Tag Archives: radio

The schematic for digi interface (ham radio)

Here is the schematic for my old digi interface. It is very basic interface with two RX lines. I made the printed circuit board years ago but was never drawn the schematic for it. Some people had asked it so there it is. It may not match perfectly with the board layout but the idea is the same.

I am going to design a new version with some improvements later. All suggestions for the new version are welcome. I will share the circuit and the board layout so you can build it too.

As you can see there is nothing new in this circuit. The same circuit has been published many times before. My whole point was to make the nice board for it. I added two RX lines for radios like FT-1000MP etc.

CAT interface

I’m using opto-isolated interfaces for connecting my radios to the computer. Here is the CAT-interface I have made. It can be used with different kind of radios. Part list will vary, depending of radio used. I’m using it with Yaesu FT-1000MP. Example IC1 have to be selected depending of which signal levels your radio will use. FT-1000MP uses RS232-levels, so 74HC04 should be fine. With TTL-levels you should use 74HC07 or 74HC17. For Icom, there is a jumper for connecting RXD and TXD signals together. Some other components have to be changed also. I haven’t tested this with Icom yet, so I’m not sure is it working or not.

Here is the schematic:


Here is the board:


Part list for Yaesu FT-1000MP:
X1 – X2 = D9-female connecotr
X3 = RCA-jack
JP1 = Do not assembly this for FT1000MP
R1 = Do not assembly this for FT1000MP
R2-R4 = 475R
R5-R6 = 4,7k
R7 = 10k
R8 = 0R = Jumper
R9 = Do not assembly this for FT1000MP
C1, C3 = 100nF
C2 = 10uF 35V
C4 – C7 = 10uF 35V
C8 – C9 = 10nF
C10 – C11 = Optional filter capacitors. I don’t use them, but you can try. It can help or make things worse.
C12 – C14 = 10nF
D1 = 1N4148
D2 = 1N4004
T1 = BC547
OK1 – OK2 = 4N25 or equivalent
IC1 = 74HC04
IC2 = MAX232 or equivalent
IC3 = 7805

Computer side of interface is powered from RS232-port. You have to set RTS and DTR lines high from your logging software. Radio side is powered with RCA-connector. You can take the power from radio or external power supply. Ensure that your radio can supply the current needed. Otherwise it is safer to use external power supply.

Some possible improvements for new versions:

  • Capacitors could be with 5mm grid, which seems to be more common and easier to get, at least here in Finland.
  • Voltage regulator could be replaced with low-drop type.
  • Some pads could be larger.

Here are some pictures of my interface:

CAT interface board.

CAT interface with IC-holders and connectors assembled.

All components for FT-1000MP assembled. Some components should not have been assembled for FT-1000MP.

CAT interface assembled to an enclosure.

Ready interface.