MFJ-259C Instruction Manual
HF/VHF SWR Analyzer
3
2.1
External Power Supply
MFJ offers an optional power supply, the MFJ-1312D, that satisfies all external supply requirements. We
strongly recommend using this supply. If you use a different power source, note that the voltage output must be
greater than 11 volts and less than 16 volts when the analyzer is powered on and running (loaded power source).
The maximum voltage in Sleep Mode (unloaded power source) should never exceed 18 volts. AC adapters must be
well filtered and the plug must have a grounded sleeve and positive center lead. The ideal voltage-source
specification is 14.5 VDC at 150 mA. Confirm your supply can deliver this output level safely without overheating
or introducing excessive AC ripple.
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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2.1 mm
The MFJ-259C 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-259C.
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-259C 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-259C 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: