MFJ MFJ-4418, Instruction Manual

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is recommended to protect the wiring from accidental shorts circuits. Connect the radio to the
MFJ-4418 using the wiring harness from the radio manufacturer. MFJ carries a number of cables
that can be used for this purpose. See page 16 for model numbers.
Figure 3 DC Wiring
Terminal connections to and from the MFJ-4418 can use the 30A Anderson PowerPole
terminals, crimp lugs, banana plugs or wires straight to the 5 way binding posts. Follow the
connector manufacturers’ instructions for attaching the terminal lugs. Make sure the lugs are
tightly crimped to insure they do not pull loose. If the binding posts are used place ring lugs or
spade lugs on the wire and make sure the binding posts are tightened down so the lug will not
pull off the post. Wires that connect to the binding posts directly are not recommended because
they can pull loose easily.
Remote and External Control Connections:
External Control: The MFJ-4418 can be enabled externally through the “EXTERNAL BOOST
ENABLE” connector allowing the unit to be enabled a number of ways including the ignition
line and the radio amplifier key line. There are a total of 4 control lines. Two will enable the
MFJ-4418 when grounded and two will enable the MFJ-4418 when tied to a 4 to 13V source.
Connecting either pin 1 or 2 to the amplifier key line of the radio if it has one will set up the
MFJ-4418 to enable only when transmitting. This will help reduce any noise that may be
generated by the switching boost circuit while receiving. See your radio manual for the proper
connections to the radio.
Connecting either pin 3 or pin 4 of the external control connector to an accessory line will allow
the booster to be enabled when the vehicle is turned on or when it is set in accessory on the
ignition switch. This will help reduce the current drain on the battery when the vehicle is off.
Not all radios are set up to be able to key the MFJ-4418. In those cases the boost button will have
to be set to ON or programmed for “Enable on input at low limit”. There is no RF sense built
into the MFJ-4418.
Figure 4 External Enable to Amp Key Line