MFJ-1278B MULTI-MODE RADIO INTERFACING
RADIO INTERFACING METHODS
The MFJ-1278B allows radio connection without any modifications to the radio or any signal
balancing devices in the cables. There are two types interfacing methods presented in this
chapter.
Method 1: Direct Connection to Microphone and Speaker
For Method 1, shown in Fig. 3-5, the MFJ-1278B's audio is fed directly into the microphone
connector or similarly connected auxiliary jack. The output of the MFJ-1278B will be
adjusted to give a proper modulation level. The receiver audio will be taken from an
earphone plug or speaker jack and fed directly to the MFJ-1278B. The user can connect a
monitor speaker to the SPEAKER jack of the MFJ-1278B. This allows you to monitor the
transmit and receive audio on the channel.
Fig. 3-5 Method One Interconnect.
The transmit audio levels for both radio ports are factory preset at 250 mV p-p to be
compatible with the mic input of most radios. However, if the transmit audio is too low or
distorted, then adjust the appropriate output level control as stated in the section. Use the
following procedure to calibrate:
Transmit Audio Level Adjustment for Method I Interface
1. Connect your MFJ-1278B and radio as shown in Fig. 3-5. Turn on the MFJ-1278B and
computer and start your terminal program. Connect the radio to a dummy load and
listen to the transmission with another nearby radio.
2. Enter the modem calibration procedure by typing
CALIBRA
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