MFJ MFJ-1784, Instruction Manual

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MFJ-1784 Giant Box Fan Portable Loop Antenna Instruction & Technical Manual
(a) Magnetic and electric field lines (b) Signal Nulling
Figure 4: Field and Null Patterns
VERTICAL POLARIZATION When the loop is oriented to provide vertical polarization the
pattern is vertically polarized in line with the loop element. There will still be a large amount of
horizontally polarized radiation broadside to the loop, especially if the ground under the loop is
less than perfect or if the loop is placed some distance above the ground.
The broadside horizontal radiation that occurs in a small vertical loop is mostly between 10
◦
takeoff angles and extends straight above the loop and to the opposite 10
◦
elevation point. True
vertical polarization occurs only in line with the loop. As you move around the loop towards the
sides, the pattern skews and eventually becomes completely horizontal broadside to the loop.
Unlike linear verticals, small vertically-polarized loops also radiate straight up and down from the
antenna. This high-angle of radiation can be used to cover short distances by sky wave. The
high-angle horizontal radiation in a vertically polarized loop antenna occurs because the ground
below the loop is either too far away or is not a good enough RF reflector to cancel the horizontal
radiation component of the vertical loop.
HORIZONTAL POLARIZATION Horizontal mounting of the loop antenna results in an
omni-direction, horizontally-polarized antenna pattern that has a null straight up in the air and
straight below the center of the antenna. This means that any ground reflection will tend to cancel
the radiation along the horizon and low takeoff angles unless the loop is mounted some distance
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