5
The
minimum
distance to any transmitting antenna from the
Four Square perimeter is 1/10-wavelength. Greater than 1/2-
wavelength is the distance to prevent coupling to other
antennas and the introduction of broadband noise into the
receive system.
Figure 1 - Site Selection Clear Distance
Proximity to Transmitting Antennas
The
DXE-AVA-2
Active Matching Units with customer supplied vertical elements, or the
DXE-
ARAV3-1P
Receive Antenna Active Vertical with Relay active elements and your transmitting
antenna need only minimal physical separation to maintain safe power levels when the
DXE-
TVSU-1B
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 1
.
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
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.
For example, transmitting legal-limit power output (1500 watts) into an ideal transmitting four
square array 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
DXE-TVSU-1B
Time Variable Sequencer Unit to remove
power from the active receive antennas used in the receive four square array.
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 70 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 antenna, if one is required.
