Yaesu SCU-17 – The Missing Manual

Yaesu SCU-17 Unit
Yaesu SCU-17 Unit

Although it is almost certain that future generations (and the more expensive versions!) of radios will have rig control and digital mode keying built in with just a USB cable to go between radio and computer (such as Yaesu’s FT-991), for previous generations of radios, such as my FT-DX1200, the Yaesu SCU-17 Interface is required to act as that bridge between radio and computer.

There is nothing particularly special about the interface – you could make one yourself at home if you wanted. It consists of 2 USB to Serial ports, a sound card interface and a little bit of wizardry to wire it all together. As for me I’d rather just spend the money to save myself the hours of frustration of putting one of these together (and troubleshooting issues) and end up with a professionally made, compact unit.

However what I wanted to address was the distinct vagueness of documentation around that covers how they operate.


Yaesu SCU-17 Rear

Looking at the rear of the unit, it looks relatively straight forward – USB to computer, CAT serial and data port. The other two ports is where the first bit of confusion was for me. The remaining jacks provide audio out, FSK and PTT functionality for radios that do not support the mini-DIN data cable.

When connected to the computer, you are presented with 2 COM Interfaces:

  • Enhanced COM Port – Used for CAT Control
  • Standard COM Port – Used for PTT Control

Along with a audio device for audio input and output.

Digital Mode Operation:

This is pretty straight forward. The SCU-17 sound card interface is responsible for audio in/out. With your favourite app (I like HRD Suite) configure the audio in/out to use the SCU-17 audio devices and standard COM port for PTT and away you go. I’ve found this pretty robust.

Voice Keying with FT-DX1200

One of the things I’ve found from many contests is that if you are going to go the full length of the contest a voice keyer is preferred, otherwise you will almost certainly go hoarse or have no voice left by the end of the contest! It’s taken me nearly 6 months to get voice keying working the N1MM Contest logger+, because I could never work out why I couldn’t get the audio to transmit. The PTT would work, but my recorded voice would not work. Finally I found the missing piece of information on the N1MM Yahoo group.

The SCU-17 transmits AF into the data-in pin on the back of radio. The FTDX-1200 (and other Yaesu radios) have a software switch to toggle microphone selection between the front mic or the data port. Why it cannot be parallel input beats me. To enable voice keying through the SCU-17:

  • Set Menu Item 103 (MIC SELECT) to “DATA”

Remember though, if you wish to respond with your mic, you need to toggle the menu item back to “FRONT”.

What about CAT Commands?

Yaesu has published CAT Commands for their radios, however a way to switch the MIC SEL from FRONT to DATA and back after transmission is not available.

Update: Dec 15 2015:

I had another look at the CAT reference manual and found it was possible to use CAT Commands with N1MM to switch the voice keyer. In my function key definitions, I now have:

F1 CQ,{CAT1ASC EX1031;}{OPERATOR}\Cq.wav{END}{CAT1ASC EX1030;}


Problem solved!