MFJ-249B Instruction Manual
HF/VHF SWR Analyzer
3
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:
Never apply unfiltered AC or incorrectly polarized DC to this jack. Peak voltage
must never exceed 18 volts !
The MFJ-249B has a standard 2.1 mm female receptacle on the top right of the case. This jack is
labeled
POWER 12VDC
. A pictorial polarity marking appears on the case near the power jack.
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
POWER
switch, the program code version is displayed. A higher number
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
MODE
or
the
GATE
time
button on the unit, it will
try to continue working with the low voltage.
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.
Remove weak batteries immediately !
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.
The MFJ-249B
must be setup
for the type of
battery used
(Alkaline or NiCd).
There is a header located inside the unit for this purpose.
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
must be placed from the center pin to the pin labeled
OFF.
The
CHARGER OFF
mode is the factory default.
WARNING:
Never use an alkaline battery pack without setting the
CHARGER
jumper to the
OFF
position !
