Theory Of Operation; Patterns, Polarization And Location - MFJ Box Fan -1780 Instruction Manual

MFJ-1780 Box Fan    Loop Antenna

THEORY OF OPERATION

When resistive losses in a small loop antenna are kept low, a small loop antenna will transmit nearly as
well as a full size dipole. MFJ was able to make this small loop antenna radiate nearly as well as a full
size dipole by paying special attention to the electrical and mechanical construction of this antenna.
MFJ uses heli-arc welds on all joints to eliminate resistive pressure connections in the antenna. A
specially constructed butterfly capacitor using arc-welded construction has much lower loss resistance
than conventional, less expensive, pressure contact, air variable capacitors.
The care and expense used in selecting the best materials, not the most convenient materials, has
resulted in an extremely efficient small size antenna. Extensive "on the air" tests have confirmed that
most stations can detect little difference between the signal from the MFJ Box Fan Loop and the signal
from a larger size none-portable loop at the same height.

PATTERNS, POLARIZATION AND LOCATION

WARNING
- Keep this antenna out of reach of adults, children, and animals. Any
contact with this antenna while transmitting will cause severe RF burns
and voltages that kill.
- Never place this antenna close to electric power lines or utility wires.
- Do not stay near the antenna if you are transmitting RF over 10 watts of
power, especially above 14 MHz.
- Keep the antenna away from you to prevent exposure to high level of
electromagnetic field radiation.
The Box Fan loop antenna can
be used to provide either
vertical or horizontal
polarization. To obtain vertical
polarization the loop should be
placed standing up on its edge.
To obtain horizontal
polarization the loop should be
laid flat on its side over a non
conductive surface. See
Figure 1.
The radiation pattern of a
the exception of two very
Figure 1
small loop antenna is essentially omni-directional with
narrow nulls in the axis of the loop. If you visualize the
3
Instruction Manual