MFJ-1784
Giant Box Fan Portable Loop Antenna
Instruction & Technical Manual
MFJ-1784 is not an option, the loop should be mounted vertically (Figure 3).
2.2.1
PATTERNS, POLARIZATION, AND LOCATION
The Box Fan loop antenna can be used to provide either vertical or horizontal polarization
(Figure 3). For vertical polarization the loop should be placed standing up on its edge, and for
horizontal polarization the loop should be laid flat on its side over a non conductive surface.
Figure 3: Various Mounting Orientations
The radiation pattern of a small loop antenna is essentially omni-directional with the exception of
two 15
◦
nulls along the axis of the loop (Figure 4a). If you visualize the loop as a wheel, the nulls
are in the same directions that the wheel’s axle would run. Signals will be attenuated more than
10 dB if they arrive within this region.
This antenna, like most others, should be placed as far away from and as high above other objects
as possible. The null be placed along the direction that you do not want to transmit or receive. If
the loop can not be placed more than fifteen feet above ground level the best placement
arrangement will be with the loop oriented vertically. Otherwise, it is possible to mount the
antenna horizontally.
In the vertical position, the Box Fan loop nulls can be used to reduce interference from undesired
directions if the unwanted signal is coming from a fixed direction and wave angle, or to minimize
interference (if transmitting) caused by the antenna itself to other household electronics equipment.
Other examples of using the null can be understood if we consider a loop antenna placed
horizontally on a second or higher floor of a building (Figure 4b). Since the null is positioned
directly below the antenna, clever placement of the antenna helps receiving by reducing the noise
pick-up from devices in the building and helps transmitting because energy is not coupled into the
building’s lossy structure. RFI in the building will also be reduced because the signal transmitted
into the building is significantly weaker.
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Summary of Contents for MFJ-1784
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