MFJ MFJ-249B User Manual
TABLE OF CONTENTS
MFJ-249B HF/VHF SWR Analyzer ............................................................................................ 2
Introduction .................................................................................................................................. 2
Powering The MFJ-249B ............................................................................................................. 3
Battery Installation ....................................................................................................................... 3
Alkaline Batteries ............................................................................................................ 3
NiCd Batteries ................................................................................................................. 4
Power Saving Mode......................................................................................................... 4
Operation Of The MFJ-249B .......................................................................................................5
SWR mode....................................................................................................................... 5
Magnitude of the Impedance Mode................................................................................. 6
Frequency Counter Mode ................................................................................................ 6
Gate time selection .......................................................................................................... 6
Adjusting Simple Antennas.......................................................................................................... 7
Dipoles............................................................................................................................. 7
Verticals........................................................................................................................... 7
Tuning an Antenna .......................................................................................................... 7
Measuring the Feedpoint Resistance of Antennas .......................................................... 8
Testing and Tuning Stubs and Transmission Lines...................................................................... 8
Velocity Factor of Transmission Lines ........................................................................... 9
Impedance of Transmission Lines................................................................................... 9
Adjusting Tuners .........................................................................................................................10
Adjusting Amplifier Matching Networks....................................................................................10
Testing RF Transformers............................................................................................................. 10
Testing Baluns ................................................................................................................11
Measuring Inductance and Capacitance ......................................................................................11
Measure Capacitance......................................................................................................12
Measure Inductance........................................................................................................12
Resonant Frequency of tuned circuits .........................................................................................12
Testing RF Chokes .........................................................................................................13
Technical Assistance ...................................................................................................................13
MFJ-249B Instruction Manual HF/VHF SWR Analyzer
MFJ-249B HF/VHF SWR ANALYZER
INTRODUCTION
The MFJ-249B SWR analyzer is an easy to operate, versatile test instrument for analyzing nearly
any 50 ohm RF system on frequencies between 1.8 and 170 MHz. In addition the MFJ-249B can
be used as a signal source and as an accurate frequency counter.
The MFJ-249B combines four basic circuits; a wide range oscillator, a frequency counter, a 50
ohm RF bridge, and a microcontroller. This combination of circuits allows measurement of the
SWR (referenced to 50 ohms), magnitude of the impedance, components of the impedance
(resistance and reactance), of any load connected to the
signal to the BNC jack labeled
its frequency
The MFJ-249B provide a sinewave signal of approximately 3 Vpp to any load in series with a 50
ohm internal resistance. The unit
1.8 - 4 MHz
4 - 10 MHz
10 - 27 MHz
27 - 70 MHz
70 - 114 MHz
114 - 170 MHz
The MFJ-249B can be used to adjust or measure the following:
Antennas: SWR, impedance, resistance, resonant frequency, bandwidth,
Antenna tuners: SWR, frequency
Amplifiers: Input and output networks
Coaxial transmission lines: SWR, velocity factor, losses, resonance
Matching or tuning stubs: SWR, resonance frequency, bandwidth
Traps: Resonant frequency
Tuned Circuits: Resonant frequency
Small capacitors: Value
RF chokes and inductors: Self resonance, series resonance, value
Transmitters and oscillators: Frequency
The MFJ-249B is also portable. It can be used with either an external low voltage supply, such
as the MFJ-1315 AC adapter or with internal AA battery packs.
WARNING:
Please read this manual thoroughly before using this instrument. Failure to
follow the operating instructions may cause false readings or even damage this
unit.
FREQUENCY COUNTER INPUT
FREQUENCY
efficiency
ANTENNA
switch selects the following frequency ranges:
connector. By connecting a
it is possible to determine
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MFJ-249B Instruction Manual HF/VHF SWR Analyzer
POWERING THE MFJ-249B
The MFJ-249B requires between 11 and 18 volts for proper operation. Any power supply used
with the MFJ-249B must be capable of supplying 180mA of current. An optional power supply,
the MFJ-1315, is available from MFJ.
WARNING:
The MFJ-249B has a standard 2.1 mm female receptacle on the top right of the case. This jack is
labeled
The outside conductor of the plug must connect to the negative supply voltage and the center
conductor of the plug must connect to the positive voltage.
After turning ON the
may indicate later software. The MFJ-249B also checks the voltage applied, then displays the
amount of volts received. If the power supply is less than 11Vdc a “Voltage LOW” blinking
message will be displayed. By pressing the
try to continue working with the low voltage.
Never apply unfiltered AC or incorrectly polarized DC to this jack. Peak voltage
must never exceed 18 volts !
POWER 12VDC
. A pictorial polarity marking appears on the case near the power jack.
POWER
switch, the program code version is displayed. A higher number
MODE or
the
GATE
time button on the unit, it will
WARNING:
The measurements will be inaccurate when the supply voltage falls below 11
volts !
BATTERY INSTALLATION
MFJ recommends the use of ten AA Alkalines or rechargeable NiCd cells to reduce the risk of
equipment damage from battery leakage. Avoid leaving any batteries in this unit during periods
of extended storage.
If batteries are used, they must be installed by removing the battery cover on the back of the unit.
This cover is secured by 2 Phillips head screws.
battery used (Alkaline or NiCd).
The header is located at the top of the PCB and is accessible by removing the back cover's eight
screws (four on each side).
Alkaline Batteries
If Alkaline AA batteries are used, the jumper for the J5 header labeled
CHARGER
OFF.
The
WARNING:
must be placed from the center pin to the pin labeled
CHARGER OFF
Remove weak batteries immediately !
The MFJ-249B must be setup for the type of
There is a header located inside the unit for this purpose.
mode is the factory default.
Never use an alkaline battery pack without setting the
OFF
position !
CHARGER
jumper to the
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MFJ-249B Instruction Manual HF/VHF SWR Analyzer
NiCd Batteries
If NiCd AA batteries are used, the jumper for the J5 header labeled
CHARGER
CHARGER OFF
The
The internal battery pack is not automatically disconnected, considering the possibility of using
10 AA rechargeable NiCd batteries.
The MFJ-249B has a NiCd battery's charger. The unit uses a 20 - 30 mA continuous trickle
charging current supply. This rate is enough to maintain a fully charged battery and low enough
to permit continuous charging while keeping cell temperature and internal cell pressure at a safe
level. The minimum supply voltage necessary to charge 1.25V AA NiCd batteries with that
current rate is 15V. The MFJ-1315 is able to provide that voltage when the power is OFF. With
power ON it is able to supply more than 13V at the maximum power required. The charger, if
enabled, is active while the power of the unit is ON or OFF.
WARNING:
It is recommended to charge the batteries with the power OFF, establishing periods according to
the hour capacity of the battery (C). NiCds, like all batteries, self-discharge. They have a
relatively high self discharge rate of about 1% per day at room temperature. The purpose of
trickle charging is to replace the charge that is draining off.
must be placed from the center pin to the pin labeled
mode is the factory default.
Do not use external power supplies with less than 13V, if NiCds are already
installed in the unit. This could discharge the batteries to the voltage supplied.
ON.
Power Saving Mode
The unit has a battery saving mode set up by default. This mode can be disabled by pressing the
MODE
disabled the message “Power Saving OFF” will be displayed while holding the
button.
push button before the initial messages are displayed. If the battery saving mode is
MODE
push
The battery saving mode is to extend the life of the batteries. If there is not any
operation or any 50 kHz frequency variation during 180 seconds, the unit will go into the power
saving mode. This mode will be indicated with a blinking
By pressing either the
MODE
or
GATE
button the unit will be back to regular operation.
SLP
text over the display right corner.
MODE
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MFJ-249B Instruction Manual HF/VHF SWR Analyzer
OPERATION OF THE MFJ-249B
Some understanding of transmission line and antenna behavior is necessary in order to use the
MFJ-249B properly. For a thorough explanation the ARRL Handbooks or other detailed books
can be used for reference.
ANTENNA
The
bridge output connection. To measure SWR or any impedance, this connector must be connected
to the load or device under test.
WARNING:
To measure the SWR or any impedance, on a predetermined frequency adjust the
FREQUENCY
By pressing the
measure on any frequency from 1.8 to 170 MHz.
The frequency counter will display a maximum of five digits. This will produce an entirely
stable reading of the internal oscillator short term drifted signal.
connector (SO-239 type) on the top of the MFJ-249B provides the measurement
Never apply power to the antenna connector !
TUNE
knobs until the counter displays the desired frequency.
MODE
push button seven different operation modes are selected. The unit can
and
SWR mode
SWR
SWR
mode when it is turned ON. The MFJ-249B will measure the standing
ANTENNA
connector. The display will show the selected
1 1.1 1.2 1.3 1.4 1.5 2 3 4 5 6 7 8
:
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13
]
The unit enters the
wave ratio (SWR) of any load referenced to 50 ohms. To measure the SWR of a 50 ohm coaxial
line simply connects the line to the
frequency and the actual SWR in a numerical and a bar graph format. The maximum numerical
SWR displayed is 25.
Any SWR adjustments have to be made at the antenna, since any adjustments at the transmitter
end of the feedline can not affect the losses, nor the efficiency of the antenna system.
The bar graph scale is as follows:
Bar graph:
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