MFJ MFJ-936C User manual

Deluxe High-Efficiency Magnetic Loop
Tuner
MFJ-936C
INSTRUCTION MANUAL
©2020
MFJ Enterprises, Inc.
300 Industrial Park Rd. Starkville, MS 39759
P: [phone]
F: [phone]

DISCLAIMER
The information in this manual is designed for user purposes only
and is not intended to supersede information contained in customer
regulations, technical manuals or documents, positional handbooks, or
other official publications. The copy of this manual provided to the
customer will not be updated to reflect current data. Customers using
this manual should report errors or omissions, recommendations for
improvements, or other comments to MFJ Enterprises, 300 Industrial
Park Road, Starkville, MS 39759.
Phone: [phone]
Fax: [phone]
Business hours: M-F 8:00 AM - 4:30 PM CST/CDT.

Contents
1 RADIO FREQUENCY HAZARDS 1
1.1 BACKGROUND INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 RADIO FREQUENCY RADIATION . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 RFPRECAUTIONS.................................... 3
1.4 OPERATING ENVIRONMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.5 RF RADIATION EXPOSURE CONCERNS . . . . . . . . . . . . . . . . . . . . . . 4
1.6 OPERATING ENVIRONMENTS & GUIDELINES . . . . . . . . . . . . . . . . . . 4
2 THE MFJ-936C 6
2.1 INTRODUCTION ..................................... 6
2.2 FEATURES......................................... 7
2.3 CONTROLS&CONNECTIONS............................. 7
3 LOOP THEORY 8
4 SYSTEM SETUP 9
4.1 LOOPCONSTRUCTION................................. 9
4.2 CONFIGURATION .................................... 10
5 SYSTEM OPERATION 10
5.1 DETAILED OPERATION INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . 11
5.2 QUICK-START INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3 MFJ-936CACCESSORIES ................................ 14
6 TECHNICAL ASSISTANCE 14
List of Figures
1 An Electromagnetic Plane Wave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 The Electromagnetic Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 TheMFJ-936C ....................................... 6
4 FrontPanel ......................................... 7
5 RearPanel ......................................... 8
6 Typical MFJ-936C Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
List of Tables
1 100W Indoor and Outdoor Operating Environment . . . . . . . . . . . . . . . . . . . 5
2 150W Indoor and Outdoor Operating Environment . . . . . . . . . . . . . . . . . . . 5
3 Efficient Loop Length Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
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MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner Instruction & Technical Manual
1 RADIO FREQUENCY HAZARDS
1.1 BACKGROUND INFORMATION
The following warning is printed on the back of the MFJ-936C Deluxe High-Efficiency Magnetic
Loop Tuner™.
WARNING
DO NOT touch or come into contact with Loop Connectors or
Loop Antenna while transmitting
YOU CAN BE SERIOUSLY INJURED
The MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner™can, and in fact does, produce
LETHAL VOLTAGES and HIGH CURRENTS during normal operation. The high-Q circuit
produced by resonating the wire loop connected to the tuner, and matching it to the 50Ω coax
supplying RF power creates this unique operating environment.
NOTICE
It is imperative that the operator specifically follows the operating
instructions and complies with all CAUTIONS, WARNINGS, and FCC
Guidelines for Human Exposure to Radio frequency (RF) Electromagnetic
Fields.
1.2 RADIO FREQUENCY RADIATION
Radio frequency (RF) energy is one type of electromagnetic energy. Electromagnetic waves and
associated phenomena can be discussed in terms of energy, radiation, or fields. Electromagnetic
radiation is defined as waves of electric and magnetic energy moving together, or radiating,
through space. The movement of electrical charges generates these waves. For example, the
movement of charge in a radio station antenna (the alternating current) creates electromagnetic
waves that are radiated away from the antenna and intercepted by receiving antennas. The term
electromagnetic field refers to the electric and magnetic environment existing at some location due
to a radiating source such as an antenna.
An electromagnetic wave (Figure 1) is characterized by its wavelength (λ) and frequency (f). The
wavelength is the distance covered by one complete wave cycle. The frequency is the number of
waves passing a given point in space over a second. For example, a typical radio wave transmitted
by a 2-meter VHF station has a wavelength of about 2 meters and a frequency of about 145 million
cycles per second (145 million Hertz): one cycle/second = one Hertz, which is abbreviated Hz.
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MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner Instruction & Technical Manual
Figure 1: An Electromagnetic Plane Wave
Electromagnetic waves travel through space at the speed of light. Wavelength and frequency are
inversely related by a simple equation: frequency ×wavelength = the speed of light, or fλ =c.
Since the speed of light is a fundamental constant, High Frequency (HF) electromagnetic waves
have short wavelengths, and Low-Frequency (LF) waves have long wavelengths. The frequency
bands used for amateur radio transmissions are usually characterized by their approximate
corresponding wavelengths, such as 12, 15, 17, 20 meters, et cetera.
The electromagnetic spectrum (Figure 2) includes all of the various energies of electromagnetic
radiation ranging from extremely low frequency (ELF) ranges (with very long wavelengths) to all
the way up to x rays and γrays, which have very high frequencies and correspondingly short
wavelengths. In between these extremes lie radio waves, microwaves, infrared radiation, visible
light and ultraviolet radiation. The RF part of the electromagnetic spectrum can generally be
defined as that part of the spectrum where electromagnetic waves have frequencies that range from
about 3 kilohertz (kHz) to 300 gigahertz (GHz).
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MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner Instruction & Technical Manual
Figure 2: The Electromagnetic Spectrum
1.3 RF PRECAUTIONS
The FCC Office of Engineering Technology (OET) Bulletin 65, Supplement B, Evaluating
Compliance with FCC Guidelines for Human Exposure to Radio frequency Electromagnetic Fields
directly impacts the use and operation of the MFJ-936C Deluxe High-Efficiency Magnetic Loop
Tuner ™. It establishes safe operating distances from the loop antenna and associated power levels
in order to permit the operator and persons that may be impacted by operation to exist in a safe
RF environment. Guidelines for Maximum Permissible Exposure (MPE) are defined in Supplement
B of the bulletin.
IMPORTANT NOTICE
Use Supplement B in connection with FCC OET Bulletin 65, Version 97-01. The infor-
mation in the supplement provides additional detailed information used for evaluating
compliance of amateur radio stations with FCC guidelines for exposure to radio frequency
electromagnetic fields. However, Supplement B users should also consult Bulletin 65 for
complete information on FCC policies, guidelines and compliance-related issues. Def-
initions of terms used in this supplement appear in Bulletin 65. Bulletin 65 can be
viewed and downloaded from the FCC’s Office of Engineering and Technology’s website
at https://www.fcc.gov/general/radio-frequency-safety-0.
1.4 OPERATING ENVIRONMENTS
Under some circumstances, such as an antenna located unusually close to humans, an indoor
antenna in a living space, or a balcony-mounted antenna a foot or so away from a neighbor’s
balcony, the FCC could require a station evaluation or take other action. Computer models of
small HF loops, for example, yield RF fields very near the antenna that are much higher than the
standard amateur radio station outdoor antenna installation fields. Therefore, when you use the
MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner™in your shack, at a portable location, or
in a hotel room, care must be taken not to exceed established MPE to yourself and others who
may encounter the RF field associated with your operation.
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MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner Instruction & Technical Manual
1.5 RF RADIATION EXPOSURE CONCERNS
Controlled population exposure limits apply to amateur licensees and members of their immediate
household but not their neighbors. A controlled environment is defined as one for which access is
controlled or restricted. In the case of a fixed or portable amateur station, the licensee or grantee
is the person responsible for controlling access and providing the necessary information and
training as described in FCC OET Bulletin 65, Supplement B.
General population or uncontrolled exposure limits apply to situations in which the general public
may be exposed, or in which persons who are exposed as a consequence of their employment, such
as hotel employees or overnight residents, may not be made fully aware of the potential for
exposure or cannot exercise control over their exposure. Therefore, members of the general public
always fall under this category when exposure is not employment-related, as in the case of
residents in an area near a broadcast tower. Neighbors of amateurs and other non-household
members would normally be subject to the general population/uncontrolled exposure limits.
1.6 OPERATING ENVIRONMENTS & GUIDELINES
Tables 1 and 2 list various MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner™operating
environments, average power level, and safe distances that should provide compliance with the
FCC’s MPE recommendations and standards for controlled and uncontrolled populations.
Distance data listed is a result of computer-modeling a circular loop, which is the most efficient
radiator configuration. Parameters used include those listed below:
•Loop perimeter: or circumference: 20% of a full wavelength for each band
•Diameter of loop conductor: #10 gauge wire
•Height of lowest section of loop above ground: 1 meter and 3 meters feedpoint heights
•Operating frequencies: 7.175, 10.1, 14.2, 18.1, 21.2, 24.95, & 28.5 MHz
•Output power: 100 Watts average for Table 1 and 150 Watts average for Table 2
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MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner Instruction & Technical Manual
Table 1: 100W Indoor and Outdoor Operating Environment
Frequency (MHz) Controlled Population
Exposure (ft|m)
Uncontrolled Population
Exposure (ft|m)
Height (m)
7.0 1.18 0.36 1.68 0.51 1
1.25 0.38 2.48 0.75 3
10.0 1.88 0.57 2.48 0.75 1
2.28 0.69 3.04 0.92 3
14.0 2.38 0.72 3.17 0.96 1
2.54 0.77 3.17 0.96 3
18.0 2.81 0.85 3.50 1.06 1
2.87 0.87 3.56 1.08 3
21.0 3.03 0.93 4.06 1.23 1
3.07 0.93 4.95 1.50 3
24.0 3.23 0.98 5.48 1.66 1
3.37 1.02 5.51 1.67 3
28.0 3.47 1.05 6.04 1.83 1
3.47 1.05 6.04 1.83 3
Table 2: 150W Indoor and Outdoor Operating Environment
Frequency (MHz) Controlled Population
Exposure (ft|m)
Uncontrolled Population
Exposure (ft|m)
Height (m)
7.0 1.45 0.44 2.05 0.62 1
1.52 0.46 3.00 0.91 3
10.0 2.28 0.69 3.00 0.91 1
2.77 0.84 3.66 1.11 3
14.0 2.87 0.87 3.83 1.16 1
3.07 0.93 4.62 1.40 3
18.0 3.40 1.03 5.15 1.56 1
3.47 1.05 5.25 1.59 3
21.0 3.70 1.12 5.94 1.80 1
3.73 1.13 6.01 1.82 3
24.0 3.93 1.19 6.63 2.01 1
4.09 1.24 6.67 2.02 3
28.0 4.19 1.27 7.33 2.22 1
4.19 1.27 7.33 2.22 3
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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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MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner Instruction & Technical Manual
the loop if wind becomes a factor in the operating environment.
2.2 FEATURES
•Powerless: No power supply required.
•Maximum Input Power: 150 Watts (all modes)
•Easy-to-Read Loop RF Current Indicator: 0-100 unitless scale with adjustable
sensitivity
•Easy-Carry Handle: Permits easy handling to/from portable location(s)
•Small Physical Profile: 9.25” wide, 7.5” deep, by 4.25” tall
•Low Radiation Angle: Rivals full size dipoles.
•Quiet Reception: Extremely quiet receiving antenna. High-Q design rejects out-of-band
interference and harmonics and reduces overloading.
•Indoor Use: Perfect for apartments, hotel rooms, antenna restricted and portable locations.
2.3 CONTROLS & CONNECTIONS
The MFJ-936C Deluxe High-Efficiency Magnetic Loop Tuner™front panel controls and indicators
(Figure 4) function to permit matching the wire or coax loop to the coaxial line at the input of the
tuner.
Figure 4: Front-panel Controls: 1.) Tuning Control, 2.) Matching
Control, 3.) Power Range, 4.) Meter Sensitivity, 5.) SWR Meter, 6.)
Antenna Current Meter, 7.) Coax Output, 8.) PVC Mount
1. TUNING: This adjusts the Butterfly capacitor.
2. MATCHING: This matches the tuned loop to a 50Ω coaxial cable.
3. POWER RANGE: Push-button selectable between 30W and 300W ranges.
4. METER SENSITIVITY: This adjusts the sensitivity of the current meter.
5. SWR METER: Measures forward and reflected power and determines the SWR.
6. ANTENNA CURRENT METER: This displays the current passing through the antenna on
a unitless 0-100 scale.
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