive 4-square requires a clear installation area approximately 1 foot diameter for every meter of the optimum band. An optimized 80 meter array would require a circle 80 feet in diameter. The installation area should be reasonably level area with less than 1 ft ground elevation change for every 10 ft of distance between elements. Trees normally won’t hurt performance, metallic structures or overhead wires are likely to degrade performance. How close can the RFS-2 be to my transmit antenna? With 1500 watts and a unity gain antenna, using the ARAV2-1P active elements, the closest element in the 4-square array can be as close as 1/10-wavelength away from transmitting antennas. This spacing requires the use of a Time Variable Sequence Unit, such as the DXE-TVSU-1 to turn off the power to the RFS-2 and active elements before transmitting. At minimum spacing, coupling with nearby antennas is likely, which may result in pattern distortion of the array or detuning of the transmit antenna. What is the frequency bandwidth of the RFS-2? The RFS-2 uses a broadband phasing system that provides F/R greater than 15 dB over an approximate 16:1 frequency range when broadband active elements are used. If your requirement is less than 3:1 frequency range, the RFS is clearly superior to EWE, Flag, Pennant, and K9AY arrays. What does DX Engineering recommend for phasing lines? The RFS-2 Receive 4-Square uses a time delay system rather than phase delay and uses three 75 Ω delay lines. One delay line is long and the two shorter lines have equal length. The length depends only on element spacing, not operating frequency. One delay line needs to be .95 the length of the diagonal across the square array corrected by the velocity factor of the cable. The other two delay lines will be exactly ½ of the longer delay line length. What spacing should I use between the elements? 1/4 wavelength provides optimum performance for single band operation. This array will provide reasonable F/R ratios with side lengths as small as 1/10 wavelength on the lowest frequency of interest. However, side lengths below 1/5 wavelength greatly reduces the signal level or array receive sensitivity and additional amplification may be needed. Side lengths longer than 1/2 wavelength caused pattern degradation. Does the active element require ground radials? No. Two ground rods six feet long, one at the base and one six feet away would normally be enough. With better soil, one ground rod at the base could be enough. In very poor soil, a more extensive ground system may be needed. What is the intermod (IM) performance of the active elements? The active elements have a third order intercept (TOI) of +30 dBm, better than most receivers. What is the lightning susceptibility of the system? The active elements typically use a 102 inch whip and have a unique patent-pending diode clamp on amplifier inputs. MOV’s, clamps, chokes and other components protect other areas of this system. The system will generally survive anything but very close or direct lightning hits. More information is available on our web-site: www.dxengineering.com Questions? Call us at (330)-572-3200 or E-mail: DXEngineering@DXEngineering.com |
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