The Yaesu SCU-17 is a digital interface to your transceiver for models such as the aforementioned branded FT-450D and makes use of a USB connection, allowing it to be easily used with a modern computer system without the need of a messy and unreliable RS-232 <-> USB converter cable. It permits computerized rig control of a Yaesu transceiver primarily through CAT communication thereby allowing CW, RTTY (FSK or AFSK), PSK31, SSTV, or even FT8 encoding as examples. This little device works such magic by acting as a high-quality external sound-card with its own microphone output and line-level input, through which digitally encoded signals can be sent and received. Because it is an external device with its own metal-casing, it does not suffer from the major EMI issues that commonly plague internal sound-cards which typically come by default with most branded computer systems. In order to communicate with non-Yaesu rigs if you decide to go down another path later in the future, it also possesses 3.5 mm audio jacks for such functionality. This article details how to setup the above-mentioned digital interface for use with common programs such as WSJT-X.

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You will firstly need to make some changes on the transceiver rig itself in the settings menu, particularly if using a Yaesu branded model. If you do not know how to do this then you'll need to consult the manual for your own, specific model as that is out of the scope of this document.

  • CAT RATE: 38400.
  • CAT TOT: 10 ms.
  • D TYPE: USER-U or USER-L (depends on whether you are using the upper side-band or lower side-band, although the former is generally used so therefore set it to that if in doubt).

If you are using a Yaesu transceiver with this digital interface, you will need to install the appropriate drivers once finishing the above-mentioned steps. To do this, search for your model of Yaesu transceiver in Google and once at the official web-page for it on the Yaesu website, go to 'Files' on the top-menu and search for the Yaesu SCU-17 USB Driver (Virtual COM Port Driver). If the file is not directly called that then search for something called similarly. Install as per the official guidelines/instructions and then continue with this document.

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The next step involves going to the Control Panel if you are using the Microsoft Windows operating system, then Hardware & Sound, and finally Sound. Double-click 'Speakers - USB Audio CODEC' and then under the Playback tab, set the volume level to a value of '50' before going to the Advanced window and choosing 16 bit, 44100 Hz (CD Quality). Exit that screen before going towards Recording.

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For the microphone input, select the 'Microphone - USB Audio CODEC' and set its volume level to a value of '50' also and under its Advanced window choose 1 channel, 16 bit, 48000 Hz (DVD Quality). You always want the highest-quality setting possible for a microphone in order to capture as much of the signal in its original form as possible, provided that your computer has the processing power and RAM needed to make such happen. Although if your computer was designed in the last few years then, without a doubt, it has enough computational power for the setting stated above. That said, exit all of the screens as you are now done with them.

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Once you have exited the Control Panel and returned back to the Desktop, you may now start the WSJT-X application (provided it is installed) as we are going to set that up for the following example. NOTE: It will be required that you power on your transceiver and connect it up to your Yaesu SCU-17 USB Digital Interface before starting said software application, otherwise errors may ensue. Go to File -> Settings... (if pressing the F2 key as a shortcut-key does not work) then proceed to the Radio screen before making the following corrections below.

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  • CAT Control
    • Serial Port: COM1 (usually the lower value as the one directly above tends to be PTT in my experience, so finding the right value may require some experimentation).
    • Serial Port Parameters
      • Baud Rate: 38400 (unless you have a very long cable in which case you will have to set a lower value; CAT RATE will need to be modified on the transceiver accordingly).
      • Data Bits: Eight.
      • Stop Bits: Two.
      • Handshake: Hardware.
      • Force Control Lines: Null.
  • PTT Method: CAT.
  • Mode: Data / Pkt.
  • Split Operation: Rig (you can expect the volume to vary greatly with change in pitch if this is set to 'none' and you will always be fighting with the ALC and power output meter otherwise).

Finally, to verify that all your hard-earned work is good and well, press the Test CAT button and if it turns green after some seconds, then there should be nothing more to do! WSJT-X is communicating successfully with your transceiver and sending/receiving commands with confidence.

You will next need to go towards the Audio section of File -> Settings... where for Input you will choose Microphone (USB Audio CODEC) and Output will be Speakers (USB Audio CODEC) thusly. Lastly, exit the Settings window and go back to the main screen of WSJT-X so that we can do one more correction. As you can see in the screenshot below, you will find in the main window to your bottom-right a Pwr-slider and it is that which we need to adjust. The exact setting for which you require depends on your transceiver, computer, local environmental factors and possibly as such the time of day, etc. and is therefore down to a whole different number of factors. You will need to connect your transceiver to a dummy load (so as not to cause any disruptive transmissions), set it to the RF POWER level that you will be using, and adjust that slider along with the second volume-knob from the left on your Yaesu SCU-17 USB Digital Interface whilst making use of the TUNE button (found near the middle of the main screen) in WSJT-X. What you are aiming for is an effective use of transmission power along with a desired amount of ALC usage.

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I suggest setting the Pwr-slider to -8 dB in order to start with and adjusting the appropriate volume knob from there. If you are not getting the results you desire, increase the slider by another 2 dB and adjust the volume knob a few more times once again. Rinse, repeat. It is rare that you'll have to decrease the slider from the starting -8 dB as I've found around that and above to be a good setting, if using a Yaesu transceiver that is.

Some individuals might state that the ALC on your transceiver should not be engaged at all but I've found through experimenting that as long as the ALC meter is not varying throughout the entire transmission of the digital signal, despite otherwise being strongly engaged, you can get by with both less stress and a better power-level output. This is only my opinion and findings so your experience may vary, and it may even vary across different models/brands of transceivers and even across different versions of firmware. I currently use a Yaesu FT-450D transceiver with firmware flashed from late-2016 at the time of writing. Just don't engage the ALC too strongly otherwise you risk both damage to your transceiver and splattering across adjacent bands! You have been WARNED!

But, that said, this is all that needs to be done! If you require any advice and/or assistance then please, leave a comment on this article and I or someone else (such as one of my friends) will get back to you as soon as possible. On this website, unregistered guests have full permissions to post comments and even receive email notifications of replies if so desired! You just need to register your confirmation in an email that is sent to you, which is done for both spam and fraud purposes. I'd even love to hear of your own experiences too, particularly if it'd be helpful to the amateur radio community as a whole for anyone coming-by this page.

Download this file (scu-17_om_eng_jpn_eak21x700.pdf)Yaesu SCU-17 Manual[Documentation for the Yaesu SCU-17 USB Digital Interface.]2693 kB