MFJ-1270C/1274C MANUAL RADIO INTERFACING
Page 29
MFJ TNC has a built audio amplifier to provide audio for an external monitor
speaker. Monitor speaker such as the MFJ- 280 can be can be connected to the
SPEAKER jack on the MFJ TNC.
If wiring of a speaker plug is necessary, use a 3.5 mm (1/8") mono or stereo plug
for this connection. Wire the plug so that the tip of the plug is connected to the
speaker and the sleeve is connected to ground. The ring (if a stereo plug is used)
is not used.
The speaker jack on the MFJ TNC is for monitoring of received and transmitted
audio. It is also used to provide a signal to the operator when a packet
connection is made. A small audio amplifier is built in the MFJ TNC to drive
the external speaker. Volume of the monitor speaker can be adjusted by using
the "Monitor" control on the left side of the MFJ TNC . If the internal amplifier
of the MFJ TNC 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 but do not wish to hear
the racket of packet, then you should disconnect JMP X to disable the
transmitted audio and disconnect JMP Y for received audio.
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