Interfacing the Yaesu FV-101DM VFO to FT-901DM radios
I have a FV-101DM and a FT-901DE (same remote VFO requirements as the FT-901DM and the FT-902 series). I've seen several notes from people who thought they would directly interface, and decided to dig into this and get mine working. After reading the notes around the web, I studied the schematics and realized that they are incorrect and would have 12vdc being applied to the VFO output and the wrong cable being modified for operation.
The FT-901Ds have a totally different interconnection design from that of the 101ZD's. The 101ZD's have two cables between the VFO and transceiver, the 901Ds utilize one. Additionally, the FV-101Z & FV-901DM have a different pinout on VFO port B than the FV-101DM.
After a bit of experimentation, I discovered the FV-101DM can be interfaced to the FT-901DM with a little work, and retain most of the functionality of the FV-101DM's original design. Here's what has to be done:
1- A jumper must be installed from pin 7 of port A to pin 1 of port B on the VFO.
2- The 6-pin cable supplied with the FV-101DM only utilizes 3 wires (with no shielded circuits for the VFO output), as it intends for the VFO communications to the 101ZD to be via VFO port A. For this reason, a new cable with 6-pin connectors must be assembled to connect from the FT-901DM to the FV-101DM VFO port B. Wire the cable, pin to pin (i.e. Pin 1 to pin 1, pin 2 t pin 2, etc). Use a piece of small coaxial cable with the center conductor connecting pin 1 to pin 1, and the shield connecting pin 2 to pin 2. Standard unshielded wire is fine for the other pins.
3- Assemble a power cord to plug into port A on the VFO, to supply an external 12 vdc source to pin 1. Include a fuse link at 250ma to protect the circuit in the event of a problem. Connect the negative of the 12 vdc source to the cabinet of the VFO (there is no ground connection in the socket for port A on the VFO).
That's it! Mine is working great, and has all functionality except the VFO memories can no be programmed from the FT-901DM, but can be programmed from the VFO just fine. This is because there is no feedback path from the FT-901's internal VFO to the FV-101DM VFO like there is with the FT-101ZD.