- 11 -
A
rray 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 75Ω feedline to the operating position from the
DXE-RCA8C-1
unit. Do not
use amplifiers, combiners, filters or splitters that are not optimized for 75Ω systems. 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 75Ω coax.
High quality, flooded 75Ω CATV F6 type coax is recommended. The
DXE-6UF-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-6UF-1000
flooded cable is the
Summary of Contents for DXE-RCA8C-SYS-4P
Page 31: ... 31 NOTES ...
