SmartSDR USB Passthrough available in SSDR 3.9

I am getting this out early, as SSDR 3.9 should be released in the next week or so. Here is one of the features that I find very useful (writing this on May 24th, 2025).

With SmartSDR v3.9 and above, FlexRadio introduces Serial Passthrough, a handy feature that lets you connect and control RS-232 serial devices—like antenna rotators or amplifiers—directly through your radio over the internet using SmartLink. 

Whether you're running third-party software like PSTRotator or other Windows-based control apps, this guide walks you through setting up your FTDI RS232-USB cable, configuring SmartSDR, and getting everything talking seamlessly.  

The hardware you are controlling must have an RS-232 connection.  

Devices that use proprietary USB protocols (e.g. NOT serial/RS-232) will not be able to connect.

Step 1: Connect the FTDI RS232-USB Cable

• Plug your FTDI USB-to-RS232 cable (the one connected to your external device like a rotor controller or amp) into one of the USB ports on your FlexRadio.  These cables are available from the FlexRadio store.

Step 2: Set Up the Cable in SmartSDR for Windows

1. Open SmartSDR for Windows.  SmartSDR must be v3.9 or greater.
2. Go to Settings > USB Cables.
3. Find your USB cable in the list (look for its serial number).
4. Click Edit, then set the Type to Passthrough.
5. Double Click on the Cable to Edit the setting
6. Click on Advanced
7. Set the Baud rate of the device.
   

Click OK or Apply to save the changes.

Step 3: Create a Passthrough Port in SmartSDR CAT

1. Launch SmartSDR CAT.
   

Click to Create a New Port, and choose Passthrough in the protocol selection.

3. Select the same USB cable from Step 2 (matched by serial number).

Step 4: Use the Passthrough Port in Your Application

• In your third-party app (like PSTRotator or another device control program), choose the COM port that was just created in Step 3.
  
  • You can find the COM port name in SmartSDR CAT.
    
• Make sure your application is set to use that port for communication.
  

📝 Tip: Double-check in SmartSDR CAT that the Process is showing the name of the application you're using (like PSTRotator, PuTTY, etc.), which confirms the connection is active.