MFJ-249C Instruction Manual
HF/VHF SWR Analyzer
3
Please read the battery installation instructions (Section 2.3) if you plan to install batteries. Never connect
external DC power if non-rechargeable batteries are installed and the battery charger is enabled. Permanent
damage could result!
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+
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2.1 mm
The MFJ-249C has a recessed
2.1 mm
power jack located on the top-right-hand side of the unit. It is labeled
Power
13.8 VDC
. The jack's outside barrel contact is negative and the center pin is positive.
Inserting a power plug into the
power jack automatically disables the internal batteries as a power source.
However, the batteries will be trickle
charged if the charger circuit is enabled.
IMPORTANT WARNING: Reverse Polarity Or Excessive Voltage Can Damage Or Destroy The MFJ-249C.
Never Apply More Than 18 Volts, Never Use AC-output or Positive Ground Supplies!
2.2
Using Internal Batteries
Before installing batteries for the first time,
check the position of the Charger Jumper.
To gain access, remove the
eight screws securing the analyzer's back cover and separate it from the unit. Look for a 3-pin header with a small
black-plastic shorting plug that fits over two of its pins. It is located at the top of the main pc board near the
OFF-
ON
switch and power connector.
The shorting plug must be properly positioned for the type of battery you intend
to use (either rechargeable or non-rechargeable)
. While you have the analyzer's case removed, you may install
batteries into their tray -- or install them later by removing the battery-tray door that is attached to the rear of the
case with two screws.
2.3
Using Rechargeable “AA” Type Batteries
IMPORTANT WARNING: Do not use an external power sources that deliver less than 13.8 volts with
rechargeable batteries installed. If the external supply voltage is too low, the charger will not work properly and
batteries will eventually discharge. We recommend charging batteries with the MFJ-249C power switch off and
allowing enough charging time to establish full battery charge. A minimum of ten hours is recommended.
When using rechargeable batteries, your power source must deliver a minimum of 13.8 volts to meet the minimum
charge-voltage threshold. Typical charging current is 10-20 mA (trickle-charge rate). The charger circuit functions
any time external power is connected, even when the analyzer is turned off. Again, the MFJ-1312D supply fulfills
all power supply and charging requirements for the MFJ-249C and is recommended.
When using rechargeable batteries, the internal black plastic jumper must be set to the proper position.
If it is not
set properly, the batteries will not charge. As described above, the jumper is located inside the analyzer, near the
external power jack on the back side of the circuit board.
For rechargeable batteries, set the jumper as shown below:
2.4
Using Conventional “AA” Drycell Batteries
Whenever possible, install a fresh matched set of high-quality alkaline batteries. Conventional zinc cells will work,
but alkaline batteries offer a lower risk of damage caused by leakage. Alkaline cells also provide longer running
time and superior shelf life.
When using any non-rechargeable dry-cell battery, always remove them immediately
when they become weak to avoid damage from leakage. Also, never store your analyzer for extended periods
(longer than a month) with non-rechargeable batteries installed.
