MFJ-1278B MULTI-MODE RADIO INTERFACING
RADIO INTERFACING
Computer interfacing, covered in the previous chapter, is only half the interfacing task. The
other half is connecting your MFJ-1278B to your radios.
MFJ-1278B Radio Ports
Interfacing the MFJ-1278B to your radios involves connecting the following signals at Radio
Port 1 and Radio Port 2. The pin outs of Radio Port 1 and Radio Port 2 are shown in Fig. 3-1.
Pin1 Microphone audio, from the MFJ-1278B to your transmitter.
Pin 2 Ground, audio and PTT common.
Pin3 Push-to-talk, to allow the MFJ-1278B to key your transmitter.
Pin 4 Receive audio, from your receiver to the MFJ-1278B.
Pin 5 Squelch input (optional) to allow the MFJ-1278B to detect activity on a
shared-mode channel.
Fig.3-1 Radio Port 1 and Radio Port 2 Connector
This chapter describes how to connect the MFJ-1278B to your radio and how to adjust the
receive and transmit audio levels appropriately. The interconnection needs to be well thought
out, to minimize pickup of stray audio and RF noise by the lines. If possible, you should set
up your station with a monitor speaker and be able to operate on voice without disconnecting
the MFJ-1278B.
MFJ-1278B MULTI-MODE RADIO INTERFACING
RADIO PORTS CONNECTION
The MFJ-1278B gives the user two (2) radio ports. This allows for both FM and HF
operation from either radio port. Since the radio ports are independent of each other, the user
is not restricted to FM or HF operations. The radio ports on the MFJ-1278B allow an FM
radio and an HF radio to be connected at all times. In fact you can have any combination of
HF radios or VHF radios connected to the radio ports at any time. The pin designations for
both radio ports are exactly the same. See Fig. 3-1 for the radio port pin designations. The
radio ports on the MFJ-1278B are switched by using the RADio command. We will discuss
radio port switching in the next chapter.
Once the user obtains the proper microphone connector (not provided), use Fig. 3-2 to wire
the 5 pin DIN cable (provided) to the microphone connector. If two radios are to be used
with the MFJ-1278B, you will need to wire two radio cables.
You may obtain the specific pin designations for your radio's microphone connector from
your radio's manual. Appendix A at the end of this Instruction Manual lists pin assignments
for some of the most popular radios. The accuracy of this information is not guaranteed.
You should verify this information with your radio manual.
Fig. 3-2 Radio Connector Pin Diagram
Two 5-pin male DIN cables are provided with the MFJ-1278B. These cables have a 5-pin
DIN connector on one end, with the other end of each cable being unterminated. The
unterminated end of each cable is for wiring the appropriate microphone connector which
matches your radio.
CHECK THIS CABLE WITH AN OHM METER TO IDENTIFY EACH
WIRE BEFORE WIRING IT TO THE MIC CONNECTOR THAT FITS
YOUR RADIO.
MFJ-1278B MULTI-MODE RADIO INTERFACING
HANDHELD RADIO CONNECTION
Some HTs key the transmitter by drawing a small amount of current from the microphone
input pin (see Fig. 3-3 below). Radios with this type of special keying circuit are ICOM-2AT
(tm) and Yaesu FT-x09, FT-x3, FT-727 (tm) and others.
Appendix A at the end of this instruction manual provided pin designation for some of the
radios. Also consult the instruction manual of your radio.
If your HT has this type of microphone circuit, you can wire the microphone like the one
shown in Fig. 3-3 or you can remove the cover of the MFJ-1278B and install a shorting
jumper at JMP L for Radio Port 1 or JMP K for Radio Port 2. Installing JMP K or JMP L
will eliminating the need of soldering "Cx" and "Rx" to the microphone cable. "Cx" and
"Rx" are installed on the MFJ-1278B mother board. Fig. 3-4 shows the location of JMP L
and JMP K connectors. On the MFJ-1278B mother board, the "Rx" resistor for Radio Port 1
is R140 and the "Rx" resistor for Radio Port 2 is R107. If your radio still will not key
properly after installing JMP L or JMP K, you may need to change R140 or R107 to a
smaller value. Be sure to remove JMP K or JMP L when connecting the MFJ-1278B to
another type of radio.
FIG. 3-3 HT Special Keying Circuit
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