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MFJ-1278B MULTI-MODE RADIO INTERFACING
MONITOR SPEAKER CONNECTION
The MFJ-1278B has a built audio amplifier to provide audio for an external monitor speaker.
A Monitor speaker such as the MFJ-280, can be can be connected to the SPEAKER jack on
the MFJ-1278B. The MFJ-1278B requires only one speaker for RADIO 1 and RADIO 2.
The MFJ-1278B will automatically switch the monitor speaker to the radio port in use.
If wiring of a speaker plug is necessary, use a 3.5 mm (1/8") mono or stereo plug for this
connection. The tip of the plug is positive and the sleeve of the plug is negative. The tip of
the plug must be connected to the positive side of the speaker. The sleeve of the plug must
be connected to the negative side of the speaker. Note that only one speaker is needed for
both radio ports. The MFJ-1278B will automatically switch the speaker to the correct radio
port in use.
The speaker jack on the MFJ-1278B is for monitoring of received and transmitted audio
including CW side tone. The speaker is used to provide a signal to the operator when a
packet connection has been established. A small audio amplifier is built in the MFJ-1278B to
drive the external speaker. Volume of the monitor speaker is adjustable by using the
"Monitor" control on the left side of the MFJ-1278B. If the internal amplifier of the MFJ-
1278B does not provide adequate volume you may use an external audio amplifier.
You can disable received audio, transmitted audio or the packet connect tone from the
speaker monitor jack by cutting a trace between the pins of the following jumpers. See
Appendix G for the locations and functions of JMP jumpers:
JMP X Transmitting Audio
JMP Y Receiving Audio
JMP Z Packet Connect Tone
For example, if you like to have the packet connect tone, then leave JMP Z intact. If you do
not wish to hear the transmitted or received packet signal, then disconnect JMP X to disable
the transmitted audio and JMP Y for received audio.