MFJ-209 SWR Analyzer Instruction Manual
3
POWERING THE MFJ-209
The MFJ-209 requires between 8 and 18 volts for proper operation. Any power supply used
with the MFJ-209 must be capable of supplying 200mA of current. An optional power supply,
the MFJ-1312B, is available from MFJ for $12.95.
The MFJ-209 has a standard 2.1 mm female receptacle on the top right edge of the case. This
jack is labeled "12VDC" and has the word "POWER" near it. 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. The internal battery pack is automatically disconnected when an external power plug
is inserted in this jack.
SWR measurement will be inaccurate when the supply voltage falls below 7 volts. To avoid
false readings maintain fresh batteries and always use the correct power supply.
Warning: Never apply AC, unfiltered or incorrectly polarized DC to this jack. Peak voltage
must never exceed 18 volts.
BATTERY INSTALLATION
If batteries are used, they must be installed by removing the 8 phillips head screws on each side
of the case. The eight batteries fit in two separate battery holders with the positive terminal of
the batteries positioned toward the round fixed connection, and the negative terminals toward
the springs of the battery holder.
The battery case has two external terminals that connect to a "pigtail" that has two terminals on
it. This connector looks like the type used for 9 volt transistor radio batteries and connects in
the same way. Do not attempt to use 9 volt batteries with this unit. After the batteries are
installed in the plastic holders and the connections are made to the battery packs, the battery
holders can be slid directly into the chrome retaining clips on the cover.
MFJ recommends the use of ALKALINE AA (or rechargeable nicad) 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!
Carefully check the following:
* The battery packs are positioned so that they do not interfere with any internal parts of the
MFJ-209.
* The leads are positioned to reach with the cover in the original position.
* The wires are not pinched between the cover and the chassis.
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