4
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-2P
system occupies less space, is much easier to install, is less conspicuous and
operates over a wider frequency range with similar or better performance.
Note: The
DXE-RFS-SYS-2P
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 into the system. This becomes apparent as reduced front-to-
rear directivity in one or more directions or a higher noise level.
Site Selection
Site selection is important. The
DXE-RFS-SYS-2P
system can be positioned as close as 1/10
wavelength to transmitting antennas.
Significant pattern distortion or coupling may result from close
spacing. To prevent pattern degradation or 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.
Figure 1 - Site Selection Clear Distance
The
minimum
distance to any transmitting antenna from the Four Square perimeter is 1/10
wavelength. Greater than 1/2 wavelength distance will prevent coupling to other antennas and
introduction of noise into the receive system.
Proximity to Transmitting Antennas
If the
ARAV3
active elements are used on this system, your transmitting antenna and the receive
four square array need only minimal physical separation to maintain safe power levels when the
DXE-TVSU-1B
sequencer is used. The
DXE-TVSU-1B
removes power from the active verticals
when the transmitter is in operation. The
DXE-ARAV3
Active Elements are bypassed to ground
when power is turned off. Using an optional programmable sequencer, such as the
DXE-TVSU-1B
,
is required for close spacing requirements. The
DXE-TVSU-1B
is included in the
DXE-RFS-SYS-
4P
complete Receive Four Square Array Package.
