MFJ MFJ-932 User Manual

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

INTRODUCTION & FEATURES

MFJ-932 MINI LOOP TUNERTM INTRODUCTION

The MFJ-932 Mini 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 20 Watts maximum input (all modes). It
consists of two functional units:

• MFJ-932 Mini Loop Tuner

TM

(Shown in Figure 1)

• Wire Loop(s) (not included)

Figure 1: MFJ-932 Mini Loop Tuner

- 1 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

INTRODUCTION & FEATURES

One function of the MFJ-932 Mini 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 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-932

Mini 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-932 Mini 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, Mini Loop Tuner

TM

height above ground

level, and operating environment.

MFJ-932 MINI LOOP TUNERTM FEATURES:

• Powerless: No power supply required.

• Maximum Input Power: 20 Watts (all modes)

• Small Physical Profile: 4 ½ ” W, 4 ½” D, 1 ½ “ H

• Low Radiation Angle: Rivals full size dipoles.

• Quiet Reception: Extremely quiet receiving antenna. Hi-Q rejects out-of-

band interference, reduces overloading, and rejects harmonics.

• Indoor Use: Perfect for apartments & hotel/motel rooms, antenna
restricted, and portable locations.

- 2 -

MFJ-932 Mini Loop Tuner

RF HAZARD BACKGROUND INFORMATION

The following WARNING should be obeyed when using the MFJ-932 MINI LOOP
TUNERTM:

TM

Instruction & Technical Manual

RF HAZARD PRECAUTIONS

WARNING

DO NOT touch or come into contact with Loop

Connectors or Loop Antenna while transmitting

YOU CAN BE SERIOUSLY INJURED !!!

Using the MFJ-932 Mini Loop Tuner
voltages and HIGH CURRENTS during normal operation. The Hi-Q circuit
produced by resonating the wire loop connected to the tuner, and matching it to
the 50-Ohm coax supplying power creates this unique operating environment.

TM

can, and in fact does, produce LETHAL

NOTICE

It is imperative that the operator specifically follows operating instructions and

complies with all CAUTIONS, WARNINGS, and FCC Guidelines for Human

Exposure to Radio frequency (RF) Electromagnetic Fields

Radio frequency (RF) 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 (i.e., radiat ing) 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 radiating away from the antenna and intercepted by
receiving antennas. Electromagnetic "field" refers to the electric and magnetic
environment existing at some location due to a radiating source such as an
antenna.

- 3 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

RF HAZARD PRECAUTIONS

An electromagnetic wave is characterized by its wavelength and frequency . The
wavelength is the distance covered by one complete wave cycle. The frequency
is the number of waves passing a point in 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, abbreviated Hz.

Electromagnetic waves travel through space at the speed of light. Wavelength
and frequency are inversely related by a simple equation: (frequency ) times
(wavelength) = the speed of light. Since the speed of light is a constant quantity,
High Frequency (HF) electromagnetic waves have short wavelengths, and Low ­Frequency (LF) waves have long wavelengths. Frequency bands used for
amateur radio transmissions are usually characterized by their approximate
corresponding wavelengths, e.g., 12, 15, 17, 20 meters, etc.

The electromagnetic "spectrum" includes all of the various forms of
electromagnetic energy ranging from extremely low frequency (ELF) energy (with
very long wavelengths) to all the way up to X-rays and gamma rays, which have
very high frequencies and correspondingly short wavelengths. In between these
extremes lie radio waves, microwaves, infrared radiation, visible light and
ultraviolet radiation, respectively. 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). Figure 2 illustrates the electromagnetic spectrum.

Figure 2: The Electromagnetic Spectrum

- 4 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

RF HAZARD PRECAUTIONS

FCC OET Bulletin 65, Supplement B, Evaluating Compliance with FCC

Guidelines for Human Exposure to Radio frequency Electromagnetic
Fields.

The FCC Office of Engin eering Technology (OET) Bulletin 65, Supplement B,

Evaluating Compliance with FCC Guidelines for Human Exposure to Radio
frequency Electromagnetic Fields impacts directly the use and operation of the

MFJ-932 Mini Loop Tuner

TM

. 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 radiation
hazard-free environment. Guidelines for Maximum Permissible Exposure (MPE)
are defined in Supplement B of the bulletin.

IMPORTANT NOTE

Use Supplement B in connection with FCC OET Bulletin 65,
Version 97-01. The information 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. Definitions 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 World Wide Web Internet Site:

http://www.fcc.gov/oet/rfsafety

OPERATING ENVIRONMENTS

Under some circumstances, such as an antenna located unusually near 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 yields. Therefore, when you use the
MFJ-932 Mini Loop Tuner
(outdoors), or one such as a hotel/motel room care must be taken not to exceed
established MPE to yourself and others who may encounter the RF field
associated with your operation.

TM

in your Ham Shack, at a portable location

- 5 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

RF HAZARD PRECAUTIONS

RF RADIATION EXPOSURE CONCERNS

Controlled population exposure limits apply to amateur licensees and members
of their immediate household (but not their neighbors - see next paragraph). In
general, a controlled environment is one for which access is controlled or
restricted.

In the case of a fixed or portabl e 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/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/motel 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.

- 6 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

LOOP THEORY

LOOP ANTENNA BACKROUND INFORMATION

A small loop antenna is one that is characterized by low -noise reception, works
well even when mounted at ground level, and has a conductor length or
circumference of less than 1/3 wavelength. The ideal small transmitting antenna
would have performance equal to a large antenna, and a small loop antenna
approaches that performance. Bandwidth is quite narrow due to the extreme hi­Q of the tuned-circuit configuration when paired with a capacitor.

The components in a resonated transmitting loop are subjected to high currents
and voltages because of the large circulating currents found in the high -Q tuned
circuit formed by the antenna. It is very important that capacitors used in this
antenna have a high RF current rating. Even a 20-W transmitter develops
currents in the tens of amperes, and voltages across the tuning capacitor in
excess of 10,000 V. This consideration also applies to any conductors used to
connect the loop to the capacitor. A piece of #14 wire may have more resistance
than the entire loop conductor! The best electrical connections possible, are
those using soldered or welded joints.

The heart of the MFJ-932 Mini Loop Tuner

TM

is the “Butterfly” loop-tuning
capacitor, which has no rotating contacts. When coupled to a low -resistance
loop conductor, such as a copper strap, it provides a high efficiency -transmitting
loop.

As the loop antenna is elevated, its efficiency improves accordingly. When
traveling, a room at some elevation above ground level makes for a better
portable operation experience with the MFJ-932 Mini Loop Tuner

TM

. At very low
heights, close coupling to the ground cau ses detuning and losses due to current
induced into a mirror image of the loop below the surface with resistance of the
image loop proportional to soil resistance. Another loss component is due to
current flowing in the soil via capacitance between the loop and soil surface.

An operational height equal to 1/2 diameter of the loop antenna is recommended
to prevent detuning and excess ground losses when using the MFJ-932 Mini

Loop Tuner

TM

loop antenna system. This means the tuner should be at that
recommended height, since it is connected to the bottom (ends) of the loop,
whatever the loop antenna configuration: Circle, Square, Hexagonal, etc.

For operation on the 14 MHz band and higher, ground losses are a minimum
near ground, so it is fine to operate on the ground floor. For the 7 MHz band and
lower, ground losses become significant on the ground floor. To reduce ground
losses, operate on a second or third floor.

- 7 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

LOOP THEORY

For minimum ground loss when operating near ground, the loop should be
mounted vertically. For higher elevations (relative to the wavelength), horizontal
mounting will also give low ground losses.

Using freeware-modeling programs, it is possible to improve the efficiency of the
loop antenna system by varying the parameters until you optimize your particular
operational configuration, even while portable. One source example for free
programs is G4FPQ’s Web site: http://www.btinternet.com/~g4fgq.regp/.

- 8 -

MFJ-932 Mini Loop Tuner

Transmitter/

TM

Instruction & Technical Manual

SYSTEM SETUP

SYSTEM SETUP CONFIGURATION

The MFJ-932 Mini Loop Tuner

TM

set up configuration is simple and consists of

the following components:

• RF Generator (Transmitter/Transceiver; ~5 Watts minimum)

• SWR/Wattmeter

• MFJ-932 Mini Loop Tuner

TM

• Coaxial cable(s)

• #10 gauge (or larger) stranded wire cut to approximately 75% of a ¼

wavelength at the chosen resonant frequency

Figure 3 is a block diagram of the typical MFJ-932 Mini Loop Tuner
configuration.

Transceiver

SWR/

Wattmeter

Matching

Network

MFJ–932 Mini Loop Tuner

Figure 3: Typical MFJ-932 Mini Loop Tuner

TM

Configuration

TM

setup

Loop

- 9 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

LOOP CONSTRUCTION

The loop can be constructed from wire, tubing, sheet, and an especially good
material is 1” wide PC board. However, finding a piece of PC board long enough
to form into a circular loop for 7.175 MHz may prove to be difficult! This leads us
to the unique opportunity to EXPERIMENT while using the MFJ-932 Mini Loop

TunerTM to resonate the loop antenna you design.

The applications and parameters can be adjusted easily with the help of the
Freeware programs previously mentioned, and you may choose to design a
totally new and unique loop antenna for on -air experimentation. Designing an
outdoor loop for a band such as 7 MHz could be a challenge and result in a very
good radiator and especially good receiving antenna for DX-ing and/or rag­chewing. We, at MFJ, think the experimental aspects of the Mini Loop Tuner

TM

are exciting, and can provide hours of quality operating, even at QRP levels.

- 10 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

SYSTEM OPERATION

MFJ-932 MINI LOOP TUNERTM OPERATION

The most important aspect of using the MFJ-932 Mini Loop Tuner

TM

is it opens­up opportunity for Hams to once again experiment while enjoying operating at
the same time. Imagine how exciting it can be to establish contact with a distant
station using an antenna that you designed for the first time. Even more so, what
if you are just using a few watts, and the antenna is just a few feet away from
your operating position inside your home !

Operation is simple, but must follow specific steps in a specific order. Moreover,
you must have first consulted the RF Hazards section of this manual to ensure
compliance with established standards for Minimum Permissible Exposure (MPE)
to certain levels of RF radiation.

WARNING

DO NOT touch or come into contact with Loop

Connectors or Loop Antenna while transmitting

YOU CAN BE SERIOUSLY INJURED !!!

Step 1

Place the MFJ-932 Mini Loop Tuner
connect the loop antenna to the wing nut terminals on the rear panel.

Step 2

Using a pre-cut prepared wire and fasteners (non -conductive plastic clothespins
for example) form a loop to enclose as much area as possible (for example,
clothespin a wire loop to a curtain around a window frame). A circle encloses the
maximum area. Otherwise, drape it across bookcases or similar objects to
fashion a loop of sorts to use. If the loop antenna is rigid, then place the Mini

Loop Tuner

TM

in a position to accommodate its particular shape and size.

Step 3

Complete the typical MFJ-932 Mini Loop Tuner
illustrated in Figure 3 of this manual.

TM

at the chosen place of operation, and

TM

setup configuration as

- 11 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

SYSTEM OPERATION

Step 4

Make the following preliminary settings on the controls of the Mini Loop Tuner:

• TUNING control to position “Low Freq”.

• MATCHING control to position “Min C”.

Step 5

Tune the transceiver or receiver to the band and frequency of interest and “Ear­ball” tune the MFJ-932 Mini Loop Tuner controls for maximum noise and S-Meter
reading. “Ear-balling”, like “Ball-parking” is a term often used to describe the
listening process as used to hear a “peak” in reception before actually applying a
transmit signal to the tuner. The tuner will produce a peak when the proper
positions for the controls are achieved. The normal process consists of the
following suggested instructions:

• Slowly rotate TUNING control clockwise while listening for a peak until you
reach position “High Freq.”

• If no peak is found, re-position TUNING control to “Low Freq.”

• Rotate MATCHING control counter-clockwise approximately 1/16 of a full

turn.

• Slowly rotate TUNING control clockwise while listening for a peak until y ou
reach position “High Freq.”

• If no peak is found, re-position TUNING control to “ Low Freq.”

• Rotate MATCHING control counter-clockwise approximately 1/16 of a full

turn.

• Slowly rotate TUNING control clockwise while listening for a peak until you
reach position “High Freq.”

• Repeat this sequence until the MATCHING control reaches position “Max
C”.

• If no peak is found, the loop length is incorrect for the frequency of
interest.

• Once a peak is found, alternately adjust TUNING and MATCHING
controls until the peak is maximized.

Step 6
Apply 5 to 10 Watts of power to the MFJ – 932 Mini Loop Tuner and adjust the

TUNING and MATCHING controls for minimum SWR on your external

- 12 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

SWR/Wattmeter. Readjust the controls until you see no further improvement in
minimum SWR.

Step 7
Once you are satisfied that the adjustments and settings are correct for minimum

SWR, you can advance the power to 20 Watts if desired. Be sure that MPE
distance standard as defined in Supplement B of the FCC OET Bulletin 65,
version 97-01 is met. Should any arcing be detected, stop transmitting and
check connections and proximity to objects that may be suspect. If arcing seems
to be inside of the MFJ – 932, Mini Loop Tuner, lower output power and re-check
for arcing.

Step 8

You can now enjoy operating in your favorite mode. However, if you change
frequency more than about 5 KHz, you may find you’ll need to re-adjust the
TUNING controls for minimum SWR. Rotate TUNING clockwise for higher
frequencies and counter clockwise for lower frequ encies. Even greater
frequency excursions can cause the MATCHING control to also require
adjustment.

This concludes the MFJ – 932 Mini Loop Tuner System Operation instructions.

- 13 -

MFJ-932 Mini Loop Tuner

TM

Instruction & Technical Manual

TECHNICAL ASSISTANCE

TECHNICAL ASSISTANCE

If you have any problem with this unit first check the appropriate section of this
manual. If the manual does not reference your problem or reading the manual
does not solve your problem, you may call MFJ Technical Service at 662-323-
0549 or the MFJ Factory at 662-323-5869. You will be best helped if you have

your unit, manual and all information on your station handy so you can answer
any questions the technicians may ask.

You can also send questions by mail to MFJ Enterprises, Inc., 300 Industrial Park
Road, Starkville, MS 39759; by Facsimile (FAX) to 662-323-6551; or by email to
[e-mail]. Send a complete description of your problem, an
explanation of exactly how you are using your unit, and a complete description of
your station.

NOTES

- 14 -