Yaesu FT-747 Digimodes Modification - G7SYW's amateur radio bits & bobs...
 
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Yaesu FT-747 Digimodes Modification

| Posted in Technical Topics

Without using a mass of tangled wires and various connectors, the ageing Yaesu FT-747GX has no easy method of connecting a PC to allow the use of digimodes, here’s how to modify the FT-747.

The CAT socket on the radio is quite useful thus I decided not to make any modifications to this.

Instead the decision was made to use the front panel microphone socket for the connection to the home made interface.

Microphone socket wiring


As can be seen in the schematic diagram, Pin 2 of the mic socket is tied to ground.

This pin is normally used as a common ground for the “Up” and “Down” buttons on the microphone.
Therefore it makes sense to use this pin and simply connect the corresponding wire within the microphone plug to either pin 7 or pin 5 as these are both tied to ground.

With the top cover removed, the front panel can be released from the bottom panel. The front panel will tilt enough to work on the rear of the mic socket without any wiring disconnections.

A short black jumper wire is connected between pins 2 and 5. After de-soldering this wire from pin 2, carefully cut it from pin 5 and remove it.
Using a length of screened audio cable, solder the center to the free pin of the mic socket. The screen can be either insulated here or connected to pin 7 – mic ground.

If you connected it to pin 7, then the other end will be insulated. Make sure you only connect the screen to ground at one end, NOT both! The reason for only connecting one end is prevent a ground loop.

Route this cable round the right hand side of the radio, following the route of existing wiring.

Rear panel connection


Looking at the rear panel you will see a phono socket marked “AF OUT”. This socket is where the audio output to the PC will be sourced.


From inside the radio, the socket can be seen mounted on the PCB (shown by the yellow arrow).
This point is used to connect the screened cable.

Each phono socket has two small metal parts. The square piece nearest the back panel is the ground connection. Solder the shield of the screened cable to this, ONLY if it’s not grounded at the mic socket end.

A small thin metal contact can be seen running down the back of the socket to the PCB. Solder the center conductor of the screened cable to this point.

Caution! Do not use too much heat when soldering as the plastic socket housing may melt. Also ensure that the cable is correctly soldered to the AF Out socket.

Interface cable wiring

Finally, construct an interface cable with these pin connections (mic plug):

  1. N/C
  2. RX Audio Out to PC soundcard input
  3. N/C
  4. N/C
  5. N/C
  6. PTT
  7. Ground
  8. TX Audio In from PC soundcard output

Once this is done, reassemble the radio, hook up your PC, load the software and get digi-moding…


Please leave any comments below if you have tried this mod and had success or otherwise…


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