MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner Instruction & Technical Manual
2 THE MFJ-936C
2.1 INTRODUCTION
The MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner™ (Figure 3) is a small, versatile,
high-efficiency device that turns any wire or coax loop into a high-efficiency multi-band
transmitting loop antenna system designed for a 50Ω input impedance and 150W RF power on all
modes. It consists of two primary components:
• MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner™
• Wire or Coax Loop (not included)
The MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner™ has two functions. First, it uses
various lengths of wire to create a very-high-Q tuned circuit that is used as a transmitting loop
antenna. An MFJ-19 low-loss Butterfly capacitor with no rotating contacts (available separately
for your own homebrew projects) is the heart of this circuit. The second function is as a matching
network that matches the high-Q transmitting loop circuit to your 50Ω coaxial cable.
Figure 3: The MFJ-936C
RF grounds, radials, or a counterpoise system are not required, though a safety ground is
recommended. While the MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner ™ can tune any
shape loop (circle, square, rectangle or any odd shape), a wire or length of coaxial cable
approaching a quarter wavelength shaped as a circle is the most efficient configuration.
The MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner™ uses fixed-length wires or coaxial
cables which will create a Standing Wave Ratio (SWR) around 1.5:1. Exact frequency coverage
depends on each individual installation’s choice of wire or coax length and diameter, shape of the
loop, height above ground level, and operating environment.
The MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner™ has a mount for either an MFJ-57B
or MFJ-58B PVC Cross assembly or your own homebrewed assembly. The assembly is inserted
into the three-quarter-inch PVC receptacle mounted on the top of the unit’s cover. Assembly takes
less than five minues from opening the packaged kit to operating! Care should be taken, to secure
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