Operating instructions

MFJ-933 Loop Tuner
TM
Instruction & Technical Manual
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INTRODUCTION & FEATURES
MFJ-933 LOOP TUNER
TM
INTRODUCTION
The MFJ-933 Loop Tuner
TM
is a small, versatile, high-efficiency device that turns
any wire loop into a high-efficiency multi-band transmitting loop antenna system
designed for 50-ohm use at 150 Watts maximum input (all modes). It consists of
two functional units:
• MFJ-933 Loop Tuner
TM
• Wire Loop(s) (not included)
One function of the MFJ-933 Loop Tuner
TM
tunes/resonates various lengths of
wire into a very Hi-Q tuned-circuit used as a transmitting loop antenna. It uses
an MFJ low-loss Butterfly capacitor with no rotating contacts (available
separately) in this circuit. The second function is a matching network that serves
to match the Hi-Q transmitting loop circuit to any length of 50-Ohm coaxial cable.
No ground, radials, or counterpoise system is required or needed. The MFJ-933
Loop Tuner
TM
tunes any shape loop: circle, square, rectangle or any odd shape.
However, a wire approaching a quarter wavelength shaped as a circle is the
most efficient configuration.
The MFJ-933 Loop Tuner
TM
uses fixed wire lengths, which cover about 1.5 to 1
frequency ranges (i.e. 28 – 18 or 10 – 7 MHz, etc.). Exact frequency coverage
depends on each individual installation configuration involving choice of wire
length and diameter, shape of loop, Loop Tuner
TM
height above ground level,
and operating environment. Figure 2 illustrates the MFJ-933 Loop Tuner
TM
.
The MFJ-933 Loop Tuner
TM
mounts an assembled PVC Cross provided in the
MFJ-57B Loop Antenna Kit by inserting the cross into a PVC receptacle mounted
on the top of the unit’s cover. This kit provides a means to operate 20 and 30
meters using an insulated 10-gauge flexible wire loop fitted with direct contact
low-resistance lugs and strung on the PVC after assembly.
Assembly takes less than five minutes from packaged kit to ready for operation.
Figure 3 illustrates the PVC Cross mounted on the MFJ-933 Loop Tuner
TM
in a
typical outdoor operation environment. Care should be taken, however, to
secure the loop if wind becomes a factor in the operating environment.